Appointment of hydraulics and its independent production. How hydraulics work

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 at the enterprises of the oil refining industry, facilities of the energy sector of the industry, in agriculture. A high level of performance and efficiency, 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 twisting it, you can change maximum height lifting the heel of the jack. 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 efficiency, which reaches 80%. The carrying capacity of the unit is due to the presence of a large gear ratio between the indicators cross section 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 large 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 process, 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.

Hydraulic system is a device designed to convert a small effort into a significant one using some kind of fluid to transfer energy. There are many types of nodes that operate according to this principle. The popularity of this type of system is primarily due to high efficiency their work, reliability and relative simplicity of design.

Scope of use

Widespread use of this type of system found:

1. In industry. Very often, hydraulics is an element of the design of metal-cutting machines, equipment designed for transporting products, loading / unloading them, etc.
2. In the aerospace industry. Similar systems are used in various kinds of controls and chassis.
3. In agriculture. It is through hydraulics that the attachments of tractors and bulldozers are usually controlled.
4. In the field of cargo transportation. Cars are often equipped with hydraulic
5. In the ship, in this case, it is used in steering, it is included in the design scheme of turbines.

Operating principle

Any hydraulic system works on the principle of a conventional liquid lever. The working medium supplied inside such a node (in most cases, oil) creates the same pressure at all its points. This means that by applying a small force on a small area, you can withstand a significant load on a large one.

Next, we consider the principle of operation of such a device using the example of such a node as a hydraulic structure. The design of the latter is quite simple. Its scheme includes several liquid-filled, and auxiliary). All these elements are connected to each other by tubes. When the driver presses the pedal, the piston in the master cylinder moves. As a result, the liquid begins to move through the tubes and enters the auxiliary cylinders located next to the wheels. After that, braking is activated.

Design of industrial systems

The hydraulic brake of a car - the design, as you can see, is quite simple. More complex liquid devices are used in industrial machines and mechanisms. Their design may be different (depending on the scope of application). but circuit diagram The industrial design hydraulic system is always the same. It usually includes the following elements:

1. Fluid reservoir with mouth and fan.
2. Coarse filter. This element is designed to remove various kinds of mechanical impurities from the liquid entering the system.
3. Pump.
4. Control system.
5. Working cylinder.
6. Two fine filters (on the supply and return lines).
7. Distribution valve. This structural element is designed to direct fluid to the cylinder or back to the tank.
8. Reverse and safety valve s.

The operation of the hydraulic system of industrial equipment is also based on the principle of a liquid lever. Under the influence of gravity, the oil in such a system enters the pump. Then it goes to the control valve, and then to the piston of the cylinder, creating pressure. The pump in such systems is designed not to suck the liquid, but only to move its volume. That is, the pressure is not created as a result of its work, but under the load from the piston. Below is a schematic diagram of the hydraulic system.

Advantages and disadvantages of hydraulic systems

The advantages of nodes operating on this principle include:

• The ability to move loads of large dimensions and weight with maximum accuracy.
• Virtually unlimited speed range.
• Smoothness of work.
• Reliability and long service life. All components of such equipment can be easily protected from overloads by installing simple pressure relief valves.
• Efficiency in work and the small sizes.

In addition to the advantages, hydraulic industrial systems, of course, have certain disadvantages. These include:

• Increased risk of fire during operation. Most fluids used in hydraulic systems are flammable.
• Sensitivity of equipment to contamination.
• The possibility of oil leaks, and therefore the need to eliminate them.

Hydraulic system calculation

When designing such devices, many different factors are taken into account. These include, for example, the kinematic fluid, its density, the length of pipelines, rod diameters, etc.

The main goals of performing calculations for such a device as a hydraulic system are most often to determine:

• Pump characteristics.
• The magnitude of the stroke of the rods.
• working pressure.
• Hydraulic characteristics of highways, other elements and the entire system as a whole.

The hydraulic system is calculated using various kinds of arithmetic formulas. For example, pressure losses in pipelines are defined as follows:

1. The estimated length of the lines is divided by their diameter.
2. The product of the density of the liquid used and the square average speed stream is divided into two.
3. Multiply the obtained values.
4. Multiply the result by the path loss factor.

The formula itself looks like this:

• ∆p i \u003d λ x l i (p) : d x pV 2: 2.

In general, in this case, the calculation of losses in the lines is carried out approximately according to the same principle as in such simple structures as hydraulic heating systems. Other formulas are used to determine pump characteristics, piston stroke, etc.

Types of hydraulic systems

All such devices are divided into two main groups: open and closed type. The schematic diagram of the hydraulic system considered by us above belongs to the first variety. open design usually have devices of low and medium power. In more complex closed systems, a hydraulic motor is used instead of a cylinder. The liquid enters it from the pump, and then returns to the line again.

How is the repair done

Since the hydraulic system plays a significant role in machines and mechanisms, its maintenance is often entrusted to highly qualified specialists of companies engaged in this particular type of activity. Such firms usually provide a full range of services related to the repair of special equipment and hydraulics.

Of course, in the arsenal of these companies there is all the equipment necessary for the production of such work. Repairs to hydraulic systems are usually done on site. Before it is carried out, in most cases, various diagnostic measures must be taken. For this, hydraulic service companies use special installations. The components necessary to fix problems are also usually brought by employees of such firms.

Pneumatic systems

In addition to hydraulic, pneumatic devices can be used to drive the nodes of various kinds of mechanisms. They work in much the same way. However, in this case, the energy of compressed air, not water, is converted into mechanical energy. Both hydraulic and pneumatic systems do their job quite effectively.

The advantage of devices of the second type is, first of all, the absence of the need to return the working fluid back to the compressor. The advantage of hydraulic systems in comparison with pneumatic ones is that the medium in them does not overheat and does not overcool, and therefore, it is not necessary to include any additional nodes and details.

2015-11-15

Hydraulic drive(volumetric hydraulic drive) is a set of volumetric hydraulic machines, hydraulic equipment and other devices designed to transfer mechanical energy and convert movement through fluid. (T.M Bashta Hydraulics, hydraulic machines and hydraulic drives).

The hydraulic drive includes one or more hydraulic motors, fluid energy sources, control equipment, connecting lines.

Work hydraulic drive based on the principle

Let's consider the system.

In this system, the force created on the piston 2 can be determined by the dependence:

It turns out that force depends on the area ratio, the larger the area of ​​the second piston, and the smaller the area of ​​the first, the greater will be the difference between the forces F1 and F2. Thanks to the hydraulic lever principle, you can get a lot of force with a small amount of force.

Winning in effort on the hydraulic lever, you will have to sacrifice movement, moving the small piston by l1, we get the displacement of piston 2 by l2:

Given that the area of ​​the piston S2 more area S1, we get that the displacement l2 is less than l1.

The hydraulic drive would not be so useful if the loss in movement could not be compensated, and this was done thanks to special hydraulic devices -.

A non-return valve is a device for blocking the flow moving in one direction, and freely passing the reverse flow.

If in the considered example, on the outlet of the chamber with piston 1, install check valve so that the liquid can exit the chamber, but cannot flow back. The second valve must be installed between the chamber with piston 1 and an additional tank with liquid, so that the liquid can enter the chamber with , and from this chamber it cannot flow back into the tank.

The new system will look like this.

Applying a force F1 to the piston and moving it to a distance l1, we get the movement of the piston with a force F2 to a distance l2. Then we take piston 1 to the initial distance, the liquid cannot flow back from the chamber with piston 2 - the check valve will not allow - piston 2 will remain in place. Liquid from the tank will enter the chamber with the piston alone. Then, you need to apply force F1 again to piston 1 and move it to a distance l1, as a result, piston 2 will again move to a distance l2 with force F2. And in relation to the initial position, in two cycles, the piston 2 will move a distance of 2*l2. By increasing the number of cycles, it is possible to obtain a greater displacement of the piston 2.

It was the ability to increase the displacement by increasing the number of cycles that allowed the hydraulic lever to get ahead of the mechanical one in terms of the possible force being developed.

Drives where it is required to develop huge forces, as a rule, hydraulic.

A unit with a chamber and piston 1, as well as with check valves in hydraulics, is called pump. Piston 2 with chamber - hydraulic motor, in this case - .

Distributor in hydraulic drive

What to do if in the system under consideration it is necessary to return the piston 2 to its initial position? In the current configuration of the system, this is not possible. The liquid from under the piston 2 cannot flow back - the check valve will not allow, which means that a device is needed to send the liquid to the tank. You can use a simple tap.

But in hydraulics there is a special device for directing flows - distributor, allowing you to direct the flow of fluid in the desired direction.

Let's get acquainted with the work of the resulting hydraulic drive.

Devices in hydraulic drives

Modern hydraulic drives are complex systems consisting of many elements. The design of which is not simple. In the presented example, there are no such devices, because they are designed, as a rule, to achieve the desired characteristics of the drive.

The most common hydraulic devices

• Safety valves
• Pressure reducing valves
• Flow regulators
• Chokes

You can get information about hydraulic devices on our website in the section -. If you have any questions, ask them in the comments to this article.

A hydraulic drive is a system in which the transfer of energy from a source (usually a pump) to a hydraulic motor (hydraulic motor or hydraulic cylinder) is carried out by means of a dropping liquid.

Structurally, the hydraulic drive consists of a pump (s), control and distribution equipment, a hydraulic motor (s), a working fluid, a container (tank) for its maintenance and means (filters and coolers) that preserve its qualities, as well as connecting and sealing fittings.

On fig. 2.1. shows a diagram of the volumetric hydraulic drive under study, consisting of a pump 1, a safety valve 2, distributors 3 and 4, hydraulic motors - a hydraulic motor 5 and a hydraulic cylinder 6, a retarding device 7 for lowering the load 8, a tank and a filter 9 installed in the drain hydraulic line blocked by a valve 10.

Rice. 2.1 Scheme of the studied hydraulic drive.

The pump 1 is designed to convert the mechanical energy flow coming from the primary energy source 11 (electric or fuel engine) into a hydraulic energy flow, i.e. into the flow of working fluid under pressure, which, depending on the positions (positions) of the valves of the distributors 3, 4, can be directed directly (idle mode) or through one or both hydraulic motors 5, 6 together (working mode) into the tank. In this case, the pressure at the outlet of the pump depends on the set of resistances encountered by the flow of the working fluid on the way from the pump to the tank. In cases where distributors 3, 4 are in positions "A" (see Fig. 2.1), the flow of working fluid from pump 1 passes into the tank through the said distributors, hydraulic lines and filter 9 (idle mode). The pressure at the outlet of the pump is:

where
are the pressures required to overcome the flow of the working fluid resistance, respectively, sections of the gyrolines, distributors and filter.

In those cases when, on command from the outside, one or both distributors 3, 4 are transferred to any position "B" or "C", one or both hydraulic motors, respectively, are switched on (s). The direction of movement of the hydraulic motors depends on the position "B" and "C" of their distributors. When only one hydraulic motor is in operation, for example, hydraulic motor 5, operating pressure at the outlet of the pump will be:

where
- pressure loss to overcome the resistance of the distributor 3, 4

– pressure loss on the hydraulic motor drive 5, depending on the load to be overcome on its shaft.

In the case when the hydraulic motor 5 and the hydraulic cylinder 6 are simultaneously included in the work, their joint operation is possible only at the same required pressures. If one of them has a lower required pressure than the other, then their joint work is impossible, since the fluid flow will mainly go in the direction of less resistance and disrupt normal work hydraulic drive as a whole.

If the required pressure in the hydraulic drive exceeds the allowable one, the safety valve 2 is activated and diverts the flow of working fluid from the pump 1 into the tank (overload mode), thereby limiting the pressure in the hydraulic drive and protecting its elements from destruction.

To ensure the smoothness of the lowered loads (working bodies) in hydraulic drives, retarding devices are used (see Fig. 2.1, item 7), usually consisting of a check valve and a throttle. When lifting the load (working body), the working fluid enters the cylinder through the check valve and throttle. When lowering the load, the liquid from the cavity of the cylinder goes into the tank only through the throttle, which provides resistance to it, the value of which depends on the magnitude of its flow, and this ensures the smoothness of its lowering. In this case, the opposite cavity of the hydraulic cylinder is filled with liquid supplied by the pump. In the event of an excess amount of fluid supplied by the pump, part of it will be discharged to the drain through the safety valve 2.

Pressure gauge 12 is designed for visual control of pressure in the hydraulic drive. To ensure the cleaning of the working fluid from solid contaminants (abrasives, wear products), filters of various designs are used in hydraulic drives.

hydraulic machines

Hydraulic machines (hydraulic machines) are mechanical devices designed to convert types of energy flows using a drop liquid as an energy carrier.

Hydraulic machines are divided into pumps and hydraulic motors.

Pumps are called hydraulic machines designed to convert a mechanical energy flow into a hydraulic energy flow.

Hydraulic motors are called hydraulic machines designed to convert hydraulic energy flow into mechanical energy flow.

Hydraulic motors, the output links of which perform linear reciprocating movements, are called hydraulic cylinders (hydraulic cylinders).

Hydraulic motors, the output links of which perform rotational movements, are called hydraulic motors (hydraulic motors).

Depending on the angle of rotation of the output link, hydraulic motors are divided into full
and semi-rotary
.

Hydraulic machines, in which the working process is based on the use of the kinetic energy of the fluid, are called dynamic, and those machines in which the working process is based on the use of the potential energy of the fluid are called volumetric.

The main feature of volumetric hydraulic machines is that they contain at least one working chamber, the volume of which varies
during the working cycle. Moreover, each working chamber contains a movable element designed to change its volume. Usually the movable element of the working chamber is called the displacer. Pistons, plungers, gear teeth, balls, rollers, plates, membranes, etc. can be used as displacers.

During the operation of a volumetric hydraulic machine, each of its chambers communicates in turn with a low and high pressure line, i.e. the working chambers of the pump alternately communicate with the suction and discharge lines, and for engines - with the high pressure output line and the drain line.

The value of the pressure developed (implemented) by the pump depends on the resistance of the consumer (usually a hydraulic motor) and the connecting hydraulic fittings.

The value of the pressure of the working fluid consumed by the hydraulic motor depends on the value of the load it implements on the output link.

According to the type of displacers, hydraulic machines are divided into piston, plunger, ball, roller, gear (gear), lamellar, membrane, etc., and according to the number of working chambers into single and multi-chamber.

Hydraulic machines, in which the working chambers, together with the displacers, perform rotational movements, are called rotary.

The value of the changing volume of the working chambers of a hydraulic machine is called its working volume. The working volume of hydraulic machines is usually expressed in cubic centimeters.

The amount of working fluid supplied by the pump to the system per unit of time is called its supply.

If the working volume is known
pump and cycle rate , then its ideal supply can be determined by the formula

.

Due to the fact that there are leaks of the working fluid between the moving elements of the pump, the actual flow will always be less than the ideal, i.e.

where
- the amount of leakage through the gaps;

is the volumetric efficiency of the pump.

The ideal speed of the hydraulic motor is determined by the formula

,

and the actual

,

where
- the value of the input flow of the working fluid;

- the working volume of the hydraulic motor;

is the volumetric efficiency of the hydraulic motor.

The volumetric efficiency of the hydraulic motor can be determined by the formula

where
- the value of the flow of the working fluid, usefully used in the hydraulic motor;

- the amount of leakage through the gaps in the hydraulic motor.

The drive power of the pump can be determined by the formula

where
- the power of the flow of the working fluid at the outlet of the pump;

– full efficiency of the pump;

- the value of pressure at the outlet of the pump;

– hydraulic efficiency of the pump;

- the pressure in the working (s) chamber (s) of the pump;

is the mechanical efficiency of the pump.

The energy quality of a hydraulic motor is characterized by its total efficiency, which can be defined as the ratio of the power on its output shaft
to the value of the power of the inlet fluid flow
, i.e.

where
- torque;

is the angular velocity;

- pressure drop in the hydraulic motor.

Most positive displacement hydraulic machines are reversible, i.e. they are capable of operating both as pumps and as hydraulic motors.

In hydraulic drives of construction and road machines, gear (Fig. 2.2) and axial (Fig. 2.3) hydraulic machines are most widely used as pumps, and axial (Fig. 2.3) and radial (Fig. 2.4) as hydraulic motors.

Due to the fact that in rotary pumps there is a movement of working chambers with liquid from the suction cavity to the discharge cavity, they differ from simple piston (plunger) pumps in the absence of valve distribution of the liquid, which in turn increases their speed up to 85 s -1 and provides high uniformity of supply and pressure. All rotary hydraulic machines can only work with clean, non-aggressive fluids that have good lubricating properties and are designed for hydraulic drives.

Gear hydraulic machines

Gears are called rotary hydraulic machines with working chambers formed by the surfaces of the gears, housing and side covers.

Gear hydraulic machines are performed with gears of external (see Fig. 2.2, a) or internal (see Fig. 2.2, b) gearing. Such a hydraulic machine is a pair of (most often identical) gears 1 and 2, which are engaged and placed in a housing with small radial clearances (usually 10 ... 15 microns).

Rice. 2.2 Schemes of gear (gear) hydraulic machines.

The working process of the external gear pump is as follows. The drive gear 1 (see Fig. 2.2, a) drives the driven gear 2 in rotation. When the gears rotate in opposite directions in the chamber "A", their teeth disengage, which leads to an increase in the volume of the working chamber and to a decrease in the pressure of the working fluid to the vacuum value. Due to the resulting pressure difference between the reservoir (tank) and the suction chamber "A", the working fluid from the tank will flow into the chamber "A" and fill the cavities between the teeth of gears 1 and 2. With further movement of the gears, the working fluid in the cavities between the teeth is transferred from the zone suction (from chamber "A") to the injection zone (to chamber "B"). In the injection zone, the teeth of the gears engage and push the liquid out of the depressions into the injection hydraulic line under pressure, the value of which depends on the resistance of the consumer and the connecting hydraulic fittings.

In pumps with internal gear engagement (see Fig. 2.2, b), the drive gear is most often internal gear 1 with external teeth. Suction "A" and discharge "B" windows are made on the front side of the gear teeth in the side cover or pump housing. Female gear 2 with internal teeth rotates in a cylindrical bore of the housing. Between the gears there is a separating sickle-shaped element 3, by means of which the suction cavity "A" is separated from the discharge cavity "B".

Recently, hydraulic machines with internal gears with a special tooth profile (see Fig. 2.2, c), in which there is no separating element of cavities with different levels of pressure, are widely used in hydraulic power steering machines. Such hydraulic machines are called gerotoric or birotoric, i.e. with two rotors. The annular rotor (wheel) 1 has one tooth more than the internal one (gear) 2. Their axes are offset one relative to the other by an amount , forming the engagement of gears in the area of ​​the upper separating jumper. The contact of the teeth when they pass the lower dividing bridge ensures the separation of the high and low pressure cavities. The input and output hydraulic lines with interdental cavities are connected by means of sickle-shaped windows "A" and "B".

Gerotor hydraulic machines are used as pumps operating at working fluid pressures up to 14 MPa and a shaft speed of 30 s -1 . They can be used as high-speed low-torque hydraulic motors. In some cases, gerotor hydraulic machines are capable of operating at pressures of 30 MPa at a rotation frequency of up to 60 s -1 .

The working process (suction and discharge) in internal gear pumps occurs in the same way as in external gear pumps.

The overall dimensions and weight of pumps with internal gear are much smaller than pumps with external gear for equal working volumes.

The spur gear engagement of pump gears is characterized by a straight-line contact of the working surfaces (profiles) of the teeth over their entire width (length), with inaccurate manufacture of which, uneven movement of the driven gear and noise occur, and rapid wear of the working surfaces is also observed.

These shortcomings are eliminated in helical (spiral) and herringbone gears (see Fig. 2.2, d and e). The engagement and disengagement of the teeth in these gears occurs gradually, due to which errors in the tooth profile are reduced and smooth and relatively silent operation of the hydraulic machine is achieved.

In pumps with helical gears, the pulsation of the flow and torque, as well as the blocking of the liquid in the cavities, is much lower than in pumps with cylindrical gears. To reduce pressure fluctuations, it is necessary to ensure that the product
was equal to
etc., where - the angle of inclination of the teeth; - gear width; - tooth pitch. Injection are chosen so that the shift of the teeth along the circumference at the ends of the gears is half the step. In practice, this angle usually does not exceed 7…10.

During the operation of pumps with helical gears, axial forces arise that press the gears against the ends of the housing (covers). This disadvantage is eliminated in pumps with chevron gears (Fig. 8.2, e). Tooth angle chevron gears used in pumps is usually 20 ... 25.

Axial hydraulic machines

Axial hydraulic machines are characterized by the fact that the axes of their cylinders are parallel to the axis of rotation of the cylinder block or make an angle of no more than 45 with it.

The positive qualities of axial hydraulic machines include:

high working pressure (35…70 MPa);

speed (80 ... 550 s -1);

low metal consumption (0.5…0.6 kg/kW);

wide range of speed control of the hydraulic motor shaft 1:100 at variable and 1:1000 at constant loads;

the ability to operate hydraulic motors at low speeds (up to 0.01 s -1);

greater durability (up to 12000 hours);

high speed (feed change from zero to maximum and vice versa in 0.04…0.08 s);

low operating costs and fast payback.

Axial hydraulic machines come with an inclined block of cylinders (see Fig. 2.3, a, b) or with an inclined washer (see Fig. 2.3, c, d). They can be piston (see Fig. 2.3, a, b) or plunger (see Fig. 2.3, c, d) with a variable (adjustable) or constant (non-adjustable) working volume. In axial-piston hydraulic machines, there is: a small radial load on the piston, a large angle of inclination of the cylinder block (up to 45), as well as a higher efficiency (by 2 ... 3%) than that of a hydraulic machine with a swash plate.

On fig. 2.3, a diagram of an axial-piston adjustable hydraulic machine with an inclined block is presented. It consists of shaft 1, cylinder block 2, end distributor 3, central axle 4, pistons 5, connecting rods 6 and universal joint 8.

The described hydraulic machine in the function of the pump works as follows. The rotation of the drive shaft through the cardan 7 and the connecting rods 6 is transmitted to the cylinder block 2. When the shaft 1 and the cylinder block 2 are coaxially located, the pistons 5 do not reciprocate and, therefore, the pump flow is 0. The deviation of the axis of the cylinder block from the axis of the drive shaft leads to reciprocating motion of the pistons.

For one revolution, each piston completes one working cycle. The strokes of the pistons depend on the angle of inclination of the cylinder block. When the angle of inclination of the cylinder block changes in the opposite direction from zero, the direction of pump delivery changes, i.e. the hydraulic machine provides reversal of the hydraulic drive.

Axial hydraulic machines with a swash plate are characterized by the following advantages compared to hydraulic machines with an inclined block of cylinders: the ability to work at higher pressures (up to 70 MPa); low noise level; small dimensions; low cost; simplicity of design and its manufacturability.

Rice. 2.3 Schemes of axial hydraulic machines.

On fig. 2.3, c shows a simplified diagram of an axial-plunger hydraulic machine with a swash plate. Plungers 2 are installed in the cylinders of its block 1, which are kinematically connected with the inclined washer 4 by means of springs 6 through shoes 3.

The described hydraulic machine in the function of the pump works as follows. Shaft 5 rotates cylinder block 1. In this case, plungers 2 reciprocate in the cylinder block. The stroke of the plungers, respectively, the pump flow, is determined by the angle of inclination of the washer 4. When the plungers, under the influence of springs 6, move out of the cylinder block, the process of suction of the working fluid occurs, and when they return, they are injected.

Swashplate axial-plunger hydraulic machines are often used in the functions of adjustable and fixed hydraulic motors, the principle of operation of which is similar to that of axial hydraulic machines with an inclined block of cylinders.