A foot valve and a check valve are both essential components in many plumbing and fluid systems, but they serve different primary purposes and have distinct designs. While both valves prevent fluid from flowing backward, their specific applications, installation locations, and features are what set them apart. This article will explore the key differences between these two types of valves, examine their specific applications, and help you determine which one is the right choice for your particular needs.

What is a Foot Valve?

Definition and basic function: A foot valve is a type of check valve that is specifically designed for the suction end of a pump's intake pipe. Its primary function is to prevent the fluid from flowing back out of the pipe when the pump is turned off, thereby maintaining the "prime" of the pump. This ensures the pump is always full of fluid and ready to operate without needing to be re-primed each time.

Key components and design features: The design of a foot valve is characterized by two main components: a check valve and a strainer. The check valve component consists of a hinged disc, a poppet, or a ball that allows fluid to flow in one direction only. The second, and most distinctive, component is the integrated strainer or screen at the valve's inlet. This strainer prevents large debris, such as rocks, leaves, or sediment, from entering the suction line and potentially damaging the pump's impeller or other internal components. The valve body is typically made of materials suitable for submersion, such as brass, bronze, PVC, or stainless steel.

How it works: When the pump is activated, it creates a suction force that pulls fluid into the intake pipe. This suction pressure is sufficient to lift the internal disc or poppet of the foot valve, allowing the fluid to flow through the valve and into the pump. When the pump is turned off, the suction pressure ceases. The force of gravity and the weight of the fluid in the pipe cause the internal valve mechanism to close, sealing the intake pipe and preventing the fluid from flowing back out. This action keeps the pipe full of fluid, maintaining the pump's prime.

What is a Check Valve?

Definition and basic function: A check valve, also known as a non-return valve or one-way valve, is a mechanical device that allows fluid (liquid or gas) to flow through it in only one direction. Its fundamental purpose is to prevent backflow in a piping system, thereby protecting equipment and maintaining system integrity. Unlike a foot valve, it is not inherently designed for a pump's suction line and does not include a strainer.

Key components and design features: The internal design of a check valve is simple, typically consisting of a valve body, an inlet and an outlet, and a movable component that acts as a gate. This component, which can be a disc, a ball, or a poppet, is responsible for blocking the reverse flow. The valve relies on the flow of the fluid itself to operate, without any external actuation from a handle or a motor. Different designs exist to suit various applications, such as:

• Swing Check Valve: Uses a hinged disc that swings open with forward flow and falls back to a closed position to block backflow.
• Lift Check Valve: Has a disc or ball that is guided to move up and down to allow or block flow.
• Spring-Loaded Check Valve: Uses a spring to assist in closing the valve, making it suitable for both vertical and horizontal installations and helping to prevent "water hammer."

How it works: A check valve operates based on the pressure differential across the valve. When the pressure on the inlet side is greater than the pressure on the outlet side, the force of the fluid pushes the internal disc, ball, or poppet away from the valve seat, allowing fluid to flow freely through the valve. When the flow stops or the pressure on the outlet side becomes higher than the inlet side, the reverse pressure, gravity, or the force of a spring pushes the internal component back onto the seat, creating a seal and preventing any backflow. The minimum upstream pressure required to open the valve is called the cracking pressure, a key parameter that can vary depending on the valve's design and spring tension.

Key Differences Between Foot Valves and Check Valves

Primary Function:

• Foot Valve: Its primary function is a dual one: it prevents backflow and, most importantly, maintains pump prime. This is crucial for systems where a pump needs to be ready to operate immediately without manual re-priming.
• Check Valve: Its sole function is to prevent backflow in a pipeline. It stops the fluid from reversing its direction, protecting upstream equipment and ensuring one-way flow.

Installation Location:

• Foot Valve: Is always installed at the suction end of a pump's intake line, typically submerged at the bottom of a well, pond, or tank.
• Check Valve: Can be installed anywhere within the pipeline where backflow needs to be prevented. Its location is not limited to the suction side of a pump.

Design and Structure:

• Foot Valve: Features a built-in strainer or screen at its inlet. This strainer is an integral part of its design, preventing large debris from entering the pump and causing damage.
• Check Valve: Has a simpler design and does not include a strainer. It is designed to be installed in a clean pipeline and relies on a clean fluid environment.

Opening Pressure:

• Foot Valve: Designed to open with minimal pressure to allow for easy suction by the pump. The pressure required to open it, often called the cracking pressure, is very low.
• Check Valve: The opening pressure, or cracking pressure, can vary significantly depending on the design. Spring-loaded check valves, for example, require sufficient pressure to overcome the spring force, which can be higher than the minimal pressure required for a foot valve.

Maintenance:

• Foot Valve: Requires periodic maintenance, specifically the cleaning of its strainer to prevent clogging. A clogged strainer can restrict flow and lead to pump cavitation and damage.
• Check Valve: Generally requires less maintenance as it doesn't have a strainer to clean. Maintenance is usually only needed if the valve's internal components fail or a leak occurs.

Applications of Foot Valves

Well Water Systems: Foot valves are essential components in well water systems. They are installed at the bottom of the drop pipe, submerged in the well water. The valve's primary role is to maintain the prime of the submersible or jet pump. When the pump turns off, the foot valve closes, preventing the water in the pipe from flowing back into the well. This ensures that the pump is ready to deliver water instantly the next time it's activated, without the need for manual re-priming. The integrated strainer is also vital here, as it stops sand, grit, and other small debris from entering the pump and causing wear and damage.

Irrigation Systems: In irrigation setups that draw water from a pond, lake, or river, a foot valve is used on the end of the suction hose. The valve keeps the pump primed, so the system can begin delivering water to sprinklers or drip lines as soon as the pump is turned on. The strainer prevents organic matter like leaves, algae, and sticks, as well as sediment, from clogging the pump and damaging sensitive irrigation components like nozzles and emitters.

Sump Pumps: While some sump pump systems use a check valve, many also benefit from the use of a foot valve, particularly in configurations where the pump is submerged in a pit. The foot valve ensures that the pump's impeller remains submerged in water, which helps with cooling and prevents it from running dry. The strainer is crucial here to keep small solids and sediment found in basements or low-lying areas from entering the pump and causing it to fail.

Other Specific Scenarios: Foot valves are used in any application where a pump is drawing fluid from a low-level source, such as a tank or cistern, and where maintaining pump prime is critical for efficiency and longevity. This can include dewatering applications, such as emptying flooded areas, or in fire suppression systems where a pump needs to be ready to deliver water on demand. The ability of the foot valve to both prevent backflow and filter the fluid makes it ideal for these demanding and often debris-filled environments.

Applications of Check Valves

Preventing backflow in pipelines: Check valves are widely used in a variety of fluid transfer systems to ensure that flow occurs in only one direction. This is critical in applications where the pressure downstream could temporarily exceed the upstream pressure, leading to a reversal of flow. For example, they are used in domestic plumbing to prevent contaminated water from a fixture (like a garden hose) from being siphoned back into the potable water supply. They are also common in heating and cooling systems to maintain the correct flow path for water or other fluids.

Protecting pumps from backflow damage: Check valves are installed on the discharge side of a pump to prevent the fluid from the pipeline from flowing backward through the pump when it shuts off. This backflow can cause the pump's impeller to spin in the reverse direction, which can lead to mechanical stress, cavitation, and significant damage. By closing immediately when the pump's pressure drops, the check valve protects the pump from these destructive forces.

Use in hydraulic systems: In hydraulic and pneumatic systems, check valves are a fundamental component. They are used to hold pressure in a specific part of the circuit, ensuring that the fluid power is directed to a specific actuator or component and does not leak or reverse direction. For example, they are used in hydraulic lifting systems to keep a piston in a raised position after the pump has stopped, preventing the load from slowly sinking.

Wastewater treatment plants: Check valves play a critical role in wastewater treatment plants. They are used to prevent sewage or treated effluent from back-siphoning into pumps or other sensitive equipment. Given the often-heavy particulate load in these fluids, a robust check valve design, such as a swing check valve, is often used to ensure reliable operation without clogging. They are also used to control flow in various stages of the treatment process, from primary settling tanks to final disinfection.

Advantages and Disadvantages

Foot Valves

• Advantages:
  • Maintains pump prime: This is the most significant advantage. By keeping the pump and suction line full of fluid, it ensures the pump is ready for immediate operation and prevents dry-running, which can cause severe damage.
  • Prevents debris from entering the pump: The integrated strainer acts as a pre-filter, protecting the pump's internal components from large particles like rocks, sand, and leaves that could cause clogs or wear.
• Disadvantages:
  • Requires submersion: A foot valve must be installed at the bottom of a fluid source, making it unsuitable for inline applications in a pipe. This limits its use to systems that draw from a tank, well, or open body of water.
  • Needs strainer cleaning: The strainer, while protective, can become clogged over time, especially in debris-heavy environments. This necessitates periodic cleaning, which can be difficult as the valve is often submerged.

Check Valves

• Advantages:
  • Versatile installation: Check valves can be installed anywhere along a pipeline, in both vertical and horizontal orientations, as long as the flow direction is correct. This flexibility makes them useful in a wide range of applications.
  • Simple design: Their simpler design, without an external strainer, means they are more compact and generally easier to install in tight spaces within a pipeline.
• Disadvantages:
  • Does not prevent debris from entering the pump: A standard check valve provides no protection against debris. If used on the suction side of a pump, foreign particles can easily enter and damage the pump's internal parts.
  • Requires sufficient pressure to open: Some check valve designs, particularly spring-loaded ones, require a minimum upstream pressure to open. If the pump's suction or the system's pressure is too low, the valve may not open, preventing flow.

Choosing the Right Valve

Factors to consider:

• Type of fluid: The nature of the fluid is a key factor. If the fluid contains significant amounts of debris, sediment, or solid particles, a foot valve is a necessary choice due to its integrated strainer. For clean fluids, a standard check valve is sufficient.
• Flow rate: Both valves are designed to handle specific flow rates. However, in applications with low flow rates or low suction pressure, a foot valve's low cracking pressure is advantageous. For high-pressure systems, a check valve with a higher cracking pressure or more robust design may be required.
• Pressure requirements: The pressure differential is a critical consideration. A foot valve is engineered to open with minimal pressure to facilitate a pump's suction. A check valve's cracking pressure must be high enough to prevent accidental opening from minor pressure fluctuations but low enough to allow for efficient flow.
• Installation environment: The physical location of the valve is a decisive factor. A foot valve must be submerged at the end of a pipe in a well or tank. A check valve can be installed anywhere in a pipeline, including vertical or horizontal runs, providing much greater flexibility in installation.

When to use a foot valve vs. a check valve:

Installation Tips

Foot Valve Installation:

• Ensuring proper submersion: The foot valve must be fully submerged in the fluid source at all times. This prevents the pump from sucking in air, which can lead to a loss of prime and pump cavitation, a condition that can cause significant damage. It is recommended to install the valve at least several feet from the bottom of the tank or well to avoid drawing in sediment.
• Connecting to the suction pipe: A secure, airtight connection between the foot valve and the suction pipe is critical. A loose connection will allow air to be pulled into the system, leading to a loss of prime. The connection should be sealed with appropriate thread sealant tape or pipe dope, and care should be taken to tighten it sufficiently without overtightening and cracking the valve body.
• Installing a check valve in line with a foot valve to prevent freezing: In cold climates, a separate in-line check valve can be installed on the discharge side of the pump, above the frost line. This allows the water in the vertical pipe leading down to the foot valve to drain back into the well or source, preventing the pipe from freezing and bursting.

Check Valve Installation:

• Orientation (vertical or horizontal): Check valves are designed for specific orientations. For example, a swing check valve must be installed with the hinge pin horizontal to allow the disc to swing open and closed properly. A lift check valve or a ball check valve may be installed vertically. Always refer to the manufacturer's instructions to ensure the valve is installed in the correct orientation for its design.
• Ensuring proper flow direction: The most critical step in installing a check valve is to ensure it is oriented correctly with the direction of fluid flow. Almost all check valves have an arrow stamped on their body indicating the intended direction of flow. Installing the valve backward will completely block the flow and could damage the valve or the system.

Maintenance and Troubleshooting

Common issues with foot valves and check valves:

• Loss of pump prime: This is a common issue for systems using a foot valve. It is often caused by a leak in the suction line, a clogged strainer, or a faulty valve disc that is not sealing properly, allowing fluid to drain back out.
• Clogging: Foot valves are particularly susceptible to this due to their integrated strainer. Debris can accumulate on the strainer, restricting flow and causing the pump to run dry or cavitate.
• Valve failure: Both types of valves can fail over time. The internal disc, ball, or poppet may become stuck open or closed due to corrosion, sediment buildup, or mechanical wear, rendering the valve ineffective.
• Water Hammer: A common issue with check valves, especially swing-type valves in high-pressure systems. It occurs when the valve slams shut suddenly, causing a pressure wave that can be heard as a loud banging noise and can damage the pipeline.

Troubleshooting steps:

• Check for leaks: For foot valve issues, first inspect the suction line and all connections for air leaks. Submerging connections can reveal bubbles.
• Inspect and clean the strainer: If a foot valve is suspected of being the problem, carefully pull the suction line and inspect the strainer. Clean any debris, sediment, or organic matter that may be obstructing the flow.
• Verify valve functionality: Visually or manually inspect the internal mechanism of the valve to ensure it is moving freely. The disc should open easily with a push and close to form a tight seal. A spring-loaded valve's spring should provide resistance but not be overly stiff.
• Listen for sounds: If you suspect water hammer, you may hear a loud banging sound when the pump shuts off. This suggests a fast-closing check valve may be needed, or a different type of check valve (e.g., a silent or spring-loaded one).

Maintenance tips for prolonging valve life:

• Routine Inspection: Periodically inspect both foot valves and check valves for signs of wear, corrosion, or leaks. Early detection of issues can prevent a larger system failure.
• Clean the strainer: For foot valves, a key maintenance task is to regularly clean the strainer to ensure proper flow and prevent pump damage. The frequency depends on the cleanliness of the fluid source.
• Install a filter or pre-filter: For systems that use a check valve in a fluid with some particulate matter, installing a separate filter upstream can protect the valve from becoming clogged or damaged.
• Replace worn parts: Valves are mechanical devices with moving parts. If a valve is not functioning correctly, it is often more cost-effective to replace the entire valve rather than attempting to repair its internal components.