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For most clean-water submersible well and cistern pumps, avoid a swing check valve unless the pump manufacturer specifically approves it. A swing check closes more slowly than a spring-loaded check valve. That delay can let water start flowing backward before the valve shuts, which can increase water hammer and stress the pump, pipe, fittings, and valve.
For example, Grundfos specifically states that swing check valves are not recommended for submersible pump applications because they tend to close slowly and allow backflow. Goulds Water Technology also specifies spring-loaded check valves for many submersible pump installations.
The important exception is submersible sewage and solids-handling pumps. Some of those systems are designed to use large, free-flowing swing-style check valves so solids can pass. Always follow the manual for the actual pump and the water being moved.
Why Submersible Pumps Need a Check Valve
A check valve is a one-way valve. It lets water move away from the pump but stops it from flowing backward when the pump switches off.
In a typical rainwater cistern or well system, the pump may push water upward through several feet of pipe. When the pump stops, gravity tries to pull that water back toward the pump.
A properly chosen check valve helps:
- Keep the discharge pipe full.
- Prevent reverse flow through the pump.
- Reduce unnecessary pump cycling.
- Maintain pressure in systems with pressure tanks.
- Limit damaging changes in water velocity.
Many submersible well pumps already include a check valve at the pump discharge. Franklin Water, for example, lists removable spring-loaded check valves on several current submersible well pump lines.
That does not mean every pump has one. Check the pump manual before adding another valve.
Why Swing Check Valves Can Be a Problem
A swing check valve contains a hinged disc or flap. Flow pushes the flap open. When flow reverses, the flap swings back onto its seat.
That simple design works well in many plumbing systems. It is not automatically a good match for a clean-water submersible pump.
It can close too slowly
When the pump switches off, the water column above it may begin moving backward before a swing valve closes.
The valve can then slam shut against moving water.
Grundfos warns that swing check valves tend to close slowly in submersible applications, allowing backflow before closure.
It can contribute to water hammer
Water hammer is a pressure surge caused by a sudden change in water velocity.
You may hear it as a bang, thump, or knock in the piping.
A long vertical pipe can hold a large amount of water. If that water starts moving backward and a valve suddenly stops it, the resulting pressure wave can stress:
- Pipe joints
- Threaded fittings
- Flexible pipe
- Pressure tanks
- Check valves
- Pump components
Grundfos notes that water hammer in submersible installations can damage piping, joints, pumps, and motors.
Orientation matters
Many swing check valves depend partly on gravity to close correctly. Their performance can change when they are installed vertically, horizontally, or at an angle.
Submersible pump discharge lines are often vertical, making valve orientation especially important.
A spring-loaded valve does not rely on a freely swinging flap in the same way.
What Check Valve Should You Use Instead?
For a typical clean-water submersible well or rainwater cistern pump, a spring-loaded check valve designed for submersible pump service is usually the better choice.
A spring-loaded valve uses a spring to push a poppet or disc toward the closed position. When the pump runs, water pressure opens it. When the pump stops, the spring helps close it quickly.
Goulds Water Technology's submersible pump guidance specifically describes spring-loaded check valves and instructs installers to verify that the spring-loaded poppet moves freely before installation.
Look for a valve that matches the complete system rather than choosing one only by pipe diameter.
Match the connection size
A 1-inch pump discharge normally needs a valve and fittings compatible with that connection.
Avoid creating an unnecessary restriction by installing a valve with a much smaller internal passage.
Check the pressure rating
The valve must withstand the pressure that the pump and vertical water column can create.
Do not assume that normal faucet pressure tells you the maximum pressure the valve may experience. Pump shutoff pressure and hydraulic surges also matter.
For deep wells or high-head pumping systems, valve selection should follow the pump manufacturer's installation instructions.
Check the flow range
An undersized valve can add friction loss and require the pump to work against more resistance.
Flow rate means how much water moves through the system over time, often measured in gallons per minute.
Goulds notes that excessive velocity through submersible check valves can increase friction, hydraulic shock, and the possibility of water hammer.
Match the water use
For irrigation or other non-potable rainwater use, choose materials suitable for the water and operating conditions.
Non-potable means water that is not intended for drinking.
Evaluating comparing check valve options helps verify assembly details that affect everyday performance.
If the system supplies water intended for drinking, every water-contact component needs to be suitable for that use as part of a properly designed collection and treatment system. A check valve certification by itself does not make collected rainwater safe to drink.
Do Not Add Check Valves Everywhere
More check valves are not automatically better.
A submersible pump may already contain one. Adding several more without following the manufacturer's design can create trapped sections of water and change how pressure waves move through the system.
Deep-well systems sometimes require several check valves, but their locations are normally based on pump depth and manufacturer instructions. For example, manufacturers provide specific spacing recommendations for deeper installations rather than simply telling installers to add valves wherever convenient.
For a shallow rainwater cistern, those deep-well recommendations may not apply at all.
Start by finding out:
- Whether the pump already has a built-in check valve.
- Whether the manual requires another valve.
- Where the additional valve should be installed.
- What pressure and flow rating it needs.
- Whether it must be installed vertically or horizontally.
What About a Check Valve at the Top of the Pipe?
Putting a check valve only near the pressure tank or at the top of a long riser is not always a substitute for one near the pump.
If a lower valve leaks while an upper valve remains tightly closed, a partial vacuum can develop in the pipe. On restart, fast-moving water may strike the stationary water column and cause water hammer. Grundfos specifically identifies this type of arrangement as one possible cause of damaging pressure surges.
The correct valve location depends on the pump design and installation depth.
For a simple rainwater tank system with a short discharge line, follow the cistern pump manufacturer's diagram rather than copying a deep-well layout.
Sewage Pumps Are an Important Exception
The advice against swing check valves is mainly aimed at clean-water submersible well and pressure-pump applications.
A sewage or solids-handling pump has different needs.
A spring-loaded valve with a narrow internal passage can catch debris or restrict solids. Because of that, some sewage systems use large free-flowing swing-style check valves.
Pentair, for example, specifies a free-flow check valve for one submersible solids-handling pump and gives installation instructions intended to keep solids from settling in the valve. Pentair also makes swing-type check valves specifically for sewage and effluent service.
That is why the rule should not be simplified to "swing valves can never be connected to anything called a submersible pump."
The liquid being pumped matters.
Choosing a Check Valve for a Rainwater Cistern Pump
For a typical rainwater tank with a submersible clean-water pump, start with the pump manual.
If an external valve is required, a spring-loaded or other fast-closing check valve approved for that pump application is usually the appropriate type.
Also check:
- Pump discharge thread and diameter
- Pipe material
- Maximum pump pressure
- Expected flow rate
- Vertical lift
- Valve installation direction
- Whether the pump already contains a check valve
- Accessibility for future inspection
Vertical lift, sometimes called part of the system's head height, is the height the pump must raise the water. Greater lift increases the amount of water held above the pump and can make check-valve behavior more important.
Do not bury or permanently enclose a serviceable valve unless the installation is specifically designed for that location.
Signs a Check Valve May Be Causing Trouble
A check valve deserves inspection if the system develops:
- A loud bang when the pump stops
- Repeated clicking or rattling
- Pressure that quickly falls after shutdown
- Water draining backward into the tank or well
- Frequent pump cycling when no water is being used
- Long delays before pressure builds
- Sudden changes in pipe movement or vibration
Some of these symptoms can also come from leaks, pressure-tank problems, incorrect controls, or other plumbing faults.
If a pressurized system is producing severe hammering, switch it off and have the cause corrected rather than repeatedly operating it. Grundfos recommends shutting down a system experiencing damaging pressure surges and having the problem resolved by a pump installer.
Frequently Asked Questions
What type of check valve should not be used with a submersible well pump?
A swing check valve is generally not recommended for clean-water submersible well pumps unless the pump manufacturer specifically approves it. Its slower closing action can allow reverse flow and contribute to water hammer. A spring-loaded valve designed for submersible pump service is commonly used instead.
Is a spring-loaded check valve better for a submersible pump?
For many clean-water submersible pumps, yes. The spring helps the valve close quickly as flow stops, reducing the amount of water that can reverse direction before the valve seats. The valve still needs the correct pressure rating, size, orientation, and flow capacity.
Does a submersible pump already have a check valve?
Many do, but not all. Several current Franklin Water submersible well pump models, for example, include removable spring-loaded check valves. Check the manual or pump specifications before adding another valve.
Can I install two check valves on one submersible pump?
Sometimes. Deep well systems may require several valves, while a shallow cistern system may need only the pump's built-in valve. Do not add valves simply because two seem safer than one. Follow the manufacturer's placement instructions.
Can a bad check valve cause a submersible pump to cycle?
Yes. If the valve leaks, water can flow backward after the pump stops. Pressure may then drop until the pressure switch starts the pump again even though nobody is using water. Leaks elsewhere in the system can cause similar symptoms.
Why does my pipe bang when the submersible pump shuts off?
The sound may be water hammer. It happens when moving water changes speed or direction very quickly. A slow-closing, leaking, incorrectly located, or unsuitable check valve can contribute to the problem. Severe water hammer should be corrected because repeated pressure surges can damage plumbing and pump components.
Can a sewage submersible pump use a swing check valve?
Yes, some can. Sewage and solids-handling systems often need valves with a large, unobstructed flow path. Some manufacturers specifically use or recommend swing-style or free-flow check valves for these applications. Follow the sewage pump manufacturer's instructions rather than applying clean-water well-pump rules.
