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Pressure Release Valve [1]

Image of a pressure relief valve

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].

Reference force element

commonly a spring [2]

Generic Pressure Release Valve Diagram [3]

Diagram of a Generic Pressure Release Valve

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, relief-system backpressure decreases the set pressure [5]. If the bonnet is vented internally to the outlet, 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]

Image of a Conventional Spring Loaded Relief Valve

AdvantagesDisadvantages
  • Most reliable type if properly sized and operated
  • Versatile — can be used in many services [4]
  • Relieving pressure affected by back pressure
  • Susceptible to chatter if built-up back pressure is too high [4]


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 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]

Image of a Balanced Spring Loaded Relief Valve

AdvantagesDisadvantages
  • Relieving pressure not affected by back pressure
  • Can handle higher built-up back pressure [4]
  • Protects spring from corrosion [4]
  • Bellows susceptible to fatigue/rupture [4]
  • May release flammables/toxics to atmosphere [4]
  • Requires separate venting system

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 actually increases as the process pressure nears the set point. [5]

Pilot Operated [4]

Image of a Pilot Operated Relief Valve

AdvantagesDisadvantages
  • Relieving pressure not affected by back pressure [4]
  • Can operate at up to 98% of set pressure [4]
  • Less susceptible to chatter (some models) [4]
  • Pilot is susceptible to plugging
  • Limited chemical and high temperature use by “O-ring” seals [4]
  • Vapour condensation and liquid accumulation above the piston may cause problems [4]
  • Potential for back flow


Suppliers

References

Contributors:

UserLast Update
Former user (Deleted) 1267 days ago
Former user (Deleted) 1269 days ago
Former user (Deleted) 1329 days ago

Faculty Advisor: Mary Robinson


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