Cause analysis: 1, pressure switch failure; 2, three-way solenoid valve failure; 3, inlet valve action; 4, discharge solenoid valve failure; 5, pressure maintenance valve action; 6, control line leakage.

Elimination methods: 1, check and replace the pressure switch; 2, check and replace the three-way solenoid valve; 3, disassembly and inspection; 4, inspection and replacement of the relief solenoid valve; 5, disassembly and inspection of the valve seat and check valve plate wear; 6, check the location of the leakage and then deal with.