Oil stop / non-return valve

Stops sump oil draining into the airend and flooding the rotors when the machine is stopped.

Also called: oil check valve · oil stop valve

How it works

A spring-assisted check in the oil supply line (or built into the thermal valve/filter head). Sump pressure opens it while running; the spring closes it at shutdown so the airend does not fill with oil and hydraulic-lock or blow oil out the intake on the next start.

Specifications

Crack pressure

1 – 5 PSI

Location

Oil supply line to airend, often in the filter head

Parts you can order

• Aftermarket / OEM

  Oil stop (anti-drainback) check valve

  Match by port size and crack pressure

  $45 – $220
• Generic / OEM

  Oil stop / anti-drainback check valve

  By line size (1/2 to 1-1/2 in.)

  $40 – $180

Field test procedure

1. Oil pushed out of the intake on start-up after a long stop is the classic symptom.
2. Remove and blow through both directions — it must flow one way only.

Symptoms & probable causes

• Oil in the intake / airend flooded on start
  Oil stop check leaking back.