A sump pump check valve is a one-way valve that prevents water from back flowing into the sump basin. It prevents water from re-entering the sump basin once it’s been discharged, and helps eliminate unnecessary wear and tear on the sump pump.
Prevent Water from Re-Entering Sump Basin
A sump pump check valve is a one-way valve, meaning that it allows water to flow in only one direction. As long as the pump is moving water from the basin into the discharge line, the valve remains open. When the water remaining in the discharge line descends, gravity closes the check valve, preventing backflow.
A properly functioning check valve will thus stop the pumped-out water from flowing back into the sump basin, eliminating the need for the pump to run as frequently, saving the homeowner money and extending the life of the sump pump.
Prevent Unnecessary Wear and Tear
When a sump pump switches off, and there is no check valve installed, the water that remains in the discharge pipe will drop back into the sump basin due to gravity. If there’s enough water involved, this may cause the pump to switch back on to pump the water back out.
With nothing to stop the water from dropping back into the sump basin, the system gets stuck in a cycle of pumping and repumping — putting unnecessary wear and tear on the pump and using vast amounts of electricity in the process. A sump pump check valve stops this cycle by preventing the just-pumped water from flowing back into the sump basin.
Types of Check Valves
Check valves are automatic valves that open when water flows forward into them and close when the flow stops or reverses. Though there are numerous types of check valves on the market, there are four basic types of check valve used in sump pump systems:
Swing or tilting-disk check valve
The design here is simple — a disk connected to a hinge swings open to allow water to flow forward, then snaps shut when flow stops, preventing backflow. On some models, movement of the disk is controlled by a spring that ensures a tight seal in both vertical and horizontal orientation.
This type of valve can make a loud popping or sucking noise when it closes. There are “quiet” check valves that eliminate the “water hammer” phenomenon that causes the noise; these are widely available online, such as on Amazon.
Lift-check valve
A lift valve opens by raising a ball or disk when water flows under it, allowing water to pass through freely. When flow stops, gravity causes the ball or disk to drop back into place, closing the valve.
Butterfly check valve
In a butterfly check valve, flow is stopped by a circular disk that spins on an axis to permit or stop the flow of liquids. A 90° turn of the axis moves the valve from closed to open.
Stop-check valve
A stop check valve has override control to stop flow regardless of pressure or direction. Where most check valves remain open until flow stops or reverses, the stop check valve can also be shut deliberately by a separate, external mechanism.
Learn more about sump pump check valves from this video:
Check Valve vs. Backflow Valve: What’s the Difference?
Backflow valves and check valves serve essentially the same purpose: preventing wastewater from flowing back into the system. But while check valves are acceptable in low-stakes scenarios — like preventing rainwater or runoff from flowing back into a sump basin — in higher-stakes scenarios, such as preventing sewage from contaminating drinking water, a backflow preventer is called for.
Backflow preventers are more reliable and offer failsafes to prevent contamination. In a sump pump system, the relatively simpler and less expensive check valve is adequate.
How Do I Tell if a Sump Pump Check Valve Is Bad?
Your sump pump’s check valve is supposed to keep water from returning through the discharge pipe and back into the sump basin. So when the valve stops working, the first thing you’re likely to notice is that your pump is running more frequently than in the past. This is because it’s pumping and re-pumping water from the basin because the valve’s not doing its job.
But check valves can malfunction in other ways, too, such as by not closing completely or getting clogged with debris. Here are some ways to check the valve’s performance:
Look for leaking around seals, at connection points, and in the valve itself.
Test the valve by pouring water into the sump basin until the pump switches on, then watch what happens when the pump switches off. If water falls back into the basin, you may have a bad check valve.
Listen to the valve when the pump switches off. An excessively loud banging sound can be caused by “water hammer,” a sudden pressure decrease that occurs when the sump pump finishes pumping the last of the water from the basin. Over time, this can put stress on the valve, eventually causing it to break.
Inspect the valve and the pipe around it, looking for dirt and debris that can cause the valve to stick open.
How to Install or Replace a Check Valve
Installing a sump pump check valve is relatively simple, but it has to be done right — installing it incorrectly could cause your pump to fail, resulting in damage to the sump pump system.
Before You Begin: Gather the Correct Parts
Because your sump pump check valve will connect to the discharge pipe, begin by checking the diameter of that pipe to determine what size valve to buy. PVC pipe commonly has dimensions printed on it, or you can measure the diameter yourself. Most discharge pipes are 1.25 inches to 1.5 inches in diameter.
Other supplies you will need include a hacksaw or pipe cutter, PVC cement, sandpaper, and PVC couplings and nuts.
Here are two videos that provide a detailed look at the process:
How to Install a Quiet Check Valve on Your Sump Pump
Step 1: Drain the Sump Pump Basin
If possible, drain water from the sump pump basin or pit. Turn off electricity to the system, and secure cords and wires away from standing water.
Step 2: Determine Positioning
If you’re installing a new check valve rather than replacing a malfunctioning one, take time to identify the correct discharge pipe leading from the sump pump.
Position the check valve as close to the pump as you can, to limit the amount of water that can accumulate between the sump basin and the valve. The best location for a check valve is 8 inches from the discharge and about a foot above floor level. If you install the check valve above floor level, it’ll be easier to check, service, or replace it in the future. You don’t have to do it this way — installing the check valve down in the sump basin is OK too, and may muffle noise caused by the valve’s operation — but installing it in the basin will make it harder to inspect or replace in the future.
You can install many check valves vertically or horizontally; in many homes, the discharge pipe runs vertically from the basement floor, so the check valve would usually be installed vertically, along this pipe. Study the arrangement of your sump pump and discharge pipe to determine the best positioning and orientation for your check valve, and follow manufacturer recommendations on orientation. Some swing check valves must be installed horizontally.
Step 3: Install the Check Valve
Using a marker, mark the pipe where you’d like to install the valve. Using the hacksaw or pipe cutter, sever the piping along that line. Remember that you can always cut more pipe but you can’t easily replace it if you cut too much, so start small and remove extra as needed.
If you’re removing an old check valve that has been cemented in place, use a hair dryer to heat the adhesive, then use pliers to remove the valve.
“Dry-fit” the valve to test to see if it fits lengthwise; remove additional pipe if needed, keeping in mind that you want the fit to be very snug to reduce leakage and motion.
Dry-fit the valve again once you’ve trimmed up the pipe and before applying cement. Sand down the ends of each section of the pipe until they are smooth. Place the PVC nuts onto each rip of the pipe ends, then apply the couplers. If the check valve came with rubber o-rings, slide those into place as well. Then position the check valve and tighten. Turn the couplers clockwise to tighten the connections.
When you are positive that the valve will fit easily but snugly into the pipe, remove the valve and apply cement to the surface areas of the couplings where the valve connects, then replace the valve. Once the valve is in place, wait several hours for the adhesive to dry (following manufacturer’s recommendations) before running the sump pump.
Step 4: Test the Check Valve
Plug in the sump pump and turn it back on. Pour water into the sump basin until the pump switches on and begins pumping water. You might hear the check valve internal flap open and close as the water moves through the pipe, then stops.
After the pump switches off, look to see if any water has backflowed into the pit. If it hasn’t, and there are no leaks where you installed the new valve, congratulations! You have successfully installed a sump pump check valve.