Valve-controlled hydraulic motor refers to an open system, in which the reversing valve is used to control the steering of the motor or the control speed of the flow valve.
Pump control refers to controlling the rotational speed or speed of the motor by controlling the displacement or oil outlet direction of the pump. Generally used in variable systems.
(a) using different energy sources
Pneumatic components and devices can adopt centralized air supply from air compressor station, and adjust the working pressure of their respective pressure reducing valves according to different use requirements and control points. The hydraulic valve is equipped with an oil return line to collect the used hydraulic oil in the oil tank. pneumatic control valve
So as to directly discharge compressed air to the atmosphere through the exhaust port.
(b) Different requirements for leakage.
Hydraulic valves have strict requirements for external leakage, but allow a small amount of internal leakage of components. For pneumatic control valves, internal leakage is not allowed in principle except for valves with clearance seals. Internal leakage of pneumatic valve may lead to accidents.
For pneumatic pipes, a little leakage is allowed; The leakage of hydraulic pipeline will cause system pressure drop and environmental pollution.
(c) Different lubrication requirements
The working medium of hydraulic system is hydraulic oil, and there is no requirement for lubrication of hydraulic valve. The working medium of pneumatic system is air, which has no lubricity, so many pneumatic valves need oil mist lubrication. Valve parts should be made of materials that are not easily corroded by water, or necessary anti-rust measures should be taken.
(4) Different pressure ranges
The working pressure range of pneumatic valve is lower than that of hydraulic valve. The working pressure of pneumatic valves is usually within 10bar, and a few can reach 40bar. But the working pressure of hydraulic valve is very high (usually within 50Mpa). If the pneumatic valve is used above the maximum allowable pressure. Serious accidents often happen.
(5) The use characteristics are different.
Compared with hydraulic valves, general pneumatic valves have the advantages of compact structure, light weight, easy integration and installation, high working frequency and long service life. Pneumatic valves are developing in the direction of low power and miniaturization, and a low-power solenoid valve with a power of only 0.5W has appeared. It can be directly connected with a microcomputer and a PLC programmable controller, and can also be installed on a printed circuit board together with electronic devices. The gas-electric circuit is connected by a standard board, which saves a lot of wiring. Suitable for pneumatic industrial manipulator, complex manufacturing assembly line and other occasions.