AirComParts ASME Safety Relief Valve, 1 in. NPT, 75 to 175 PSI

One inch ASME coded brass safety valves for large air receivers and rotary screw discharge, with relieving capacity from 693 to 1477 CFM depending on set pressure. Male NPT inlet, stainless pull ring, factory set and sealed.

Set pressures

• 75 PSI, 693 CFM (S1500)
• 100 PSI, 889 CFM (S1501)
• 125 PSI, 1085 CFM (S1502)
• 135 PSI, 1164 CFM (S1503)
• 175 PSI, 1477 CFM (S1505)

The 150 PSI and 200 PSI builds are stocked as separate items, S1504 and S1506.

The 135 PSI one exists for a reason

135 looks like an odd set point next to 125 and 150, and it is there because a lot of rotary screw packages run a 125 PSI line pressure with the package relief set just above it. Setting the vessel's safety valve at 150 on that system leaves a 25 PSI window where the machine can run hard against a fault with nothing lifting. 135 closes that gap while still clearing normal operating pressure. If your screw compressor is set for 125, this is usually the valve you want.

Capacity notes

These figures are the valve's rated relieving capacity in CFM of free air. Compare them against the total output of everything feeding the vessel, not one machine. A plant with three 50 HP screws manifolded into one dry receiver needs the valve sized for all three running, because that is the condition in which a stuck control valve will pressurise the tank.

Multiple relief devices on one vessel are allowed and their capacities add, which is often cheaper and easier to pipe than hunting for a single enormous valve.

A note on seat life

Large safety valves that sit just below their set pressure for years tend to stick. Lift the ring once a quarter with the system at working pressure and let it snap shut. If it weeps after the test, it has been holding debris on the seat and it needs replacing, not another pull.