Short definition
A check valve is a one-way valve that permits flow in one direction only — opens automatically under forward pressure, closes automatically under reverse pressure. No external operator. Common applications include sump-pump discharges, well-pump suction lines, and the inlet of a pressure tank.
What it is
The check valve has a single moving element — a disc, ball, or piston — that’s pushed open by forward flow and pushed closed by reverse flow. No handle, no power, no operator. It’s the simplest possible automatic valve.
Common types:
- Swing check. Hinged disc that swings open under flow and closes under reverse flow. Low pressure drop when open. Direction-dependent (must be installed with the hinge axis horizontal so gravity helps the disc close).
- Spring-loaded check. Disc held against the seat by a small spring. Works in any orientation. Faster closure than swing — preferred where reverse-flow events would otherwise cause water hammer.
- Ball check. Free-floating ball that seats on an O-ring. Low capacity; used in low-flow specialty applications.
- Foot check (foot valve). A spring or disc check at the suction inlet of a well pump, with a screen to keep debris out. Holds the pump prime between cycles.
- Tilting-disc, lift, piston, stop check. Industrial variants for special service.
The big-picture distinction: check valves are automatic and one-way. Manual valves (gate, ball, globe) require operator action and are two-way. Both can shut off flow; only checks shut off reverse flow without intervention.
Why it matters to a homeowner
Check valves matter where reverse flow would be a problem:
- Sump-pump discharge. Without a check valve, the lifted column of water siphons back into the pit when the pump stops, the pit refills with the same water, and the pump runs again — a “runs but doesn’t pump down” symptom.
- Well-pump suction (foot valve). Without it, water in the suction pipe drains back into the well overnight, the pump loses prime, and it can’t restart in the morning.
- Toilet fill valve. Has a small built-in check that prevents backflow into the supply if pressure inverts.
- At-meter dual check. Some WA water utilities install a dual-check valve at every residential meter as containment protection — keeps any potential homeowner-side cross-connection out of the public main.
A failed check valve usually shows up indirectly: water keeps cycling through a pump, a fixture refuses to refill, or a backflow inspection fails. Replacement is straightforward in most cases — a $20–$80 part plus 30–60 minutes of labor in accessible locations.
Common variants and what a check valve isn’t
- Check valve vs. gate / ball / globe valve. Check is automatic and one-way; the others are manual and two-way.
- Swing vs. spring check. Swing has a hinged disc and depends on orientation; spring has a spring-loaded disc and works in any direction.
- Single check vs. dual check. Dual-check has two checks in series for redundancy (ASSE 1024). Required by some utilities at the meter.
Common failure modes
- Disc, O-ring, or spring degradation — slow reverse leak.
- Debris caught at the seat — won’t fully close.
- Slam-induced fatigue on swing checks under rapid reverse-flow events.
- Stuck-open from corrosion or scale buildup.