Pneumatic control valves are divided into two types: air-opening and air-closing according to the action form, namely the so-called normally open type and normally closed type. The air-opening or air-closing of the pneumatic control valve is usually through the positive and negative action of the actuator and the valve state structure. of different assembly methods.
Pneumatic control valve is to use compressed air as the power source, the cylinder as the actuator, and with the help of electrical valve positioner, converter, solenoid valve, retaining valve and other accessories to drive the valve, to achieve switching or proportional adjustment, receiving industrial The control signal of the automatic control system is used to adjust the pipeline medium: flow, pressure, temperature and other process parameters. Pneumatic control valves are characterized by simple control, fast response, and intrinsic safety, without the need for additional explosion-proof measures.
Pneumatic control valve is one of the industrial process control instruments widely used in petroleum, chemical, electric power, metallurgy and other industrial enterprises. In chemical production, the regulating valve is necessary in the regulating system. It is an important part of the industrial automation system. It is like the hands and feet of the automation of the production process. Below, we will take you to a comprehensive understanding of pneumatic control valves.
Pneumatic regulating valve is usually composed of pneumatic actuator and regulating valve connection, installation and debugging. Pneumatic actuator can be divided into single-acting and double-acting. There is a return spring in the single-acting actuator, while there is no return spring in the double-acting actuator. . Among them, the single-acting actuator can automatically return to the open or closed state initially set by the valve in the event of loss of origin or sudden failure.
(1) Different pressure ranges
The working pressure range of the pneumatic control valve is lower than that of the hydraulic valve. The working pressure of pneumatic control valves is usually within 10bar, and a few can reach within 40bar. But the working pressure of hydraulic valve is very high (usually within 50Mpa). If the pneumatic control valve is used above the high allowable pressure. Serious accidents often occur.
(2) Different use characteristics
Generally, the pneumatic control valve is more compact and lighter than the hydraulic valve, and is easy to integrate and install. The valve has a high working frequency and a long service life. Pneumatic control valves are developing in the direction of low power and miniaturization, and low-power solenoid valves with only 0.5W of power have appeared. It can be directly connected with microcomputer and PLC programmable controller, and can also be installed on the printed circuit board together with electronic devices, and the gas-electric circuit is connected through the standard board, which saves a lot of wiring, and is suitable for pneumatic industrial manipulators, complex production and manufacturing. assembly line, etc.
(3) Different requirements for leakage
The hydraulic valve has strict requirements on external leakage, but a small amount of leakage inside the component is allowed. For pneumatic control valves, in principle, internal leakage is not allowed, except for gap-sealed valves. Risk of accident due to internal leakage of pneumatic control valves.
For the pneumatic pipeline, a little leakage is allowed; while the leakage of the hydraulic pipeline will cause the system pressure to drop and the environment to be polluted.
(4) The energy used is different
Pneumatic components and devices can adopt the method of centralized air supply in the air compressor station, and adjust the working pressure of their respective pressure reducing valves according to the different use requirements and control points. Hydraulic valves are equipped with oil return lines to facilitate the collection of used hydraulic oil in the oil tank. The pneumatic control valve can directly discharge the compressed air to the atmosphere through the exhaust port.
(5) Different requirements for lubrication
The working medium of the hydraulic system is hydraulic oil, and the hydraulic valve has no requirement for lubrication; the working medium of the pneumatic system is air, and the air has no lubricity, so many pneumatic control valves require oil mist lubrication. The parts of the valve should choose materials that are not easily corroded by water, or take necessary anti-rust measures.
