Check valve is a type of non-return valve that only allows fluid to flow only in one direction. They are used to prevent backflow of the fluid.
Most check valves work automatically. Minimum differential upstream pressure is required to operate the check valve automatically and this pressure is known as cracking pressure. When the pressure differential is less than specified cracking pressure, the valve gets closed. Click this link to know various types of valves and their applications.
Check Valve Symbol
- Stainless Steel
- PVC (Polyvinyl Chloride)
- PP (Polypropylene)
How does a Check Valve work?
Check valve works on the principle of pressure difference between inlet and outlet port. For the flow of liquid pressure differential shall be greater than the cracking pressure. And the value of cracking pressure depends on valve design. If pressure differential is less than the cracking pressure, the the valve will close.
Mechanism of the opening and closing of the valve depends on the type and mechanism of the valve.
Types of Check Valves
- Spring Loaded Check Valves
- In-line Spring-Loaded
- Spring Loaded Y
- Ball Check-valves
- Swing Check-Valves
- Diaphragm Check valve
- Lift Check-Valve
- Butterfly or Wafer Check Valves
- Foot Valve
- DuckBill valve
- Stop Valve
1. Spring Loaded Check Valves
1.1 Spring Loaded in-line
A spring loaded in-line check valve also known as nozzle check valves or silent check valve consist of a disk along with a compression ring. When at the inlet fluid pressure becomes greater than the cracking pressure. Disk moves and the fluid starts flowing through the valve. Whereas as the pressure reduces, the disk moves back to its original position and the valve gets closed.
1.2 Spring Loaded Y
Compared to in-line check valves, in spring loaded y-check valves, spring and disk are located at an angle. Their working principle is similar to the in-line valves but they have the advantage of servicing the valve without disconnecting the valve from the system.
2. Ball Check Valves
Ball check valve consists of a spring loaded spherical ball. When the pressure difference between inlet and outlet is greater than the cracking. Ball moves away from the sealing seat and fluid starts flowing. Whereas when the pressure difference between inlet and outlet is less than cracking pressure, spring loaded ball rests on the sealing seat to close the orifice.
The value of cracking pressure depends on the design of spring, spherical ball and the valve section design. Ball check valves are mostly used in small pumps but require frequent maintenance.
3. Swing Check Valves
Swing check valves consist of a disk mounted on a hinge at the inlet of the valve. This disk can swing about the hinge. When the inlet and outlet pressure difference is greater than the cracking pressure, the disk swings off the resting seat and fluid starts flowing. Whereas when the pressure difference is less than cracking pressure of fluid is back flowing, the disk will swing back to the closed position.
Disk returns to its original position due to gravitational force. Therefore orientation of the valve during installation is very important. The value of cracking pressure depends on the disk and hinge characteristics.
4. Diaphragm Check Valve
The Diaphragm Check valve utilizes a flexible membrane known as diaphragm to control the flow of liquid. These valves can be normally open or normally closed type. In a normally closed valve, the flow of liquid cracking pressure shall be greater than the pressure required to overcome diaphragm elasticity. Higher the pressure at the inlet, more liquid will flow through the valve. Due to low cracking pressure, diaphragm valves are used in pharmaceutical, food and semiconductor industries where the pressure requirement is relatively small.
5. Lift Check-Valve
A lift check valve consists of a round disk that moves upward when the pressure difference at inlet and outlet becomes greater than the cracking pressure. For the flow of fluid, cracking pressure has to work against weight of the disk, spring force and the back pressure.
6. Butterfly or Wafer Check-Valve
Butterfly or wafer check valves are compact, lightweight and available for various pipe sizes. They consist of butterfly or wafer type of disk attached on a hinge and spring. When inlet / outlet pressure difference is greater than cracking pressure, liquid starts flowing. Whereas when the pressure difference is less than cracking pressure or fluid is back flowing, the valve gets closed.
7. Foot Valve
Foot valve is a type of check valve along with a strainer at the inlet to prevent debris out of the line and keep the pump primed. They are installed at the end of the inlet.
8. DuckBill Valve
Duckbill valves consist of a soft tube with flattened shape at the end. When fluid flows from inlet to outlet, the flattened end opens up and fluid starts flowing. Whereas when fluid pressure at inlet is less than cracking pressure, flow of fluid stops.
9. Stop Valve
Stop check valve is a combination of globe valve and check valve. Therefore it works as a check valve to prevent backflow and actuator to open or close the valve. Stop check valves are widely used in power plants, boilers, turbines and other safety applications.
Applications of various types of Check Valve
Various types of check valves in a wide variety of sizes and costs are available in the market. They are mostly used in applications where backflow of fluid can be a concern. Following are the applications of check valves in our day to day life.
- Non-return valves are used in sewer lines to ensure waste water does not re-enter inside the system.
- Protect drinking water from contamination by backflow.
- Used in reverse osmosis filters to ensure fluid flow only in one direction.
- Used in pumps to hold water in a pipe when flow is turned off.
- Check valves are used along with solenoid valves to reduce the risk of backflow of water in case of valve failure.
- Used in unidirectional flow requirements.
Advantages and Disadvantages of Check Valve
Advantages of Check Valve
- Low Cost and Smaller Size
- Self Automated valves
- Prevents backflow of the fluid.
- Maintains minimum cracking pressure in the system.
- Do not require any power to operate the valve.
- Works as a safety device in a system.
- Effective in preventing water hammer.
- Eliminate chatter
- Low maintenance cost
Disadvantages of Check Valve
- Can not be used in a pulsating system.
- Water hammer and reverse flow of the liquid can be a problem.
We will keep adding more information on the Various types of check valves, their working and applications. Please add your comments or questions on the various types of check valves and their applications in the comment box. We suggest you also read this article on various types of flanges.