Model 520A-1M Relief Valve

0.5-150 PSIG Relief Valve


Circle Seal Controls Model 520A-1M Relief Valve

Catalog literature: Relief Valves Catalog.pdf Acrobat DC

The Circle Seal Controls model 520A-1M Relief Valve provides a combination of absolute leak-proof sealing when closed and virtually maintenance-free dependability in a small, lightweight package.

How it Works


  • Zero leakage: to 95-98% of cracking pressure
  • Increased sealing efficiency: as pressure increases, resilient quad-ring seal is forced against metal seat up to set cracking pressure
  • Cracking pressure accuracy: valves can be factory pre-set to required cracking pressure; 100% seat leakage tested
  • Wide range: wide range of cracking pressures, without sacrificing flow characteristics, provided through interchangeable springs and simple adjustment
  • Tamper-proof adjustment: adjustable only from the inlet side for safety against tampering; permits precise setting for the most exacting system requirements
  • Sticking eliminated: poppet head provides metal seat on low pressure side of seal, limits squeeze on resilient seal ring; prevents water and dirt from entering valve
  • Long, maintenance-free service: parts will not wear out in normal service; overhaul, if necessary, is quickly made by replacing resilient seal
  • Variations: vent-to-atmosphere or inline connections; various materials for both body and seals; PED certifications and CE marking available for most models


  • System overpressure protection
  • Storage tanks
  • Freon recovery systems
  • Medical equipment
  • Refrigeration & heating equipment
  • Measuring & dispensing pumps
  • Communications equipment
  • Process control instruments
  • R&D pilot plants
  • Vacuum pump safety

Technical Data:

  • Configuration: Popoff
  • Cracking pressure: 0.5-150 PSIG
  • Operating pressure:  Vacuum to 200 PSIG
  • Body material: Aluminum
  • Seal material: PTFE
  • Connections: 1/8″ MNPT
  • Temp range: -100 to +400F


  • “L1″ dimension (length): 0.98”
  • Hex dimension: 1/2″
  • “L” dimension: N/A (no deflector cap installed)
  • “D” diameter: N/A (no deflector cap installed)

520A-1M Relief Valve