What is a hydraulic pump made of? The principle of operation of the hydraulic system of attachments

Hydraulic systems are used in a variety of equipment, but each of them is based on a similar principle. It is based on the classical law of Pascal, discovered back in the 17th century. According to him, the pressure that is applied to a volume of liquid creates a force. It is evenly transmitted in all directions and creates the same pressure at every point.

The basis of the work of hydraulics of any kind is the use of the energy of liquids and the ability, with little effort, to withstand an increased load over a large area - the so-called hydraulic multiplier. Thus, all types of devices operating on the basis of the use of hydraulic energy can be attributed to hydraulics.

Special equipment with hydraulic units
Hydroficated robots at the Kamaz plant

Types of hydraulics by application

Despite the common "foundation", hydraulic systems are striking in variety. From basic hydraulic designs consisting of several cylinders and tubes, to those that combine hydraulic elements and electrical solutions, they demonstrate the breadth of engineering and bring application value in a wide variety of industries:

• industry - as an element of foundry, pressing, transportation and handling equipment, metal-cutting machines, conveyors;
• agriculture- attachments of tractors, excavators, combines and bulldozers are controlled precisely by hydraulic units;
• automotive industry: hydraulic braking system - a "must have" for modern cars and trucks;
• aerospace industry: systems, independent or combined with pneumatics, are used in landing gear, control devices;
• construction: almost all special equipment is equipped with hydraulic units;
• marine engineering: hydraulic systems are used in turbines, steering;
• oil and gas production, offshore drilling, energy, logging and storage, housing and communal services and many other areas.

Hydraulic station for lathe

In industry (for metal-cutting and other machine tools), modern productive hydraulics are used due to its ability to provide an optimal mode of operation using stepless regulation, to obtain smooth and accurate movements of equipment and ease of automation.

Systems with automatic control, and in construction, landscaping, road and other works - excavators and other caterpillar or wheeled with hydraulic units. The hydraulic system is powered by the engine of the equipment (ICE or electric) and ensures the functioning of attachments - buckets, booms, forks, and so on.

Hydraulic Backhoe Loader

Types of hydraulics with different hydraulic drives

In equipment for different areas hydraulic drives of one of two types are used - hydrodynamic, operating mainly on kinetic energy, or volumetric. The latter use the potential energy of liquid pressure, provide high pressure and, due to technical excellence, are widely used in modern machines. Systems with compact and productive volumetric drives are installed on heavy-duty excavators and machine tools - their working pressure reaches 300 MPa and more.

An example of equipment with volumetric hydraulic drive
Hydro turbine impeller for hydropower plant

Volumetric hydraulic drives are used in most modern hydraulic systems installed in presses, excavators and construction equipment, metalworking machines, and so on. Devices are classified according to:

• the nature of the movement of the output links of the hydraulic motor - it can be rotational (with a driven shaft or housing), translational or rotary, with movement at an angle of up to 270 degrees;
• regulation: adjustable and unregulated in manual or automatic mode, throttle, volumetric or volumetric-throttle method;
• circulation schemes of working fluids - compact closed, used in mobile technology, and open, which communicates with a separate hydraulic tank;
• sources of liquid supply: with pumps or hydraulic drives, main or autonomous;
• engine type - electric, internal combustion engines in cars and special equipment, ship turbines, and so on.

Siemens turbine with hydraulic drive

The design of hydraulics of different types

In industry, machines and mechanisms with a complex device are used, but, as a rule, hydraulics in them work according to a general concept. The system includes:

• working hydraulic cylinder that converts hydraulic energy into mechanical movement(or, in more powerful industrial systems, a hydraulic motor);
• hydraulic pump;
• a tank for the working fluid, which provides a neck, a breather and a fan;
• valves - check, safety and distributive (directing liquid to the cylinder or to the tank);
• filters fine cleaning(one each on the supply and return lines) and coarse cleaning - to remove impurities of a mechanical nature;
• a system that controls all elements;
• circuit (pressure vessels, piping and other components), seals and gaskets.

The classic scheme of a separate hydraulic system

Depending on the type of hydraulic system, its design may differ - this affects the scope of the device, its operating parameters.

Standard brake hydraulic cylinder for Niva SK-5 combine

Types of structural elements of the hydraulic system

First of all, the type of drive is important - the part of the hydraulics that converts energy. The cylinders are of the rotary type, and can direct liquids only in one end or both (single or double action, respectively). Their efforts are directed in a straight line. Hydraulics open type with cylinders that reciprocate output links, used in low- and medium-power equipment.

Special equipment with hydraulic motor

In complex industrial systems, hydraulic motors are installed instead of working cylinders, into which fluid flows from the pump and then returns to the line. Hydroficated motors provide the output links with a rotational movement with an unlimited angle of rotation. They are driven by a working hydraulic fluid coming from the pump, which, in turn, causes the mechanical elements to rotate. In equipment for different areas, gear, vane or piston hydraulic motors are installed.

Radial piston hydraulic motor

The flows in the system are controlled by hydraulic distributors - throttling and directing. According to the design features, they are divided into three varieties: spool, crane and valve. The hydraulic distributors of the first type are most in demand in industry, engineering systems and communications. Spool models are easy to operate, compact and reliable.

hydraulic pump- one more important important element hydraulics. Equipment that converts mechanical energy into pressure energy is used in closed and open hydraulic systems. For equipment operating in "hard" conditions (drilling, mining, and so on), dynamic-type models are installed - they are less sensitive to pollution and impurities.

Hydraulic pump
Hydraulic pump in section
Pair of hydraulic pump-hydromotor

Also, pumps are classified by action - forced or non-forced. In most modern hydraulic systems using increased pressure, pumps of the first type are installed. By design, models are distinguished:

• gear;
• bladed;
• piston - axial and radial types.
• and etc.

Hydroficated manipulators for 3D printing

There are uses for the laws of hydraulics - manufacturers come up with new models of machinery and equipment. Among the most interesting are hydraulic systems installed in manipulators for 3D printing, collaborative robots, medical microfluidic devices, aviation and other equipment. Therefore, any classification cannot be considered complete - scientific progress supplements it almost every day.

pi4 workerbot is an ultra-modern industrial robot that reproduces facial expressions

3D printed hydraulic manipulator

Hydraulic equipment on the lines of an aircraft plant

HYDRAULIC DRIVE

DRIVE TYPES

To transfer mechanical energy from the internal combustion engine to the actuators of the working equipment, a hydraulic drive (hydraulic drive) is used, in which the mechanical energy at the input is converted into hydraulic, and then on the exit again into the mechanical one, which drives the mechanisms of the working equipment. Hydraulic energy is transmitted by a fluid (usually mineral oil) that serves as the working fluid of the hydraulic drive and is called the working fluid.

Depending on the type of transmission used, the hydraulic drive is divided into volumetric and hydrodynamic.

In volumetric hydraulic drive volumetric hydraulic transmission is used. In it, energy is transferred by static pressure (potential energy) of the working fluid, which is created by a positive displacement pump and implemented in a hydraulic motor of the same type, for example, in a hydraulic cylinder.

In a volumetric hydraulic drive, a volumetric pump serves as a converter of mechanical energy at the input to the hydraulic transmission. The displacement of liquid from the working chambers of the pump and the filling of the suction chambers with it occurs as a result of a decrease or increase in the geometric volume of these chambers, hermetically separated from each other. . The reverse energy converter in a volumetric hydraulic transmission is a hydraulic motor, the working stroke of which is carried out as a result of an increase in the volume of the working chambers under the action of a pressurized fluid entering them.

Energy converters in a hydraulic drive (pumps and an engine are called hydraulic machines. The operation of a hydraulic machine is based on a change in the volume of working chambers as a result of the supply of mechanical energy (pump) or as a result of the supply of hydraulic energy by a flow of working fluid under pressure (engine).

Energy is transmitted through pipelines, including flexible hoses, to any place in the machine. This feature of the hydraulic drive is called distance. With the help of a hydraulic drive, it is possible to drive several executive motors from one pump or a group of pumps, while independent switching on of the motors is possible.

The principle of operation of the hydraulic drive is based on the use of two main properties of the working fluid of the hydraulic transmission - the working fluid. The first property is that the liquid is an elastic body and is practically incompressible; the second - in a closed volume of liquid, a change in pressure at each point is transmitted to other points without change. We will consider the operation of the hydraulic drive using the example of the action of a hydraulic jack (Fig. 56). Volumetric hydraulic drive includes a pump, tank and hydraulic motor. The volumetric pump is formed by a cylinder /, a plunger 2 s earring 3 and handle 4. Hydraulic translational motor includes cylinder 7 and plunger 6. These components are connected by pipelines, which are called hydraulic lines. Reverse valves are installed on the hydraulic lines

Rice. 56. Hydraulic jack:

/, 7 - cylinders, 2, 6 - plunger, 3 - earring, 4 - handle, 5 - tank, 8 - hydraulic line, 9 - valve, 10, 11 - valves

valves 10 and //. Valve 10 allows fluid to pass only in the direction away from the cylinder cavity 1 to the cylinder cavity 7, and the valve 11 - from tank 5 to cylinder /. The cavity of the cylinder 7 is connected by an additional hydraulic line to the tank 5. A shut-off valve is installed in this hydraulic line 9, which closes this line when the pump is running.

swing arm 4 plunger 2 reciprocating motion is reported. When moving up, the plunger sucks the working fluid from the tank 5 through the valve // ​​into the cylinder cavity /. The liquid fills the cavity of the cylinder under the influence of atmospheric pressure and the liquid in the tank. When entering down, the liquid from the cylinder cavity / is displaced into the cylinder cavity 7 through the valve 10. The volume of the liquid displaced from the cylinder cavity due to the incompressibility of the next completely enters the cavity of the cylinder 7 and raises the plunger to a certain height.

plunger stroke 2 pump down - working, and moving up - idle, the hydraulic line connecting the tank to the pump is called suction, the hydraulic line connecting the pump to the hydraulic motor is pressure. Multiple valves perform the function of flow distributors and ensure the continuity of the pump.

Plunger 6 When the pump is running, it only moves in one direction - up. To plunge 6 drop down (under

external load or gravity), it is necessary to open the valve and release the liquid from the cavity of the cylinder 7 into the tank.

Consider the main specifications pump. When the pump plunger moves from one extreme position to another, the volume of the cylinder 1 change the value toVi = fi* Si, where Fi and Si - respectively, the area and stroke of the plunger. This volume defines theoretical submission pump in one stroke and is called working volume a. In pumps where the input link does not reciprocate, but continuous rotational motion, the working volume is called the feed per shaft revolution. The working volume is measured in dm 3, l, cm 3.

The product of the working volume by the number of strokes or revolutions of the pump shaft input per unit of time - theoretical pump flow Q , measured in l/min, determines the speed of the actuators.

The liquid enclosed in a closed volume between the plungers of the pump and the slave cylinder, at rest, acts on their working areas with the same pressure. This pressure also acts on the walls of cylinders and pipelines. It depends on the magnitude of the external load. liquid pressure, or working pressure hydraulic drive is the force per unit of the working surface of the plungers, cylinder walls and pipelines, etc. Exceeding the working pressure for which the parts and mechanisms of the hydraulic drive are designed leads to premature wear and can cause rupture of pipelines and other breakdowns.

Since the fluid pressure is transmitted uniformly in all directions and the forces are balanced by this pressure, then, provided that the friction of the plungers and their seals is neglected, the working pressure Pi == pF- i; Pg == pFs, where p is the working pressure.

This inverse proportionality ratio is the gear ratio of the hydraulic drive with hydraulic machines of translational motion. It is similar to the gear ratio of a simple lever. Indeed, if the long end of the handle 4 apply force R, then this lever can overcome the force P, so many times greater d R[, how many times the short arm of the lever is less than the long one, and the path S 1 is as much less than the path S2, how many times the short lever arm is less than the long one. This right lever is also represented as an inverse proportionality.

In sources of mechanical energy of a hydraulic drive, an internal combustion engine and electric motors, the output link is a rotating shaft, from which one or more hydraulic pumps are driven, which also have a rotating shaft as an input link. The rotary hydraulic drive (Fig. 57) includes, for example, a pump and a motor of the same design.

The pump consists of a fixed housing (stator), a rotating rotor 3, in longitudinal grooves 4 which sliding gates 5 and 6. ( The rotor is displaced relative to the stator axis (to the left in the figure), therefore, when rotating, its outer surface either approaches or is given away from the inner surface of the housing. Gates 5, rotating together with the rotor and sliding along the walls of the stator, simultaneously move into the grooves or move out of the grooves of the rotor. If you rotate the rotor in the direction indicated by the arrow, then between its wall, the housing wall and the gate 5 a continuously expanding crescent-shaped cavity is formedAI, into which the working fluid will be sucked from tank 1. CavityBiat this time, it will continuously decrease in volume and the liquid in it will be displaced from the pump housing through the tap 8 and go to the motor.

In the valve position shown in the figure 8 liquid will fill the cavity AI and put pressure on the gate 11, forcing it along with the rotor 10 turn clockwise. From cavity 5.2 liquid through the tap 8 will be forced into the tank. With further rotation of the rotor 3 pump ta- __________

Fig, 57, Rotary hydraulic drive:

1 - tank, 2, 13 - cases, 3, 10 - rotors. 4 - groove, 5, 6, 9, II - gates, 7 - valve, 8 - tap, A i, Bi- pump cavities, A i, B i - motor cavities

what kind of work will the gate do 6 pump and gate 9 motor, and the process of rotation of the rotor will proceed continuously.

In order to rotate the rotor of the motor in the opposite direction, it is necessary to switch the valve 8. Then the cavity B1 pump will communicate with the cavity B2 of the motor and the working fluid will flow into this cavity under pressure, and from the cavity Lz the liquid will drain into the tank. If the motor is overloaded, its rotor will stop while the pump continues to supply liquid. As a result, the pressure in the cavity of the pump, hydraulic motor and pressure pipeline will increase until the safety valve 7 opens, releasing liquid into the tank and thereby preventing the hydraulic transmission from breaking.

Rotational motion is transmitted in the same way as in a belt drive. In the latter, mechanical energy is transmitted by means of a belt, in hydraulic transmission - by the flow of the working fluid. In a belt drive, the number of revolutions of the driving and driven pulleys is inversely proportional to the ratio of their radii. With the same amount of fluid passing through, the speed of rotation of the pump and motor rotors is inversely proportional to their working volumes. These ratios are valid in the absence of volume losses in transmissions.

The power transmitted through a belt drive can be increased by increasing the width of the belt at a constant rotational speed. Obviously, in hydraulic transmission this can be achieved (at constant pressure) by increasing the working volume of the pump by, for example, expanding the housing and rotor with plates.

For a hydraulic drive that includes a drive pump and a hydraulic motor on the actuator, the overall efficiency is the ratio of the power taken from the hydraulic motor shaft to the power supplied to the pump shaft.

The loader hydraulic drive includes components inherent in any hydraulic drive: a pump, hydraulic motors and devices for controlling the flow and protecting the hydraulic system from overloads.

Rice. 58. Structural diagram of the hydraulic drive:

1, 2, 3, 4. 5. 6 - hydraulic lines; ICE - internal combustion engine, H - pump, B - tank, P - safety valve, M - manometer, R- distributor;

D1, D2, D3 - hydraulic motors. N - supplied energy, N 1, N 2, N 3 - consumed energy

rice. 58 shows a typical block diagram of a hydraulic drive. ut Yes, internal combustion engine ICE energy goes to the pump H can be consumed through hydraulic motors D1, D2 and D3 a drive of the working mechanisms of the machine. The working fluid enters the pump from the tank B along the suction line 1 and is supplied through a pressure hydraulic line 2 to distributor R, in front of which a safety valve is installed P. Distributor R connected to each hydraulic motor by actuating hydraulic lines 4, 5 and 6. A pressure gauge is installed in the pressure line M to control the pressure in the hydraulic system.

When the hydraulic motors are turned off, the working fluid of the hydraulic drive - liquid - is pumped by the pump H from the tank B to distributor R 0 back to tank B. Suction, pressure and drain hydraulic lines form a circulation circuit. coming from ICE energy is expended to overcome mechanical and hydraulic losses in the circulation circuit. This energy is mainly used to heat the liquid and hydraulic system.

The hydraulic motor is switched on by the distributor R, at the same time, it performs the functions of regulating the flow both in terms of flow (at the moment of switching on) and in the direction of fluid movement (reversal) to the engines. Reversible hydraulic motors are connected to the distributor by two executive lines, connected, in turn, alternately with the pressure 2 or drain 3 lines of the circulation circuit, depending on the required direction of movement of the engine.

During the operation of the hydraulic motor, the circulation circuit turns on the engine and its executive hydraulic lines, when it stops, for example, when the hydraulic cylinder rod approaches the extreme position, the circulation circuit is interrupted and the state of the hydraulic system overload occurs, since the pump H continues to receive power from the engine ICE. In this case, the pressure will begin to increase sharply and, as a result, either the engine will stop ICE, either one of the mechanisms of the hydraulic system fails, for example, a hydraulic line breaks 2. To prevent this from happening, a safety valve is installed on the pressure line. P and pressure gauge M. The valve is adjusted to a pressure higher than the working one, as a rule, by 10-15%. When this pressure is reached, the valve operates and connects

pressure line 2 with drain 3, restoring the fluid circulation.

In some cases, to reduce the speed of the hydraulic motor, a throttle is installed in one executive line, which limits the fluid supply to the engine at a given pressure. If the pump capacity is greater than the set value, then the valve releases part of the liquid to drain into the tank. pressure gauge M designed to control the pressure in the hydraulic system.

The hydraulic systems of machines usually include additional devices: reverse controlled valves (hydraulic locks), rotating joints (hydraulic hinges), filters; distributors are used o built-in safety and check valves. Loaders use power steering, which also refers to the hydraulic drive, but has its own characteristics devices and work.

In a hydrodynamic drive hydrodynamic transmission is used, in which energy is also transferred by the liquid, but it is not the pressure (pressure energy) that is of primary importance, but the speed of movement of this liquid in the circle of its circulation, i.e. kinetic energy.

In the hydromechanical transmission, the clutch and gearbox are excluded, and the mode of movement of the machine changes without disconnecting the transmission from the engine by changing its speed, which made it possible to reduce the number of controls.

Rice. 59. Hydrodynamic transmission:

1 - axis, 2, 16 - shafts, .3 - coupling, 4, 5, 9 - wheels. 6 - ring gear, 7 - flywheel, 8 - oil indicator, 10, 22, 23 - gears, II, 14- T op mosaic. 12, I3 - blockgears, 15 - drum, 17 - lid, 18 - distributor, 19 - screw, 20 - n aco With 21 - filter, 24 - crankcase

Hydrodynamic transmission (Fig. 59) contains a torque converter located in one crankcase and two planetary gears. The torque converter is designed to change the torque on the output shaft, replacing the clutch and gearbox, and the planetary gears are used to change the direction of the machine, replacing the reverse mechanism.

The torque converter consists of a pump 9, turbine 5 and reactor 4 wheels. The pump wheel is connected to the flywheel 7 of the engine, the turbine wheel is connected to the shaft 2, reactor wheel through freewheel 3 connected to the axis / fixed on the crankcase 24. Planetary block gear 13 attached to the output shaft 16 and interacts on the one hand with the satellite gears of the block gear 12, with the other is sun gear brake drum 15. block gear 12 loosely seated on the crankcase shaft, engages with pinion satellites 13, and the outer surface forms a brake pulley interacting with the brake 11. pump wheel 9 contains gear 10, which is connected to the gear through the wheel 22 hydraulic pump 20.

Pump, turbine and reactor wheels are made with blades located at an angle to the plane of rotation.

Band brakes are actuated by hydraulic cylinders using a distributor 18, which is controlled from the handle on the control panel. When moving forward, the drum is braked 15, at the rear - block 12. Pump 20 designed to pump oil to the torque converter, planetary gears and brake control cylinders.

When the engine is running, the oil between the blades of the pump wheel under the action of centrifugal forces is squeezed out to the periphery of the wheel and directed to the blades of the turbine wheel, and then towards the fixed blades of the reactor wheel.

At low engine speeds, the oil rotates the reactor wheel, while the turbine wheel remains stationary. As the rpm increases, the overrunning clutch 3 gets stuck on the shaft and the turbine wheel starts to rotate, transmitting the engine torque through the planetary gears to the output shaft 16. The direction of rotation of this shaft depends on which brake is applied. With an increase in the engine speed, the torque on the shaft 16 decreases and the rotation speed increases. Between input shaft 16 and a single-stage gearbox with a gear ratio of 0.869 is installed as a driving axle.

Under operating conditions, the oil level and its purity are monitored. Filter 21

systematically washed, its frequent clogging indicates the need to change the oil.

WORKING LIQUIDS

The working fluid of hydraulic systems is considered as an integral part of the hydraulic drive, since it serves as the working fluid of the hydraulic transmission. At the same time, the working fluid cools the hydraulic system, lubricates the friction parts and protects the parts from corrosion. Therefore, the performance, service life and reliability of the hydraulic drive depend on the properties of the fluid.

Loaders work on outdoors in various parts of the country. In the cold season, the machine and the working fluid can be cooled down to -55 ° C, and in some areas of the Middle Asia in summer, during operation, the liquid heats up to 80 ° C. On average, the fluid should ensure the operation of the hydraulic drive within themes temperatures from -40 to +50 "C. The fluid must have a long service life, be neutral to the materials used in the hydraulic drive, especially rubber seals, and also have good heat capacity and at the same time thermal conductivity in order to cool the hydraulic system.

Mineral oils are used as working fluids. However, there are no oils that would be suitable for all operating conditions at the same time. Therefore, oils, depending on their properties, are chosen for specific working conditions (climatic zone in which the machine is used and season).

The reliability and durability of the hydraulic system largely depend on the correct selection of the working fluid, as well as on the stability of the properties.

One of the main indicators by which they select and evaluate

oils, this is the viscosity. Viscosity characterizes the ability of a working fluid to resist shear deformation; measured in centistokes (cSt) at a given temperature (usually 50°C) and in conventional units- Engler degrees, which are determined using a viscometer and express the ratio of the time a liquid of a given volume (200 cm 3) will flow through a calibrated hole to the time the same volume of water will flow. The ability of the hydraulic drive to operate at low and high temperatures primarily depends on the viscosity. During the operation of the machine, the viscosity of the working fluid decreases and its lubricating properties deteriorate, which reduces the service life of the hydraulic drive.

During oxidation, resinous deposits fall out of the oil, forming a thin hard coating on the working surfaces of parts that destroy rubber seals and filter elements. The intensity of oil oxidation increases sharply with increasing temperature, so it should not be allowed to increase tempe oil temperatures above 70 °C.

Typically, working fluids are completely replaced in spring and autumn.

If all-weather oil is used, then it must be replaced after 300-1000 hours of hydraulic drive operation, depending on the May variety (the replacement period is indicated in the instructions), but at least once a year. In this case, the system is washed with kerosene at idle. The frequency of replacement depends on the brand of liquid, the mode of operation of the volume of the system and the tank in relation to the pump flow. The larger the capacity of the system, the less often you need to change the oil.

The durability of the hydraulic system is affected by the presence of mechanical impurities in the oil, therefore, filters are included in the hydraulic system to oil purification from mechanical impurities, as well as magnetic plugs.

The choice of oil for the hydraulic system is based on the temperature of the limit of use of this fluid, depending on the type of hydraulic drive pump. The lower temperature limit of application is determined not by the pour point of working fluids, but by the pumpability limit of the pump, taking into account losses in the suction line. for gear pumps, this limit is a viscosity of 3000-5000 cSt, which corresponds to the pumpability limit during short-term (start-up) operation. The lower temperature limit of stable operation is determined by filling the working chamber of the pump, at which the volumetric efficiency reaches the highest value, which approximately for gear pumps corresponds to a viscosity of 1250-1400 cSt.

The upper temperature limit for the use of a working fluid is determined by the lowest viscosity value, taking into account its heating during operation. Exceeding this limit causes an increase in volume losses, as well as sticking of the surfaces of mating friction pairs, their intense local heating and wear due to the deterioration of the lubricating properties of the oil.

The basis for the use of one or another type of oil is the recommendation of the manufacturer of the hydraulic drive machine.

Before topping up or changing the oil, check the neutrality of the mixed oils. The appearance of flakes, precipitation and foaming indicate the inadmissibility of mixing. In this case, the old oil must be drained and the system flushed.

When filling the system, measures are taken to ensure the purity of the oil being filled. To do this, check the serviceability of the filling filters, the cleanliness of the funnel and the filling tank.

HYDROMACHINES

In a volumetric hydraulic drive, hydraulic machines are used: pumps, pump motors and hydraulic motors, the operation of which is based on the alternate filling of the working chamber with a working fluid and displacing it from the working chamber.

Pumps convert the mechanical energy supplied to them from the engine into the energy of the fluid flow. The input shaft of the pump is given a rotational movement. Their input parameter is the shaft speed, and the output parameter is the fluid supply. The liquid moves in the pump due to its displacement from the working chambers by pistons, gates (vanes), gear teeth, etc. In this case, the working chamber is a closed space, which, during operation, alternately communicates with either the suction hydraulic line or the pressure one.

In hydraulic motors, the energy of the working fluid flow is converted into mechanical energy at the output link (hydromotor shaft), which also performs rotational motion. According to the nature of the movement of the output link, rotary motion engines are distinguished - hydraulic motors and translational - hydraulic cylinders.

Hydraulic motors and pumps are subdivided according to the possibility of regulation, according to the possibility of changing the direction of rotation, according to the design of the working chamber and other design features.

Some designs of pumps (hydraulic motors) can perform the functions of a hydraulic motor (pump), they are called pump-motors.

On loaders, unregulated (non-reversible pumps of various designs are used: gear, vane, axial piston. Adjustable hydraulic motors (pumps) are performed with a variable volume of working chambers.

The gear pump (Fig. 60) consists of a pair of interlocking gears placed in a housing tightly enclosing them, which has channels from the side of the inlet to the engagement and exit from it. Pumps with external spur gears are the simplest and are characterized by reliable operation, small overall dimensions and weight, compactness, and others. positive qualities. Maximum pressure of gear pumps 16-20 MPa, flow rate up to 1000 l/min, speed up to 4000 rpm, service life

Rice. 60. The scheme of the gear pump

average 5000 h.

When the gears rotate, the fluid contained in the cavity of the teeth is transferred from the suction chamber along the periphery of the housing to the discharge chamber and further, to pressure hydraulic line. This is due to the fact that during the rotation of the gears, the teeth drive in more liquid than can fit in the space freed by the teeth in engagement. . The difference in the volumes described by these two pairs of teeth is the amount of fluid that you displace into the discharge cavity. As you approach the injection chamber, the fluid pressure increases, as shown by the arrows. In hydraulic systems, pumps NSh-32, NSh-46, NSh-67K are used, their modifications are NSh-32U and NSh-46U.

Pump NSh (Fig. 61) contains placed in the housing 12 leading and led 11 gears and bushings 6. The body is closed with cover 5 screwed on 1. Between body 12 and cover 5 gasketed sealing ring 8. Drive gear made in one piece c splined shaft, which is sealed with a cuff 4, installation in the bore of the cover 5 using the support 3 and spring 2 rings The front bushings 6 are placed in the bores of the cover 5 and sealed) with rubber rings. They can move along their axes. The discharge cavity of the pump is connected by a channel to the space between the ends of said bushings and the cover. Under fluid pressure, the front bushings, together with the gears, are pressed against the rear, which, in turn, are pressed against the body 12, providing automatic sealing of the ends of bushings and gears.

In the discharge cavity of the pump near the elbow 13 the pressure on the ends of the bushings is many times greater than on the opposite side. At the same time, the pressure on the ends of the covers from the side of the body tends to press the bushings against the cover 5. Together, this can cause the bushings to skew towards the suction cavity, one-sided wear of the bushings and increased oil leakage. In order to reduce the uneven loading of the bushings, part of the end area of ​​the bushings is covered with an unloading plate 7, which is sealed along the contour with a rubber ring. This ring is tightly clamped between the ends of the body and the cover, and as a result, a relative equality of forces acting on the bushings is created.

The bushings wear out as the pump operates, and the distance between the ends and the cover increases. In this case, the ring of the relief plate 7 expands, maintaining the necessary seal between the cover and the bushings. Reliable and reliable depends on the tightness of this ring. long work pump.

Rice. 61. Gear pump NSh:

/ - screw, 2, 3, 8 - rings. 4 - cuff, 5 - cover, 6 - gear sleeve, 7 - plate, 9 - cotter pin, 10,II - gears, 12 - frame, 13 - square

During assembly, a gap of 0.1-0.15 mm is left between the mating bushings. After assembly this gap is forced. To do this, the bushings are deployed and fixed with spring pins, which are installed in the holes of the bushings.

NSh pumps produce right and left rotation. On the pump housing, the direction of rotation of the drive shaft is indicated by an arrow. For a left hand pump (when viewed from the cover side), the drive gear rotates counterclockwise and the suction side is on the right. The pump of right rotation differs from the pump of left rotation in the direction of rotation of the drive gear and its location.

When replacing a pump, if the new and replaced pumps differ in the direction of rotation, the direction of the inlet and outlet of the liquid into the pump must not be changed. Pump suction port ( large diameter) must always be connected to the tank. Otherwise, the drive gear seal will be under high pressure and will be damaged.

If necessary, the left-hand rotation pump can be converted into a right-hand rotation pump. In order to assemble the pump of right rotation (Fig. 62, a, b) it is necessary to remove the cover, remove the front bushings / from the housing, 2 complete with spring pins 4, rotate 180° and reinstall. In this case, the joint line of the bushings will be rotated, as shown in Fig. 62. Then the driving and driven gears are interchanged and their trunnions are inserted into the previous bushings. The front bushings are rearranged in the same way as the rear ones. After that, the unloading plate 7 is installed in the same place (see Fig. 61) with a sealing ring 8, a then the roof is pre-rotated by 180°.

Pumps NSh-32 and NSh-46 are unified in design, their rods differ only in the length of the tooth, which determines the working volume of the pumps.

NShU pumps (index U means "unified") differ from NShU the following features. Instead of relief plate and ring 8 a solid rubber plate is installed 12 (fig. (Sandwiched between the cover 3 and body 1. At the passage of the trunnions of the bushings in the plate 12 holes are made in which the sealing rings are installed 13 with thin steel washers adjacent to the cover. On the ends of the bushings adjacent to the gears, arcuate channels are made 14. Guide spring pins 9 (see fig. 61) are removed, and on the suction side, a segmented rubber seal is inserted into the body bore 15 (see fig. 63) and aluminum insert 16.

Rice. 62. Assembly of pump bushings NSh:

a - left rotation, b - right rotation; I, 2- bushings, 3 - well, 4 - cotter pin, 5 - body

Rice. 63. Gear pump NShU:

/ - frame, 3, 4 - gears, 9 - cover 5, 6 - bushings, 7, 9, 13 - rings, 8 - cuff, 10 - bolt, // - washer, 12 - plates 14 - bushing channels, 15 - seal. 16 - liners; A - space under the pump cover

During the operation of the NShU pump, oil from the discharge chamber enters the space above the front bushings and tends to press these bushings against the ends of the gears. At the same time, from the side of the teeth, the bushing is affected by the pressure of the oil entering the arcuate channels 14 in as a result of the pressure on the gear bushings, the operating time of the pump is also under some force directed from the cover into the depths of the pump housing. This design provides automatic preload and, consequently, face wear of gears and bushings and affects the sealing properties of the plate. 12. Rubber seal 15 necessary to ensure that oil from the space above the bushings does not penetrate into the suction cavity.

On a number of loader models, pumps NSh-67K and HUJ-100K (Fig. 64). These pumps consist of a body / cover 2, clamping 7 and bearing 5 clips, driven 3 and leading 4 gears, centering sleeve, seals and fasteners.

Rice. 64. Hydraulic pump NSh-67K (NSh-100K):

/ - frame, 2 - lid, 3, 4- gears, 5, 7, - clips, 6. 11, 14, 15 - cuffs, 8 - bolt, 9 - washer, 10 - ring, 12 - plate,I3 - platyki

Bearing cage 5 is made in the form of a half-cylinder with four bearing seats, in which the driven 3 and leading 4 gears. Clamping clip 7 provides a radial seal, it rests on the pins of the gears with bearing surfaces. A lip is also used for radial sealing. 13, in which creates a force for pressing the clip to the gear teeth. Base plate 12 designed to bridge the gap between the housing and the clamping clip. The clamping sleeve 7 compensates for the radial gap between its own sealing surface and the gear teeth as the bearing surfaces wear out.

At the ends of the gears are sealed with two plates 13, which rise by force from the pressure in the cavity, sealed with cuffs 14. The force created in the chambers of the clamping cage, sealed with cuffs 15, balances the clip 7 from the force that is transmitted from the chambers through the cuffs 14. The drive shaft is sealed using collars, which are held in the housing by a support ring and a circlip. The pumping element (gears assembled with clips and plates) is fixed from rotation in the housing by a centering sleeve.

Ring 10 seals the connector between the housing and the cover, which are bolted together.

Correct operation and durability of pumps are ensured by compliance with the rules of technical operation.

The hydraulic system must be filled with clean oil. good quality and the corresponding brand, recommended for this pump when operating in a given temperature range; monitor the serviceability of the filters and the required oil level in the tank. In the cold season, you can not immediately turn on the pump to the working load.

It is necessary to let the pump idle for 10-15 minutes at medium engine speeds. During this time, the working fluid will warm up and the hydraulic system will be ready for operation. It is not allowed to give the pump maximum speed when warming up.

Cavitation is dangerous for the pump - local release of gases and pars from the liquid

(liquid boiling up) with subsequent destruction of the evolved gas-vapor bubbles, accompanied by local hydraulic microshocks of high frequency and pressure surges. Cavitation causes mechanical damage to the pump and can damage the pump. To prevent cavitation, it is necessary to eliminate the causes that can cause it: foaming of oil in the tank, which causes a vacuum in the suction cavity of the pump, air infiltration into the suction cavity of the pump through the shaft seal, clogging of the filter in the suction line of the pump, which worsens the conditions for filling its chambers, separation of air from the liquid in the intake filters (as a result, the liquid in the tank is saturated with air bubbles and this mixture is sucked in by the pump), a high degree of vacuum in suction line for the following reasons: high liquid velocity, high viscosity and increased liquid lift,

The operation of the pump is largely dependent on the viscosity of the working fluid used. There are three operating modes depending on the viscosity Slip mode characterized by significant volume losses due to internal leakage and external leakage, which decrease with increasing viscosity. In this mode, the volumetric efficiency of the pump decreases sharply, for example, for the NSh-32 pump with a viscosity of 10 cSt it is 0.74-0.8, for the NPA it is 0.64-0.95. Steady Mode is characterized by the stability of volumetric efficiency in a certain viscosity range, limited by the upper limit of viscosity, at which the working chambers of the pump are completely filled. Feed failure mode - disruption due to insufficient filling of the working chambers.

Gear pumps are characterized by the widest range of stable operation depending on the viscosity. This property of the pumps made them effective for use on machines operating in the open air, where, depending on the time of year and day, the ambient temperature varies significantly.

Due to the wear of gear pumps, their performance deteriorates. The pump does not develop the required working pressure and reduces the flow. In NSh pumps, due to the wear of the end mating surfaces of the bushings, the tightness of the sealing ring around the unloading plate decreases. This causes the oil to circulate inside the pump and reduce its supply. The misalignment of the gears and bushings in the complex in the vertical plane has the same consequences due to uneven wear of the bushings on the side of the suction cavity of the pump.

The vane pump (Fig. 65) is used on some models of loaders to drive the power steering, while using the power steering pump of the ZIL-130 car. Rotor 10 pump, freely seated on the splines of the shaft 7, has grooves in which the gates move 22. Working surface of the stator 9, attached to the body 4 pump, has an oval shape, due to which two suction and discharge cycles are provided per shaft revolution. Distribution disc // in the cavity of the cover 12 at. is compressed by the pressure of the oil entering the cavity from the injection zone. Oil is supplied to the suction zones from both sides of the rotor through two windows at the end of the housing.

Piston pumps and hydraulic motors are made of various types and purposes, depending on the location of the pistons in relation to the axis of the cylinder block or the axis of the shaft, they are divided into axial piston and radial piston. Both types can work with both pumps and hydraulic motors. A piston hydraulic motor (pump), in which the axes of the pistons are parallel to the axis of the cylinder block or make angles with it of no more than 40 °, is called axial piston. The radial piston hydraulic motor has piston axes perpendicular to the axis of the cylinder block or located at an angle of not more than 45 °,

Axial piston motors are made with an inclined block (Fig. 66, a), in them, movement is carried out due to the angle between the axis of the cylinder block and the axis of the output link or with an inclined washer (Fig. 66, b), when the movement of the output link is carried out due to the connection (contact) of the pistons with the flat end of the disk, inclined to the axis of the cylinder block.

Swashplate hydraulic motors are made, as a rule, unregulated (with a constant displacement), and hydraulic motors (pumps) with an inclined block - unregulated or adjustable (with a variable displacement). I regulate the working volume by changing the angle of inclination of the block. When the ends of the cylinder block) washers are parallel, the pistons do not move in the cylinders and the feed to coca stops, at the largest angle of inclination - the maximum feed.

b) d)

Rice. 66. Piston hydraulic motors:

a -axial piston with an inclined block, b - too, with an inclined washer. 9 - radial piston cam, G - also. crank; / - block. 2 - connecting rod. 3 - piston, 4 - rotor, 5-case, 6 - washer

Radial piston hydraulic motors are cam and crank. In cam (Fig. 66, v) the transmission of motion from the pistons to the output link is carried out by a cam mechanism, in cranks (Fig. 66, G) - crank mechanism.

hydraulic cylindersby appointment are divided into main and auxiliary. The main hydraulic cylinders are an integral part of the actuator, its engine, and the auxiliary ones ensure the operation of the control system, control or actuate auxiliary devices.

There are single-acting cylinders - plunger and double-acting - piston (Table 4). For the first ones, the extension of the input link (plunger) occurs due to the pressure of the working fluid, and the movement in the opposite direction - due to the force of the spring or gravity, for the second - the movement of the output link; (rod) in both directions is produced by the pressure of the working fluid.

The plunger cylinder (Fig. 67) is used to actuate the forklift. It consists of a welded body 2, plunger 3, bushings 6, nuts 8 and sealing elements, cuffs, sealing 5 and wiper rings.

Sleeve 6 serves as a plunger guide and at the same time limits its upward travel. It is fixed in the body with a nut. 8. The cuff seals the plunger and sleeve interface, and ring 5 seals the sleeve and housing interface. To the plunger with a pin 10 traverse is attached. Air periodically accumulates in the cylinder. A cork is used to release it into the atmosphere. 4. The plunger surface has a high finish. In order for it not to be damaged during operation, a wiper ring is installed so that dust and abrasive particles do not get into the plunger interface 3 and bushings 6; sleeve 6 made of cast iron so that the steel plunger does not bully; the cylinder is supported on the movable and fixed parts of the forklift through spherical surfaces to eliminate bending loads.

Rice. 67, Plunger cylinder:

/ - pin, 2 - frame; 3 - plunger, 4 - cork, 5, 9 - rings, 6 - sleeve,- 7 - sealing device, 8 - screw, 10- hairpin

Oil is supplied to the cylinder through a fitting at the bottom of the housing 2. At the extreme upper position, the plunger 3 rests with a shoulder in the bushing 6.

Piston cylinders (Fig. 68) have a variety of designs. For example, the forklift tilt cylinder consists of a body 12, including a sleeve and a rod bottom welded to it // with a piston 14 and sealing rings 13. Piston 14 fixed on the stem shank 11 with a nut 3 co cotter pin 2. The shank has a groove for the O-ring 4. In front of the cylinder is placed the head of the 5th cylinder with a sleeve. The stem in the head has a seal in the form of a cuff 9 with thrust ring 10. The head is fixed in the cylinder with a threaded cap 6 with wiper 7.

A necessary condition for the operation of a hydraulic cylinder is the sealing of the rod (plunger) at the point of its exit from the cylinder body, and in the piston cylinder - sealing of the rod and piston cavities. In most designs, standard rubber rings and cuffs are used for sealing. Fixed sealing is carried out by means of rubber O-rings.

On the pistons, rubber O-rings or cuffs are installed as seals. The service life of the O-ring is greatly increased when it is installed with one (for one-sided sealing) or two (for double-sided sealing) rectangular Teflon rings.

One or two seals are installed in the stem caps, as well as a wiper for cleaning the stem when it is retracted into the cylinder. Plastic seals with smaller overall dimensions have a significantly longer service life compared to rubber seals.

Rice. 68. Piston cylinder:

1 - plug, 2 - cotter pin, 3 - screw, 4, 10, 13 - rings.S - cylinder head, 6 - cover, 7 - wiper, 8 - butter dish. 9 - cuff, // - stock, 12 - case, 14 - piston

During the technical operation of hydraulic cylinders, the following basic rules should be observed. During operation, do not allow dirt to enter the working surface of the rod and protect this surface from mechanical damage; even a scratch breaks the tightness of the cylinder.

If the machine has been standing for a long time with the working surface of the rod open, then the rod is cleaned with a soft cloth soaked in oil or kerosene before work.

Leakage between the piston and rod ends while the cylinder is under heavy load may result in damage to the body or rupture of the rod cover due to the rod effect,

The pressure drop that occurs at a given flow rate, at which the valve moves to throttle the flow, is determined by the spring setting with the nut. The more the spring is tightened, the more load the valve will operate. Spring adjustable So to ensure stable lowering of the forklift without a load.

The installation of a reverse-throttle valve ensures a constant lowering rate, but does not exclude the lowering of the load and the loss of fluid in the event of a sudden break in the supply hydraulic line, which is a disadvantage of the described design. The possibility of adjusting the lowering speed by changing the pump flow is realized yc by setting the valve block of the lift cylinder, which you attach directly to the cylinder.

The valve block performs four functions: it allows the entire flow of fluid into the cylinder with minimal resistance and locks the fluid in the cylinder when the distributor spool is in the neutral position and, if the inlet hydraulic line is damaged, it regulates the fluid flow leaving the cylinder using a controlled throttle valve, while the flow rate from the cylinder is proportional to the pump performance ; provides emergency lowering of the load in case of failure of the hydraulic drive (hydraulic pump, pipelines) at the engine.

The valve block (fig. 74) consists of a body 10, in which the check valve is located 4 with rod 5 and spring 6, pilot operated valve / spring 2, fittings 3 and 9, caps, valve seats and seals. in fitting 9 a damper nut with a calibrated hole is fixed.

Turning on the distributor to lift the liquid through the fitting 3 goes to the end of the valve 4, compressing the spring with pressure, opens it and enters the cavity A cylinder. Spring force 2 valve / tightly pressed to the seat. in the cavity B there is no pressure.

Rice. 74. Valve block:

1,4 - valves, 2, 6 - springs. 3,9 - fittings. 5 - rod, 7 - locknut; 8 - cap, 10 - frame

In the neutral position of the distributor spool, the pressure of the liquid in the cylinder and the force of the spring force the valve 4 tightly pressed to the saddle; also pressed against its seat valve / spring 2, except for fluid leakage from the cylinder. By turning on the distributor for lowering, the pressure hydraulic line from the pump is connected to the cavity B and through a throttle washer with a drain V, and the cavity D communicates with plum. The higher the pump performance, the greater the pressure created in the cavity B, as the pressure drop across the throttle plate increases. By fluid pressure, the valve / moves to the left, informing the cavity A with cavity D, and the liquid passes through the annular gap into the tank.

When the valve is moved, the compression of the spring and the pressure in the cavity increase. V, since the hydraulic resistance of the drain

line increases with increasing flow proportionally opened the valve, and the pressure in the cavity is balanced B. The movement of the valve will also decrease and the valve will move to the right under the action of the spring. 2 and pressure in the cavity V, partially covering the annular gap. If, at the same time, the pump flow is reduced and thus the pressure in front of the damper nut, then the pressure in the cavity B will also decrease and by the force of spring 2 the valve will move to the right, partially blocking the annular gap.

Smooth and reliable operation of the controlled valve is ensured by the selection of the spring 2, valve diameter 1 and the angle of its conical part, the volume of the cavity and the diameter of the calibrated hole in the damper nut. In this regard, any change in the controlled valve is unacceptable, as it can lead to violations of its correct operation, for example, to the occurrence of self-oscillations, which is accompanied by valve strikes on the seat and noise.

If the drive fails, the emergency descent of the lift is carried out in the following sequence: the distributor handle is set to the neutral position, the protective cap is removed 8; the rod 5 is kept from turning by inserting a screwdriver into the slot and unscrewing the lock nut 7; the rod 5 is turned with a screwdriver counterclockwise by 3-4 turns (counting the turns along the slot); the handle of the distributor is set to the “descent” position and the forklift is lowered. If the load lifter does not lower, then the distributor handle is set to the neutral position and the rod 5 is additionally unscrewed.

After descent, the rod must be returned to its original position by rotating clockwise and the lock nut and protective cap must be replaced.

If, when the distributor handle is set to the neutral position, the load falls under the action of gravity, this indicates that the valves are not completely closed. The reasons may be: leaks at the junction of the seats with the conical surfaces due to the ingress of solid particles; jamming of one of the valves as a result of solid particles entering the gap between the body and the valves; the controlled valve does not rest against the seat due to clogging of the calibrated hole in the damper nut (liquid in the cavity B appears to be locked).

If, when moving the handle to the “lowering” position, the forklift does not lower c repents, this indicates a clogging of the calibrated hole.

To ensure safety when changing the inclination of the forklift, throttles are installed in the hydraulic lines to the tilt cylinders, an adjustable throttle with a check valve. The latter is installed in the hydraulic line to the piston cavity of the tilt cylinder.

A throttle with a check valve (Fig. - 75) consists of a housing. in which the valve 7 is located, the spring 6, nut 5, plug with seal 2, screw 4 and locknut. When the forklift is tilted back, the liquid passes into the cylinder through the check valve 7, during the reverse stroke, the liquid from the cylinder cavity is forced out to the drain through the annular gap between the side opening of the body and the plunger cones and the inclined hole in the body. By turning the nut, a gap is set that ensures a safe forward tilt speed of the forklift.

Loaders typically use two separate pumps to drive power steering implements. In the case of using one pump to supply consumers, a flow divider is installed in the hydraulic system. It is designed to divide the fluid flow into the drive of the working equipment and into the hydraulic booster, while it must be provided constant speed rotation of the wheels at different supply of the pump.

The flow divider (Fig. 76) has a body 1 with a hollow plunger 5, safety valve 4, spring 2, cork 3 and fitting 7. A diaphragm is fixed in the plunger 6 s hole. From the pump, liquid enters the cavity A and through the hole in the diaphragm into the cavity B to the hydraulic booster (or hydraulic steering wheel). The diameter of the hole in the diaphragm is chosen so that the cavity B 15 l / min enters at low engine speeds. With increasing pump performance, the pressure in the cavity A rising, plunger 5 rises by compressing the spring 2, and through the side holes in the plunger part of the fluid flow enters the distributor. At the same time, the fluid flow into the cavity increases B, the pressure in it increases and the excess fluid through the safety valve 4 goes into the cavity V and on to the tank. Plunger movement 5 and valve operation 4 provide a constant flow of fluid to power the hydraulic booster.

Rice. 75. Throttle with check valve:

/ - body, 2 - seal, 3 - plunger,

4, 5 - screw, 6 - spring, 7 - valve

Rice. 76. Flow divider:

/ - frame. 2 - spring. 3 - Cork, 4 - valve, 5 - plunger, 6 - diaphragm, 7 - fitting; A, B, C, D - cavities

In other designs of dividers, an adjustable choke is installed instead of a diaphragm with a hole.

By turning the valve handle, the siphon is connected to the atmosphere, preventing fluid from flowing out of the tank under the influence of gravity.

If the valve is opened and the pump is started, the liquid will foam, the pump will work with noise and will not develop pressure in the hydraulic system. Therefore, always before starting work, before starting the engine, check that the valve is closed.

A shut-off valve is installed in the hydraulic system of the loader to disconnect the pressure gauge. To measure the pressure, it is necessary to unscrew the valve by one or two turns, after measuring, turn off the distributor and turn on the valve. Work with the pressure gauge on permanently is not allowed.

HYDROTANKS, FILTERS, PIPING

hydraulic tankdesigned to accommodate and cool the working fluid of the hydraulic system. Its volume, depending on the supply by the pump and the volume of the hydraulic cylinders, is equal to 1-3-minute supply of the pump. The hydraulic tank includes a filler neck with a strainer and a valve connecting its cavity with the atmosphere, a liquid level indicator, a drain plug. Tank reservoir - welded, with a transverse partition. Suction and drain tubes in the form of siphons are placed on different sides of the partition, which makes it possible to dismantle the hydraulic lines suitable for the hydraulic tank without draining the liquid. 10-15% of the tank volume is usually occupied by air.

Filtersare used to clean the working fluid in the hydraulic system.

Filters are built into the tank or installed separately. The filter in the hydraulic tank filler neck provides cleaning when refueling. He made of wire mesh; its filtering qualities are characterized by the size of the cell in the light and the area of ​​the passage section of the cells per unit surface area. In some cases, mesh filters with 2-3 layers of filter meshes are used, which increases the cleaning efficiency.

A drain filter with a bypass valve is installed on the drain hydraulic line of domestic loaders (Fig. 77). The filter consists of a housing 6 with lid 10 and fitting 1, in which the filter elements are placed on the tube 5 4 with felt rings 7 at the ends tightened with a nut 16. The body is fixed on top of the tube 14 relief valve. Ball 13 pressed by a spring /5, which is held in the tube with brackets 17, 18. The filter is installed on the drain line from the power steering.

The liquid enters the outer side of the filter elements and, passing through the cells of the elements and through the slot in the tube 5, enters the central channel connected to the drain hydraulic line. By As the hydraulic system operates, the filter elements become contaminated, the filter resistance increases, when a pressure of 0.4 MPa is reached, the bypass valve opens, and the liquid is drained into the uncleaned tank. The passage of liquid through the valve is accompanied by a specific noise, which indicates the need to clean the filter. Cleaning is carried out by partial disassembly of the filter and washing of the filter elements. Installing a filter on the drain from the hydraulic booster operating at a lower pressure does not cause pressure losses in the hydraulic system of the working equipment.

On loaders "Balkankar" the filter is installed in the suction line (suction filter) and placed in the hydraulic tank. The suction filter (Fig. 78) contains a housing /,

Rice. 77. Drain filter with bypass valve:

/ - Union, 2, 7, 11, 12 - rings, 3 - pin, 4 - filter element, 5 - a tube, 6 - frame, 8 - cap. 9, 15 - springs, 10 - lid, 13 - ball. 14 - body, valve, 16 - screw, 17, I8 - staples

Rice. 78. Suction filter:

/ - frame, 2 - spring, 3 - lid, 4 filter element, 5 - valve

between covers 3 which the filter element is located 4. The covers and the element are pressed against the body by a spring 2. The filter element is made of brass mesh, which has 6400 holes per 1 cm2, which provides a cleaning accuracy of 0.07 mm. If the mesh becomes clogged, the liquid is sucked in by the hydraulic pump through the bypass valve. 5. The factory setting of the bypass valve should not be disturbed in operation - this can cause backwater on the drain if the filter is installed in the drain line, or cavitation of the hydraulic pump if the filter is installed in the suction line.

Pipelineshydraulic drive is made of steel pipes, high and low pressure hoses (suction hydraulic line). Sleeves are used to connect parts of hydraulic systems that are movable relative to each other.

For the installation of parts of pipelines, connections with an internal cone are used (Fig. 79, a). The tightness of the connection is ensured by tight contact of the surface of the steel ball nipple with conical surface nipple / with nut 2. The nipple is butt welded to the pipe.

Rice. 79. Piping connections:

a - with an inner ring, b - with flaring, c - with a cutting ring;

1 - Union, 2 - screw, 3, 5 - nipples, 4 - pipe, 6 - crash ring

Pipes of small diameter (6.8 mm) are connected with flaring (Fig. 79, b) or with a cutting ring (Fig. 79, v). In the first case, the pipe 4 is pressed against the fitting with a conical nipple 5 with the help of a nut, in the second - the seal is made by the sharp edge of the ring when the union nut is screwed.

When installing hoses, they must not be bent at the place of termination, twisted along their longitudinal axis. It is necessary to provide a margin in length for shortening the length of the hose under pressure. Sleeves must not touch any moving parts of the machine.

LOADER HYDRAULIC DIAGRAMS

Schematic hydraulic diagrams show the structure of hydraulic systems using conventional graphic symbols (Table 5),

Consider a typical hydraulic diagram of a 4045P loader (Fig. 80). It includes two independent hydraulic systems with common tank 1. The tank is equipped with a filling filter 2 with a ventilation valve-prompter, and the suction hydraulic line coming from the tank has a jet break valve 3. Two small hydraulic pumps are driven from a common shaft 5 - for driving the hydraulic booster and a large 4 - to drive working equipment. From the large pump, liquid is supplied to a monobloc distributor that includes a safety valve and three spools: one to control the lift cylinder, another to control the tilt cylinder, and a third to work with additional attachments. From the spool 6 liquid through one hydraulic line is directed to the block 12 valves and into the cavity of the lift cylinder, and through another parallel to the control cavity of the valve block and into the drain line through the throttle 13.

The executive hydraulic lines of the spool 7 are connected in parallel with the tilt cylinders of the forklift: one - with piston cavities, the other - with rod cavities. Throttles are installed at the entrance to the cavity. The third spool is a reserve. one

In the neutral position of the distributor, the liquid from the pump is supplied to each spool of the distributor and through open channel in the spools merges into the tank. If the spool is shifted to one or another working position, then the drain channel is locked and through the other channel opened at the same time, the liquid enters the executive hydraulic line, and the opposite hydraulic line is connected co drain.

In the “Lift” position of the lift cylinder spool, fluid flows into the cylinder cavity through the check valve of the valve block and lifts the forklift. In the specified and neutral positions of the spool, the return flow of liquid is excluded, i.e. the forklift cannot lower. In the spool position Ha lowering” the pressure line from the pump communicates with the drain through the throttle and simultaneously enters the control cavity of the valve block. At low engine speeds, the pressure in the cavity of the small controlled valve will open slightly, the flow from the cylinder cavity will be small and the speed of lowering the load will be limited.

To increase the lowering speed, it is necessary to increase the engine speed, the pressure in front of the throttle will increase, controlled, the valve will open by a large amount and the flow from the cylinder cavity will increase.

Throttles are installed in the hydraulic lines to the cavities of the tilt cylinders, which limit the tilt speed of the forklift.

In the hydraulic system of loaders "Balkankar" (Fig. 81) to drive the working equipment and the mechanism for turning the wheels is used

Rice. 80. Hydraulic diagram of the loader 4045R:

I-tank, 2 -filter, 3 - valve, 4, 5 - hydraulic pumps, 6, 7 - spools. 8 - tap, 9 - manometer. 10,II - cylinders, 12 - valve block, 13 - choke, 14, - filter, 15 - hydraulic booster

one pump. The working fluid to the pump comes from the tank / through the filter 2 s bypass valve and is fed to the flow divider, which directs part of the liquid to the hydraulic steering 17, and the rest of the flow - to the sectional distributor // containing four spools and a safety valve 5. From the spool 9 to lift cylinder cavity 13 through the check valve 12 there is one hydraulic line. When lifting, the entire fluid flow will go into the cylinder cavity, and when lowering, the flow rate is limited by the flow area of ​​the throttle. Also through the back-throttle valve ,

Rice. 81. Hydraulic system loader "Balkankar": I

1 - tank, 2- filter. 3 - pump, 4, 5, 10, It, 15 - valves, 6-9 - spools, 11 - distributor. 13, 14, 16 - cylinders, 16 - flow divider, 17 - hydraulic steering

oil is directed to the rod ends of the tilt cylinders, allowing the forklift to slowly tilt forward for safety.

Spools b and 7 are designed for attached working equipment. The fluid pressure in the hydraulic actuators of the attachments is controlled by a separate relief valve.

Modern mechanisms, machines and machine tools, despite the seeming complex device, are a collection of so-called simple machines - levers, screws, gates and the like. The principle of operation of even very complex devices is based on the fundamental laws of nature, which are studied by the science of physics. Consider, as an example, the device and principle of operation of a hydraulic press.

What is a hydraulic press

A hydraulic press is a machine that generates a force that is much greater than that originally applied. The name "press" is rather arbitrary: such devices are often really used for compression or pressing. For example, to get vegetable oil oilseeds are strongly pressed, squeezing out the oil. In industry, hydraulic presses are used to manufacture products by stamping.

But the principle of the hydraulic press device can be used in other areas. The simplest example: a hydraulic jack is a mechanism that allows, with the application of a relatively small effort of human hands, to lift loads, the mass of which obviously exceeds the capabilities of a person. On the same principle - the use of hydraulic energy, the action of a variety of mechanisms is built:

• hydraulic brake;
• hydraulic shock absorber;
• hydraulic drive;
• hydraulic pump.

The popularity of mechanisms of this kind in various fields of technology is due to the fact that huge energy can be transmitted with the help of quite simple device consisting of thin and flexible hoses. Industrial multi-ton presses, booms of cranes and excavators - all these are indispensable in modern world machines work efficiently thanks to hydraulics. In addition to industrial devices of gigantic power, there are many manual mechanisms, such as jacks, clamps and small presses.

How a hydraulic press works

To understand how this mechanism works, you need to remember what communicating vessels are. This term in physics refers to vessels interconnected and filled with a homogeneous liquid. The law of communicating vessels says that a homogeneous fluid at rest in communicating vessels is at the same level.

If we disturb the state of rest of the liquid in one of the vessels, for example, by adding liquid, or by applying pressure on its surface in order to bring the system to the equilibrium state that any system strives for, the liquid level will increase in the remaining vessels communicating with this vessel. This happens on the basis of another physical law, named after the scientist who formulated it - Pascal's law. Pascal's law is as follows: the pressure in a liquid or gas is distributed equally to all points.

What is the principle of operation of any hydraulic mechanism based on? Why can a person easily lift a car weighing more than a ton to change a tire?

Mathematically, Pascal's law looks like this:

The pressure P is directly proportional to the applied force F. This is understandable - the harder you push, the greater the pressure. And inversely proportional to the area of ​​the applied force.

Any hydraulic machine is a communicating vessel with pistons. The schematic diagram and device of the hydraulic press are shown in the photo.

Imagine that we have pressed a piston in a larger vessel. According to Pascal's law, pressure began to spread in the liquid of the vessel, and according to the law of communicating vessels, in order to compensate for this pressure, the piston rose in a small vessel. Moreover, if in a large vessel the piston has moved one distance, then in a small vessel this distance will be several times greater.

Conducting an experiment, or a mathematical calculation, it is easy to notice a pattern: the distance by which the pistons move in vessels of different diameters depends on the ratio of the smaller area of ​​the piston to the large one. The same will happen if, on the contrary, force is applied to a smaller piston.

According to Pascal's law, if the pressure obtained by the action of the force applied to the unit area of ​​the piston of the small cylinder is distributed equally in all directions, then the pressure will also be applied to the large piston, only increased by as much as the area of ​​the second piston is larger than the area of ​​the smaller one.

This is the physics and structure of the hydraulic press: the gain in strength depends on the ratio of the areas of the pistons. By the way, in a hydraulic shock absorber, the reverse ratio is used: a large force is damped by the shock absorber hydraulics.

The video shows the operation of a model of a hydraulic press, which clearly illustrates the operation of this mechanism.

The device and operation of the hydraulic press obeys the golden rule of mechanics: winning in strength, we lose in distance.

From theory to practice

Blaise Pascal, theoretically thinking through the principle of the hydraulic press, called it a "machine for increasing forces." But more than a hundred years have passed from the moment of theoretical research to practical implementation. The reason for this delay was not the uselessness of the invention - the benefits of the machine for increasing strength are obvious. Designers have made numerous attempts to build this mechanism. The problem was the difficulty of creating a sealing gasket that would allow the piston to fit snugly against the walls of the vessel and at the same time allow it to slide easily, minimizing friction costs - after all, there was no rubber then.

The problem was solved only in 1795, when the English inventor Joseph Bramah patented a mechanism called the Bramah press. Later, this device became known as a hydraulic press. The scheme of operation of the device, theoretically outlined by Pascal and embodied in Brahma's press, has not changed at all over the past centuries.

Appointment of pressure and flow.

When studying the basics of hydraulics, the following terms were used: force, energy transfer, work and power. These terms are used to describe the relationship between pressure and flow. Pressure and flow are the two main parameters of every hydraulic system. Pressure and flow are related but do different jobs. Pressure compresses or applies force. The flow moves objects The water gun is good example pressure and flow in application. Pulling the trigger creates pressure inside the water gun. Pressurized water flies out of a water pistol and thus knocks down a wooden soldier.

What is pressure?

Let's think about how and why pressure is created. The fluid medium (gas and liquid) tends to expand or resistance occurs when they are compressed. This is pressure. When you inflate a tire, you create pressure in the tire. You are pumping more and more air into the tire. When the tire is completely filled with air, there is pressure on the walls of the tire. This pressure is a type of pressure. Air is a type of gas and can be compressed. Compressed air presses against the tire walls with the same force at each point. The fluid is under pressure. The main difference is that gases can be compressed into balls.

Equal force at every point

Pressure in a compressed liquid

If you press on a compressed liquid, pressure will build up. As with a tire, the pressure is the same at every point on the barrel containing the liquid. If the pressure is too high, the barrel may break. The barrel will break at the weak point, not where there is more pressure, because the pressure is the same at every point.

The liquid is almost incompressible

A compressible fluid is useful for transferring force through pipes, bends, up, down, because fluids are almost incompressible and the transfer of energy is immediate.

Many hydraulic systems use oil. This is because oil is almost incompressible. At the same time, oil can be used as a lubricant.

Pascal's law: The pressure produced by external forces on the surface of a liquid or gas is transmitted in all directions without change.

Section 2

Relationship between pressure and force

According to Pascal's law, the relationship between pressure and force is expressed by the formulas:

F = P / S, where P is pressure, F is force, S is area

hydraulic lever

In the piston model shown in the figure below, you can see an example of balancing different weights through a hydraulic lever. Pascal discovered, as seen in this example, that the light weight of a small piston counterbalances the large weight of a large piston, proving that the area of ​​the piston is proportional to the weight. This discovery is applied to a compressible fluid. The reason why this is possible is that a fluid always acts with equal force over an equal area.

The figure shows a load of 2 kg and a load of 100 kg. The area of ​​one load, weighing 2 kg - 1 cm?, pressure is 2 kg / cm?. The area of ​​another cargo weighing 100 kg is 50 cm?, the pressure is 2 kg/cm?. Two weights balance each other.

mechanical lever

The same situation can be illustrated by the example of a mechanical lever in the figure below.

A 1 kg cat sits 5 meters from the center of gravity of the lever and balances a 5 kg cat 1 meter from the center of gravity, similar to the weight on the example of a hydraulic lever.

Hydraulic arm energy conversion

It is important to remember that a fluid acts with an equal force on an equal area. It helps a lot at work.

There are two cylinders of the same size. When we press one piston with a force of 10 kg, the other piston is pushed out with a force of 10 kg, because the area of ​​each cylinder is the same. If the areas are different, the forces are also different.

For example, let's say that the large piston has an area of ​​50 cm², and the small piston has an area of ​​1 cm², with a force of 10 kg, the small piston is subjected to an impact of 10 kg/cm². for each part of the large valve according to Pascal's law, so the large piston receives a total force of 500 kg. We use pressure to transfer energy and do work.

Available important point in the transformation of energy, namely the relation between force and distance. Remember, on a mechanical lever, low weight requires a long lever to achieve balance. In order to lift a 5 kg cat by 10 cm, a 1 kg cat must lower the lever 50 cm down.

Let's look at the drawing of the hydraulic arm again and think about the stroke of the small piston. The small piston stroke of 50 cm is needed to transfer enough fluid to move the large cylinder piston 1 cm.

Section 3

Flow creates movement

What is a stream?

When there is a difference in pressure between two points in a hydraulic system, the fluid tends to the point with the lowest pressure. This movement of fluid is called flow.

Here are some examples of flow. Water in the city water supply creates pressure. When we turn the faucet, water flows out of the faucet due to the pressure difference.

In a hydraulic system, the flow is created by a pump. The pump creates a continuous flow.

Flow rate and magnitude

The flow rate and magnitude are used to measure the flow.

Speed ​​shows the distance traveled in a given period of time.

The flow rate shows how much fluid flows through a certain point at a given time.

Flow rate, lit./min.

Flow rate and speed

In a hydraulic cylinder, it is easy to see the relationship between flow and speed.

First, we need to think about the volume of the cylinder that we need to fill and then think about the piston stroke.

The figure shows cylinder A, 2 meters long and with a volume of 10 liters, and cylinder B, 1 meter long and with a volume of 10 liters. If you pump 10 liters of fluid per minute into each cylinder, the full stroke of both pistons lasts 1 minute. The piston of cylinder A is moving twice as fast as cylinder B. This is because the piston has to cover twice as much distance in the same amount of time.

This means that a cylinder with a smaller diameter moves faster than a cylinder with a larger diameter at the same flow rate for both cylinders. If we increase the flow rate to 20 l/min, both chambers of the cylinder will fill twice as fast. The piston speed should double.

Thus, we have two ways to increase the speed of the cylinder. One by reducing the size of the cylinder and the other by increasing the flow rate.

The speed of the cylinder is thus proportional to the flow rate and inversely proportional to the area of ​​the piston.

pressure and force

Building pressure

If you push on the cork in a barrel filled with liquid, the cork will be stopped by the liquid. When pressed, the liquid under pressure presses against the walls of the barrel. Pressing too hard may break the barrel.

path of least resistance

If there is a barrel with water and a hole. When you press the lid on top, water flows out of the hole. Water passing through the hole meets no resistance.

When a force is applied to a compressed fluid, the fluid seeks the path of least resistance.

Equipment malfunctions using oil pressure.

The characteristics of hydraulic fluids described above are useful for hydraulic equipment, but they are also the source of many problems. For example, if there is a leak in the system, hydraulic fluid will flow out as it seeks the path of least resistance. Typical examples are leaking loose connections and seals.

natural pressure

We talked about pressure and flow, but often there is pressure without flow.

Gravity is a good example. If we have three interconnected reservoirs of different levels, as shown in the figure, gravity keeps the liquids in all reservoirs at the same level. This is another principle that we can use in a hydraulic system.

Liquid mass

The mass of the fluid also creates pressure. A diver who dives into the sea will say that he cannot dive too deep. If the diver goes too deep, the pressure will crush him. This pressure is created by the mass of water. Thus, we have a kind of pressure that appears independently from the weight of water.

Pressure increases with depth and we can accurately measure pressure at depth. The figure shows a square column with water 10 meters high. It is known that one cubic meter water weighs 1000 kg. By increasing the height of the column to 10 meters, the weight of the column will increase to 10,000 kg. One is formed at the bottom square meter. Thus, the weight is distributed over 10,000 square centimeters. If we divide 10,000 kg by 10,000 square centimeters, we get that the pressure at this depth is 1 kg per 1 square centimeter.

The meaning of gravity

Under the influence of gravity, oil flows from the tank to the pump. The oil is not sucked up by the pump as many people think. The pump is used to supply oil. What is commonly understood as pump suction refers to the supply of oil to the pump by gravity.

Oil is supplied to the pump by gravity.

What causes pressure?

When pressure mixes with flow, we have hydraulic force. Where does the pressure in the hydraulic system come from? Part is the result of gravity, but where does the rest of the pressure come from.

Most of the pressure comes from the impact of the load. In the figure below, the pump supplies oil continuously. The oil from the pump finds the path of least resistance and is directed through the hose to the slave cylinder. The weight of the load creates pressure, the magnitude of which depends on the weight.

Hydraulic power of the working cylinder

(1) The law of inertia says that the property of a body to maintain its state of rest or rectilinear uniform motion until some external force takes it out of this state. This is one reason why the slave cylinder piston does not move.

(2) Another reason why the piston does not move is that there is a weight on it.

Flow

Earlier we said that the flow does work and moves things. There is another key moment- How does the flow rate relate to the operation of the hydraulic system?

The answer is that the flow rate is constant,

Increasing flow rate creates high speed

Many people think that increasing pressure increases speed, but this is not true. You cannot make the piston move faster by increasing the pressure. If you want to make the piston move faster, you must increase the flow rate.

Pressure in parallel connection

There are three different weights connected in parallel in one hydraulic system, as shown in the figure below. Oil, as usual, seeks the path of least resistance. This means that the lightest weight will rise first because cylinder B will need the least pressure. When the lightest weight is lifted, the pressure builds up to lift the next heaviest weight remaining. When cylinder A reaches the end of its stroke, the pressure will increase to lift the heaviest load. Cylinder C will rise last.

(3) When the pump presses against the cylinder, the working piston and weight resist the oil flow. Thus, the pressure increases. When this pressure overcomes the resistance of the piston, the piston begins to move.

(4) When the piston moves up, it lifts the load. Pressure and flow are used together to get the job done. This is hydraulic force in action.

When the safety valve is closed, the speed does not increase

Here is one common mistake when troubleshooting a hydraulic system. When the cylinder speed drops, some mechanics go straight to the relief valve because they think that increasing the pressure will increase the operating speed. They try to lower the relief valve setting, which is supposed to increase the maximum pressure in the system. Such changes do not lead to an increase in the speed of action. Safety valve serves to protect the hydraulic system from excessive pressure. The pressure setting must never be higher than the set pressure. Instead of raising pressure settings, mechanics should look for other causes of system failure.

Conclusion

Now you have knowledge of the basics of the theory of hydraulics. You know that Pascal's Law says that the pressure produced by external forces on the surface of a liquid or gas is transmitted in all directions without change.

You also learned that pressurized hydraulic fluid takes the path of least resistance. This is good when it works for us and bad when it causes a leak in the system. You have seen how we can use low weight on one cylinder to propel heavy weight on another cylinder. In this case, the small load piston stroke is longer. You also gained a clear understanding of the relationship between pressure and force, flow and speed, and of course pressure and flow.

Hydraulic mechanisms

Hydraulic systems

Hydraulic systems are used to transfer mechanical energy from one place to another. This happens through the use of pressure energy. The hydraulic pump is driven by mechanical energy. The mechanical energy is converted into pressure energy and kinetic energy of the hydraulic fluid and then converted back into mechanical energy to do work.

Energy conversion value

The energy that is transferred to the hydraulic system is converted from the mechanical energy of the engine, which drives the hydraulic pump. The pump converts mechanical energy into fluid flow by converting mechanical energy into pressure energy and kinetic energy. The fluid flow is transmitted through the hydraulic system and directed to the cylinder and motor drives. The pressure energy and the kinetic energy of the fluid cause the actuator to move. With this movement, another transformation into mechanical energy occurs.

How it works in a hydraulic excavator.

In hydraulic excavators, the primary mechanical energy of the engine drives the hydraulic pump. The pump directs the flow of oil to the hydraulic system. When the actuator moves under the action of oil pressure, the conversion into mechanical energy occurs again. The excavator boom can be raised or lowered, the bucket is moving, etc.

Hydraulics and work

Three elements of work

When there is any work, then certain conditions are necessary for the performance of this work. You need to know how much power is needed. You have to decide how quickly the work needs to be done and you have to determine the direction of the work. These are the three working conditions: force, speed and direction are used in hydraulic terms as shown below.

Hydraulic System Components

Main Components

The hydraulic system consists of many parts. The main parts are the pump and the drive. The pump supplies oil by converting mechanical energy into pressure energy and kinetic energy. The drive is the part of the system that converts hydraulic energy back into mechanical energy to do work. Parts other than the pump and drive are essential for the complete operation of the hydraulic system.

Tank: oil storage

Valves: control of the direction and magnitude of flow or pressure limitation

Piping lines: connection of system parts

Let's look at two simple hydraulic systems.

Example 1, hydraulic jack

What you see in the picture is called a hydraulic jack. When you apply force to the lever, the hand pump pumps oil into the cylinder. The pressure of this oil presses on the piston and lifts the load. The hydraulic jack is in many ways similar to Pascal's hydraulic lever. A hydraulic tank has been added here. A check valve is installed to keep oil in the tank and cylinder between piston strokes.

In the top figure, pressure is held, check valve is closed. When the pump handle is pulled up, the inlet check valve opens and oil flows from the tank into the pump chamber.

The bottom drawing shows an open check valve to connect the tank and cylinder, allowing oil to flow into the tank while the piston moves down.

Example 2, hydraulic cylinder operation

1. First, there is a hydraulic tank filled with oil and connected to a pump.

3. The pump is running and pumping oil. It is important to understand that the pump only moves volume. The volume sets the speed of the hydraulic action. The pressure is generated by the load and not generated by the pump.

4. The hose from the pump is connected to the control valve. Oil flows from the pump to the valve. The operation of this valve is to direct the flow either to the cylinder or to the tank.

5. The next step is the cylinder that does the actual work. Two hoses from the control valve are connected to the cylinder.

6. The oil from the pump is directed to the lower cavity of the piston through the control valve. The load causes resistance to flow, which in turn creates pressure.

7. The system looks complete, but it's not. Still very much needed important detail. We must know how to protect all components from damage in the event of a sudden overload or other incident. The pump continues to run and supply oil to the system, even if the system has experienced an accident.

If the pump delivers oil and there is no way for the oil to escape, the pressure builds up until a part breaks. We install a safety valve to prevent this. Usually it is closed, but when the pressure reaches the set value, the safety valve opens and oil flows into the tank.

8. Tank, pump, control valve, cylinder, connecting hoses and safety valve are the basis of the hydraulic system. All these details are necessary.

Now we have clear view how the hydraulic system works.

Pump classification

What is a pump?

Like your heart, which pumps blood through your body, the pump is the heart of the hydraulic system. The pump is the part of the system that pumps oil to do work. As we wrote earlier, a hydraulic pump converts mechanical energy into pressure energy and kinetic energy of the fluid.

What is a hydraulic pump?

Each pump creates a flow. Fluid moves from one place to another.

There are two types of displacement pumps.

Forced action pump

Non forced action pump

The water circle in the figure is an example of a non-forced pump. The circle lifts the liquid and moves it.

Another forced action pump. It is called forced action, since the pump pumps fluid and prevents it from returning back. If the pump cannot do this, there will not be enough pressure in the system. Today, all hydraulic systems use high pressure, and thus positive-acting pumps are needed.

Types of hydraulic pumps

Today, many machines have one of three pumps installed:

• Gear pump
• Vane pump
• piston pump

All pumps operate on a rotary piston type, the fluid is driven by the rotation of a part inside the pump.

Piston pumps are divided into two types:

Axial piston type

Radial piston type

Axial piston type pumps are so named because the pump pistons are parallel to the pump axis.

Radial piston pumps are so named because the pistons are perpendicular (radial) to the pump axis. Both types of pumps are reciprocating. The pistons move forward and backward and use rotary piston motion.

Displacement of hydraulic pump

Displacement means the amount of oil that the pump can pump or move in each cylinder. Hydraulic pumps are divided into two types:

Fixed working volume

Variable working volume

Fixed displacement pumps pump the same amount of oil every cycle. To change the volume of such a pump, it is necessary to change the speed of the pump.

Variable displacement pumps can change oil volume depending on the cycle. This can be done without changing the speed. Such pumps have an internal mechanism that regulates the output amount of oil. When the pressure in the system drops, the volume increases; when the pressure in the system increases, the volume decreases automatically.

Power

Fixed displacement pump Variable displacement pump

Design

Drive classification

What is a drive?

The drive is part of the hydraulic system that produces power. The actuator converts hydraulic energy into mechanical energy to do work. There are linear and rotary drives. The hydraulic cylinder is a linear actuator. The force of the hydraulic cylinder is directed in a straight line. The hydraulic motor is a rotary drive. The output force is torque and rotary action.

Rotary drive

Linear drive

Hydraulic cylinders

Hydraulic cylinders are like a lever. There are two types of cylinders.

Single acting cylinders.

Hydraulic fluid can only move to one end of the cylinder. The return of the piston to its original position is achieved by the action of gravity.

Double acting cylinders.

Hydraulic fluid can move to both ends of the cylinder, so the piston can move in both directions.

In both types of cylinders, the piston moves in the cylinder in the direction in which the fluid pushes against the piston. Various types of seals are used in pistons to prevent leakage.

Single acting cylinder

Double acting cylinder

hydraulic motor

Like a cylinder, a hydraulic motor is a drive, only a rotary drive.

The principle of operation of a hydraulic motor is exactly the opposite of that of a hydraulic pump. The pump delivers fluid and the hydraulic motor is powered by that fluid. As we wrote earlier, a hydraulic pump converts mechanical energy into pressure energy and kinetic energy of the fluid. The hydraulic motor converts hydraulic energy into mechanical energy.

With hydraulic drive, pumps and motors work together. The pumps are mechanically driven and pump fluid into hydraulic motors.

The motors are driven by fluid from the pump and this movement in turn rotates the mechanical parts.

Types of hydraulic motors

There are three types of hydraulic motors and they all have internal moving parts that are driven by the incoming flow, their name is:

• gear motor
• vane motor
• piston motor

displacement and torque

The operating time of the motor is called torque. This is the rotational force of the motor shaft. Torque is a measure of force per unit length, it does not include speed. Motor torque is determined by the maximum pressure and volume of fluid that can move during each cycle. The motor speed is determined by the amount of flow. More flow, faster speed.

Torque is the force of rotation of the motor shaft.

Torque equals force x distance

Valve classification

What are the valves?

Valves are the controls in a hydraulic system. Valves control the pressure, direction of flow, and amount of flow in a hydraulic system.

There are three types of valves:

The figure below shows how the valves work.

Pressure control valves

These valves are used to limit pressure in a hydraulic system, unload a pump, or adjust circuit pressure. There are several types of pressure control valves, some of them are safety valves, pressure reducing valves and unloading valves.

Pressure control valves

The pressure control valve is used for the following purposes:

System pressure limits

pressure reduction

Circuit inlet pressure setting

Pump unloading

A safety valve is sometimes called a safety valve because it relieves excessive pressure when it reaches its extreme. The safety valve prevents parts of the system from being overloaded.

There are two types of safety valve:

Safety valve direct action that simply open and close.

Pilot Relief Valve, which has a pilot line to control the main relief valve.

The direct operated relief valve is usually used in places where the flow volume is small and the work is rarely repeated. A pilot line safety valve is required in places where a large volume of oil must be reduced.

Direction control valve

This valve controls the flow direction of the hydraulic system. A typical directional control valve is a control valve and spool.

Value control valve

This valve controls the oil flow rate of the hydraulic system. Control occurs by restricting the flow or diverting it. Several different types of quantity control valve are the flow control valve and the flow dividing valve.

These valves are controlled different ways: manually, hydraulically, electrically, pneumatically.

Directional Control Valves

This valve sets the flow of oil, just like a traffic controller controls traffic. These valves are:

check valve

Spool valve

Are used different types direction control structures.

A check valve uses a poppet valve and a spring to direct flow in one direction. The spool valve uses a movable cylindrical spool. The spool moves back and forth, opening and closing channels for flow.

check valve

The check valve is simple. It is called a single flow valve. This means that it is open for flow in one direction, but closed for oil to flow in the opposite direction.

In the figure below you can see the operation of the check valve. This is a check valve that is designed for through flow in one line. The poppet valve opens when the inlet pressure is greater than the outlet pressure. When the valve is open, oil flows freely. The poppet valve closes when the intake pressure drops. The valve interrupts the flow in the opposite direction and stops the flow under the action of the outlet pressure.

Spool valve

A spool valve is a typical control valve that is used to control the operation of an actuator. What is commonly referred to as a control valve is a spool valve. The spool valve directs the flow of oil to start, run and end work.

When the spool moves from the neutral position to the right or to the left, some channels open and other channels close. In this way, oil is supplied to and from the drive. The collar of the spool tightly blocks the incoming and outgoing oil flows.

The spool is made of durable material and has a smooth, precise, strong surface. It's even chrome plated to resist wear, rust and damage.

The spool valve in the figure shows three positions, neutral, left and right. We call it four-position because it has four possible directions, which are directed to both cavities of the cylinder, to the tank and to the pump.

When we move the spool to the left, the oil flow is directed from the pump to the left side of the cylinder and the flow from the right side of the cylinder is directed to the tank. As a result, the piston moves to the right.

If we move the spool to the right, the actions are exactly the opposite, respectively, the piston moves to the right.

In the center position, neutral, the oil is directed to the tank. Channels in both cavity of the cylinder are closed.

neutral

Value Control Valves

As we wrote earlier, the value control valve works in one of two directions. It either blocks the flow or changes its direction.

flow control valve used to control the drive speed by measuring the flow. Measurement involves measuring or controlling the flow rate to or from the actuator. The flow split valve regulates the amount of flow, but also splits the flows between two or more circuits.

Split valve manages the amount of flow, but also splits flows between two or more chains.

Proportional flow divider

The purpose of this valve is to divide the flow from one source.

The flow divider in the figure below divides the flows in a ratio of 75-25 at the output. This is possible because input #1 is larger than input #2.

Hydraulic circuit

Earlier in the text, drawings were given to help understand the principles of the hydraulic system and its constituent parts. We tried to show the construction with different examples and used different types of drawings.

The drawings we use are called graphic diagrams.

Each part of the system and each line is represented by a graphic symbol.

The following are examples of a graphical chart.

It is important to understand that the purpose of a graphic diagram is not to show device details. The graphical diagram is only used to show functions and connections.

Line classification

All components of the hydraulic system are connected by lines. Each line has its own name and performs its function. Main lines:

Working lines: Pressure line, Suction line, Drain line

Non-working lines: Drainage line, Pilot line

The oil of the working line is involved in the conversion of energy. The suction line delivers oil from the tank to the pump. The pressure line delivers oil from the pump to the drive under pressure to do the work, and the drain line returns the oil from the drive back to the tank.

Non-working lines are additional lines that are not used in the main functions of the system. The drain line is used to return excess oil or pilot line oil to the tank. The pilot line is used to control the working bodies.

Advantages and disadvantages of the hydraulic system

We have learned the basic principles of the hydraulic system.

Before concluding, let's look at the advantages and disadvantages of the hydraulic system over other systems.

Advantages

1. Flexibility - limited fluid is more flexible energy source and has good energy transfer properties. The use of high pressure hoses and hoses instead of mechanical parts eliminates many problems.

2. Power increase - Small power can control big power.

3. Smoothness - The operation of the hydraulic system is smooth and quiet. Vibration is kept to a minimum.

4. Simplicity - There are few moving parts and a small number of hydraulic connections, as well as self-lubricating.

5. Compact - The arrangement of the component parts is very simple compared to mechanical arrangements. For example, a hydraulic motor is much smaller than an electric motor that produces the same amount of power.

6. Savings - Simplicity and compactness ensures the economy of the system with small power losses.

7. Safety - The safety valve protects the system from overloads.

Flaws

NEED FOR TIMELY MAINTENANCE - The components of the hydraulic system are precision parts and work under high pressure. Timely maintenance is necessary to protect against rust, oil contamination, increased wear, so the use and replacement of the appropriate oil is a must.

A little more about hydraulics

Loss of energy (pressure)

Another important point to understand the basics of hydraulics is the loss of energy (pressure) in the hydraulic system.

For example, some resistance to flow causes a decrease in flow pressure, resulting in energy loss.

Now let's look at some details.

Oil viscosity.

Oil has viscosity. The viscosity of the oil itself creates resistance to flow.

Resistance to flow due to friction.

During the passage of oil through the pipes, the pressure decreases due to friction.

This decrease in pressure increases in the following cases:

1) When using a long pipe

2) Use of small diameter pipe

3) With a sharp increase in flow

4) With high viscosity

Reduced pressure for other reasons

In addition to pressure reduction due to friction, losses can occur due to a change in the direction of flow and a change in the oil flow channels.

Oil flow through throttle

As we said before, pressure reduction occurs when oil flow is restricted.

A throttle is a type of restriction often installed in a hydraulic system to create a pressure difference in the system.

However, if we stop the flow behind the throttle, Pascal's law applies and the pressure equalizes on both sides.

Loss of energy

As you well know, there are many pipes, fittings (connections) and valves included in the hydraulic system.

A certain amount of energy (pressure) is only used to move oil from one place to another, before work is done.

Lost energy is converted into heat

The energy loss due to pressure reduction is converted into heat. An increase in oil flow, an increase in oil viscosity, an increase in the length of a pipe or hose, and similar changes cause an increase in resistance and cause overheating.

To avoid this problem, use replacement parts identical to the original ones.

Pump efficiency

As we said earlier in the preceding text, a hydraulic pump converts mechanical energy into hydraulic energy. The efficiency of the pump is checked by its performance and is one of the points in the performance test. Pump efficiency refers to how well a pump does its job.

There are three approaches to determining pump efficiency.

FEEDING EFFICIENCY

TORQUE EFFICIENCY (MECHANICAL)

TOTAL EFFICIENCY

Torque efficiency

Torque efficiency is the ratio of the pump's actual output torque to the pump's input torque.

The actual output torque of the pump is always less than the input torque of the pump. Torque loss occurs due to friction of the moving parts of the pump.

Full Efficiency

Total efficiency is the ratio of the hydraulic power output to the mechanical power input of the pump.

It is the magnitude of both: feed efficiency and torque efficiency. In other words, the overall efficiency can be expressed as the output power divided by the input power. The output power is less than the input power due to losses in the pump due to friction and internal leakage.

In general, the efficiency of gear and piston pumps is 75 - 95%.

A piston pump is usually rated higher than a gear pump.

Feed efficiency

Delivery efficiency is the ratio of the actual pump delivery to the theoretical pump delivery. In reality, the actual pump flow is less than the theoretical pump flow.

This is usually expressed as a percentage.

The difference is usually expressed as an internal leak in the pump due to holes in the working parts of the pump.

Some holes are made in all parts for lubrication.

Internal leakage occurs when pump parts are worn, produced with a small tolerance.

We consider increased internal leakage as a loss of efficiency.

Power required to run the pump

For the reasons given earlier, the power required to run the pump must be greater than the output power.

Here is an example of a 100 HP pump.

If the pump efficiency is 80%, then 125 hp must be supplied.

Power Needed = Output Power/Efficiency = 100/80

In other words, a 125 hp engine. required to operate a 100 hp pump. with an efficiency of 80%.

Pump failure

What reduces pump efficiency?

Dirty oil is the main cause of pump failure.

Solid particles of dirt, sand, etc. in oil are used in the pump as abrasive material.

This causes intensive wear of the parts and increases the internal leakage, thereby reducing the efficiency of the pump.

drainage channel

The channel that is used to drain the oil into the tank is called the drain channel.

Pump cavitation

When does cavitation occur?

Cavitation occurs when oil does not completely fill the intended fill space in the pump.

This contributes to the appearance of air bubbles, which are harmful to the pump.

Imagine that the inlet line of the pump is narrow, this causes a drop in the inlet pressure.

When pressure is low, oil cannot enter the pump as quickly as it can leave it.

The result is that air bubbles form in the incoming oil.

air in oil

This decrease in pressure leads to the appearance of some dissolved air in the oil and the air fills the cavity.

The air in the oil in the form of bubbles also fills the cavities.

When air-filled cavities, which are formed at low pressure, enter the high pressure area of ​​the pump, they collapse.

This creates an explosion-like action that shatters or carries out small particles of the pump and causes excessive noise and vibration of the pump.

Consequences of the explosion

Destruction, occurring constantly, causes an explosion.

The strength of this explosion reaches 1000 kg/cm² and fine metal particles are carried out of the pump. If the pump is operated under cavitation for a long time, it can be seriously damaged.

hydraulic motor

The motor works in reverse order when compared to the pump.

The pump delivers oil, while the motor runs on this oil.

The motor converts hydraulic energy into mechanical energy to do work.

Motor efficiency

Like a hydraulic pump, the efficiency of a motor is determined by its capacity.

Flow efficiency is one of the indicators in determining the performance of a motor.

Internal leakage occurs due to holes in the working parts of the motor. Some holes are provided in all parts for lubrication. The increase in leakage is associated with wear of parts with a small tolerance.

We consider increased internal leakage as a loss of efficiency.

Checking the operation of the motor

As we said before, the channel through which oil enters the tank is called the drain channel.

This gives us one method to check the operation of the motor by comparing the actual amount of oil drained from the motor into the tank with the set value. The greater the amount of oil drained into the tank, the greater the energy loss and, accordingly, the decrease in motor performance.

Hydraulic cylinder

Cylinder leak - external leak

When the cylinder rod is pulled out, dirt and other material may enter. Then, when the rod retracts, dirt enters the cylinder and damages the seals.

The cylinder rod has a protective seal that prevents dirt from entering the cylinder when the rod is retracted. If leakage occurs from the cylinder rod, all rod seals must be replaced.

Cylinder leak - internal leak

A leak inside the cylinder can cause slow motion or stop under load.

Piston leakage can be caused by a faulty piston seal, ring, or a scratched surface inside the cylinder.

The latter can be caused by the ingress of dirt and the presence of sand in the oil.

Slow motion

The presence of air in the cylinder is the main cause of slow action, especially when installing a new cylinder. All air trapped in the cylinder must be bled.

Cylinder deflation

If the cylinder deflates when stopped, check for internal leakage. Other causes of failure may be a faulty control valve or a broken safety valve.

Irregularities or rust of the cylinder rod

An unprotected cylinder rod can be damaged by impact with a hard object. If smooth surface stem is damaged, stem seals may be destroyed.

Irregularities on the stem can be corrected special tool.

Another problem is rust on the stem.

When storing the cylinder, retract the stem to protect it from rust.

valves

The preceding text has covered the basic knowledge of valves and their differences in operation.

It is necessary to learn a few technical terms related to control valves.

Cracking pressure and full flow pressure

Cracking pressure is the pressure at which the relief valve opens.

Full flow pressure is the pressure at which the most complete flow passes through the relief valve.

The full flow pressure is slightly higher than the cracking pressure. Relief valve setting is set to full flow pressure.

Cracking pressure and pressure adjustment

In the foregoing text, we learned that there are two types of safety valves: a direct acting safety valve and a pilot operated safety valve.

Let's look at the pressure adjustments of these valves.

A pilot operated relief valve has a lower set pressure than a direct acting relief valve.

The figure shows a comparison of these two types of valves.

While the direct acting relief valve in the figure opens at half full flow pressure, the pilot operated relief valve is open at 90% of its full flow pressure.

Pressure regulation

As we said before, the full flow pressure is slightly higher than the cracking pressure.

This is because the spring tension is adjusted to open the valves. This condition is referred to as pressure regulation and is one of the disadvantages of a simple relief valve.

What's better?

Pilot operated relief valve is better for high pressure and large capacity system.

Because these valves do not open until full flow pressure is reached, effective protection systems - oil is retained in the system.

Although slower than a direct acting relief valve, a pilot operated relief valve maintains a more constant pressure in the system.

pressure reducing valve

What it is?

A pressure reducing valve is used in the hydraulic motor circuit to create back pressure for control during operation and to stop the motor when the circuit is in neutral.

Pressure reducing valve for faucets

The pressure reducing valve is usually closed together with the pressure control valve with an internal check valve.

When the pump supplies oil to the winch motor for lowering, the motor runs by inertia under the weight of the load, in other words, when the motor exceeds the allowable speed, the pressure reducing valve applies back pressure, thus preventing the load from falling freely.

An internal non-return valve allows reverse flow to rotate the motor in the opposite direction to lift the load.

Pressure reducing valve for excavators.

The excavator pressure relief valve provides a soft start and an increase in travel / turn speed, and also prevents motor cavitation.

The pressure in the pressure line of the pump is always higher than the pressure in the motor line.

An attempt to exceed the set motor speed due to inertia causes a decrease in pressure in the pressure line and the valve closes the motor line immediately until pressure is restored to the pressure line.

Maintenance valves

Keep your valves in good condition

As you well know, valves are precision products and must accurately read the pressure, direction, and volume of hydraulic oil.

Therefore, valves must be properly installed and maintained in good condition.

Causes of valve failure

Contaminants such as dirt, fluff, corrosion and sediment can cause improper operation and damage to valve parts.

Such contaminants cause the valve to stick, not fully open, or peel off the mating surface until it begins to leak.

Such malfunctions are excluded by keeping the equipment clean.

Verification points

When troubleshooting or repairing, check the following items.

Pressure Control Valve - Relief Valve

Check the valve seat (valve seat and valve disc) for leaks and scoring.

Check for a stuck plunger in the body.

Check rubber rings.

Check if the throttle is clogged.

flow control valve

• Check the spool and passages for burrs and scratches.
• Check seals for leaks
• Check for uneven edges.
• Check for scratches on the spool.

The flow control valve spools are installed in the body at calculated locations.

This is done to ensure the smallest gap between body and spool to prevent internal leakage and maximize build quality. Therefore, install the spools in the appropriate holes.

The hydraulic jack has a device and principle of operation based on the physical properties of liquids that retain their volume during compression.

The hydraulic jack is a portable lifting device designed for heavy objects.

The purpose of the hydraulic jack

A hydraulic jack is a stationary, portable or mobile lifting device designed for heavy objects. It is used when performing repair and construction work and as part of cranes, presses, hoists.

Modern designs of hydraulic devices are used in the oil refining industry, facilities in the energy sector of industry, and in agriculture. High level productivity and efficiency index, ease of operation and maintenance allow the use of hydraulic jacks in the domestic sector.

This type of equipment is able to easily operate both in horizontal and vertical positions, which has found its application on sites for installation and construction work. The unit is used for tensioning reinforcing structures made of stressed concrete.

The structure of the hydraulic lifting device

The unit is set up as follows:

• frame;
• working fluid;
• working piston.

The design of the device can have an elongated or short body, for the manufacture of which hardened special steel is used. The body of the device is assigned to perform several functions. It is a guide cylinder for the working piston and serves as a reservoir for storing the working fluid.

A screw with a lifting heel is capable of being screwed into the plunger using a special thread. By unscrewing it, you can change the maximum height of the jack heel. Hydraulic devices are equipped with working pumps that have a manual, foot or air drive. The design provides for the installation of safety valves and some structural elements ensuring long and trouble-free operation of the lift.

The hydraulic pump and the cylinder with the piston are arranged in such a way that they provide the extension and lifting of the special platform. After the rod is extended, return to the initial position is carried out using the bypass valve.

There are several different modifications of lifting hydraulic units, which have their own areas of application.

The most common are:

• bottle type devices;
• rolling type devices;
• hydraulic jacks of hybrid design;
• hook-type units;
• diamond aggregates.

Various designs of hydraulic jacks have their own characteristics in the device, which are determined by the scope of the device.

Each of the types of hydraulic jacks is designed in its own way, however, the principle of operation is the same for all.

The principle of operation of the hydraulic jack is based on the use in the design of the apparatus of communicating vessels with a working fluid, the role of which is played by a special oil. Before use, the device must be placed on a flat, solid surface and the bypass valve closed. After installation and preparation of the unit, you can use it in operation.

The rod is lifted from the fifth by means of a pump that injects the working fluid into a special cylinder.

Due to the property of the liquid to resist compression with increasing pressure, the piston moves in the working cylinder. This leads to the movement of the rod with the lifting heel. The descent of the latter occurs by opening the bypass valve counterclockwise.

Pumping of working oil is carried out by a drive pump and a lever mounted on it. Oil moves from the pump to the working cylinder through a special valve.

The return of liquid during the operation of the device is prevented by two valves: discharge and suction.

To install the lift in its original position, a special valve is provided in its design, when opened, the working fluid flows from the cylinder to the pump of the unit.

The presence of a screw under the working heel in the jack device allows you to expand the possibilities of using the device.

For lifting, a special heel is made of high-strength steel. The force of the hydraulic jack is regulated by a built-in pressure gauge.

Advantages and disadvantages of hydraulic jacks

The physical features of the liquid allow for a smooth lifting, lowering of the load and fixing it at a certain height. Hydraulic jacks provide high rate Efficiency that reaches 80%. The carrying capacity of the unit is due to the presence of a large gear ratio between the cross-sectional indicators of the pump and working cylinder, plunger.

It is necessary to regularly flush the hydraulic jack, as well as change the oil and pump it.

Hydraulic lifts have a number of disadvantages. First of all, it should be noted that any model of this equipment has a certain starting height for lifting the load, below which the device cannot be operated. The disadvantage of this equipment is also the inability to accurately adjust the height of the lowering. In order to ensure trouble-free operation of the device, it is recommended to constantly monitor the cleanliness, quality and level of oil in the jack reservoir. The normal operation of the device is ensured by the tightness of the valves and glands used in the design of the unit. Transportation and storage of the device is carried out exclusively in a vertical position, if this requirement is violated, the working fluid can flow out of the device reservoir.

One of the disadvantages is the slowness of the units in operation. The disadvantages also include the weight of the device, its big size and high cost. In addition, single-plunger devices have a small stroke of the working rod, which is another drawback.

Possible malfunctions in the operation of the hydraulic jack

In any case, hydraulic jacks require care and maintenance, which consists in adding oil to the working tank of the unit. In addition, after a certain period of operation, it is required to flush the fixture, change the oil and pump it. Oil from the working tank is able to leak through the seals and various seals used in the design of the device. In addition to leakage during operation of the device, malfunctions such as jamming during lifting and the impossibility of lowering the rod may occur.

To eliminate oil leakage during the operation of the device, seals and seals are replaced. For this purpose, specially designed repair kits are used. During the repair, the unit is disassembled, the seals are replaced, the hydraulic jack is assembled, after which the working fluid is filled and pumped.

To eliminate jamming, the device is disassembled and its components are inspected for corrosion and contamination. If the first is detected, a special treatment is carried out, and the dirt is washed out.