Electro-hydraulic actuators and pneumatic, electric actuator used in pneumatic valves

the pneumatic valve system use mostly is pneumatic actuator, electric actuator and the electro-hydraulic actuator, according to the characteristics of the three actuators itself, we have to analyze their application in the pneumatic valve system:
pneumatic system, pneumatic system depend on air compressor, the air is compressed, clean after processing supply pneumatic actuators, pneumatic valve drive action. Gas in the process of driving actuator is directly discharged to the atmosphere, gas path system need to deal with the uninterrupted air supply. Air compressor, therefore, usually need a spare one, and actuator in front of the branch of the main air processing components, such as drying machine, filter decompression, oil mist device, etc. All needs to preventive maintenance, replacement. Pneumatic joint more, also need to regularly check, in case of gas leakage, affect the system pressure. So all the work is to ensure that pneumatic actuators in the system need to switch to the right action. Large diameter pneumatic valve actuator cylinder, are generally according to the selection of a certain air pressure, but the scene is often appear pneumatic actuators is not action, or action does not reach the designated position, or action is slow, the movement is not smooth, usually is caused by several reasons:
( Gas path contains water, such as air temperature is below freezing, the water freezes, frozen pneumatic actuators, pneumatic actuators to action;
( Pneumatic oil mist lubrication processing, pneumatic actuator inside is in a state of dry run for a long time, due to friction, actuator is unsmooth or unable to move;
( Air compressor output air pressure is insufficient or point of leak in the gas circuit, the pneumatic actuators can't get enough driving moment, unable to quickly open the pneumatic valves or not fully closed pneumatic valves;
( Gas in the cold and the thermal environment, thermal coefficient is different, lead to all pneumatic actuators running time difference;
( Gas compressibility, may lead to a pneumatic actuators irregularities in the operation process, wrong operation.
if requires fast, the pneumatic actuators will generally equipped with a gas tank, in fast, even gave up the ghost, power outages, can still guarantee quick switch pneumatic valve, but due to the output is limited, a short fast closing time will not.
that hydraulic system, hydraulic station system and pneumatic system operation mechanism, to produce high pressure oil, need oil filter, laying oil needs. Difference is the advantage of hydraulic system, hydraulic system is the inner loop, the oil pressure in commonly ~ kilograms, hydraulic actuator volume pneumatic actuators are much smaller, and the hydraulic oil no compressibility, hydraulic cylinder run smooth unsmooth dithering phenomenon will not occur. Hydraulic system can completely solve the shortage of the pneumatic system.
the advantages of the hydraulic system itself is the best choice to ensure reliable pneumatic valve operation, but high pressure oil, such as improper maintenance, often produces oil leakage. Hydraulic system parts such as servo pneumatic valve, filters, high-pressure pipe is not cheap, such as higher maintenance costs.
electric actuator, electric actuator is completely different from pneumatic actuators and hydraulic actuators, electric actuators are completely get rid of the bondage of the air compressor and hydraulic station, only need to get power supply and signal, can drive the bypass system action. Relative to the pneumatic system and hydraulic system, electric actuators are small size, simple installation and maintenance workload is reduced greatly.
but electric actuator due to its structure determines: run slower, whole journey typically take a few seconds or longer; Once the power outages, actuators can't action. Once the fault, such as electric actuator power supply is normal, pneumatic valve opened slowly; Such as power electric actuators, pneumatic valves will not be able to action. It is almost impossible to avoid power outages in the factory, so the characteristics of electric actuators is still a great potential safety hazard.