What is a Check Valve? Working Principle & Function

What Is Check Valve?

In fluid flow systems, a check valve restricts the flow of fluids in one direction. Media enters through one port, while the output is through another.

Basics of Check Valves

Known as one-way valves or non-return valves, check valves only allow media to flow in one direction. The primary purpose of a check valve is to prevent backflow. A check valve is shown in the above figure.

The pressure differential is necessary for a check valve to function. Valve opening requires a greater pressure on the input side than on the output side. The valve will close if the pressure on the outlet side is too high (or if the input pressure is too low). Closure mechanisms vary depending on the type of valve. In contrast to other valves, they do not require a handle, lever, actuator, or a human to operate.

Typically, they are installed in applications where backflow would be a problem. In any case, since these non-return valves are cheap, effective, and easy to install, they are a good solution to a potential problem. The media upstream can become contaminated by backflow if the backflow is contaminated. In a sewer system, a non-return valve is installed to prevent re-entry of waste. In addition, they are used if media backflow can damage equipment upstream that only permits one-way flow.

In reverse osmosis filters, water can only flow one way, so a one-way valve is placed downstream to prevent this. A check valve can be found in a variety of sizes, designs, and materials for every application.

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Working Principle of a Check Valve

Three basic principles govern the operation of a check valve:

Cracking Pressure

For a check valve to open and allow flow, there must be a minimum upstream pressure. At this minimum upstream pressure, the valve opens, which is called the 'cracking pressure.' The cracking pressure of a check valve depends on its design and size. Make sure that your system can produce this pressure and that it is appropriate for the application.

Closing

The valve will close if the pressure in the upstream side of the valve ever falls below the cracking pressure or if a backpressure exists (flow attempting to move upstream). The closing mechanism of a check valve can differ depending on its design. Shortly put, back pressure forces a diaphragm, ball, or disc against an orifice and seals it. According to the design, either gravity or spring can assist the closing process.

Installation Orientation

One-way valves work only in one direction, so it is important to know how to install them correctly. There is often an arrow on the valve housing to indicate the direction of the flow. In any case, you will need to check that the valve is installed in the correct direction. When it is reversed, the flow will not be able to move throughout the system, resulting in pressure building up or damage.

Function of a Check Valve

Check valves serve as one-way or non-return valves in nearly every industrial application. The check valve is a simple device that prevents reverse flow, thus preventing damage and ensuring optimal performance. Water hammer, for example, occurs when reverse flow occurs. Pipework, valves, and pumps can be subject to repeated extreme pressure surges that can irreversibly damage the system and its components. Water hammer may not cause a failure immediately, but repeated impacts could lead to fatigue and eventually to a loss of system integrity.

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Usage of Check Valves

Check valves are utilized in a variety of different applications. They protect a pump from backflow, for example, when placed on the outlet side. Due to the fact that centrifugal pumps do not self-prime, check valves are used to keep the water in the pipes. Check valves are also commonly used in HVAC (Heating, Ventilating, and Air Conditioning) systems. A coolant is pumped up many floors in the HVAC systems of large buildings. Here, check valves are installed to prevent coolant from flushing back down.

Common Applications of Check Valves

The following are examples of check valve applications:

Pumps

Several types of pumps are equipped with check valves. Diaphragm and piston pumps, including metering pumps and pumps for chromatography, commonly use ball check valves at the inlet and outlet of the pump. Water slides are also supplied with water through pumps that use check valves.

Industrial Process

There are many fluid systems that use check valves, such as chemical and power plants.

Feedwater control, dump lines, make-up water, and other process systems, and monitoring and sampling systems are typical applications in the nuclear industry.

When high vibrations, large temperature fluctuations, and corrosive fluids are present in an aircraft or aerospace system, check valves are used.

When multiple gases are mixed in one gas stream, check valves are also commonly used. In order to prevent the mixing of gases in the source, each individual gas stream is equipped with a check valve.

Domestic Use

When sanitary water is connected to an unsanitary system, a backflow preventer, a check valve, prevents contaminated water from entering the domestic water system.

Sprinklers and drip irrigation emitters can be equipped with small check valves to prevent lines from draining when the system is turned off.

In some instances, rainwater harvesting systems that connect to a utility provider's main water supply may be required to have a check valve installed to prevent contamination of the primary water supply by rainwater.

On the lifting side of hydraulic jacks, ball check valves are used to build pressure.

FAQ about Check Valve

1. What Is a Check Valve?

The check valve is a safety valve that allows water to simply flow one way and prevents unwanted backflow of water in the other direction. It is also known as a non-return valve. The potable water supply could be contaminated if there is no check valve.

1. What Are Check Valves Used for?

Check valves prevent backflow damage to pumps and other equipment when pressure changes in the piping cause flow reversal. In addition to being used for flow control, they can also be used for line isolation, pump-priming, media injection, or maintaining head pressure.

1. Should a Check Valve Be Installed Vertically or Horizontally?

A horizontal line is always preferred when installing a check valve, since gravity is not involved.

1. Why Do You Need a Check Valve?

In pipelines, check valves are generally installed to prevent backflow. There can be water hammer if the flow turns without a check valve. Water hammer occurs with extreme force and can easily damage a pipeline or component.