Poppet-type inlet (intake) valve

Spring-loaded poppet between the air filter and the airend that opens on load and slams shut on unload or shutdown.

Also called: unloader valve · intake valve · suction regulator

Spring-closed with no control air present — that's what stops oil from spewing out the intake at shutdown.

How it works

A piston or diaphragm actuator, fed by the load solenoid, lifts the poppet off its seat against a return spring. Airend suction helps hold it open. On unload or shutdown the actuator vents, the spring closes the poppet and its integral check function stops oil blowing back out the air filter.

Specifications

Control pressure to open

Typically 30 – 45 PSIG (2 – 3 bar) pilot

Return spring

Closes valve within 0.5 s of vent

Seal kit

Piston O-ring, poppet seal, shaft seal, spring

Service interval

Inspect at every separator change (typically 8,000 h)

Parts you can order

• Aftermarket service kit

  Inlet valve rebuild kit, 2 in. class

  Match by OEM valve casting number

  $120 – $400
• OEM assembly

  Inlet valve complete assembly, 3 in. class

  OEM number from parts list

  $900 – $3,200

Field test procedure

1. Lock out, bleed to 0 PSIG, remove the air filter housing and check the poppet moves freely by hand — it must snap shut.
2. Look for a wear ring / scored bore on the piston: a leaking piston seal gives soft loading and low capacity.
3. Apply 60 PSIG shop air to the actuator port off the machine and watch it stroke fully open and spring shut.
4. Oil in the air filter housing = the valve is not sealing on shutdown.

Symptoms & probable causes

• Oil blows out the intake at shutdown
  Poppet/check seal failed or the valve is hanging open.
• Low capacity / never reaches setpoint
  Valve only cracking open — weak pilot pressure or a swollen seal.
• Machine surges when unloaded
  Poppet chattering because the blowdown is too slow.
• Loud intake whistle
  Partly closed poppet or a collapsed air filter element.