Hydraulic and pneumatic technology

Hydraulic pressure is a term in mechanical industry and electromechanical industry. Hydraulic power transmission can be used as hydraulic transmission. Hydraulic pressure can also be used as a control mode, which is called hydraulic control.

Hydraulic transmission takes liquid as working medium and uses the pressure energy of liquid to transmit power.

Hydraulic control is a kind of control with pressurized liquid as the transmission mode of control signal. The control system composed of hydraulic technology is called hydraulic control system.

A complete hydraulic system consists of five parts, namely, energy device, executive device, control and adjustment device, auxiliary device and liquid medium. Hydraulic pressure has been widely used in industrial and civil industries because of its characteristics of large transmission power and easy transmission and configuration. The function of the executive components of the hydraulic system (hydraulic cylinder and hydraulic motor) is to convert the pressure energy of liquid into mechanical energy, so as to obtain the required linear reciprocating motion or rotary motion. The function of the energy device (hydraulic pump) of the hydraulic system is to convert the mechanical energy of the prime mover into the pressure energy of the liquid.

Pneumatic transmission technology is an energy transmission technology with compressed air as the medium and air source as the power. It has high reliability, long service life and no pollution to the environment, so pneumatic technology is often used in the driving system of manipulator. Manipulators are generally composed of executive system, driving system, control system and artificial intelligence system, which mainly accomplish the actions of moving, rotating and grabbing. Compared with other types of manipulators, pneumatic manipulators have the characteristics of simple structure, low cost, easy control and convenient maintenance.

Development history of hydraulic transmission

Hydraulic transmission and pneumatic transmission are collectively called fluid transmission, which is a new technology developed according to the hydrostatic transmission principle put forward by Pascal in17th century. Braman (1749- 18 14) used water as working medium in London and applied it to industry in the form of hydraulic press, thus giving birth to the world's first hydraulic press. 1905, the working fluid water is replaced by oil, which is further improved.

After World War I (1914-1918), hydraulic transmission was widely used, especially after 1920. Hydraulic components began to enter the formal industrial production stage from the end of 19 to the beginning of the 20th century. 1925, F.Vikers invented the pressure balance vane pump, which laid the foundation for the gradual establishment of modern hydraulic component industry or hydraulic transmission. Constantine in the early 20th century? Newcastle (g? Constantimsco) conducted theoretical and practical research on energy fluctuation transmission; 19 10's contribution to hydraulic transmission (hydraulic coupling, hydraulic torque converter, etc. ) these two fields have been developed.

During World War II (194 1- 1945), 30% of machine tools in the United States used hydraulic transmission. It should be pointed out that the development of hydraulic transmission in Japan is nearly 20 years later than that in Europe and America. Around 1955, Japan developed hydraulic transmission rapidly, and 1956 established the "Hydraulic Industry Association". In recent 20~30 years, Japan's hydraulic transmission has developed rapidly and occupied a leading position in the world.

Hydraulic transmission has many outstanding advantages, so it is widely used, such as general engineering. Industrial plastic processing machinery, pressure machinery, machine tools, etc. Construction machinery, construction machinery, agricultural machinery, automobiles, etc. In mobile machinery; Metallurgical machinery, lifting device, roller adjusting device, etc. Used in steel industry; Flood control dam device, river bed lifting device, bridge control mechanism, etc. Used in civil and hydraulic engineering; Turbine speed regulating devices in power plants and nuclear power plants. Deck crane (winch), bow door, bulkhead valve, stern propeller, etc. For ships; Giant antenna control device for special technology, measuring buoy, lifting turntable, etc. Gun control device for military use, ship anti-rolling device, aircraft simulation, aircraft landing gear retracting device, rudder control device.

Advantages and disadvantages of hydraulic pressure

Compared with mechanical transmission and electric transmission, hydraulic transmission has the following advantages:

1. Various components of hydraulic transmission can be conveniently and flexibly arranged as required.

2. Light weight, small volume, small motion inertia and fast reaction speed.

3. The operation and control are convenient, and a wide range of stepless speed regulation can be realized (the speed regulation range is 2000: 1).

4, can automatically realize overload protection.

5. The working medium is generally mineral oil, and the relatively moving surface can be lubricated by itself, with long service life;

6, it is easy to realize linear motion/

7. It is easy to realize the automation of the machine. When electro-hydraulic combined control is adopted, not only a high degree of automatic control process can be realized, but also remote control can be realized.

Of course, hydraulic transmission also has some disadvantages:

1, because the fluid flow resistance is large, there are many leaks and the efficiency is low. If not handled properly, the leakage will not only pollute the site, but also cause fire and explosion accidents.

2. Because the working performance is easily affected by temperature changes, it is not suitable for working under very high or low temperature conditions.

3. The manufacturing precision of hydraulic components is high, so it is expensive.

4. Due to the leakage and compressibility of liquid medium, strict transmission ratio cannot be obtained.

5. When the hydraulic transmission fails, it is not easy to find out the reason; Use and maintenance require a high level of technology.

Composition and function of hydraulic system

A complete hydraulic system consists of five parts, namely, power component, executive component, control component, component and hydraulic oil.

The function of the power element is to convert the mechanical energy of the prime mover into the pressure energy of liquid, which refers to the oil pump in the hydraulic system and provides power for the whole hydraulic system. The structural forms of hydraulic pumps generally include gear pumps, vane pumps and plunger pumps. See 1- 1 for their performance comparison.

The function of executive components (such as hydraulic cylinder and hydraulic motor) is to convert the pressure energy of liquid into mechanical energy and drive the load to do linear reciprocating motion or rotary motion.

Control elements (i.e. various hydraulic valves) control and adjust the pressure, flow and direction of liquid in the hydraulic system. According to different control functions, hydraulic valves can be divided into village force control valve, flow control valve and direction control valve. Pressure control valve is divided into beneficial flow valve (safety valve), pressure reducing valve, sequence valve, pressure relay, etc. The flow control valve includes throttle valve, regulating valve, shunting and collecting valve, etc. Directional control valves include one-way valves, hydraulically controlled one-way valves, shuttle valves, reversing valves, etc. According to different control methods, hydraulic valves can be divided into on-off control valves, fixed value control valves and proportional control valves.

Auxiliary components include oil tank, oil filter, oil pipe and pipe joint, sealing ring, pressure gauge, oil level and oil temperature gauge, etc.

Hydraulic oil is the working medium to transfer energy in hydraulic system, including various mineral oil, emulsion and synthetic hydraulic oil.

Edit the three disadvantages of this hydraulic system.

1, heating Due to the different flow rates of the force transfer medium (hydraulic oil) in different parts during the flow process, there is some internal friction in the liquid, and there is also friction between the liquid and the inner wall of the pipeline, which are the reasons for the temperature rise of the hydraulic oil. The increase of temperature will lead to the increase of internal and external leakage and reduce its mechanical efficiency. At the same time, due to the high temperature, hydraulic oil will expand, resulting in increased compressibility, so that the control action can not be transmitted well. Solution: heating is an inherent characteristic of hydraulic system, which can't be carved at the root and can only be minimized. Use high-quality hydraulic oil, avoid elbows in hydraulic pipeline layout, and use high-quality pipelines, pipe joints, hydraulic valves, etc.

2. Vibration of vibration hydraulic system is also one of its chronic diseases. The vibration of the system is caused by the impact caused by the high-speed flow of hydraulic oil in the pipeline and the impact caused by the opening and closing of the control valve. Strong vibration will lead to errors in the control actions of the system, as well as errors in some more precise instruments in the system, leading to system failures. Solution: Fix the hydraulic pipeline as far as possible to avoid sharp bends. Avoid changing the direction of liquid flow frequently, and take vibration reduction measures when it is inevitable. The whole hydraulic system should have good vibration reduction measures and avoid the influence of external vibration sources on the system.

3. The leakage of hydraulic system is divided into internal leakage and external leakage. Internal leakage refers to the leakage process occurring inside the system, such as the leakage on both sides of the piston of the hydraulic cylinder and the leakage between the valve core and the valve body of the control valve. Although internal leakage will not lead to the loss of hydraulic oil, it may affect the established control actions until the system fails. External leakage refers to the leakage between the system and the external environment. The direct leakage of hydraulic oil into the environment will not only affect the working environment of the system, but also lead to the failure caused by insufficient system pressure. Hydraulic oil leaking into the environment is also in danger of fire. Solution: Use better quality seals to improve the machining accuracy of the equipment.

In addition, for the three major ills of the hydraulic system, some people summed it up as: "Fever and diarrhea for show" (the summoner is a Northeastern).

hydraulic pressure system

Used in elevators, excavators, pumping stations, dynamic compactors, cranes and other large industries, buildings, factories and enterprises, as well as elevators, lifting platforms, boarding bridges and other industries.