Sump Pump Check Valve

Sump Pump Check Valve

Sump pump

Figure 1: Sump pump

A sump pit is a hole made into the basement of a building to collect excess water and moisture. A sump pump drives the water out of the pit into a drainage outlet. A check valve is usually installed at the outlet of a sump pump to prevent the water from flowing back into the pump. The valve plays a crucial role in protecting the sump pump and increasing its efficiency; hence, it is essential to maintain the check valve and the pump in good condition to ensure the system properly runs. This article discusses the working of a sump pump, the importance of a check valve in a sump pump, and tips to maintain the valve for optimal performance.

Table of contents

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What is a sump pump

A sump pit is typically a hole installed at the lowest point in the floor of a building basement. The pit collects water that would otherwise overflow onto an adjacent space and cause flooding. The bottom of the pit is usually layered with stone or gravel. This allows the water to collect in the pit so that it can be pumped out. The sump pump (Figure 2) turns on when the water reaches a certain height within the sump pit and drives it into exterior drainage.

A sump pump typically consists of a mechanical pump and a liquid level sensor like a float switch. The entire structure is placed in a sump pit. The sump pit water level rises when surface moisture or excess water seeps into the basement. The increase in water level lifts the float switch high enough to activate the pump. The water is then driven out of the sump pit through an outlet pipe connected to the sump pump. Without a sump pump, the basement may get flooded, damaging other devices and stored objects in the process. Also, sump pumps minimize the surface dampness that can lead to the growth of mold and fungus.

Discharge pipe connected to sump pump

Figure 2: Discharge pipe connected to sump pump

Sump pump check valve

A check valve is installed at the sump pump’s discharge line to prevent the backflow of water into the sump pump either by gravity or when another parallel pump on the same system is operating. The check valve keeps the water in place in a discharge line. Other factors for why to add a check valve in the discharge line include:

  1. Pumping efficiency: Once the water reaches a certain set level, the pump automatically runs, forcing the excess water out through the check valve. Sump pumps generally drive water from beneath the floor up to a higher point. Gravity tends to push the water remaining in the discharge pipe back into the sump pit when the pump shuts off. Therefore, it is important to stop the column of water left in the pipe from flowing back into the pump. In smaller sumps, the amount of water held in the outlet line may be nearly as much as the sump pump can hold, so the pump would clear the sump and have it re-fill it in an infinite cycle. This can flood the basement quickly and damage the floor or foundation. The check valve prevents this backflow.
  2. Protecting the sump pump: Without the check valve, the sump pump is forced to pump the same water twice, resulting in multiple pumping cycles and premature burnout as the pump motor runs. The pump is likely to run into regular failures without a check valve.

Sump pump check valve location

Sump pump check valves are generally installed vertically in the discharge pipe rising out of the pump. The valve is usually positioned just below the pipe elbow structure that turns the vertical pipe in the horizontal direction of the discharge area. Also, the valve is placed close to the ground level to aid its maintenance and repair works in a smooth manner.

Sump pump check valve selection criteria

Use the following pointers as a guide while choosing a check valve for the sump pump:

Discharge size

Measure the drain lines and check the sump pump manufacturer's sheet to determine the right size for the discharge line. The check valve may not fit correctly on the line if the wrong size is chosen for the valve.

Water pressure and head height

Head height is the maximum height that a pump can move fluid against gravity. The head height and the water pressure should be considered while choosing a sump pump check valve. The check valve may leak if the pump has high driving power. Estimate the system head height and the distance of the pump from the ends of the discharge lines to ensure that the system functions at a nominal driving power.


Sump pump check valves should be compatible with water and withstand heavy loads and high water pressure; therefore, a durable valve is necessary by choosing durable materials for the valve. ABS (Acrylonitrile butadiene styrene) plastic and metals like brass or stainless steel are used to construct the check valve. Plastic is easier to install, but metal valves are more durable. Also, metals like brass and copper are prone to corrosion, while plastic is corrosion-resistant. Read our chemical resistance guide for more details.

Connection style

Check valves are attached to the sump pump via threaded or slip-on connections. Ensure the check valve’s connecting ends match the sump pump’s ends. Threaded check valves are more suitable for metal piping, like steel pipes.

Sump pump check valve maintenance

A sump pump keeps the basement dry and the foundation intact. Therefore, it's essential to maintain the pump and check the valve to ensure everything is in order. Sump pump check valve maintenance also entails proper installation, testing, repair, and replacement.

Inspecting and cleaning the sump pump check valve

Sump pump check valve failure

Check for water flowing back into the sump pump and the pit once the pump turns off. This signals a faulty check valve at the sump pump outlet. Perform the following steps:

  1. Check for leaks or moisture on seals, connections, and the check valve.
  2. Fill half of the sump pit with water and check if it drains.
  3. Check for water backlash into the basement during testing and rainstorms.

Shifted sump pump

Seismic activities or unstable ground can cause a sump pump to shift from its destined location. The check valve may no longer be aligned properly if the sump pump moves. In this case, the pump may never know when to shut down.

Debris blocking discharge

The water flow in a sump pump check valve can get blocked by debris. It may have to be cleaned by hand if the blockage is severe. Ensure the water flows out of the discharge pipe after removing the blockage.


What does a sump pump check valve do?

A sump pump check valve is a non-return valve that helps ensure that the water that was pumped out doesn't flow back into the sump pit, thus keeping the basement and floor dry.

What happens when a sump pump check valve fails?

The check valve in a sump pump may result in water in the outlet pipe flowing back into the sump pump and the pit after the pump turns off. The backflow can flood the basement or wear out the sump pump in the long run.

Where should a sump pump check valve be installed?

The best location to install a sump pump check valve is at the sump pump outlet, closest to the ground level.