Applicable to excavator PC60-7 relief valve hydraulic control valve 709-20-52300

The main relief valve is installed on the upper and lower ends of the main control valve, one upper and one lower. The valve sets the maximum pressure for the entire hydraulic system to work. When the system pressure exceeds the set pressure of the main relief valve, the main relief valve opens the oil circuit of the return tank to overflow the hydraulic oil back to the tank to protect the entire hydraulic system and avoid excessive oil pressure

How it works:

① Pump pressure PP rises;

② More than 355kg/cm2 (380kg/cm2 when the pilot oil pressure ON);

③ Pump pressure to push the lifting head (2) to overcome the spring (1) force to push upward;

④ The small hole (only φ0.5) in the plunger (3) begins to have oil flow;

⑤ The plunger (3) is pushed upward due to the pressure difference between the front and back (large below, small above);

⑥ Pressure oil back to the tank;

⑦ Pump pressure drop to 355kg/cm2 (380kg/cm2 when the pilot oil pressure ON)

When the pump pressure is less than 355kg/cm2:

① The lifting head (2) is closed under the pressure of the spring (1);

No oil flow in the small hole in the plunger (3);

③ The pressure difference between the two ends of the plunger (3) is 0, and it returns under the action of spring force and oil pressure;

④ The pressure oil is disconnected from the tank path;

⑤ Pump pressure can be maintained;