Flow opens it and back-pressure or gravity closes it, with no handle or actuator. Common styles are swing checks with a hinged disc, lift checks with a guided disc, dual-plate wafer checks, ball checks, and spring-assisted nozzle or silent checks that shut before reverse flow builds up. Sizing matters: a swing check that sees too little velocity never fully opens and wears out from fluttering.
Pump two is spinning backwards on standby, the discharge check valve must be hung open.
Look for the arrow cast on the body; a check valve installed backwards is a classic first-week mistake.
Also heard as
- non-return valve
- NRV
- one-way valve
Related terms
Slam
A check valve banging shut after flow has already reversed, sending a pressure surge through the line.
Water hammer
A pressure surge, heard as a bang, when moving liquid is stopped or reversed suddenly.
Cracking pressure
The pressure at which a check valve or relief valve first starts to open and pass a trickle of flow.
Chatter
Rapid, violent opening and closing of a relief or check valve that hammers the disc against the seat.