The check valve can prevent the air from returning to the air compressor  and a series of problems as follows:

(1)The air returning will result in the faults of the starting under load. If the inner pressure during the starting is too high ,this will lead to the re-starting of the motor. At the same time, the too-high re-starting electric current will have a great impact on the drive disk assembly.

(2)In the system of multiple generating units, the air returning may make the oil tank filled with the water and result in the units, cannot start normally.

(3)The unloading valve during the downtime is in the starting state. So if the air returns ,it will bring about the energy loss.