Can I Use A Check Valve On A Drain Line To Stop Flow From Coming Back Up?
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Time to read 2 min
Short Answer: Not usually. In many cases, check valves do not function properly on a drain line due to the orientation of the pipe line and the lack of water pressure.
How do Check Valves Work?
There are several different types of check valves, but all of them are made to perform a similar function. Check valves allow water to flow in one direction and contain a mechanism that blocks flow of water in the opposite direction.
Why Are Check Valves Not Always Compatible with Drain Lines?
Most check valves require a certain amount of water pressure to properly close the valve so no backflow occurs. This is one problem with using check valves on a drain line. Another is the orientation of the pipe. Most check valves work best when installed in a vertical position. This allows gravity to assist in closing the valve so it is water-tight.
Many drain lines are positioned at a decline so gravity carries the water away from the source. Because of this, flap check valves tend to hang in the open position when installed on a drain line. This allows the drain water to flow back up the pipe past the open valve. Because of this, most check valves work best when installed on pressurized pipe applications. This allows the water pressure to properly open and close the valve, preventing backflow.
What Can I Use?
There are some specialized valves that are made for preventing backflow in drain lines. These valves usually have to be installed in a particular way to be effective. Always follow manufacturer instructions, and if unsure, consult a licensed plumber.
Generally Not Effective: Standard check valves usually fail on drain lines because gravity-fed drains lack the water pressure required to force the valve closed.
Orientation Issues: Standard check valves work best vertically, whereas sloped drain pipes cause internal flaps to hang open and allow backflow.
Alternative Required: Use specialized sewer backwater valves or drain-specific backflow preventers installed strictly to manufacturer guidelines instead.
FAQs
Can I use a standard check valve on a drain line to stop backflow?
Usually no. Standard check valves rely on continuous fluid pressure and a vertical orientation to seal properly. Gravity-fed drain lines typically lack the pressure needed to keep the valve closed against incoming backflow.
Why do check valves fail on sloping or horizontal drain lines?
Because drain lines run at a decline, internal mechanisms like flappers often rest in a partially open position. Without gravity or water pressure assisting the closure mechanism, backflow can easily slip past the open valve.
What should I use instead to prevent backflow in a drain system?
You should use specialized backwater or backflow valves engineered specifically for unpressurized drain lines. Always follow manufacturer installation guidelines or consult a licensed plumber to ensure proper placement.
Mark Ligon
Mark Ligon is the marketing manager at PVC Fittings Online, a supplier of commercial PVC and CPVC pipe, fittings and valves. Ligon enjoys educating businesses on the parts of piping systems so managers can make informed decisions. He can be reached at webmaster@commercial-industrial-supply.com.
