Check Valves
Updated February 20, 2026
Allow water to flow in one direction only, preventing backflow. Essential for protecting water supply from contamination.
Overview
Check valves allow water to flow in one direction only. When flow reverses, the valve closes automatically. No handle, no manual operation -- purely mechanical, activated by water pressure and gravity. Essential for preventing backflow in sump pump discharge lines, water heater recirculation loops, booster pump outlets, and anywhere cross-contamination must be prevented. Spring-loaded, swing, and inline are the three main residential types.
Pros & Cons
- Prevents backflow
- Automatic operation
- No external power needed
- Creates slight pressure drop
- Can cause water hammer
- Needs regular inspection
Key Features
- Automatic one-way flow -- no manual operation required
- Prevents backflow and cross-contamination of water supply
- Spring-loaded: works in any orientation, positive closure
- Swing check: gravity-assisted, lower pressure drop, horizontal or vertical (flow-up) only
- Inline (disc): compact, fits tight spaces, moderate pressure drop
Sizing & Selection
Match the check valve size to the pipe: 1-1/2 inch for sump pump discharge, 3/4 inch for water heater recirculation, 1 inch for main backflow prevention. The valve must be rated for the system pressure and flow rate. Oversized check valves may not close reliably at low flow rates.
Installation
Sump pump discharge: install vertically on the discharge pipe above the pump, arrow pointing up (direction of flow). Recirculation: install at the water heater return line. Backflow prevention: install per local code requirements (may require a certified backflow device instead of a simple check valve). Orientation matters -- the arrow on the valve body indicates flow direction.
Maintenance
- Check valves fail by sticking open (backflow occurs) or sticking closed (no flow).
- Test annually by shutting off the pump or supply and listening for backflow through the valve.
- Sump pump check valves: if the pump short-cycles, the check valve may be stuck open -- water flows back into the pit after each cycle.
- Replace every 5-7 years as preventive maintenance. A failed check valve on a sump pump means the pump works twice as hard.
Buying Tips
- Spring-loaded check valves (-25) are the most reliable for residential sump pump and recirculation applications.
- Brass or stainless steel for potable water. PVC for sump pump discharge and drainage.
- Quiet check valves (spring-loaded with soft closure) prevent the loud clank when the valve closes. Worth the premium if the pump is near living space.
- For backflow prevention on irrigation or commercial connections, local code may require a certified reduced pressure backflow assembly (RPZ) instead of a simple check valve. Check with your water utility.