Check Valve vs Foot Valve: Two Check Functions, Two Different Jobs

Check Valve vs Foot Valve: Two Check Functions, Two Different Jobs

The Short Answer: A check valve prevents reverse flow in a pipeline at any point, while a foot valve is a check valve mounted at the bottom end of a suction line, usually with an integrated strainer, to keep a pump or system primed. If the question is about holding pump suction on startup, you need a foot valve; if it is about stopping backflow anywhere else in the line, a standard check valve is the answer.

What Each Design Is

Check Valve

A check valve is an automatic, one-directional valve that opens with forward flow and closes when flow reverses. Common types include swing check, lift check, ball check, and dual-plate designs. It can be installed horizontally or vertically depending on the type, and it is selected by size, pressure class, and media.

Foot Valve

A foot valve is essentially a check valve with a strainer screen fitted to the inlet, designed to sit at the bottom of a vertical suction pipe. Its main job is to keep the suction line and pump casing full of liquid when the pump stops, so the pump does not have to be re-primed every time it starts. Foot valves are common on end-suction pumps, irrigation systems, and tanker offloading lines.

Key Differences

Feature	Check Valve	Foot Valve
Primary job	Prevent reverse flow	Keep suction line primed
Location	Anywhere in the pipeline	Bottom of suction line only
Strainer	Not included	Integrated screen or basket
Typical mounting	Horizontal or vertical	Vertical, submerged in liquid
Service	All process lines	Pump suction, wells, tanks
Failure mode	Backflow if stuck open	Loss of prime if leaking

Which to Choose

Install a foot valve only where the pump suction is below the liquid level or where priming must be retained between runs—typically a vertical pipe entering a tank or well. For every other location, including discharge lines, bypass lines, and horizontal suction runs, use a standard check valve. Some installations use both: a foot valve to keep prime and a check valve on the discharge to stop reverse flow through the pump.

Common Pitfalls

• Using a foot valve in place of a discharge check valve—it will not protect the pump from reverse flow on the pressure side.
• Oversizing the foot valve, which slows the strainer velocity and increases the risk of debris settling around it.
• Ignoring foot valve leakage—a leaking foot valve slowly drains the column and causes repeated re-priming.
• Choosing a swing check where a spring-loaded design is needed to prevent slamming on rapid flow changes.

Practical Recommendation

Use a foot valve with a correctly sized strainer on vertical suction inlets that must stay primed, and verify its cracking pressure is low enough for the pump to open it easily. Use standard check valves everywhere else in the line, and select the check type by flow velocity and shutoff characteristics rather than by price alone. Check the seat and screen materials against the media to avoid corrosion and clogging.

Quick Selection Checklist

• Ask where the valve sits: at the bottom of a vertical suction line means foot valve; anywhere else means check valve.
• For pump systems, check whether priming must be retained between runs—if yes, add a foot valve with a correctly sized strainer.
• Verify the cracking pressure of the foot valve is low enough for the pump to lift reliably.
• Confirm screen or basket mesh against the largest solids in the liquid to avoid clogging.
• Check seat and spring materials for corrosion resistance in the actual media.

In irrigation and tanker offloading, a common arrangement is a foot valve on the suction with a swing check on the discharge—the foot valve keeps prime, and the discharge check protects the pump from reverse flow. Keeping both in the design avoids starting problems without losing backflow protection.

Conclusion

The foot valve is a specialized check valve for pump suction priming, while the check valve is a general-purpose backflow preventer. Picking the right one is about location and duty: bottom of a suction line means foot valve; anywhere else means check valve.

Sources & Further Reading

API, ASME

Tags: Check Valve