- By Charles Kolstad
- February 09, 2022
Let's take a look at various types of check valves and discuss how they work, how they're applied and how to select the right type.
Systems that are designed to allow fluid media in only one direction often feature a check valve. Examples of such systems include a sewer line where the waste should only flow in one direction. Check valves are also used where backflow could cause equipment damage.
Before we look at the different check valve types, applications, and selection criteria, let’s first understand how a check valve works.
What is a check valve, and how does it work?
A check valve, or a non-return valve, is a device that restricts fluid flow to only one direction. Check valves have two ports, an inlet, and an outlet port, designed to prevent fluid backflow in various industrial systems.
There are different check valve types and they differ by the mechanism that causes them to open and close. However, they all rely on a pressure differential to either allow or restrict fluid flow. Unlike the other valves in the market, check valves do not need a lever, a handle, an actuator, or human intervention to work correctly. They are cheap, effective, and easy to deploy.
That said, the check valve will only operate if there’s a pressure differential between the inlet and outlet ports. The minimum pressure differential that the system must exceed for the valve to open is called the ‘cracking pressure.’ The value of this cracking pressure varies from one checking valve to another based on the design and size.
When there’s a back pressure or the cracking pressure is higher than the inlet pressure, the valve will close. The check valve’s closing mechanism varies based on the design, i.e., a ball check valve pushes a ball against the orifice closing it. This closing action can also be assisted either by gravity or a spring.
Types of check valves
As stated earlier, there are multiple types of check valves, each designed for their unique applications. However, one type, called the spring loaded in-line check valve, is used in various industrial settings.
The spring-loaded in-line check valve has a spring, a valve body, a disc and a guide. When the inlet pressure is high enough to overcome the cracking pressure and spring force, it pushes the disc, opening the orifice and allowing fluid to flow through the valve.
If backpressure occurs, it pushes the spring and the disc against the hole/orifice, sealing the valve. The short travel distance and the fast-acting spring allow for a quick reaction time during closing. This type of valve can be installed in a horizontal or vertical orientation, in line with the system, hence must be removed entirely for inspection or servicing.
Here are the other types of check valves:
- Spring-loaded Y check valve: works just like the spring-loaded in-line type, but the movable disc and spring are positioned at an angle. This makes it possible to inspect the check valve while still connected. The Y-check valve also takes up more room inside the system.
- Ball check valve: contains a spring-loaded or free-floating ball resting on the sealing seat and closing the orifice. When the inlet pressure is high enough, it pushes the ball from its seat, allowing the fluid to flow.
- Diaphragm check valve: consists of a rubber diaphragm that flexes open when the inlet pressure increases. It’s either normally open or normally closed.
- Lift check-valve: it has a guided disc that lifts off the valve seat to allow media to flow. To open the valve, the inlet pressure must overcome the cracking pressure.
- Swing check valve: consist of a disc that’s on a hinge and that swings open with an inlet pressure. As the inlet pressure decreases, the disc immediately swings and closes the orifice.
Other types of check valves include the stop check valve, the butterfly/ wafer check valve, the foot valve, and the duckbill check valve.
Check valve applications
Check valves find applications in nearly all the industries where fluids have to flow in one direction. These valves are also used in household appliances such as washing machines and dishwashers.
Based on the design and mode of operation, check valves can be used for any of the following use cases:
- Prevent equipment damage due to fluid backflow.
- Prevent siphoning.
- Prevent contamination due to backflow.
- To keep a vacuum seal in place.
Check valve selection criteria
Some of the factors you need to consider when choosing a check valve include:
The compatibility of the check valve material with the fluid medium.
- The size of the system line for precise connection.
- The envelope dimensions.
- The maximum and cracking pressure requirements.
- Accessibility needs for repairs and maintenance.
- Installation orientation.
- Temperature specifications of the valve with respect to the fluid media.
Check valves are popular devices in the industrial setting that are not only cheap and reliable but also relatively easy to use. When buying a check valve, make sure you understand your unique needs and the check valves’ selection criteria. Similarly, ensure you know the installation requirements to avoid flow direction issues or damaging your system due to pressure build-up.
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