What is A Overflow Valve

Figure 1: Overflow valve.

Overflow valve also called relief valve is a kind of hydraulic pressure control valve, which mainly plays the role of constant pressure overflow, pressure stabilization, system unloading and safety protection in hydraulic equipment. When the system pressure exceeds the specified value, the safety valve is jacked to discharge part of the gas in the system into the atmosphere, so that the system pressure does not exceed the allowable value, so as to ensure that the system will not have accidents due to excessive pressure.

1. Classification

According to different structures, overflow valve can be divided into direct acting type and pilot type.

1.1 Direct Acting Overflow Valve

The direct acting overflow valve is a valve in which the hydraulic pressure of the main oil circuit acting on the valve core is directly balanced with the pressure regulating spring force. Three basic structures are formed according to different structural forms of valve port and pressure measuring surface. Regardless of the structure, the direct acting overflow valve is composed of pressure regulating spring, pressure regulating handle, overflow port and pressure measuring surface.

Figure 2: Structure of a direct acting overflow valve.

1.2 Pilot Overflow Valve

The main valve spring is mainly used to overcome the friction of the valve core, and the spring stiffness is small. When the spring compression of the main valve changes due to the change of overflow flow, the spring force changes little, so the change of valve inlet pressure is also small. It is widely used in high pressure and large flow systems. The valve core of the overflow valve will be affected by friction in the process of moving. The friction direction of the valve port when it is opened and closed is just opposite, which makes the characteristics of the overflow valve when it is opened and closed different.

Figure 3: Structure of a pilot overflow valve.

2. Function

2.1 Constant Pressure

In the throttling regulation system of the constant flow pump, the constant flow is provided by the constant flow pump. When the system pressure increases, the flow demand decreases. At this time, the overflow valve is opened to overflow the excess flow back to the oil tank to ensure the inlet pressure of the overflow valve, then the pump outlet pressure is constant (the valve port is often opened with pressure fluctuations).

2.2 Stabilizing Effect

The overflow valve is connected in series on the oil return circuit, which generates back pressure and increases the stability of moving parts.

2.3 System Unloading

Solenoid valve is connected in series at the remote control port of the overflow valve. When the solenoid iron is energized, the remote control port of the overflow valve is connected to the oil tank, and the hydraulic pump is unloaded. The overflow valve is now used as a unloading valve.

2.4 Safety Protection

When the system works normally, the valve is closed. Only when the load exceeds the specified limit (the system pressure exceeds the set pressure) can the overflow be opened for overload protection, so that the system pressure will not increase (usually the set pressure of the overflow valve is 10%~20% higher than the maximum working pressure of the system).

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