As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
A check valve can go before or after a pump, but the right location depends on what job the valve needs to do.
For many rainwater systems, a check valve is placed after the pump on the discharge line. This stops pressurized water from flowing backward through the pump when it shuts off.
A check valve may also be installed before the pump on the suction line when it is needed to keep the pump primed. In that case, the valve is often placed near the water source as a foot valve.
The pump maker's instructions should take priority because some pumps already have a built-in check valve.
What a Check Valve Does
A check valve is a one-way valve. Water can flow through it in one direction, but the valve closes when water tries to flow backward.
In a rainwater system, this can help:
- Keep water from draining backward into a tank.
- Hold water inside a suction pipe so a pump stays primed.
- Keep pressure in a household or irrigation line.
- Reduce reverse flow through a stopped pump.
- Prevent some pumps from spinning backward after shutdown.
A check valve does not control pressure. It also does not replace an isolation valve, pressure relief device, or pump controller when those parts are required.
Installing a Check Valve After the Pump
A discharge-side check valve is installed in the pipe carrying water away from the pump.
This is a common location for rainwater pumps supplying:
- Garden irrigation.
- Hose bibs.
- Toilets or other approved non-potable fixtures.
- Pressure tanks.
- Cabin water systems.
- Long distribution lines.
When the pump stops, pressure in the plumbing may try to push water backward toward the rainwater tank. The check valve closes and limits that reverse flow.
Why a Discharge Check Valve Can Help
Without a check valve, water may drain backward through some pumps.
This can cause problems such as:
- Loss of system pressure.
- More frequent pump cycling.
- A pressure tank draining backward.
- Water flowing back toward the storage tank.
- Reverse rotation in pumps that are not designed for it.
Whether these problems can occur depends on the pump and plumbing layout.
Some pumps contain their own non-return valve. Adding another valve without checking the pump instructions can create unnecessary restriction or other operating problems.
Installing a Check Valve Before the Pump
A suction-side check valve serves a different purpose.
It is mainly used when the pump sits above the water level and must pull water up from the tank, cistern, or well.
A typical example is a surface-mounted centrifugal pump connected to an underground cistern.
Once the suction pipe is filled with water, a check valve helps keep that water from draining back into the cistern when the pump stops. This helps the pump stay primed.
A Foot Valve Is a Type of Check Valve
When the check valve is installed at the submerged end of the suction pipe, it is usually called a foot valve.
A foot valve often includes a screen that keeps large debris from entering the suction pipe.
Placing the valve near the water source keeps more of the suction line full when the pump is off.
This matters because many centrifugal pumps cannot move water properly when their suction line is full of air.
When a Suction-Side Check Valve May Not Be Needed
Not every rainwater pump needs a check valve before it.
Consider an above-ground rainwater tank with the pump installed below the tank's water level.
Water naturally flows from the tank toward the pump because gravity keeps the pump inlet flooded. This is called a flooded suction arrangement.
In this setup, a suction-side check valve may provide little benefit.
It can also add resistance to the inlet.
That matters because pumps generally work best when their suction side has as little restriction as practical. Small pipes, clogged filters, unnecessary valves, and long suction runs can make it harder for the pump to receive enough water.
If the pump maker does not require a suction check valve, adding one "just in case" is not always helpful.
Before or After the Pump: A Simple Guide
| System condition | Typical check valve location | Main purpose |
|---|---|---|
| Pump is above the water level | Suction side, often near the intake | Helps maintain pump prime |
| Pump is below tank water level | Often no suction check valve needed | Gravity keeps inlet flooded |
| Pressurized plumbing can flow backward | After the pump | Stops reverse flow |
| Pump feeds a pressure tank | Often after the pump or as specified by the pump maker | Helps hold system pressure |
| Submersible pump | Usually on the pump's discharge side | Stops water column from flowing backward |
| Pump has a built-in check valve | Follow pump instructions | Another valve may not be needed |
These are general layouts rather than universal rules. Pump design can change the correct arrangement.
Check Valves With Surface Rainwater Pumps
Surface pumps are common beside rain barrels, larger tanks, and cisterns.
Their check-valve needs depend heavily on where the pump sits compared with the water level.
Pump Below the Tank Outlet
This is usually the easiest arrangement.
Gravity supplies water to the pump inlet. Keeping the suction pipe short and unrestricted is normally more important than installing an extra check valve before the pump.
A discharge check valve may still be useful if the downstream plumbing can send water backward through the pump.
Pump Above the Water Level
This layout requires the pump to lift water through the suction line.
The vertical distance between the water surface and pump matters. This is part of the pump's suction lift.
A foot valve or suitable suction-side check valve can help keep the suction line filled after priming.
Air leaks become especially important in this layout. Even a connection that does not visibly leak water can sometimes draw air into a suction pipe while the pump is running.
Check Valves With Submersible Pumps
A submersible pump sits in the stored water.
Because the pump is already underwater, it does not need a suction-side foot valve to maintain prime in the same way that a surface centrifugal pump might.
Instead, the check valve is normally associated with the pump's discharge line.
Some submersible pumps contain a built-in check valve. Others require an external one.
For long vertical pipe runs, additional check valves are sometimes used, but their number and spacing should follow the pump manufacturer's design guidance. Adding several check valves without a reason can create pressure changes and maintenance problems.
Check Valves and Pressure Tanks
A pressure tank stores pressurized water so the pump does not have to start every time a small amount of water is used.
A working check valve is often important in these systems.
Without one, stored pressure may push water backward through the pump after it turns off.
That can cause the pressure to fall. The pump may then restart even though nobody has used water.
Frequent starting and stopping is called short cycling. Many things can cause it, so a leaking check valve is only one possible cause.
Planning around practical when to use a foot valve helps verify the benefits and drawbacks at this design stage.
Also check the pressure tank, pressure switch, plumbing leaks, and pump controls when diagnosing cycling problems.
Do Not Put Unnecessary Restrictions on the Suction Line
The suction side of a pump deserves special care.
A pump cannot pull water well through a badly restricted inlet.
Possible restrictions include:
- A check valve that is too small.
- A clogged foot valve.
- A clogged screen.
- A dirty filter.
- Undersized suction pipe.
- Too many elbows.
- Long pipe runs.
A valve should be sized for the pipe and expected flow.
The flow rate is the amount of water moving through the pipe during a set time, such as gallons per minute or liters per minute.
A check valve that causes too much pressure loss can reduce pump performance.
This is one reason filters are not automatically best placed directly on a pump's suction line. Some pumps need a low-restriction inlet, and filtration should be arranged according to the pump and treatment system design.
Pay Attention to the Flow Arrow
Most check valves have an arrow molded, stamped, or printed on the body.
The arrow shows the allowed direction of water flow.
For a discharge check valve, the arrow normally points:
Pump → plumbing or pressure tank
For a suction-side valve, the arrow normally points:
Rainwater source → pump
Installing the valve backward can block water flow almost completely.
Make Sure the Valve Matches the Pump and Pipe
Check-valve location is only part of the decision.
The valve also needs to match:
- Pipe size.
- Connection type.
- Expected flow.
- Working pressure.
- Water temperature.
- Pump type.
- Installation orientation, if the valve has orientation limits.
A small valve placed in a large pump line can create unnecessary pressure loss.
Check the valve manufacturer's flow direction and installation requirements before fitting it.
Keep the Valve Accessible
A check valve can wear, stick, collect debris, or leak backward.
Whenever possible, install serviceable valves where they can be reached without dismantling a large part of the system.
Rainwater can contain sediment and organic material even when the collection system has screens and prefiltration.
A valve that works well when new may stop sealing fully if debris collects on its internal seat.
Periodic inspection and cleaning can therefore be important.
What About Freeze Protection?
A check valve can trap water in a pipe.
That becomes important in freezing climates.
A section of pipe that normally drains after the pump stops may stay full after a check valve is installed. Trapped water can expand when it freezes and damage valves, fittings, pipes, or pump parts.
The full system should be designed so exposed plumbing can either remain protected from freezing or be properly drained and winterized.
Do not assume that adding a drain valve somewhere in the system guarantees that every trapped section can empty.
A Common Rainwater Tank Layout
For a simple above-ground tank with a surface pump below the tank outlet, the water path might be:
Tank → suitable tank outlet → pump → check valve if required → pressure or distribution equipment → fixtures or irrigation
A suction-side check valve may not be needed because gravity keeps water at the pump inlet.
For a cistern with a surface pump above the water level, the layout may instead be:
Cistern intake with foot valve → suction pipe → pump → discharge check valve if required → distribution system
This arrangement may use check valves on both sides, but each one has a different job.
The correct layout still depends on the pump instructions and the rest of the system.
When to Follow the Pump Manufacturer Instead
Check the pump manual before changing valve locations.
This is especially important for:
- Self-priming pumps.
- Booster pumps.
- Multistage pumps.
- Submersible pumps.
- Variable-speed pressure systems.
- Pumps with built-in check valves.
- Pumps connected to pressure tanks.
Some pump makers require a particular valve position. Others warn against placing certain valves or filters close to the inlet.
Those instructions should take priority over a generic plumbing layout.
Frequently Asked Questions
Should a check valve go before or after a water pump?
For many systems, a check valve goes after the pump to stop pressurized water from flowing backward. A check valve can also go before the pump when it is needed to maintain prime in a suction line.
Does a rainwater pump need a check valve?
Not always. The need depends on the pump design and plumbing layout. Some pumps have built-in check valves. A surface pump above the water level may need a suction-side valve, while a flooded-suction pump may not.
What is a foot valve?
A foot valve is a check valve installed near the submerged end of a pump's suction pipe. It helps keep the suction pipe full of water when the pump stops. Many foot valves also have a debris screen.
Can I put a check valve on both sides of a pump?
Sometimes. A suction-side valve may maintain prime while a discharge-side valve prevents pressurized water from flowing backward. Do not add both automatically. Check the pump manufacturer's instructions first.
How close should a check valve be to the pump?
There is no single spacing rule that applies to every pump. A discharge valve is often near the pump, while a suction foot valve is commonly near the water intake. Follow the pump and valve manufacturer's installation instructions.
Can a check valve reduce pump flow?
Yes. Every valve creates some resistance to water flow. A valve that is undersized, clogged, poorly selected, or installed incorrectly can reduce pump performance. Suction-side restrictions are especially important to avoid.
Can a bad check valve make a pump cycle on and off?
It can. In a pressure system, a leaking check valve may allow water to flow backward after the pump stops. Pressure falls and the pump may restart. Plumbing leaks, pressure tank problems, and control problems can cause similar symptoms.
