(1) valve operation

When the control lever is neutral, the oil pressure at port P is equal to that at port R. When the oil pressure of port P increases, the pressure area of plunger, the pressure of port P, the elasticity of tension spring and the pressure of chamber G are balanced, so the valve starts to operate.

When the piston moves, the pressure of chamber g changes, so the safety pressure is affected by the tension spring and piston.

Because the piston moves, the safety pressure increases from P1 to P, and the pressure (P2) and tension spring force change accordingly.

(2) valve pressure increase operation

When the pressure of port P increases, oil pressure is generated in chamber g, which makes the force of tension spring balance with pressure (PA), and then piston 21 moves to the left.

The valve operates (releases) under P1 safety pressure and the piston moves to the left. Piston 21 forces oil flow through the orifice to port R. When the piston reaches the top of the stroke, the pressure in chamber G is greater than that of the tension spring, so the piston moves to the right. The piston begins to move, and the chamber h and piston 7 dump on the sliding surface through the groove. The valve pressure set in chamber g slowly rises from P2 to P.

When piston 7 reaches the regulating socket, the oil pressure of chamber g reaches the safety set pressure.

(3) valve pressure drop operation

When the oil pressure of port P becomes 0, the oil pressure of chamber g rises to the pressure of oil tank. The plunger 9 moves to the right, the piston 7 is pushed to the left by the tension spring 16, and the piston is pushed to the right by the tension spring 1. When the check valve is opened, oil is pumped from port R, and piston 21 returns to the original port.

3. Function of preventing cavitation

When the rotary motor is rolling, if the control valve is in the neutral state, the weight of the upper structure will make the device rotate continuously, and the pressure on port B will continue to increase. At this time, the valve at port B should be opened to avoid the influence of high pressure on the circuit. In this way, a hole phenomenon will be produced. Therefore, oil should be supplied immediately after the control valve is closed. Turn over the make-up plunger, the oil flows through the return oil circuit to make up for the oil supply, so as to prevent cavitation.

Source: Excavator gear accessories http://www.hx-machinery.cn/