Check valves in hydraulic system the role of the following points:
(1) If the check valve is installed in the outlet of the pump, you can prevent the system from a sudden rise in pressure and damage to the pump, that is, to play the role of check.
(2) If the check valve is connected in parallel with the throttle valve or pressure reducing valve, it can form the actuator forward slow speed, reverse fast; or forward deceleration, reverse free flow circuit.
(3) If the check valve is connected in series with the pressure valve, the adjustment pressure can be gradually increased to prevent the reaction of pressure.
(4) For the liquid control check valve, you can use the control oil circuit to open the check valve, in order to achieve the purpose of enabling the oil to flow in the reverse direction.
There are two kinds of check valves: straight-through type and right-angle type. Straight-through check valve with threaded connections installed in the pipeline. Right-angle check valve has a threaded connection, plate connection and flange connection in three forms. Pilot-operated check valves, also known as lock valve or pressure maintaining valve, it is the same as the check valve, to prevent the reverse flow of oil.
But in the hydraulic circuit requires the flow of oil reverse flow and can be used to control the oil pressure, open the check valve, so that the oil flow in both directions can flow. Pilot-operated check valves use a conical spool, so the sealing performance is good.
In the requirements of the closed oil circuit, the valve can be used as a one-way lock of the oil circuit and play a role in maintaining pressure. Pilot operated check valve control oil leakage mode has two kinds of internal and external leakage type. In the oil flow reverse outlet without back pressure in the oil line can be used in the internal leakage; otherwise need to use the external leakage, in order to reduce the control oil pressure.
Reference: Baidu Encyclopedia-Check Valve