Work program on the topic: work program "hydraulic and pneumatic systems" base.

16.04.2019

Brake system

APPROVE

First Deputy directors

Full name

"__" ___________ 20__

Evaluation fund

main educational program

middle vocational education(PPSSZ, PPKRS)

Full-time form of education

Qualification: technologist

Specialty: 15.02.01Installation and technical operation industrial equipment

Course: 2

Gr.251

Ulan-Ude, 2016

CONTENT

WITH.

Passport
appraisal fund
by discipline HYDRAULIC AND PNEUMATIC SYSTEMS
1. The fund of evaluation funds allows you to evaluate:
Mastering professional competencies (PC), corresponding to the type of professional activity, and general competencies:
PC 1.2. To slaughter livestock, poultry and rabbits.
1. Ability to use various types of machines and mechanisms and their principle of operation,
Acquisition of practical experience in the course of mastering the academic discipline "Technical Mechanics"
Evaluate the efficiency, reliability and simplicity of the design of hydraulic and pneumatic drives of various machine tools according to the established indicators.
1. Evaluation of the efficiency, reliability and simplicity of the design of hydraulic and pneumatic drives of various machine tools.
Mastering skills and mastering knowledge
Evaluation of the efficiency, reliability and simplicity of the design of hydraulic and pneumatic drives of various machine tools according to the established indicators.
1. - abilityensure control of work on the installation and repair of industrial equipment using instrumentation;
1.2. The system of control and evaluation of the development of the program of the academic discipline
"Hydraulic and pneumatic systems»
Forms of intermediate certification for the OPOP when mastering an academic discipline
The current control of the development of the program of the academic discipline is carried out within the study time allotted for the study of the academic discipline using such methods as oral, written, practical, self-control.
Skills and knowledge are the subject of assessment of mastering the discipline. Differentiated credit for academic discipline is carried out taking into account the results of the current control. The current control includes an assessment of the implementation of practical work, the implementation of independent work of the student and tests in sections of the academic discipline.
Monitoring and evaluation by industrial practice is carried out on the basis of the attestation sheet of the student from the place of internship, compiled and endorsed by a representative of an educational institution or a responsible person of the organization (internship base). The attestation sheet reflects the types of work performed by the student during the practice, the quality of performance in accordance with the technology or the requirements of the organization in which the practice took place, the characteristics of the student's educational and professional activities during the practice.
The final control of the development of the type of professional activity The performance of work on the organization and conduct of professional tasks is carried out on a differential test.
The condition for admission to the test is the delivery of all practical work.
The differential test is carried out in the form of a competence-oriented practical task, which is professional and comprehensive. Tasks are focused on checking the development of the type of professional activity in general.
The condition for positive attestation (the type of professional activity is mastered) at the qualification exam is a positive assessment of the development of all professional competencies in all controlled indicators.
With a negative conclusion for at least one of the prof. Competences, the decision “the type of professional activity is not mastered” is made
Name

evaluation tool**

Controlled competency code (or part of it)

Hydraulics

Individual task

OK-1…9,

PC-1.1-1.5, 2.1-2.4, 3.1-3.4

Pneumatic drive

Individual task

OK-1…9,

PC-1.1-1.5, 2.1-2.4, 3.1-3.4

Dynamics

Individual task

OK-1…9,

PC-1.1-1.5, 2.1-2.4, 3.1-3.4

4.2. Typical tasks for the current certification in the academic discipline
Lecture material kit
HYDRAULIC AND PNEUMATIC SYSTEMS
Attached electronically
1. 1. 1. 1. Introduction
        Physical basis of functioning
        The concept of hydraulic drive
        Laws of gases
        The concept of pneumatic drive
        Hydro and pneumatic systems
        Fundamentals of gas dynamics
1. Practical work
  1. Calculation of parameters of the hydraulic system
  2. Determination of the main dimensions and parameters of the compressor
  3. Construction of indicator charts
  4. Calculation of power consumption and selection of electric motor
  5. Motor selection
  6. Drive power calculation
  7. Power calculation of the drive
  8. Calculation of the pneumatic system
  9. Air flow calculation
  10. Calculation of the actuation time of the drive
  11. Calculation of cylinder B
  12. Drive power calculation
  13. Calculation of the pneumatic system
  14. Calculation of the actuation time of the drive
3. Questions for final control
  1. Structural diagram of the hydraulic drive
  2. Classification and principle of operation of hydraulic drives
  3. Advantages and disadvantages of hydraulic drive
  4. Characteristics of working fluids
  5. Selection and operation of working fluids
  6. Hydraulic lines
  7. Connections
  8. Calculation of hydraulic lines
  9. Gear type hydraulic machines
  10. Vane pumps and hydraulic motors
  11. Radial piston pumps and hydraulic motors
  12. Axial piston pumps and hydraulic motors
  13. Mechanisms with flexible dividers
  14. Classification of hydraulic cylinders
  15. Straight-line hydraulic cylinders
  16. Calculation of hydraulic cylinders
  17. Rotary hydraulic cylinders
  18. Spool valves
  19. Crane hydraulic distributors
  20. Valve hydraulic distributors
  21. Pressure hydraulic valves
  22. Pressure reducing valve
  23. Check valves
  24. Flow limiters
  25. Dividers (adders) flow
  26. Throttles and flow regulators
  27. Hydraulic tanks and heat exchangers
  28. Filters
  29. Sealing devices
  30. Hydraulic accumulators
  31. Water locks
  32. Hydraulic pressure and time switches
  33. Measuring instruments
  34. Classification of hydraulic boosters
  35. Hydraulic booster spool type
  36. Hydraulic booster with nozzle and damper
  37. Hydraulic booster with jet tube
  38. Two-stage amplifiers
  39. Methods for unloading pumps from pressure
  40. Throttle regulation
  41. Volume control
  42. Combined regulation
  43. Comparison of regulation methods
  44. Hydraulic systems with adjustable pump and throttle
  45. Hydraulic systems with two-stage amplification
  46. Hydraulic systems of continuous (oscillatory) motion
  47. Electro-hydraulic systems with variable pump
  48. Hydraulic systems with two twin pumps
  49. Power supply by one pump to two and several hydraulic motors
  50. General information about the use of gases in technology
  51. Features of the pneumatic drive, advantages and disadvantages
  52. Air flow
  53. Compressed air preparation
  54. Executive pneumatic devices
  55. Installation of volumetric hydraulic drives
  56. Operation of volumetric hydraulic drives at low temperatures
  57. The main problems in hydraulic systems and how to eliminate them

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

FEDERAL AGENCY FOR EDUCATION

State educational institution higher professional education

"South-Russian State University of Economics and Service" (GOU VPO "YURGUES")

HYDRAULICS. HYDRAULIC AND PNEUMATIC

SYSTEMS IN CARS AND GARAGE EQUIPMENT

Workshop

for full-time and part-time students of specialties 190603 "Service of transport and technological machines and equipment"

(Automobile transport), 190601 "Automobiles and automotive industry"

UDC 629.3.01(076) BBK 39.33-08ya73 G464

Compiled by:

Candidate of Technical Sciences, Associate Professor of the Department of Energy and Life Safety

IN AND. Timchenko

I.K. Guguev

Associate Professor of the Department " car service, organization and traffic safety"

A.I. Shilin

assistant of the department "Energy and life safety"

A.G. Iliev

Reviewers:

Doctor of Technical Sciences, Professor of the Department of Energy and Life Safety

Candidate of Technical Sciences, Associate Professor of the Department of Automotive Service, Organization and Traffic Safety

S.G. Solovyov

G464 Hydraulics. Hydraulic and pneumatic systems in cars and garage equipment: workshop / compiled by V.I. Timchenko, I.K. Guguev, A.I. Shilin, A.G. Iliev. - Mines: Publishing house

in YURGUES, 2007. - 57 p.

The workshop consists of eight research laboratory works, brief explanations on the implementation of these works and the main theoretical provisions of the course “Hydraulics. Hydraulic and pneumatic systems in cars and garage equipment” and bibliographic list.

UDC 629.3.01(076) BBK 39.33-08ya73


INTRODUCTION .................................................. ................................................. .
Lab #1
Research of cooling processes in automobile engines..........
Lab #2
Investigation of the car lubrication system .............................................................. ....
Lab #3
Study of carburation processes in the car power system......
Lab #4
Investigation of hydraulic processes in the brake system
car................................................. ................................................. ..
Lab #5
The study of gear hydraulic machines ............................................... .............
Lab #6
Investigation of rotary vane hydraulic machines..................................................
Lab #7
Testing of centrifugal fans............................................................... ......
Lab #8
Fluid flow measurement in engineering networks ..........................................................
BIBLIOGRAPHICAL LIST.................................................................. ...........

INTRODUCTION

The laboratory workshop was developed to provide methodological assistance in the performance of laboratory work in the discipline “Hydraulics. Hydraulic and pneumatic systems in cars and garage equipment” by students of specialties 190603 “Service of transport and technological machines and equipment (Motor transport), 190601 “Automobiles and automotive economy” of full-time and part-time forms of education.

By the start of class, students should have completed the following:

1. Read the instructions for the relevant laboratory work.

2. Prepare a backlog, which includes:

− job title;

− the purpose of the work;

− basic theoretical provisions;

− scheme and description of the experimental setup (full-scale assembly of a car or garage equipment);

− description of the principle of operation of the hydraulic or pneumatic system, the procedure for conducting the experiment;

− table of experimental data;

− calculation results table.

After completing the work, the teacher signs the table of experimental data. In writing, the calculation of one experiment is given. The calculation of each value is given by the formula: the desired value, the calculation formula, numerical values, numerical result, dimension.

On laboratory work, the student makes a report, which includes

− completed tables of observations and calculations;

− detailed calculation of one experience;

− graphs of dependencies of functional quantities;

− conclusions.

To defend a report on laboratory work, a student must know:

− necessary theoretical material;

− arrangement of an experimental installation (full-scale assembly of a car or garage equipment);

− necessary calculation formulas;

− answers to control questions.

A student who did not report on the previous three laboratory work, to perform subsequent work is not allowed.

Laboratory work No. 1 STUDY OF COOLING PROCESSES IN CAR ENGINES

Goals and objectives:

1) To study the dependences of hydrodynamic parameters - flow rate, pressure, temperature of the coolant depending on the frequency of revolutions of the crankshaft, the speed of the vehicle.

2) Develop schematic diagrams of cooling processes in a small and large circle.

3) Carry out experimental tests on a moving vehicle.

4) Develop a hydraulic cooling scheme.

Brief information from the theory

1) Purpose of cooling systems.

2) The main elements of the hydrodynamic cooling system.

3) Properties of the coolants used: density, crystallization temperature, specific gravity, coefficients of kinematic viscosity, thermal and volume expansion, heat capacity.

6) Determination of the main parameters of the hydrodynamic cooling system: flow rate, speed, pressure, temperature.

7) Measuring instruments used for control optimal mode operation of the cooling system.

Figure 1.1 - Engine cooling system VAZ 2106

Explanation for the figure:

1. Fluid drain pipe from the heater core to the coolant pump.

2. Coolant outlet hose from intake pipe.

3. Coolant outlet hose from heater core.

4. Hose for supplying fluid to the heater radiator.

5. Thermostat bypass hose.

6. Cooling jacket outlet.

7. Radiator inlet hose.

8. Expansion tank.

9. Tank plug.

10. Hose from radiator to expansion tank.

11. Radiator cap.

12. Outlet (steam) plug valve.

13. Inlet valve.

14. Upper radiator tank.

15. Radiator filler neck.

16. Radiator tube.

17. Radiator cooling fins.

18. Fan cover.

19. Fan.

20. Coolant pump drive pulley.

21. Rubber support.

22. A window on the side of the cylinder block for supplying coolant.

23. Gland clip.

24. Coolant pump shaft bearing.

25. Pump cover.

26. Fan pulley hub.

27. Pump roller.

28. Locking screw.

29. Seal collar.

30. Pump housing.

31. Pump impeller.

32. Pump inlet.

33. Lower radiator tank.

34. Outlet radiator hose.

35. Fan belt.

36. Coolant pump.

37. Coolant supply hose to the pump.

38. Thermostat.

39. Rubber insert.

40. Inlet pipe.

41. main valve.

42. bypass valve.

43. thermostat housing.

44. Bypass hose fitting.

45. Hose connection for supplying coolant to the pump.

46. Thermostat cover.

47. The piston of the working element.

Theoretical information. The cooling system is designed to forcefully remove excess heat from engine parts and transfer it to the surrounding air. This creates a certain temperature regime in which the engine does not overheat and does not overcool. Heat in engines is removed in two ways: liquid or air. These systems absorb 25-35% of the heat released during fuel combustion. The temperature of the coolant in the cylinder head should be 80–95º. This temperature regime is the most beneficial, ensures the normal operation of the engine and should not change depending on the ambient temperature and engine load. The temperature during the working cycle of the engine changes from 80-120º at the end of the descent to 2000-2200º at the end of the combustion of the mixture.

If the engine is not cooled, then the high-temperature gases heat up the engine parts very much, and they expand. The oil on the cylinders and pistons burns out, and friction and wear increase, and from excessive expansion of parts, the pistons in the engine cylinders seize and the engine can fail. To avoid the negative effects caused by overheating of the motor, it must be cooled down.

However, excessive cooling of the engine adversely affects its operation. When the engine is overcooled, fuel vapors condense on the walls of the cylinders, washing off the lubricant, diluting the oil in the crankcase. Under these conditions, intensive wear of piston rings, pistons, cylinders occurs and the efficiency and power of the engine are reduced. normal operation cooling system helps to get the most power, reduce fuel consumption and increase the life of the engine without repair.

Most engines have liquid cooling systems (open or closed). With an open cooling system inner space communicates directly with the surrounding atmosphere. Closed cooling systems have become widespread, in which the internal space only periodically communicates with the environment using special valves. In these cooling systems, the boiling point of the coolant rises and the boiling point decreases.

Electric thermal pulse manometer

The thermal pulse electric pressure gauge consists of a sensor and a pointer, which use the property of a bimetallic plate to deform when the temperature changes. In the pressure gauge sensor, the active metal is located at the bottom, i.e. from the contact side. The bimetallic plate has a U-shape; a heating winding is located on one arm of the plate. The other shoulder of the plate is isolated from the "mass" and fixed on a movable bracket. A diaphragm is fixed in the sensor housing. When the pressure changes, it bends and changes the force of the elastic plate that closes the contacts.

In the index, the bimetallic plate with the winding also has a U-shape. One arm of the plate is fixed on the support, and the other is hinged to the earring, which is integral with the arrow. The earring is pivotally connected to the elastic hook of the support.

Operating principle

The thermopulse manometer works as follows. Before the ignition switch is turned on, the movable contact of the sensor is pressed against the fixed contact with little force, and the pointer arrow is to the left

"zero". When the ignition is on, before starting the engine, in the sensor and pointer circuits appear short-term impulses current, while the active metal of the indicator plate, expanding, deforms the plate, and the arrow of the device moves to the right until the “zero” division. This allows the driver to judge the health of the device. The current pulses are short-term, since when the bimetallic plate of the sensor is heated, the contacts open with a slight deflection of the plate.

Table 1.1 - Experimental data

Measured quantities

Determined quantities

t cool,

t load,

Vzh ,

∆P ,

t | 2,

t ||2,

fan

Note. ∆P - pressure loss; V - vehicle speed; n - number of revolutions of the crankshaft; V W - coolant speed; t cool - initial temperature of the coolant; G - coolant flow rate; t | 2, 0 С – the final temperature of the coolant in the variant with a small cooling cycle; t || 2, 0 C - the final temperature of the coolant in a large circle of cooling.

It is necessary to compare experimental data with theoretical ones and draw conclusions on optimizing the operating mode of cooling systems in vehicles that ensure traffic safety.

Control questions:

1) List the elements of local resistance in the cooling system.

2) Give the characteristics of radiators and an axial fan.

3) Show a schematic diagram of the movement of coolant in the system.

4) List the types of coolants.

5) How to determine the head loss of a pump in a system.

6) What determines the pressure and temperature of the coolant in the system.

Laboratory work No. 2 STUDY OF THE VEHICLE LUBRICATION SYSTEM

Goals and objectives:

1) To study the modes of motion and the properties of the liquid (automotive, motor, transmission oils), purpose of lubrication.

2) Explore hydraulic characteristics lubrication systems: flow, pressure, local resistances - in the lubrication system (filter, line, channels).

3) Show the dependence of lubrication parameters on engine temperature.

Brief information from the theory:

1) The purpose of the lubrication system.

2) The main elements of the hydraulic lubrication system.

3) Working fluid properties: density, freezing point, specific gravity, coefficients of kinematic viscosity, thermal expansion and volumetric expansion.

4) The principle of operation of the system, malfunctions, causes, troubleshooting.

5) Types of local resistances in the system.

6) Determination of the main parameters of the hydrodynamic lubrication system: flow rate, speed, pressure.

7) Measuring instruments used to control the optimal operation of the lubrication system.

The engine lubrication system is used to supply oil to the rubbing surfaces of parts, which reduces friction between them and their wear, and also reduces the loss of engine power to overcome friction forces. During engine operation, the oil introduced between the parts circulates continuously, cooling the parts and carrying away their wear products. A thin layer of oil on the pistons piston rings and cylinders not only reduces their wear, but also improves engine compression.

The lubrication system is a series of devices and units for storing, supplying, cleaning and cooling oil:

− engine oil pan;

− oil intake;

− coarse oil filter;

− oil filter fine cleaning;

− oil pump;

− oil pipelines;

− oil radiator;

− control and measuring devices and sensors.

Linear drives designed to set in motion parts of machines and mechanisms in linear translational motion. Actuators convert electrical, hydraulic or compressed gas energy into motion or force. This article presents an analysis of linear actuators, their advantages and disadvantages.

How Linear Actuators Work

Due to the absence of liquids, there is no risk of environmental pollution.

Flaws

The initial cost of electric actuators is higher than pneumatic and hydraulic ones.

Unlike pneumatic actuators, electric actuators (without additional funds) are not suitable for use in explosive areas.

During extended operation, the motor may overheat, increasing gear wear. The motor may also be large, which can lead to installation difficulties.

Drive force, allowable axial loads and speed parameters of the electric drive are determined by the selected electric motor. When changing the set parameters, it is necessary to change the electric motor.

Linear electric drive, including a rotating electric motor and a mechanical converter

Pneumatic drives

Advantages

Simplicity and economy. Most pneumatic aluminum actuators have a maximum pressure of up to 1 MPa with a cylinder bore from 12.5 to 200 mm, which approximately corresponds to a force of 133 - 33000 N. Steel pneumatic actuators usually have a maximum pressure of up to 1.7 MPa with a cylinder bore of 12 .5 to 350 mm and create a force from 220 to 171000 N.

Pneumatic actuators allow precise control of movement, providing accuracy within 2.5 mm and repeatability within 0.25 mm.

Pneumatic actuators can be used in areas with extreme temperatures. Standard temperature range -40 to 120 ˚C. In terms of safety, the use of air in pneumatic actuators eliminates the need for hazardous materials. These actuators meet the requirements of explosion protection and safety, as they do not create a magnetic field, due to the absence of an electric motor.

In recent years, advances have been made in the field of pneumatics in miniaturization, materials, and integration with electronics. The cost of pneumatic actuators is low compared to other actuators. Pneumatic actuators are lightweight, require minimal maintenance and have reliable components.

Flaws

Pressure loss and air compressibility make pneumatic actuators less efficient than other methods of generating linear motion. Compressor and supply system limitations mean that low pressure operation will result in low forces and speeds. The compressor must run all the time even if the drives are not moving anything.

For really effective work pneumatic actuators must be sized for each task. Because of this, they cannot be used for other tasks. Precise control and efficiency require valves and valves of the appropriate size for each application, which increases cost and complexity.

Although air is readily available, it can be contaminated with oil or grease, resulting in downtime and maintenance.

Hydraulic drives

Advantages

Hydraulic actuators are suitable for tasks that require large forces. They can generate up to 25 times more force than pneumatic actuators of the same size. They operate at pressures up to 27 MPa.

Hydraulic motors have high rate power per volume.

Hydraulic actuators can keep force and torque constant without additional fluid or pressure being supplied by the pump, since liquids, unlike gases, are practically incompressible.

Hydraulic drives can be located at a considerable distance from pumps and motors with minimal power loss.

Flaws

Like pneumatic actuators, fluid loss in hydraulic actuators results in less efficiency. In addition, fluid leakage leads to contamination and potential damage to nearby components.

Hydraulic actuators require many accompanying components, including a fluid reservoir, motors, pumps, relief valve, heat exchanger, etc. Therefore, such actuators are difficult to place.

^ Pneumatic drive
11.1. General information about the use of gases in technology

Any object in which a gaseous substance is used can be attributed to gas systems. Since the most accessible gas is air, which consists of a mixture of many gases, its widespread use for various processes is due to nature itself. Translated from Greek pneumatikos - airy, which explains the etymological origin of the name pneumatic systems. The technical literature often uses the shorter term - pneumatics.

Pneumatic devices began to be used in ancient times (wind turbines, musical instruments, bellows, etc.), but they are most widely used as a result of the creation of reliable sources of pneumatic energy - superchargers capable of giving gases the necessary supply of potential and (or) kinetic energy.

Pneumatic drive , consisting of a complex of devices for driving machines and mechanisms, is far from the only direction for using air (in general case gas) in technology and human life. In support of this provision, we will briefly consider the main types of pneumatic systems, which differ both in purpose and in the method of using a gaseous substance.

According to the presence and cause of gas movement, all systems can be divided into three groups.

The first group includes systems with natural convection (circulation) of gas (most often air), where the movement and its direction are determined by temperature and density gradients of a natural nature, for example, the atmospheric shell of the planet, ventilation systems of premises, mine workings, gas ducts, etc.

The second group includes systems with closed cells , not communicating with the atmosphere, in which the state of the gas may change due to changes in temperature, chamber volume, pressurization or suction of gas. These include various storage tanks (air cylinders), pneumatic braking devices (pneumatic buffers), all kinds of elastic inflatable devices, pneumohydraulic systems of aircraft fuel tanks, and many others. An example of devices using vacuum in a closed chamber can be pneumatic grippers (pneumatic suction cups), which are most effective for moving piece sheet products (paper, metal, plastic, etc.) in automated and robotic production.

The third group should include such systems where energy is used pre-compressed gas for execution various works. In such systems, gas moves along pipelines with relatively high speed and has a significant amount of energy. They can be circulation (closed) and non-circulating . In circulating systems, the exhaust gas is returned through the lines to the supercharger for reuse (as in a hydraulic drive). The use of systems is very specific, for example, when gas leakage into the surrounding space is unacceptable or air cannot be used due to its oxidizing properties. Examples of such systems can be found in cryogenic technology, where aggressive, toxic gases or volatile liquids (ammonia, propane, hydrogen sulfide, helium, freons, etc.) are used as an energy carrier.

In non-circulating systems, gas can be used by the consumer as a chemical reagent (for example, in welding production, in the chemical industry) or as a source of pneumatic energy. In the latter case, air is usually used as an energy carrier. There are three main areas of application of compressed air.

To the first direction include technological processes where air directly performs the operations of blowing, drying, spraying, cooling, ventilation, cleaning, etc. Pneumatic conveying systems through pipelines have become very widespread, especially in the light, food, and mining industries. Piece and lumpy materials are transported in special vessels (capsules), and dusty materials mixed with air move over relatively long distances similar to fluid substances.

Second direction - the use of compressed air in pneumatic control systems (PSU) for automatic control of technological processes (pneumatic automation systems). This direction has been intensively developed since the 60s thanks to the creation of a universal system of industrial pneumatic automation elements (USEPPA). A wide range of USEPPA (pneumatic sensors, switches, converters, relays, logic elements, amplifiers, inkjet devices, command devices, etc.) allows you to implement on its basis relay, analog and analog-relay circuits, which in their parameters are close to electrical systems . Due to their high reliability, they are widely used for cyclic program control of various machines, robots in large-scale production, and in motion control systems for mobile objects.

third direction application of pneumatic energy, the largest in terms of power is the pneumatic drive, which in scientific terms is one of the sections of the general mechanics of machines. At the origins of the theory of pneumatic systems was I.I. Artobolevsky. He was the head of the Institute of Mechanical Engineering (IMASH) in Leningrad, where, under his leadership, in the 40s - 60s, the accumulated information on the theory and design of pneumatic systems was systematized and generalized. One of the first works on the theory of pneumatic systems was an article by A.P. German "Application of compressed air in mining", published in 1933, where for the first time the movement of the working body of a pneumatic device is solved together with the thermodynamic equation of state of air parameters.

A significant contribution to the theory and practice of pneumatic actuators was made by scientists B.N. Bezhanov, K.S. Borisenko, I.A. Bukharin, A.I. Voshchinin, E.V. Hertz, G.V. Kreinii, A.I. Kudryavtsev, V.A. Marutov, V.I. Mostkov, Yu.A. Zeitlin and others.

^ 11.2. Pneumatic drive features, advantages and disadvantages

The scope and scale of application of a pneumatic drive are due to its advantages and disadvantages arising from the characteristics of air properties. Unlike liquids used in hydraulic drives, air, like all gases, has high compressibility and low density in the initial atmospheric state (about 1.25 kg / m 3), significantly lower viscosity and greater fluidity, and its viscosity increases significantly with increase in temperature and pressure. The lack of lubricating properties of air and the presence of a certain amount of water vapor, which, under intense thermodynamic processes in the changing volumes of the working chambers of pneumatic machines, can condense on their working surfaces, prevents the use of air without giving it additional lubricating properties and moisture reduction. In this regard, there is a need for air conditioning in pneumatic actuators, i.e. giving it properties that ensure operability and extend the service life of drive elements.

Taking into account the above-described distinctive features of air, let's consider the advantages of a pneumatic drive in comparison with its competitors - hydraulic and electric drives.

1. ^ Simplicity of design and Maintenance . The manufacture of parts for pneumatic machines and pneumatic devices does not require such high precision in manufacturing and sealing of joints, as in a hydraulic drive, because possible air leaks do not significantly reduce the efficiency and efficiency of the system. External air leaks are environmentally friendly and relatively easy to fix. The cost of installation and maintenance of the pneumatic drive is somewhat less due to the lack of return pneumatic lines and the use in some cases of more flexible and cheap plastic or rubber (rubber-fabric) pipes. In this regard, the pneumatic drive is not inferior to the electric drive. In addition, the pneumatic drive does not require special materials for the manufacture of parts, such as copper, aluminum, etc., although in some cases they are used solely to reduce weight or friction in moving elements.

2. ^ Fire and explosion safety . Due to this advantage, the pneumatic drive has no competitors for mechanization of work in conditions dangerous for ignition and explosion of gas and dust, for example, in mines with abundant methane emissions, in some chemical industries, in flour mills, i.e. where sparking is unacceptable. The use of a hydraulic drive under these conditions is possible only if there is a centralized power source with hydropower transmission over a relatively long distance, which in most cases is not economically feasible.

3. ^ Reliable operation over a wide temperature range, in dusty and humid environments . Under such conditions, hydraulic and electric drives require significantly higher operating costs, because when temperature drops, the tightness of hydraulic systems is violated due to changes in the gaps and insulating properties of electrical materials, which, together with a dusty, humid and often aggressive environment, leads to frequent failures. For this reason, the pneumatic actuator is the only reliable source of energy for the mechanization of work in the foundry and welding industries, in forging and pressing shops, in some industries for the extraction and processing of raw materials, etc. Due to its high reliability, the pneumatic actuator is often used in brake systems mobile and stationary machines.

4. ^ Significantly longer service life than hydraulic and electric drives. The service life is evaluated by two indicators of reliability: gamma-percentage time between failures and gamma-percentage resource. For cyclic pneumatic devices, the resource is from 5 to 20 million cycles, depending on the purpose and design, and for non-cyclic devices, about 10-20 thousand hours. This is 2-4 times more than that of a hydraulic drive, and 10-20 times more than that of an electric drive.

5. ^ High performance . Here we mean not the speed of signal transmission (control action), but the realized speeds of working movements provided by high speeds of air movement. translational movement the rod of the pneumatic cylinder is possible up to 15 m/s or more, and the rotational speed of the output shaft of some pneumatic motors (pneumatic turbines) is up to 100,000 rpm. This advantage is fully realized in cyclic drives, especially for high-performance equipment, for example, in manipulators, presses, spot welding machines, in braking and fixing devices, and an increase in the number of simultaneously operating pneumatic cylinders (for example, in multi-place fixtures for clamping parts) practically does not reduce response time. A high rotational speed is used in the drives of separators, centrifuges, grinders, drills, etc. The implementation of high speeds in a hydraulic drive and an electric drive is limited by their greater inertia (fluid mass and rotor inertia) and the absence of a damping effect that air has.

6. ^ Ability to transmit pneumatic energy over relatively long distances through main pipelines and compressed air supply to many consumers. In this regard, the pneumatic drive is inferior to the electric drive, but significantly superior to the hydraulic drive, due to lower pressure losses in long main lines. Electrical energy can be transmitted over power lines for many hundreds and thousands of kilometers without tangible losses, and the transmission distance of pneumatic energy is economically feasible up to several tens of kilometers, which is implemented in pneumatic systems of large mining and industrial enterprises with centralized power supply from a compressor station.

The experience of creating a city compressor station in 1888 by one of the industrialists in Paris is known. It supplied plants and factories along 48 km long highways at a pressure of 0.6 MPa and had a capacity of up to 18,500 kW. With the advent of reliable power transmission, its operation became unprofitable.

The maximum length of hydraulic systems is about 250-300 m in mechanized mine complexes for coal mining, and they usually use a less viscous water-oil emulsion.

7. ^ No need for protective devices from pressure overload at consumers . The required air pressure limit is set by a common safety valve located on the pneumatic power sources. Air motors can be fully braked without danger of damage and remain in this state for a long time.

8. ^ Safety for service personnel subject to the general rules that exclude mechanical injuries. Damage is possible in hydraulic and electric drives electric shock or liquid in case of violation of insulation or depressurization of pipelines.

9. ^ Improving the ventilation of the workspace through the exhaust air. This property is especially useful in mine workings and premises of chemical and metalworking industries.

10. ^ Insensitivity to radiation and electromagnetic radiation . In such conditions, electro-hydraulic systems are practically unsuitable. This advantage is widely used in control systems for space and military equipment, in nuclear reactors, etc.

Despite the advantages described above, the applicability of the pneumatic drive is limited mainly by economic considerations due to big losses energy in compressors and air motors, as well as other disadvantages described below.

1. ^ The high cost of pneumatic energy . If the hydraulic and electric drives have an efficiency of about 70% and 90%, respectively, then the efficiency of the pneumatic drive is usually 5-15% and very rarely up to 30%. In many cases, the efficiency can be 1% or less. For this reason, the pneumatic drive is not used in machines with a long operating time and high power, except for conditions that exclude the use of electricity (for example, mining machines in mines that are dangerous for gas).

2. ^ Relatively large weight and dimensions of pneumatic machines due to low operating pressure. If the specific gravity of hydraulic machines per unit of power is 5-10 times less than the weight of electric machines, then pneumatic machines have approximately the same weight and dimensions as the latter.

3. ^ Difficulty in maintaining a stable speed output link with a variable external load and its fixation in an intermediate position. However, soft mechanical characteristics pneumatic drive in some cases are also its advantage.

4. ^ High level noise , reaching 95-130 dB in the absence of means to reduce it. The noisiest are reciprocating compressors and pneumatic motors, especially pneumatic hammers and other mechanisms of shock-cyclic action. The noisiest hydraulic drives (these include drives with gear machines) create noise at a level of 85-104 dB, and usually the noise level is much lower, approximately like that of electric machines, which allows you to work without special noise reduction equipment.

5. low speed signal transmission (control pulse), which leads to a delay in the execution of operations. The signal propagation speed is equal to the speed of sound and, depending on the air pressure, is approximately 150 to 360 m/s. In a hydraulic drive and an electric drive, respectively, about 1000 and 300,000 m/s.

These shortcomings can be eliminated by using combined pneumoelectric or pneumohydraulic drives.

^ 11.3. air flow

Engineering calculations of pneumatic systems are reduced to determining the speeds and air flow rates during filling and emptying of tanks (engine working chambers), as well as with its flow through pipelines through local resistances. Due to the compressibility of air, these calculations are much more complicated than those hydraulic systems, and are fully implemented only for especially critical cases. A complete description of the processes of air flow can be found in special gas dynamics courses.

The main patterns of air (gas) flow are the same as for liquids, i.e. take place laminar And turbulent flow regimes, steady and unsteady nature of the flow, uniform and non-uniform flow due to the variable cross section of the pipeline, and all other kinematic and dynamic characteristics of the flows. Due to the low viscosity of air and relatively high velocities, the flow regime is in most cases turbulent.

For industrial pneumatic actuators, it is enough to know the regularities of the established nature of the air flow. Depending on the intensity of heat exchange with the environment, air parameters are calculated taking into account the type of thermodynamic process, which can be from isothermal (with complete heat exchange and fulfillment of the condition T= const) to adiabatic (no heat transfer).

At high speeds executive mechanisms and gas flow through resistances, the compression process is considered adiabatic with the adiabatic exponent k= 1.4. In practical calculations, the adiabatic exponent is replaced by the polytropic exponent (usually taken n= 1.3…1.35), which makes it possible to take into account losses due to air friction and possible heat transfer.

In real conditions, some heat exchange inevitably occurs between the air and the parts of the system, and the so-called polytropic change in the state of the air takes place. The entire range of real processes is described by the equations of this state

pV n= const

Where n- polytropic index, varying from n= 1 (isothermal process) up to n= 1.4 (adiabatic process).

The calculation of air flow is based on the well-known Bernoulli equation of motion ideal gas

The terms of the equation are expressed in units of pressure, which is why they are often referred to as "pressures":
z - weight pressure;
p - static pressure;
- high-speed or dynamic pressure.

In practice, the weight pressure is often neglected and the Bernoulli equation takes the following form

The sum of the static and dynamic pressures is called the total pressure. P 0 . Thus, we get

There are two things to keep in mind when designing gas systems. fundamental differences from the calculation of hydraulic systems.

The first difference is that it is not defined volume flow air, but massive. This allows you to unify and compare the parameters of various elements of pneumatic systems for standard air (ρ = 1.25 kg/m3, υ = 14.9 m2/s at p= 101.3 kPa and t= 20°C). In this case, the cost equation is written as

Q m1 = Q m2 or υ 1 V 1 S 1 = υ 2 V 2 S 2

The second difference is that at supersonic air flow speeds, the nature of the dependence of the flow rate on the pressure drop across the resistance changes. In this regard, there are concepts of subcritical and supercritical air flow regimes. The meaning of these terms is explained below.

Consider the outflow of gas from a tank through a small hole while maintaining a constant pressure in the tank (Fig. 11.1). We will assume that the dimensions of the reservoir are so large compared to the dimensions of the outlet that we can completely neglect the velocity of gas inside the reservoir, and, consequently, the pressure, temperature and density of the gas inside the reservoir will have the values p 0 , ρ 0 And T 0 .

Fig.11.1. Outflow of gas from a hole in a thin wall

The gas outflow rate can be determined from the formula for the outflow of an incompressible liquid, i.e.

The mass flow rate of gas flowing through the hole is determined by the formula

Where ω 0 is the cross-sectional area of the hole.

Attitude p/p 0 is called the degree of expansion of the gas. An analysis of formula (11.7) shows that the expression under the root in square brackets vanishes when p/p 0 = 1 and p/p 0 = 0. This means that at a certain value of the pressure ratio, the mass flow reaches a maximum Q max. Plot of gas mass flow versus pressure ratio p/p 0 shown in Figure 11.2.

Fig.11.2. The dependence of the mass flow rate of gas on the ratio of pressures

Pressure ratio p/p 0 , at which the mass flow reaches its maximum value, is called critical. It can be shown that the critical pressure ratio is

As can be seen from the graph shown in Fig. 11.2, with a decrease p/p 0 compared to the critical flow rate should decrease (dashed line) and at p/p 0 = 0 flow value must be equal to zero ( Q m= 0). However, this does not actually happen.

In fact, with the given parameters p 0 , ρ 0 And T 0 flow rate and outflow rate will increase with decreasing pressure outside the tank p as long as this pressure is less than the critical pressure. When the pressure p reaches a critical value, the flow rate becomes maximum, and the outflow velocity reaches a critical value equal to the local speed of sound. The critical speed is determined by the well-known formula

After the speed has reached the speed of sound at the outlet of the hole, a further decrease in back pressure p cannot lead to an increase in the outflow velocity, since, according to the theory of propagation of small perturbations, the internal volume of the reservoir will become inaccessible to external perturbations: it will be "locked" by a flow with sound speed. All external small perturbations cannot penetrate into the reservoir, since they will be prevented by a flow having the same speed as the perturbation propagation velocity. In this case, the flow rate will not change, remaining maximum, and the flow curve will take the form of a horizontal line.

Thus, there are two flow zones (regions):

subcritical regime, at which

supercritical regime, at which

In the supercritical zone, maximum speed and flow rate corresponding to the critical expansion of the gas. Based on this, when determining the air flow rates, the outflow mode (zone) is preliminarily determined by the pressure drop, and then the flow rate. Air friction losses are taken into account by the flow coefficient μ, which can be calculated with sufficient accuracy by the formulas for an incompressible liquid (μ = 0.1 ... 0.6).

Finally, the speed and maximum mass flow in the subcritical zone, taking into account the compression of the jet, are determined by the formulas

^ 11.4. Compressed air preparation

In industry, various designs of air supply machines are used under the general name blowers. When creating excess pressure up to 0.015 MPa, they are called fans, and at pressures over 0.115 MPa - compressors.

Fans belong to the bladed machines of dynamic action and, in addition to their main purpose - ventilation - are used in pneumatic transport systems and low-pressure pneumatic automation systems.

In pneumatic actuators, compressors with a working pressure in the range of 0.4 ... 1.0 MPa serve as an energy source. They can be volumetric (usually piston) or dynamic (vane) action. The theory of operation of compressors is studied in special disciplines.

According to the type of source and method of delivery of pneumoenergy, there are main, compressor And rechargeable pneumatic drive.

Trunk the pneumatic drive is characterized by an extensive network of stationary pneumatic lines connecting the compressor station with workshop, local consumers within one or more enterprises. The compressor station is equipped with several compressor lines that provide a guaranteed supply of compressed air to consumers, taking into account the possible uneven work the latter. This is achieved by installing intermediate pneumatic energy storage devices (receivers) both at the station itself and at the sites. Pneumatic lines are usually reserved, which ensures the convenience of their maintenance and repair. A typical set of devices included in the air preparation system is shown in the schematic diagram of the compressor station (Fig. 11.3).

Fig.11.3. Schematic diagram of the compressor station

Compressor 2 with a drive motor 3 draws air from the atmosphere through the intake filter 1 and pumps it into the receiver 7 through the check valve 4, cooler 5 and filter-drier 6. As a result of cooling the air with a water cooler 5, 70-80% of the moisture contained in the air is condensed, The air captured by the filter-moisture separator and with 100% relative humidity enters the receiver 7, which accumulates pneumoenergy and smooths out the pressure pulsation. It further cools the air and condenses a certain amount of moisture, which, as it accumulates, is removed along with mechanical impurities through valve 10. The receiver is necessarily equipped with one or more safety valves 8 and a pressure gauge 9. Air is discharged from the receiver to pneumatic lines 12 through taps 11. valve 4 eliminates the possibility of a sharp drop in pressure in the pneumatic network when the compressor is turned off.

^ Compressor pneumatic drive differs from the above-described backbone in its mobility and limited number of simultaneously operating consumers. Mobile compressors most widely used in the performance of various types of construction and repair work. According to the set of devices included in the air preparation system, it practically does not differ from the compressor station described above (the water cooler is replaced by an air cooler). Air supply to consumers is carried out through rubber-fabric sleeves.

^ Battery pneumatic actuator due to the limited supply of compressed air in industry, it is rarely used, but is widely used in autonomous systems control mechanisms with a given time of action. Figure 11.4 shows several examples of battery powered pneumatic systems.

For uninterrupted supply of fluid to the hydraulic system or fuel to engines internal combustion devices with a variable orientation in space, a pressurization of a tank with liquid is used (Fig. 11.4, a) from a pneumocylinder 1.

The displacement of liquid from tank 5, divided by a membrane into two parts, is ensured by a constant air pressure, which depends on the setting of the pressure reducing valve 3 when the electric valve 2 is turned on. The limiting pressure is limited by valve 4.

The attitude control system of the aircraft (Fig. 11.4, b) consists of control jet air motors 4, powered by ball air bellows 1 through a pressure reducing valve 2 and electric valves 3.

Fig.11.4. Schematic diagrams of battery power
pneumatic systems (a, b, c) and closed pneumatic system (d)

To power industrial pneumatic automation systems, not only the average (normal) range of air pressure (0.118 ... 0.175 MPa), but also the low range (0.0012 ... 0.005 MPa) is often used. This allows you to reduce the consumption of compressed air, increase the flow area of the elements and, consequently, reduce the likelihood of clogging of the throttling devices, and in some cases obtain a laminar air flow regime with a linear relationship Q = f(Δ p), which is very important in pneumatic automation devices.

In the presence of a high pressure source, it is possible to supply a low-pressure pneumatic system with a large air flow using an ejector (Fig. 11.4, c). From the high-pressure air cylinder 1, equipped with a pressure reducing valve 4, a pressure gauge 2 and a charging valve 3, air enters the supply nozzle 5 of the ejector. In this case, a reduced pressure is created inside the ejector housing, and air is sucked from the environment through the filter 6, which enters the receiving nozzle 7 of a larger diameter. After the ejector, the air is again cleaned of dust by the filter 8 and enters the devices 10 of pneumatic automation. Manometer 9 is controlled operating pressure, the value of which can be adjusted by reducer 4.

All the above pneumatic systems are open (non-circulating). Figure 11.4, d shows closed circuit power supply of the pneumatic automation system used in a dusty atmosphere. Air is supplied to the pneumoautomatic unit 3 by a fan 1 through a filter 2, and the suction channel of the fan is connected to the internal cavity of the sealed casing of the unit 3, which simultaneously communicates with the atmosphere through a fine filter 4. Often, household electric vacuum cleaners are used as a fan, capable of creating pressure up to 0.002 MPa.

The air supplied to consumers must be cleaned of mechanical impurities and contain a minimum of moisture. For this, filters-moisture separators are used, in which fabric, cardboard, felt, cermet and other porous materials with a filtration fineness of 5 to 60 microns are usually used as a filter element. For a deeper drying of the air, it is passed through adsorbents that absorb moisture. Most often, silica gel is used for this. In conventional pneumatic drives, receivers and filters-moisture separators provide sufficient drying, but at the same time, lubricating properties must be imparted to the air, for which wick or ejector-type oil atomizers are used.

Fig.11.5. Typical air preparation unit:
a - schematic diagram; b - symbol

Figure 11.5 shows a typical air preparation unit, consisting of a filter-drier 1, a pressure reducing valve 2 and an oil sprayer 3.

The air entering the filter inlet receives rotational movement due to the fixed impeller Kp. centrifugal force particles of moisture and mechanical impurities are thrown to the wall of the transparent case and settle into its lower part, from where they are removed through the drain valve as necessary. Secondary air purification takes place in a porous filter Ф, after which it enters the gearbox inlet, where it is throttled through the valve gap Cl, the value of which depends on the outlet pressure above the membrane M. Increasing the spring force P provides increased valve clearance Cl and hence outlet pressure. The body of the oil atomizer 3 is made transparent and filled through the plug lubricating oil. The pressure created on the surface of the oil forces it out through the tube T up to the nozzle WITH where the oil is ejected and atomized by the air flow. In wick-type oil sprayers instead of a tube T a wick is installed through which the oil enters the spray nozzle due to the capillary effect.

^ 11.5. Executive pneumatic devices

Pneumatic actuators are called various mechanisms that convert excess air pressure or vacuum into working force. If at the same time the working body moves relative to the pneumatic device, then it is called an air motor, and if there is no movement or it occurs together with the pneumatic device, then it is called a pneumatic clamp or pneumatic grip.

Pneumatic motors can be, like hydraulic motors, rotary or translational and are called, respectively, pneumatic motors And pneumatic cylinders. The design of these devices is in many ways similar to their hydraulic counterparts. Gear, lamellar and radial-piston pneumatic motors of volumetric action have received the greatest application. Figure 11.6, a shows a diagram of a radial piston motor with torque transmission to the shaft through crank mechanism.

Cylinders 2 with pistons 3 are symmetrically located in housing 1. The force from the pistons is transmitted to the crankshaft 5 through the connecting rods 4, which are hinged to the pistons and the crankshaft crank. Compressed air is supplied to the working chambers through channels 8, which alternately communicate with the inlet Vp and exhaust Vx channels of the distribution spool 6, rotating synchronously with the motor shaft. The spool rotates in the switchgear housing 7, to which the intake and exhaust air lines are connected.

Radial piston pneumatic motors are relatively low-speed machines with a shaft speed of up to 1000 ... 1500 rpm. Gear and vane motors are faster (2000 ... 4000 rpm), but the fastest (up to 20,000 rpm or more) can be turbine pneumatic motors that use the kinetic energy of the compressed air flow. In particular, such motors are used to rotate the impellers of fans in mining enterprises.

Fig.11.6. Schemes of pneumatic motors of volumetric (a) and dynamic (b) action

Figure 11.6, b shows a diagram of the pneumatic drive of the fan wheel, consisting of a hub 9 with blades 10, to which a rotating rim with the blades of the pneumatic motor 11 is rigidly attached. causes the fan wheel to rotate at high speed. The described device can be called a pneumatic converter that converts a high pressure air stream into a low pressure stream with a much higher flow rate.

The pneumatic drive is distinguished by a wide variety of original actuators with elastic elements in the form of membranes, shells, flexible threads, sleeves, etc. They are widely used in clamping, fixing, switching and brake mechanisms modern automated productions. These include membrane And bellows pneumatic cylinders with a relatively small stroke of the rod. A flat rubber diaphragm allows the rod to be moved by 0.1...0.5 of its effective diameter. When the membrane is made in the form of a corrugated stocking, the working stroke is increased to several membrane diameters. These pneumatic cylinders are called bellows. They can be with external and internal air supply. In the first case, the length of the corrugated tube decreases under the action of pressure; in the second case, it increases due to the deformation of the corrugations. Rubber, rubber-fabric and synthetic materials, as well as sheet steel, bronze, brass are used as an elastic element.

An increase in the speed of operations in many cases is achieved by using pneumatic grippers, the schemes of which are shown in Fig. 11.7.

To move sheet products, pneumatic suction cups are used, related to vacuum grippers of non-pump and pump type. In non-pumping grips (Fig. 11.7, a) the vacuum in the working chamber TO is created during the deformation of the gripping elements themselves, made in the form of a flexible plate, with its edge adjacent to the part and a movable piston, to which an external force is applied. The amount of vacuum when lifting a part is proportional to its weight and is usually not more than 55 kPa. To ensure better attraction, especially for an insufficiently smooth surface of the part, pump-type grippers are used, in which air from the working chamber is sucked off by a pump to a vacuum depth of 70 ... 95 kPa.

Often simple devices of the ejector type are used (Fig. 11.7, b), in which the kinetic energy of a jet of liquid, steam or air is used to suck air from the working chamber TO located between the suction cup P and detail. Compressed air inlet A, passes at high speed through the nozzle B ejector and creates a reduced pressure in the chamber IN and channel G communicating with the working chamber TO.

Fig.11.7. Schemes of pneumatic grippers

To clamp cylindrical parts, pneumatic grippers are used, made according to schemes c and d (Fig. 11.7). When air is supplied to the working chamber TO an elastic cylindrical cap covers the neck of the shaft and creates a force sufficient to clamp it. Scheme d shows a double-sided pneumatic gripper, the working elements of which are bellows with a one-sided corrugation. When pressurized inside the bellows, the corrugated side is stretched to a greater length than the smooth side, which causes the loose (cantilevered) side of the tube to move towards the male part. Such devices can fix parts not only of a round shape, but also with any shaped surfaces.

In some cases, there is a need to move the working bodies over long distances up to 10 ... 20 m or more along a straight or curved path. The use of conventional rod pneumatic cylinders is limited to a working stroke of up to 2 m. The designs of rodless pneumatic cylinders that meet these requirements are shown in Fig. 11.8.

Fig.11.8. Schemes of rodless air motors
forward movement

The absence of a rigid rod makes it possible to almost halve the length of the cylinder in the extended position. Diagram a shows a long-stroke pneumatic cylinder with power transmission through a strong permanent magnet. Absolutely hermetic cylinder liner is made of non-magnetic material, and its internal cavity is divided by a piston into two chambers, to which compressed air. In piston and carriage TO connected to the working body, the opposite poles of the magnet are built in S And N, the interaction of which ensures the transfer of the driving force to the carriage sliding along the guides on the outer surface of the sleeve. The travel of the carriage is limited by the end stops At.

Pneumatic cylinders with an elastic sleeve (Fig. 11.8, b) covered by two rollers connected by a carriage have a practically unlimited stroke length TO. Such pneumatic cylinders are very effective for moving piece goods along complex trajectories and in drives with low operating forces.

A pneumatic cylinder with a flexible rod is shown in the diagram in Fig. 11.8, c. In such a design pulling force transferred to the carriage TO from the piston through a flexible element (usually a steel cable lined with elastic plastic), covering the bypass and tension rollers located on the cylinder covers.

^ Top of page

The fundamentals of functioning of hydraulic and pneumatic systems are considered: hydrostatics and hydrodynamics; laws of ideal gases, thermodynamics. Hydraulic, pneumatic and combined drives, their structure, constituent elements, working fluids and oils, types of drives, types of control in machine-building production; given lubrication systems, basic calculation of hydraulic and pneumatic systems.
For students of mechanical engineering specialties of secondary vocational schools. May be useful for engineering and technical workers.

Liquids. Continuity hypothesis. Liquid density.
Liquids. All substances in nature have a molecular structure. By the nature of molecular motions, as well as by the numerical values of intermolecular forces, liquids occupy an intermediate position between gases and solids. Properties of liquids at high temperatures And low pressures closer to the properties of gases, and at low temperatures and high pressures - to the properties of solids.

In gases, the distances between molecules are greater, and the intermolecular forces are smaller than in liquids and solids, therefore gases differ from liquids and solids in greater compressibility. Compared to gases, liquids and solids are less compressible.

Liquid molecules in continuous chaotic thermal motion differ from the chaotic thermal motion of gases and solids: in liquids, this motion occurs in the form of oscillations (1013 oscillations per second) relative to instantaneous centers and abrupt transitions from one center to another. Thermal motion of molecules of solids - vibrations relative to stable centers. The thermal motion of gas molecules is continuous spasmodic changes of places.

Free download e-book in a convenient format, watch and read:
Download the book Hydraulic and pneumatic systems, Skhirtladze A.G., Ivanov V.I., Kareev V.N., 2006 - fileskachat.com, fast and free download.

Hydraulics in mechanical engineering, Part 2, Skhirtladze A.G., Ivanov V.I., Kareev V.N., 2008
Tooling of technological processes of metalworking, Skhirtladze A.G., Perevoznikov V.K., Ivanov V.A., Ivanov A.V., 2015
Deep hole drilling technologies, Zvontsov I.F., Serebrenitsky P.P., Skhirtladze A.G., 2013
Organization and installation and repair of industrial equipment, Part 2, Skhirtladze A.G., Feofanov A.N., Mitrofanov V.G., 2016

The following tutorials and books.