Categorization and Characterization of Relief Valves and Safety Valves in Boiler

Relief Valves Service Application Distinguishing Feature Action:

  1. Spring-Operated & Pilot-Operated : Both types used for incompressible fluids. (i.e., liquids). Both types used where there is no danger of explosion from overpressure.
  • Downward seating, relying on spring pressure to seal.
  • “Lifts” upward when pressure is at setpoint.
  • Reverse (upward) seating, relying on system pressure to seal.
  • Downward acting when pressure is at setpoint, gradually opens.
  • Relies on pilot valve to actuate relief action.

Safety Valves Service Application Distinguishing Feature Action:

  1. Spring-Operated & Pilot-Operated Both types used for compressible fluids (i.e., gases and vapors). Both types used where there is danger of explosion from overpressure.
  • Downward seating, relying on spring pressure to seal.
  • “Pops” fully open when pressure is at setpoint.
  • Blowdown setpoint adjustable
  • Downward seating, relying on system pressure and spring pressure to seal.
  • “Pops” fully open when pressure is at setpoint.
  • Relies on pilot valve to actuate relief action.

Blowdown setpoint adjustable.

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