Hydraulic Relief Valve

Hydraulic relief valves are used to limit the pressure in a hydraulic machiney or a hydraulic sytem. There are different types of valves used in a hydraulic system but the most commonly used is the hydraulic relief valve. Infact this is usually the first encountered valve in any hydraulic circuit. The basic purpose of using a hydraulic relief valve is to protect hydraulic circuits. Relief valves protect the pump, the electric motor and other components of the hydraulic circuit. These valves protect hydraulic machinery from being exposed to high pressures that cross the mechanism's specified limits.

How does Hydraulic Relief Valve Operate?

Hydraulic relief valves limit the pressure in a hydraulic system by allowing the pressurized hydraulic fluid to flow out of the system into an auxiliary passage. If the pressure in a hydraulic pump exceeds its designed pressure limit, internal leakage or damage to the pump components can take place. Relief valves may be of pilot-operated type or the direct-acting type. The pilot-operated type employs a small control spring while the direct-acting type uses a large one. Either type usually uses different springs for different pressure ranges. The relief valve is normally closed, i.e., the valve piston keeps the exhaust core or connection closed until such a time as the pressure exceeds the spring setting, when the valve opens and oil is returned to the oil reservoir. After the excess pressure is relieved, the exhaust passage is quickly and positively closed.

For deatils, check out the article Working of Hydraulic Relief Valves

Use of Relief Valve in a Hydraulic System

In hydraulic control systems, the relief valve acts as a check valve, with a ball and an adjustable spring. When the fluid is diverted into the auxiliary passage, the pressure inside the hydraulic cylinder drops, allowing the valve to close again.

Applications of Hydraulic Relief Valves

Hydraulic relief valves are used in almost any mechanism that runs on hydraulic power. Some examples where hydraulic relief valves are used are as follows:

• Brakes
• Automobile transmissions
• Power steering
• Aviation
• Industrial machinery
• Construction machinery

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Working of Hydraulic Relief Valves