product knowledge

The main function of the relief valve is to stabilize pressure or provide safety protection for the hydraulic system. Almost all hydraulic systems require it, and its performance has a great impact on the normal operation of the entire hydraulic system. Connected to the outlet of the pump to ensure constant system pressure is called a constant pressure valve; it is connected to the outlet of the pump to limit large values of system pressure and protect the system. It is called a safety valve.

Cause analysis of pressure regulation failure of relief valve:

Pressure regulation failures sometimes occur in relief valves during use. There are two situations where the pilot relief valve fails to regulate pressure: one is that the pressure regulating handwheel cannot establish pressure, or the pressure cannot reach the rated value; the other is to adjust the handwheel pressure without reducing or even increasing the handwheel pressure. In addition to the radial clamping of the valve core due to various reasons, the reasons for pressure regulation failure include:

(1) Damper on main valve body is blocked

If oil pressure cannot be transmitted to the upper chamber of the main valve and the front chamber of the pilot valve, the pilot valve will lose its regulation of the main valve pressure. Because there is no oil pressure in the upper chamber of the main valve and the spring force is very small, the main valve becomes a direct-acting relief valve with very small spring force. When the pressure in the oil inlet chamber is very low, the main valve opens the relief valve and the system cannot build up pressure.

The reasons why the pressure cannot reach the rated value are deformation or improper selection of the pressure regulating spring, insufficient compression stroke of the pressure regulating spring, excessive internal leakage of the valve, or excessive wear of the pilot valve cone valve.

(2) Plugged orifice on conical seat

If oil pressure cannot be transmitted to the cone valve, the pilot valve will lose its main valve pressure regulation function. After the baffle (small hole) is blocked, the cone valve will not open the overflow oil under any pressure. There is always no oil flow in the valve, and the pressures in the upper and lower chambers of the main valve are always equal. Since the annular pressure bearing area at the upper end of the main valve core is greater than the annular pressure bearing area at the lower end, the main valve is always closed without overflow, and the main valve pressure increases with the increase of load. When the actuator stops working, the system pressure will rise infinitely. In addition, it is also necessary to check whether the external control port is blocked and whether the conical valve is well installed.

(3) Radial clamping of valve core

Due to the influence of machining accuracy, the main valve core is clamped radially, so the main valve cannot be opened or closed without pressure relief. In addition, it is clamped radially due to contamination.

Other faults:

During assembly or use of the relief valve, excessive leakage may occur due to damage to the O-ring and combination sealing ring, or loosening of the mounting screws and pipe joints. If the cone valve or main spool is too worn or the sealing surface is in poor contact, it will also lead to excessive internal leakage and even affect normal operation.

Common faults of electromagnetic relief valves include pilot solenoid valve faults, main valve pressure adjustment faults, and impact noise during unloading. The latter can be reduced by adjusting the buffer added. If there is no buffer, add a back pressure valve at the overflow port of the main valve. (The pressure is generally adjusted to 5kgf/cm)³ or about 0.5MPa).