How Does A Check Valve Work? | What is a Foot Valve?

The valves have become a most vital part of all industries. The main objective of the valves is to regulate the flow of the fluid. Therefore, they are used in various household and industrial applications. There are multiple types of valves, and a check valve is one of them. The check valve is also known as a foot valve, retention valve, reflux valve, non-return valve (NRV), or one-way valve.

The check valve uses to stop the backflow of the fluid. To stop backflow, these valves require more pressure on the suction side than the pressure of the discharge side. If the pressure on the suction side will not be more than the pressure on the discharge side, the valve will not be closed and stop the backflow of fluid. In this article, we will mainly discuss check valve working, different types, applications, advantages, and disadvantages.

What is a Check Valve?

A check valve is a mechanical device used to stop the backflow of the fluids in the pipelines and piping systems.  A check valve also knows as a non-return valve (NRV) or one-way valve because it permits the fluids to flow in only one direction. 

A symbol or arrow sign on the outer body of the check valve represents the flow direction.

Check Valve symbol
Check Valve symbol

The non-return valve (NRV) or foot valve works on the differential pressure principle. In simple words, it will open only when the downstream pressure is less than the upstream pressure. As the pressure of the downstream becomes higher than the upstream pressure, the valve will shut off to prevent the backflow of the fluid.

A concept of cracking pressure (pressure difference between the inlet and outlet sides) is used for the opening and closing of the check or one-way valve. Therefore, check valves have a specific cracking pressure that can be indicated as a specific cracking pressure.

These valves have automatic operations. Therefore, labor is not needed for the closing and opening of this valve, unlike other valves. As a result, mostly check valves do not have a valve stem or handle. Maximum valves are constructed of metal or plastic.

These valves are made in different materials, designs, and sizes. The check valves are most commonly used in compressors, engines, pumps, turbines, boilers, furnaces, etc. These are inexpensive, simple, and small valves.  

This type of valve has two ports. In simple words, it has two openings, one for the fluid suction and one for discharging the fluid. Nowadays, various check valve types are using in industries for multiple applications. Check, or foot valve is also very popular for household applications. 

Working Principle of Check Valve

A check valve works on the differential pressure principle. In a check valve, the minimum differential upstream pressure (pressure difference between the outlet side and inlet side) is called a cracking pressure.

check valve

For opening and closing the check valve, the cracking pressure plays an important role. This cracking pressure varies according to the size and design of the different check valves.

As the upstream pressure becomes equal to the cracking pressure, the valve opens, and fluid starts to enter inside the valve.

As the cracking pressure becomes higher than the upstream pressure, the fluid tries to flow from the discharge side to the suction side. At this point, the valve shuts and prevents the fluid from flowing back.

This shutting process of the valve changes according to the size and design of the valves. Gravity or Spring pressure helps to shut the valve.

Maximum check valves have an arrow sign on their body which represents the direction of the fluid flow.

Check, or foot valves usually install in applications that have fluid backflow issues. However, these valves have high efficiency, low cost, and excellent performance. These types of valves are simple solutions of potential problems.

If the backflow fluid contains contaminations, it can generate problems and contaminate the upstream medium. E.g., sewage pipeline systems have check valves to ensure the discharge of sludges or debris and stop this debris from re-entering the system.

Terms Used in Check Valve

Following are some main terms that need to be understood for the check valve operation.

1) Cracking Pressure

Check valve needs the lowest upstream pressure (pressure difference between suction and discharge sides) for its opening. As it touches this lowest upstream pressure, it permits fluid flow.

The cracking pressure is the lowest upstream pressure at which the valve opens. Therefore, for the proper operation of the valve, make sure that it produces adequate cracking pressure. 

2) Closing Pressure

The pressure at which the check or one-way valve closes is known as a closing pressure.

As the upstream pressure becomes less than the opening/cracking pressure and fluid moves from the discharge side to the suction side, then the foot valve closes. This closing mechanism varies according to the design of the valve. In simple words, the backward pressure pushes the diaphragm, ball, gate, or disk against the opening and seal it. According to the design, the closing process can be supported by gravity or springs.

Types of Check Valves

The check valve has the following types:

  1. Spring Loaded In-Line Valve
  2. Spring Loaded Y
  3. Ball Valve
  4. Diaphragm Valve
  5. Lift Foot Valve
  6. Swing Valve
  7. Stop non-return Valve
  8. Duckbill non-return Valve
  9. Butterfly or Wafer Valve

1) Spring Loaded In-Line Valve

These types of check valves have simple designs and easy operation. This is the most common type of check valve. It is known as a spring check valve because it uses a spring for the valve closing. The below-given diagram represents a spring-loaded in-line foot or non-return valve.

The below-given diagram represents the parts and flow direction inside the valve.  As the fluid tries to enter the valve’s suction port, it contains sufficient pressure to beat the spring force and cracking pressure. After overcoming the cracking pressure, the fluid forces the disk and opens the orifice.

Spring loaded in-line valves

When the valve orifice opens, the fluid starts flowing into the valve. If the fluid pressure at the suction port becomes lower than the cracking pressure, then the spring force and the cracking or backpressure force the disk in the opposite direction to the orifice and close the valve.

The short travel distance by the spring for the disk accelerates the valve closing reaction time.

The design of this non-return valve (NRV) has the capability to stop pressure fluctuations in the pipeline and stop the occurrence of water hammering. This water hammer occurs due to a sudden stoppage of the fluid flow in the system.

The most famous spring-loaded in-line check valve types are silent valve or nozzle valve. These types of valves can install horizontally or vertically.

Advantages of Springe loaded inline valves
Advantages of Spring Loaded In-line Valve
  1. It has an easy operation.
  2. It has a simple design.
  3. This valve has a low cost.
  4. You can install it in any direction according to the direction of the flow.
  1. It prevents the system from any damage due to backflow.
  2. It also works as a pressure relief valve for the safety of the system.
  3. These valves stop the contaminations from flowing back toward the inlet side.
  4. This is an automatic valve.
Disadvantages Springe loaded inline valves
  1. For the inspection or maintenance of these valves, you need to remove them completely from the system.

Read More: Different Types of Valves

2) Spring Loaded Y

This foot valve has a very similar operation as the spring-loaded in-line valve. In the case of the spring-loaded Y valve, the flexible disk and spring are installed at a specific angle. This specific angle of the valve makes a “Y” shape; due to that, it is known as a spring-loaded Y valve.

Spring Loaded Y check valve

These types of check valves have a similar operation as the spring in-line valve, but you don’t have to detach them from the system for repairing and cleaning. The spring-loaded Y valve has a high weight, and it needs more space inside the system for installation.

Advantages and disadvantages of Spring-Loaded Y valve
You don’t need to remove them from the system for their repairing and cleaning.These types of valves have a large size.
They prevent the backflow of the fluid.They have a high weight.
They prevent the system from damage due to fluid blockage.The spring-loaded Y valve needs more space for installation inside the system.

3) Ball Non-return Valve

A ball valve is a mechanical device that uses a perforated hollow ball to control the fluid that flows through the ball. This valve opens as the ball hole is aligned with the inlet flow and shuts when the valve handle is turned up to 90 degrees to stop the flow.

ball valve

It has a spring-loaded ball which uses to open and shut the orifice of the valve. This ball installs on the sealing seat. This is a conically tapered sealing seat which assists to direct the ball inside the seat and provides an excellent seal to stop the backflow.

As the fluid pressure on the suction end of the valve becomes more than the cracking pressure, the ball moves away from its seat and permits the fluid flow.

As the pressure of the suction end becomes lower than the cracking pressure, or the valve’s discharge side pressure becomes more than the suction side pressure, then the ball comes back on its original position, closes the orifice, and stops the backflow of the fluid.

Advantages and Disadvantages of Ball Valves
These have low weight.This is not best for throttling applications.
This foot valve opens and closes quickly.The handle of this valve has a rotated position.
It has small dimensions.The cleaning of this valve is very hard.
It doesn’t need any lubrication. 
The ball valve has a long-life cycle. 

Read More: Working of Ball Valve

4) Diaphragm Valve

A diagram valve has more than one port (i.e., suction port and discharge port), a valve housing, rubber diaphragm, and a saddle or weir or seat on which the diaphragm sits. It is known as a diaphragm check valve because it uses a diaphragm to control the fluid flow.

The casing or housing of this NRV (non-return valve) is made of wood, metal, plastic, or other material according to the valve type. It is a bi-directional on-off throttling valve.

The diaphragm valve uses a membrane to start and shut the fluid flow. This membrane or diaphragm is made of rubber. Below given diagram represents a normally open diaphragm non-return valve.

diaphragm valve

This valve doesn’t use the cracking pressure concept for opening and closing the valve. It uses a free-floating self-centering diaphragm for the normal opening (NO) and normal closing (NC). This valve also needs a higher suction end pressure to overcome the elasticity of the diaphragm.

When the suction end pressure becomes higher than the discharge end pressure, the rubber membrane will flex, and a large amount of the fluid will start to flow.

As the suction or inlet end pressure reduces, the membrane will seal the orifice and stop the backflow. These foot valves are the best vacuum or low-pressure applications.

Advantages and Disadvantages of Diaphragm Valve
It provides a leak-proof leaking.  This valve is not best for high-pressure applications.
It can repair without any interruption in the system.  It can operate only from -60 to 450o F temperature.
This check valve has easy maintenance.  It can’t use for multi-turn applications.
There is no need of cracking pressure for the valve opening and closing. 

Read Also: Working of Diaphragm Valve

5) Lift Foot Valve

This non-return valve uses a guide disk to regulate the fluid flow. This disk lifts from the valve seat to allow the fluid flow. This type of foot valve uses in high pressure and high fluid velocity applications.

These valves need cracking pressure to amazed the spring or gravity force and a guide to keep the disk in a vertical direction so that the disk can re-settle with proper sealing and alignment on its original position.

In the case of the lift check valve, the fluid needs to turn itself at a 90-degree angle for discharging. 

Lift Valve

When the suction end pressure becomes lower than the cracking pressure or fluid tries to flow back from the discharge to the suction side, the spring or gravity force uses to close the valve.  If spring force is not available to close the lift valve, in that case, the gravity force plays a vital role in turning the disk for valve closing.

The lift valves are accessible in WYE, T, and straight-through designs. You can install the lift valves in the vertical or horizontal direction, but those valves that rely on gravity force must be installed in order to travel the disk in the vertical direction.

Advantages and Disadvantages of Lift Valves
They stop backflow.These valves have high energy costs.
They have very high reliability.They are relatively inefficient.
These types of check valves are economical. 
It is a very flexible valve. 

6) Swing Valve

The swing valve is also known as the “tilting disk” check valve. This valve has a disk, inlet, and outlet ports. The disk sits on a trunnion which opens as the inlet pressure overcomes the cracking pressure.

When the pressure of the inlet side becomes lower than the backflow pressure, this valve swings and shuts the valve. When spring force is not available, gravity’s mounting orientation plays a vital role in swinging and closing the valve.

Swing check valve

The angle between the vertical plane and the seat of the valve is called the seating angle. The range of this angle varies from 0 to 45 degrees. In maximum cases, the range of this seat angle sets between 5 degrees to 7 degrees.

By increasing the seating angle, the valve disk travel distance can be decreased. In this way, the disk will close the fluid flow more quickly and minimize the possibility of water hammering. The angle of the vertical seat is 0 degrees.

Advantages and Disadvantages of Swing Valve
It has very low pressure and turbulence drop.The continuous flapping may destroy the seating elements.
It provides an easy opening.These valves are not perfect for pulsating flows.
This valve delivers excellent sealing. 

7) Stop Non-return Valve

The operation of the stop valve is very similar like a lift valve or spring-loaded y-check valve, but the stop valve has a manual dominant characteristic. This characteristic of the stop foot valve permits it to work as a normal check valve and prevents backflow. But an external mechanism may use to overcome it and keep the proper closing and opening function of the valve.

Stop valve

The stop valve has very low cost and high efficiency.  They can use in a wide variety of applications, from household to industrial.

These types of check valves are used in hydroelectric power plants, safety systems, turbine cooling, steam generators, and boilers.

Advantages and Disadvantages of Stop Valve
Advantages of Stop Valve
  1. These types of valves have a simple design.
  2. They have easy maintenance.
  3. The stop valve takes a very short time for closing and opening.
  4. It has a long service life.
Disadvantages of Stop Valve
  1. They have poor regulation performance.
  2. They are not best suitable for viscous fluids.
  3. These valves are not appropriate for fluids having large particles.

8) Duckbill Non-return Valve

These check valve types permit fluid to flow via a soft pipe with a flat shape that has a natural flattened end. This flattened design of the end looks like a duckbill which permits the fluid flow. As the suction side pressure releases, the duckbill end returns to its flattened form and blocks the fluid flow.

Duckbill Valve

This valve is made of synthetic elastomer or rubber. The duckbill valves are most commonly used in medical, sewage treatment plants, tidal, and outfalls applications to stop the impurity because of backflow.

Advantages of Duckbill Valve
  1. It doesn’t need maintenance.
  2. The duckbill valve has a very low cost.
  3. It doesn’t need any manual or external power source.

9) Butterfly or Wafer Valve

The butterfly or wafer check valve can use interchangeably. These types of check valves have a wafer or butterfly-type disk installed on a spring and a hinge.

Butterfly valves

Both sides or ports of the valve open as the suction side pressure go higher than the cracking pressure. As this suction side pressure drops or backflow occurs, the spring forces the disk to shuts the valve. The butterfly valve permits the fluid to flow directly with minor blockage.

Maximum large butterfly valves have a gearbox and a handle installed on the valve stem. This simplifies the work of the valve, but at the speed expense. A disk is attached to the rotating shaft.

The disk locates in the middle of the pipe. When these valves are fully closed, they block the pipe completely. When you try to open the valve fully, the valve disk forms an angle of 90 degrees with the media flow.

Butterfly valves use to change or adjust operations. These valves are famous due to their high-speed operation, low cost, small size, lightweight, and easy access. These valves can use with handles, gears, or automatic actuators.

Advantages and Disadvantages of Butterfly Valve
The butterfly valve has a small size.These valves have complex cleaning.
These types of foot or non-return valves have low costs.This one-way check valve has poor sealing characteristics.
They have lightweight.These valves generate cavitation and choked flow issues.
These valves require low maintenance than the ball valves. 

Read More: Working of Butterfly Valve

Advantages and Disadvantage of Check Valves

The check or foot valve has the following advantages and disadvantages:

Advantages of Check Valve

  • These valves prevent the compressor and pump from damage due to backflow.
  • These types of valves decrease production loss that may occur due to unstable valves stoppage.
  • The foot valve has a very low-pressure drop.
  • These valves require low cost for maintenance.
  • Check valve eliminates the chatter and decreases the sudden failure of the valve.
  • These valves have low footprint than a conventional check valve.
  • A check or non-return valve prevents the reverse flow.
  • It maintains the pressure.
  • These valves can be used vertically as well as horizontally.
  • Flexible support for different flow conditions.
  • Replaceable with most traditional check valves without the need for costly pipeline changes.
  • They are used as a backup system.
  • These are fast acting problems. 

Disadvantages of Check Valve

  • These valves allow the fluid to flow in only one direction.
  • These are not best for the pulsation system.
  • The check valves generate water hammering issues in the system. 
  • It can’t inspect in open or close conditions. 
  • The internal components of the check valve are impossible to inspect in operating conditions.
  • The disk can be trapped as the valve opens.

What are the applications of Check Valve?

The check valves use for the following applications:

  1. Pumps
  2. Compressors
  3. Aircraft Hydraulic Systems
  4. Fuel Pump
  5. Boilers
  6. Turbines
1) Pumps

Certain types of pumps often use non-return valves. Diaphragm pumps and Piston pumps (such as chromatography pumps and metering pumps) often use outlet and inlet ball check valves.

The check valve usually looks like a small cylinder and is connected to the pump heads on the outlet and inlet lines. Many pumps like mechanisms are used to move large amounts of fluid around the use of check valves (like ball check valves). The ejector or feed water pump that supplies water to the steam boiler is equipped with these valves to prevent backflow.

These types of valves also use in pumps that deliver water to the water slide. The water from the slides flow by the pipes, and the tower secures the ladder to the slide. As the facility with slides is closed at night, a check valve prevents water from flowing through the pipeline. As the facility is reopened the next day, the valve will open, the flow will continue, and the slides will be available again.

Read Also: Different types of Pumps

2) Industrial Processes
  1. These types of alves use in the chemical industries.
  2. These valves use in the powerplants.
  3. Foot valve uses in irrigation, potable water, and wastewater applications.
  4. These valves use in the oil & gas industries.
  5. Uses in Food & Beverage industries.

This valve uses in different applications due to the following reasons.

  • To avoid backflow of the fluid.
  • To avoid contamination due to backflow.
  • These valves use to maintain vacuum sealing.
  • To avoid siphoning.
3) Boilers

The check valves are used in different boilers to stop the backflow of the hot water. These valves also use to control the flow of the water from the feed pump into the boiler.

Read More: Working and different types of Boilers

4) Compressor

In compressors, the check valve uses to stop the backflow of the compressed air or gas. These valves are used on the inlet and outlet sides of the compressors.

Read Also: Different types of Compressors

FAQ Section

What does a check valve do?

 A check valve stops the backflow of the fluid. It prevents the system from damage due to backflow.

What is Check Valve used for?

A check valve uses to stop the backflow of the system inside the system.

Is check valve a type of pressure relief valve?

A check valve is a type of pressure relief valve. It is a one-way valve which allows the fluid to flow in only one direction.

What is the function of the check valve?

The main purpose and function of the check valve are to stop the reverse flow.

What are common check valve problems?

The most common problems of the check valves problems are given below:

  1. These generate extensive noise.
  2. They have water hammering issues.
  3. They have leakage and backflow issues.
  4. The check valves also have vibration problems.

Will a check valve stop the water hammer?

If the check valve acts quickly, it can stop water hammering issues. This process stops the pressure fluctuations, which can produce shock waves in the entire fluid. These produced shock waves may lead to complete failure or damage of the ruptured pipeline, pipe supports, or equipment.

Why is my check valve not working?

In case of improper working of the check valve, the backflow starts into the system, which can cause of system damage or failure. A check valve doesn’t work because of the following reasons:

  1. Slow closing of the valve.
  2. If a filter is not installed in the valve, the backflow of the contaminations occurs. Due to the absence of a filter, these contaminations stuck between the body and disk of the valve, which forces the valve to be opened during the whole operation.
  3.  The corroding or wearing of the valve material may cause valve seat or disk damage. Due to this damage, the valve will not properly seal the backflow. This can lead to backflow.

Which valve is NRV?

A check valve, foot valve, retention valve, or one-way valve is known as an NRV (non-return valve).

Read More
  1. Different Types of Boilers
  2. Types of Pumps
  3. Different Types of Valves
  4. Different Types of Ball Valves

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