Relief Valves

What are Relief Valves?

A relief valve  is a type of safety valve designed to open at a preset pressure, and discharge fluid until pressure drops to acceptable levels [1]. The valve's release of elevated liquid, gas, or steam pressures acts to prevent damage to the system. 

Types of Relief Valves

Conventional Spring Loaded

With a conventional spring loaded relief valv, the bonnet, spring, and guide are exposed to the released fluids. If the bonnet is vented to the atmosphere, relief-system backpressure decreases the set pressure. If the bonnet is vented internally to the outlet, relief-system backpressure increases the set pressure. The conventional spring-loaded valve is used in noncorrosive services and where backpressure is less than 10% of the set point. [5]

Balanced Spring Loaded

The balanced spring-loaded valve incorporates a means to protect the bonnet, spring, and guide from the released fluids and minimizes the effects of backpressure. The disk area vented to the atmosphere is exactly equal to the disk area exposed to backpressure. These valves can be used in corrosive or dirty service and with variable backpressure. [5]

Pilot Operated

The pilot-operated valve is combined with and controlled by an auxiliary pressure pilot. The resistance force on the piston in the main valve is assisted by the process pressure through an orifice. The net seating force on the piston actually increases as the process pressure nears the set point. [5]

Components of a Relief Valve

Relief valves are comprised of three main elements:

1. Valve element - typically a spring loaded poppet valve. [1]
2. Sensing element - typically a diaphragm or piston. [1]
3. Reference force element.  Most commonly a spring. [1]

Operation of a Relief Valve

Suppliers

• Grainger
• Watts

References