Minimum pressure / check valve (MPV)

Holds roughly 65 – 75 PSIG in the sump so oil circulates and the separator element is protected, and acts as a check back from the plant air system.

Also called: MPV · minimum pressure check valve · MPCV

Normally closed — cracks open at the spring setting, typically 4.5 bar / 65 PSIG.

How it works

A spring-loaded poppet downstream of the separator element. It stays closed until sump pressure exceeds the spring setting, guaranteeing minimum oil-circulation pressure and low separator velocity on start-up. Its check function stops the shop air system back-feeding the sump on shutdown.

Specifications

Typical crack pressure

60 – 75 PSIG (4.0 – 5.2 bar)

Body sizes

3/4" – 3" NPT / flanged

Wear items

Poppet seal, spring, O-rings

Service

Rebuild at separator change or on high separator dP

Parts you can order

• Aftermarket service kit

  Minimum pressure / check valve kit

  Match by valve body number

  $80 – $350
• OEM assembly

  Minimum pressure valve, complete

  OEM number from parts list

  $350 – $1,400
• Aftermarket service kit

  Minimum pressure valve rebuild kit

  By body size (3/4, 1, 1-1/2, 2 in.)

  $55 – $260
• Kaeser (OEM)

  Minimum pressure / check valve kit

  Serial-specific (Kaeser Parts portal)

  $110 – $420
• Ingersoll Rand (OEM)

  Minimum pressure / check valve assembly

  Serial-specific (IR parts portal)

  $220 – $900

Field test procedure

1. Cold start and watch the sump gauge: it should reach ~65 PSIG before service-line pressure begins to rise.
2. Blows back through the intake or the sump won't depressurise at stop = failed check seat.
3. Compare sump vs line pressure while loaded — more than about 15 PSI difference at full load means a restricted separator or a stuck MPV.

Symptoms & probable causes

• Separator element ruptured
  MPV stuck open — high velocity through the element on start-up.
• Sump stays pressurised after stop
  Blowdown blocked, or the MPV check is holding shop pressure back into the sump.
• High separator dP alarm
  Restricted element, or MPV stuck partly closed.