Model D520N-2M ASME Relief Valve

15-150 PSIG ASME Relief Valve


Circle Seal Controls Model D520N-2M ASME Relief Valve

Catalog literature: Relief Valves Catalog.pdf Acrobat DC

The Circle Seal Controls model D520N-2M ASME Relief Valve is constructed in Naval Brass with a PTFE seal, has a 1/4″ MNPT inlet connection, and can be set between 15-150 PSIG.

Terminology for ASME relief valves:

  • Safety Relief Valves: An automatic pressure relieving device actuated by the static pressure upstream of the valve, which opens in proportion to the increase over the opening pressure.
  • Start-to-Leak Pressure: The pressure at the valve inlet where the relieved fluid is first detected (on the downstream side of the seat) before normal relieving action takes place.
  • Opening Pressure (Set Pressure): The valve inlet pop point pressure at which there is a measurable lift or discharge becomesĀ  continuous as determined by seeing, hearing or feeling. In the pop type of safety valve, it is the inlet pressure at which the valve opens, allowing a larger amount of fluid as compared with corresponding valve movements at higher or lower pressures. Note: A safety relief valve is not considered to open when it is simmering at a pressure just below the popping point even though the simmering may be audible. This set pressure distinguishes our ASME relief valves from our standard relief valves whose cracking pressure indicates initial flow.
  • Relieving Pressure: (Opening pressure plus overpressure) The pressure measured at the valve inlet at which the relieving capacity is determined.
  • Closing Pressure: (Reseat pressure) The pressure measured at the valve inlet, at which the valve closes, flow is substantially shut off, and there is no measurable lift.
  • Seal-off Pressure: The pressure (measured at the valve inlet) after closing at which no further gas is detected at the downstream side of the seat.
  • Operating Pressure: The actual pressure at which a vessel is maintained in normal operation.
  • Accumulation: Pressure buildup or overpressure beyond the set pressure of a safety relief valve, at which capacity flow is rated. Capacities are usually based on 10% accumulation.

Technical Data:

  • Configuration: Popoff with Delector cap
  • Cracking pressure: 15-150 PSIG
  • Operating pressure: Vacuum to 200 PSIG
  • Body material: Naval Brass
  • Seal material: PTFE
  • Connection: 1/4″ MNPT
  • Temp range: -100 to +400F


  • “A” dimension (length): 1.1875″
  • “B” Hex dimension: 0.625″
  • “C” dimension (diameter): 0.90″

D520N-2M ASME Relief Valve