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A foot valve is fitted at the intake end of a pump’s suction pipe. It lets water enter the pipe but helps stop it from draining back when the pump shuts off. This keeps the suction line full and can make priming a surface pump much easier.
The valve must point in the correct flow direction, stay below the water level, and connect to an airtight suction line. It should also sit above the bottom of the tank or cistern so it does not pull in settled dirt.
What Is a Foot Valve?
A foot valve is a one-way valve installed at the lowest end of a suction pipe.
Most foot valves have two main parts:
- A check valve that lets water move toward the pump but limits reverse flow.
- A screen or strainer that helps keep leaves, gravel, insects, and larger debris out of the suction pipe.
Foot valves are commonly used with surface pumps drawing from:
- Rainwater tanks
- Cisterns
- IBC totes
- Storage barrels
- Shallow wells
- Ponds or other suitable water sources
They are normally used on the suction side of a pump rather than the discharge side.
Make Sure a Foot Valve Is Right for Your Pump
Before installing one, check the pump instructions.
A foot valve is most useful when a surface pump must lift water through a suction pipe. It helps keep that pipe full after the pump stops.
Do not assume every pump needs one. Many submersible pumps, for example, use a built-in or separately installed check valve instead.
Also check the maximum suction lift specified for your pump. A foot valve can help hold prime, but it cannot make a pump draw water from farther below than the pump is designed to handle.
Choose the Correct Foot Valve Size
Match the valve to the suction pipe and the pump's intake requirements.
For example, if the pump requires a 1-inch suction line, using a much smaller valve can restrict flow.
Check:
- Pipe diameter
- Valve connection size
- Male or female threads
- Thread type
- Hose or pipe connection method
- Valve material
- Water temperature limits
- Pump manufacturer's suction-line requirements
Do not identify a threaded connection by outside diameter alone. Pipe threads are often named by their nominal size, which may not match the diameter you measure with a ruler.
For water that may eventually be treated for drinking, every component that contacts the water should also be suitable for that intended use. The foot valve alone does not make collected rainwater potable.
Potable means suitable for drinking. Non-potable water is intended for uses such as irrigation, toilet flushing, or cleaning where permitted.
Where Should the Foot Valve Go?
Install the foot valve at the bottom end of the suction pipe, below the lowest water level you expect during normal use.
The valve should remain submerged while the pump operates.
However, do not simply let it rest on the bottom of a tank.
Sediment often settles there. A valve sitting directly in this material can clog its screen or send fine debris toward the pump.
A better setup holds the intake above the bottom while still keeping it underwater.
The exact clearance depends on the tank, sediment level, valve design, and pump setup. Follow the pump and valve manufacturer's instructions where they specify positioning.
If your rainwater tank collects significant roof debris, good upstream screening and regular tank maintenance are also important. A foot-valve screen is not a substitute for proper rainwater prefiltration.
How to Fit a Foot Valve
1. Shut the Pump Off
Disconnect electrical power before working on the pump or suction pipe.
Do not work on wiring, damaged electrical equipment, or wet electrical connections unless you are qualified to do so.
If the pump system is pressurized, relieve pressure according to the manufacturer's instructions before opening connections.
2. Check the Flow Direction
Look for an arrow or other flow marking on the valve body.
The arrow should point toward the pump.
Water needs to enter through the screened end and then travel up the suction line toward the pump.
Installing the valve backward can prevent the pump from drawing water.
3. Inspect the Valve and Pipe
Before assembly, check the valve for:
- Cracks
- Damaged threads
- Loose parts
- Debris inside the screen
- A sticking internal valve
Also inspect the suction pipe and fittings.
An air leak on the suction side can cause poor pumping even when no water leaks are visible. The pump may pull air through a loose connection instead of drawing water properly.
4. Seal Threaded Connections Correctly
For threaded fittings, use a thread-sealing method suitable for the pipe and valve materials.
Follow the fitting or pump manufacturer's instructions for the correct sealant.
Do not put excessive sealing tape or compound inside the pipe where pieces could break loose and enter the pump.
Be especially careful with plastic fittings. Over-tightening can split a plastic valve, adapter, or pump port.
The goal is a secure, airtight connection, not maximum tightening force.
5. Connect the Foot Valve to the Suction Pipe
Attach the valve directly to the intake end or to the correct adapter.
Keep the suction line at least as large as required by the pump manufacturer.
Avoid unnecessary restrictions such as:
- Undersized pipe
- Small adapters
- Excessive elbows
- Kinked hose
- Collapsed flexible suction hose
Ordinary garden hose is often unsuitable for a pump suction line because it may flatten when subjected to suction. Use hose or pipe intended for the application.
6. Lower the Valve Into the Water
Position the valve so that it remains submerged but does not sit in sediment.
Support the pipe independently where needed. Do not rely on a plastic valve or tank fitting to carry the weight of a long suction pipe.
In a rainwater tank, also make sure the suction line cannot rub against sharp edges or pull sideways on a bulkhead fitting.
A bulkhead fitting is a fitting that passes through the wall of a tank and creates a sealed pipe connection.
7. Prime the Pump
Many surface pumps must be filled with water before their first start or after the suction line has emptied.
This is called priming.
Follow the pump manufacturer's priming procedure. Do not run a pump dry unless it is specifically designed to do so.
A working foot valve should help hold water in the suction line after the system has been primed.
8. Start the Pump and Check Its Operation
With reasons a water pump will not prime, you can assess operating limits before the pump runs for long periods.
Restore power and operate the pump according to its instructions.
Check for:
- Normal water flow
- Stable pressure
- Unusual pump noise
- Air bubbles
- Loss of prime
- Leaking fittings
- Repeated cycling
If the pump cannot establish flow, shut it down rather than allowing it to continue running dry.
Why an Airtight Suction Line Matters
Leaks behave differently on the suction side of a pump.
A pressure-side leak usually pushes water outward. A suction-side leak may instead pull air inward.
That means you can have a serious suction leak without seeing water dripping from the fitting.
Common leak points include:
- Threaded adapters
- Hose clamps
- Pump inlet connections
- Cracked fittings
- Damaged suction hose
- Loose unions
Air entering the line can reduce flow, make the pump noisy, or cause it to lose prime.
How Deep Should a Foot Valve Be Underwater?
The valve needs enough water above it that the pump does not draw air as the water level falls.
It should also be kept away from bottom sediment.
There is no single installation depth that works for every tank because the correct position depends on:
- Tank depth
- Lowest expected water level
- Pump flow rate
- Intake design
- Sediment buildup
- Water movement inside the tank
A high-flow pump can create a stronger draw around the intake than a small garden pump.
If the valve frequently becomes exposed as the tank empties, consider changing the intake height, adding low-water protection, or reviewing whether the tank and pump are appropriately sized.
Common Foot Valve Installation Problems
The Valve Is Backward
Water cannot flow properly toward the pump.
Check the arrow on the valve body.
The Valve Is Above the Water
Once the water level drops below the valve, the pump can begin drawing air.
The intake needs to remain submerged during normal operation.
The Valve Is Sitting in Sediment
This can clog the strainer and reduce flow.
Raise the intake and clean accumulated sediment when needed.
The Suction Line Has an Air Leak
This may cause slow priming, low flow, or loss of prime even if the foot valve is working.
Inspect every suction-side connection.
The Valve Is Too Small
An undersized valve can restrict the pump.
Match the suction system to the manufacturer's requirements rather than reducing pipe size simply because a smaller valve is easier to fit.
The Foot Valve Does Not Seal
Dirt can lodge in the valve and stop it from closing completely.
The suction line may then drain back between pump cycles.
Clean or replace the valve if inspection shows that it is damaged or no longer sealing reliably.
Maintaining a Foot Valve
Foot valves need occasional inspection, especially in rainwater systems where sediment and organic debris can reach the storage tank.
Check the valve when you notice:
- Longer priming times
- Reduced water flow
- A pump that loses prime
- Air entering the line
- Frequent pump cycling
- Visible debris on the screen
Clean the screen without damaging it.
Also inspect the suction pipe, adapters, and seals while the valve is accessible.
If the system is in a freezing climate, protect the pump and water-filled plumbing according to the equipment manufacturer's winterization instructions. Water trapped in valves and pipes can expand when frozen and damage components.
When to Get Professional Help
A basic foot valve on an accessible rainwater-tank suction line can often be fitted as a straightforward plumbing job.
Stop and get qualified help when the work involves:
- Electrical faults or permanent wiring
- Deep wells
- Difficult or unsafe tank access
- Entering a tank or confined space
- Complex pressure systems
- Repeated pump cavitation or loss of prime
- Uncertain pump sizing
- Drinking-water plumbing
- Connections that must comply with local plumbing requirements
Never enter a cistern or storage tank simply to reach a foot valve. Tanks and confined spaces can present serious hazards.
Frequently Asked Questions
Does a foot valve have to be underwater?
Yes. A foot valve on a normal pump suction line needs to remain submerged so the pump can draw water rather than air. It should also be positioned above settled sediment.
Which way should a foot valve point?
The flow arrow should point toward the pump. Water enters through the screened end and moves through the suction pipe to the pump.
Can I put a foot valve directly on the bottom of a rainwater tank?
It is usually better to keep it above the bottom. Sediment can collect there and clog the screen or enter the pumping system.
Why does my pump still lose prime with a foot valve?
Possible causes include a leaking foot valve, debris preventing it from closing, or an air leak somewhere in the suction pipe or fittings. Excessive suction lift can also cause pumping problems.
Can a foot valve be smaller than the suction pipe?
Reducing the intake size can restrict flow. Use a valve and suction line that meet the pump manufacturer's requirements.
Do submersible pumps need a foot valve?
Usually not in the same way a surface suction pump does. Many submersible systems use a check valve instead. Follow the pump manufacturer's installation instructions.
Can I use flexible hose with a foot valve?
Yes, if the hose is suitable for pump suction and compatible with the fittings. Some soft hoses can collapse under suction, so ordinary garden hose may not be appropriate.
Does a foot valve filter rainwater?
Its screen can stop larger debris from entering the suction line, but it is not a complete water-treatment filter. It does not make roof-collected rainwater safe to drink.
