Safety valves are used to protect compressed air systems from over-pressurization. They are factory set to a non-adjustable pressure setting, at which point the valve will release system air to atmosphere.
ASME-coded valves that are also CRN approved.
LISTED BELOW ARE SAFETY RELIEF VALVE SIZES   1/8" -  1/4" - 3/8" -  1/2" -  3/4" -  1" -  1.25" 
1/8" NPT
1/4" NPT
1/8" SAFETY VALVE
1/4" SAFETY VALVE 25psi through 140psi
1/4" SAFETY VALVE 150psi through 350psi
3/8" NPT
3/8" SAFETY RELIEF VALVES
1/2" SAFETY RELIEF VALVES
1/2" NPT
1/4" NPT (LOW CFM)
1/4" (LOW SCFM FLOW RATE)
3/4" NPT
3/4" SAFETY VALVE