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Which Check Valve Is Best for a Rainwater System?
The best check valve depends on where it will be used.
For most pressurized rainwater pump systems, a spring-loaded inline check valve is usually the best general choice. It closes quickly when the pump stops, which helps limit reverse flow.
For a low-pressure or gravity-fed system, a swing check valve can be a better fit because it usually creates less resistance to flow.
If the valve sits at the end of a pump suction pipe inside a tank or cistern, a foot valve may be needed instead. A foot valve is a check valve designed to help keep a suction line full of water.
There is no single valve that is best everywhere. The valve must match the pump, pipe size, pressure, water quality, installation position, and intended use.
Quick Guide to Choosing a Check Valve
| Application | Commonly Suitable Type | Main Reason |
|---|---|---|
| Pump discharge line | Spring-loaded check valve | Fast closing and compact |
| Gravity-fed garden line | Swing check valve | Low resistance to slow flow |
| Pump suction line that must stay primed | Foot valve | Holds water in the suction pipe |
| Submersible pump discharge | Pump-approved spring or non-slam check valve | Helps control reverse flow |
| Dirty water with small debris | Full-flow valve designed for the water quality | Less likely to clog |
| Connection involving potable plumbing | Approved backflow protection, not just a single check valve | Protects the drinking-water system |
The last point is especially important. A normal check valve prevents reverse flow during ordinary operation, but it should not be treated as complete protection between a rainwater system and a drinking-water supply.
Spring-Loaded Check Valves: Best for Many Pump Systems
A spring-loaded check valve contains a disc or poppet held against a seat by a small spring.
When the pump creates enough pressure, water pushes the valve open. When flow stops or reverses, the spring closes it.
This design works well on many rainwater pump discharge lines because it closes quickly.
Quick closing can be useful in pumped systems where a slow-closing valve could allow water to reverse direction before the valve shuts. Grundfos, for example, recommends quick-closing check arrangements for submersible pump systems and notes that slow-closing swing valves can contribute to reverse flow in some installations.
Advantages
- Closes quickly.
- Works well with pressurized systems.
- Usually compact.
- Can often work in more installation positions than a basic swing valve, although the manufacturer's instructions still control.
- Helps keep pressure from pushing water backward through a stopped pump.
Disadvantages
The spring creates some resistance.
Every valve causes some pressure loss, but a spring-loaded valve must also overcome the force holding it closed. That matters with small pumps, low-pressure irrigation systems, and gravity-fed water.
The minimum pressure needed to begin opening the valve is called cracking pressure.
A valve with a high cracking pressure may work perfectly on a powerful household rainwater pump but poorly on a rain barrel sitting only a few feet above a garden.
For low-pressure systems, look for a valve intended to open with very little pressure.
Swing Check Valves: Often Better for Gravity Flow
A swing check valve uses a hinged disc.
Forward-moving water swings the disc open. Reverse flow pushes it closed.
Because there is normally no spring pushing against the water, a swing valve can create relatively little resistance when fully open.
That makes it useful for systems such as:
- elevated rain tanks,
- gravity-fed garden lines,
- large pipes with modest pressure,
- systems where conserving every bit of available head pressure matters.
Head pressure is the pressure created by the height of the water above the outlet. In a gravity system, even a small amount of unnecessary resistance can noticeably reduce flow.
The drawback
Swing valves close more slowly than many spring-loaded valves.
That can make them less suitable for some pumped systems, especially where rapid pump shutdown causes significant reverse flow. Grundfos specifically advises against swing check valves in certain submersible-pump applications for this reason.
They can also be sensitive to installation position. Follow the flow arrow and mounting instructions supplied with the valve.
Foot Valves: Best When a Suction Line Must Stay Full
A foot valve is installed near the submerged end of a pump's suction pipe.
It normally combines:
- a check valve, and
- a screen or strainer.
When the pump stops, the valve helps stop water in the suction pipe from draining back into the tank.
This can help a pump maintain its prime, meaning the pump and suction pipe remain filled with enough water for the pump to start properly.
A foot valve may make sense with an above-ground pump drawing water from a cistern or other tank.
It is not automatically needed with every rainwater pump. A submersible pump, for example, may already have a built-in check valve or require a different arrangement.
Adding unnecessary valves also adds resistance.
Follow the pump manufacturer's installation requirements before adding a second check valve or foot valve.
What About Ball Check Valves?
A ball check valve uses a moving ball rather than a hinged disc or spring-loaded poppet.
Forward flow moves the ball away from its seat. Reverse flow pushes the ball back against the opening.
These valves can work well in applications where water contains some suspended material because the flow path may be less vulnerable to certain types of debris than a small spring-loaded mechanism.
They are common in some wastewater and sump applications.
For ordinary filtered roof-water systems, however, there is usually no reason to choose a ball check valve simply because it looks more rugged. Valve design, pressure loss, pipe size, debris tolerance, and the manufacturer's intended application matter more.
Choose the Valve Based on Available Pressure
Pressure is one of the most important differences between a rain barrel and a pumped cistern.
Imagine two systems.
Elevated rain barrel
A barrel feeds a garden hose using gravity.
There is little available pressure. A restrictive spring-loaded valve could reduce the already modest flow.
A low-resistance swing valve or another valve specifically designed for low-pressure gravity service may work better.
Pumped cistern
A pump sends rainwater to garden irrigation or household non-potable fixtures.
The system has much more pressure. A spring-loaded check valve on the discharge side can normally operate easily and close promptly when the pump stops.
In this system, reliable closing may matter more than squeezing out the smallest possible pressure loss.
Match the Valve to the Pipe Size
Do not choose a smaller check valve simply because it is easier to find.
A smaller valve can become a restriction.
For example, putting a small valve in a larger pump line can:
- reduce flow,
- increase pressure loss,
- increase water velocity,
- make the pump work farther from its intended operating point.
Usually, the check valve should match the pipe and pump connection size unless the system design specifically calls for something different.
Also check the actual internal opening. Two valves with the same nominal pipe connection can have very different internal flow paths.
Check the Valve's Flow Capacity
Pipe diameter alone does not tell the whole story.
A check valve needs to pass the required flow rate, which is the amount of water moving through the system over a certain time.
A garden drip system may need relatively little flow. A pump supplying several irrigation zones or household non-potable fixtures may need considerably more.
Valve manufacturers normally publish pressure-loss or flow information for their valves.
For a pumped system, make sure the expected flow falls within the valve's intended operating range.
For a gravity system, pressure loss becomes even more important because there may be very little pressure available to begin with.
Pay Attention to Cracking Pressure
Cracking pressure is especially important when selecting a spring-loaded check valve.
It is the pressure needed to push the valve off its seat and begin allowing water through.
A valve designed for a high-pressure plumbing system may require more opening pressure than a gravity-fed rainwater system can reliably provide.
For a pumped system, a modest cracking pressure may be insignificant.
For a rain barrel or elevated IBC tote, it can make the difference between acceptable flow and barely any flow.
Do not assume that all spring check valves open at the same pressure. Check the manufacturer's specification.
Choose Materials That Suit the System
Common check valve body materials include:
- PVC,
- other engineered plastics,
- brass,
- bronze,
- stainless steel.
The right material depends on the plumbing around it and the environment.
PVC and plastic valves
Alongside practical steps for fiting a foot valve, verify long-term maintenance priorities for the installation.
Plastic valves can be a practical fit for PVC rainwater plumbing. They resist corrosion and are common in irrigation systems.
They need proper support. Plastic pipe and fittings should not be forced into alignment by tightening threaded connections.
Brass or bronze valves
These are common in pressurized plumbing systems and can be durable when appropriate for the water and surrounding fittings.
If water may eventually be used in a potable-water treatment system, every wetted component needs to be suitable for that intended application.
Stainless steel
Stainless valves can be useful where corrosion resistance, strength, or demanding service conditions justify them.
That does not automatically make stainless steel the best option for a simple garden rainwater system.
Compatibility and hydraulic performance matter more than choosing the strongest-looking material.
Look at the Seal Material Too
The body is only part of the valve.
Check valves also contain seals, seats, or O-rings. Common materials include EPDM and other elastomers.
The correct material depends on:
- water temperature,
- additives or treatment chemicals,
- pressure,
- expected service life,
- manufacturer specifications.
For ordinary untreated rainwater, this usually is not complicated. But avoid assuming that any valve designed for industrial fluids is suitable for a household water system.
Debris Can Stop a Check Valve From Sealing
Rainwater systems carry material that municipal plumbing normally does not.
Roof runoff may contain:
- grit,
- leaf fragments,
- pollen,
- insects,
- roofing particles,
- organic sediment.
A small piece of debris caught between a check valve and its seat can prevent it from closing completely.
That is why check-valve performance starts farther upstream.
A well-planned system may include gutters and screens, inlet screening, appropriate prefiltration, and tank sediment management before water reaches sensitive pumps and valves.
Do not solve a debris problem by simply installing more check valves.
Put the Check Valve in the Right Place
The correct location depends on what the valve is supposed to accomplish.
On a pump discharge
This is one of the most common locations.
The valve prevents pressurized water from flowing backward through the pump when it stops.
Some pumps already have an internal check valve. Others require an external one. Pump manufacturers may also give specific instructions about how far from the pump an additional valve should be installed.
Do not automatically stack several check valves together. The placement of multiple valves can affect pressure changes and water hammer in some pump systems.
On a pump suction line
A check valve or foot valve may be used to keep an above-ground pump primed.
However, every fitting on the suction side increases resistance and creates another potential place for an air leak.
Use a suction-side valve only when it serves a clear purpose and is allowed by the pump manufacturer.
On a gravity outlet
A check valve may be useful where reverse flow is possible.
If reverse flow cannot reasonably occur, adding a valve may provide little benefit while reducing available flow.
Do Not Confuse a Check Valve With a Backflow Preventer
This distinction matters when rainwater plumbing is anywhere near a drinking-water system.
A normal single check valve can stop ordinary reverse flow. It is not automatically an approved device for protecting potable water from a rainwater cross-connection.
EPA guidance notes that a single check valve does not provide the inspection and failure protection expected from proper backflow-prevention assemblies. Different hazards can require devices such as double-check assemblies, vacuum breakers, reduced-pressure assemblies, or physical air gaps.
If municipal or well drinking water can supply a rainwater tank or share plumbing with the rainwater system, follow current local plumbing and cross-connection requirements.
Do not rely on a hardware-store check valve as the only separation between untreated rainwater and potable plumbing.
Consider Water Hammer in Pumped Systems
Water hammer is a pressure surge caused by a rapid change in water movement.
It can sometimes sound like a bang or thump when a pump or valve operates.
A check valve that allows substantial reverse flow and then suddenly closes can contribute to pressure changes. Pump selection, pipe velocity, valve location, pressure tanks, controls, and other parts of the system can also be involved.
Fast-closing or non-slam check valves are often used in pump systems where reverse flow needs to be controlled.
If a large rainwater pump system repeatedly produces severe banging, vibration, or pipe movement, do not keep adding valves at random. The hydraulic system should be evaluated as a whole.
Make the Valve Easy to Service
Even a correctly selected check valve can eventually collect debris, wear out, or stop sealing.
Install it where practical maintenance is possible.
That may mean adding unions or another suitable removable connection around an inline valve.
A buried valve with no access may turn a small maintenance job into an excavation project.
For tank installations, also think about whether servicing the valve would require entering a cistern. Avoid entering confined tanks. Design components so they can be inspected or removed safely from outside whenever possible.
Think About Freezing Conditions
A check valve can trap water in a section of pipe.
That matters in climates where exposed plumbing freezes.
A line that previously drained by gravity may remain full after a check valve is added.
Freeze planning should therefore consider the entire section of pipe on both sides of the valve.
Depending on the system, the solution may involve seasonal draining, burying suitable pipe below the locally appropriate frost depth, insulating vulnerable equipment, or placing pumps and valves in protected spaces.
A check valve by itself does not provide freeze protection.
A Simple Selection Rule
For many residential rainwater systems, these starting points work well:
Choose a spring-loaded check valve when you have a pressurized pump system and want prompt closing with little reverse flow.
Choose a swing check valve when the system relies on low-pressure gravity flow and minimizing flow resistance is more important.
Choose a foot valve when an above-ground pump needs the suction pipe to remain primed and the pump design calls for one.
Then verify:
- correct pipe size,
- acceptable pressure loss,
- appropriate cracking pressure,
- pressure rating,
- material compatibility,
- installation orientation,
- accessibility for cleaning,
- pump manufacturer requirements.
That is more reliable than choosing a valve based only on its material or appearance.
Frequently Asked Questions
Is a spring check valve better than a swing check valve?
Neither is universally better. A spring-loaded valve is often better for pressurized pump discharge lines because it closes quickly. A swing valve can be better for low-pressure gravity systems because it usually creates less resistance.
Do I need a check valve on my rainwater pump?
Many pump systems need one, but the pump may already contain an internal check valve. Follow the pump manufacturer's instructions before adding another valve. Extra check valves can add pressure loss and may change how the system behaves when the pump starts and stops.
Where should a check valve go on a rainwater pump?
A common location is the pump discharge line. An above-ground pump may instead or additionally require a foot valve on its suction line. Exact placement depends on the pump and piping design.
Can I use a check valve with a rain barrel?
Yes, but first decide whether reverse flow is actually possible. If the barrel feeds by gravity, use a valve with very low resistance. A spring-loaded valve with too much cracking pressure can noticeably reduce flow.
Can a check valve stop rainwater from entering my drinking-water supply?
A basic single check valve should not be relied on as complete potable-water backflow protection. Systems that combine or closely connect rainwater and potable plumbing may require an approved backflow-prevention method or physical separation under local requirements.
Why does my check valve leak backward?
Common causes include debris on the valve seat, a worn seal, incorrect installation, damage, or a valve that is poorly matched to the application. Isolate the system safely before inspection. Replace damaged components rather than depending on a leaking valve.
Does a bigger check valve improve water flow?
Not automatically. The valve should normally match the correctly sized piping. An oversized valve may not operate properly at very low flow, while an undersized valve can create excessive pressure loss. Use the manufacturer's flow data when sizing a pumped system.
