Table of Contents
Pressure Release Valve [1] |
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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 [2]. The valve's release of elevated liquid, gas, or steam pressures acts to prevent damage to the system.
Components of a Relief Valve
Relief valves are comprised of three main elements, a valve, sensing and reference force element.
Valve Element
Pressure relief valves often use a spring loaded poppet valve as the valve element [2].
Sensing Element
Piston style designs are often used when higher relief pressures are required [2]. In low-pressure applications or when high accuracy is required, the diaphragm style is preferred [2].
Reference Force Element
The reference force element of a relief valve is commonly a mechanical spring [2].
Generic Pressure Release Valve Diagram [3] |
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Types of Relief Valves
Conventional Spring Loaded
With a conventional spring loaded relief valve, the bonnet, spring, and guide are exposed to the released fluids. If the bonnet is vented to the atmosphere, the relief-system back pressure decreases the set pressure [5]. If the bonnet is vented internally to the outlet, the relief-system back pressure increases the set pressure. The conventional spring-loaded valve is used in noncorrosive application and in which back pressure is less than 10% of the set point [5].
Conventional Spring Loaded [4] |
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Advantages | Disadvantages |
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Balanced Spring Loaded
The balanced spring-loaded valve protects the bonnet, spring, and guide from the released fluids and minimizes the effects of back pressure. The disk area vented to the atmosphere is equal to the disk area exposed to back pressure [5]. These valves may be used in corrosive or dirty service and with variable back pressure [5].
Balanced Spring Loaded [4] |
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Advantages | Disadvantages |
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Pilot Operated
The pilot-operated valve is combined with and controlled by an auxiliary pressure pilot [5]. 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 increases as the process pressure nears the set point. [5]
Pilot Operated [4] |
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Advantages | Disadvantages |
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Faculty Advisor: Mary Robinson