Check Valves

What is Check Valve?

Check valves are devices that allow one-way passage of liquids. These devices, which have two ports, one of which gives the inlet of the fluid to the fluid outlet, are also called “one-way valves” or “non-return valves” in the market, as they allow the passage of the fluid in one direction. In order for check valves to work, a pressure difference is required between the fluid inlet and outlet. In order for the check valve to allow flow, the pressure at the inlet must be greater than the outlet. The check valve will close when the pressure on the outlet side is greater than the inlet pressure. Check valves have different closing mechanisms. Unlike other valves, they do not need auxiliary energies (hand control, electric or pneumatic actuators) to close.

Check valves are preferred in applications where backflow will cause problems (prevention of the return of waste sewage water, the possibility of damaging an equipment, reverse-cosmosis applications, etc.).

Another reason why check valves are preferred is that they are cheap and easily available. It is a shelf product and can generally be found in stocks.

How Does a Check Valve Work?

A check valve is a mechanical device that allows liquid (liquid or gas) to flow through it in only one direction. It consists of a valve body with a movable disc or vane attached to a hinge or stem. The disc is spring loaded or gravity dependent, so it automatically opens when fluid flows in the allowed direction and closes when fluid tries to flow in the opposite direction.

The check valve works like this:

When the fluid flows in the allowed direction, it pushes the disc and opens the valve. The disc is pulled out of the way, allowing the fluid to pass.

When the fluid flow stops or changes direction, it returns to its place, closing the disc valve.

If the fluid flow tries to go in the opposite direction, it pushes the disc and prevents the fluid from passing through, keeping the disc closed.

Check valves are used in a variety of applications to prevent backflow and protect equipment. They are often found in pipelines, plumbing systems, and irrigation systems.

What Are Check Valves Used For?

A check valve is a mechanical device that allows liquid (liquid or gas) to flow through it in only one direction. It is used to prevent backflow of liquid and is often found in systems using pumps or compressors. For example, in a plumbing system, a check valve may be installed in a pipe leading to the pump to prevent water from flowing back into the pump when the pump is turned off. A check valve may be used in a compressor to prevent air from flowing back into the compressor when the system is not in use. Check valves are also used in a variety of other applications, such as fuel systems and medical equipment.

Where Are Check Valves Used?

Check valves are used in a variety of applications and industries, including:

• Plumbing: Check valves are commonly used in plumbing systems to prevent backflow of water. For example, they can be installed in the pipes to the pumps to prevent water from flowing back into the pump when turned off.
• HVAC: Check valves are used to prevent backflow of air or other gases in heating, ventilation and air conditioning systems.
• Process control: Check valves are used in process control systems to prevent backflow of liquids or gases in pipelines.
• Fuel systems: Check valves are used in fuel systems to prevent backflow of fuel.
• Medical equipment: Check valves are used to prevent backflow of gases in medical equipment such as ventilators.
• Water treatment: Check valves are used in water treatment plants to prevent backflow of water in pipelines.
• Mining: In mining, check valves are used to prevent backflow of slurry in pipelines.
• Marine: Check valves are used in marine systems to prevent backflow of sea water in pipes.
• Aerospace: Check valves are used in aviation applications to prevent backflow of gases in fuel and hydraulic systems.

These are just a few examples, but check valves can also be found in many other industries and applications.

What are the Types of Check Valves?

There are several types of check valves, including:

• Swing Check Valve: This type of check valve has a hinged disc that swings open to allow fluid to flow through it and swings shut to prevent backflow.
• Lift Check Valve: This type of check valve has a disc that is lifted from its seat by the fluid flow and allows it to pass through. When flow stops, a spring pushes the disc back into its seat, preventing backflow.
• Ball Check Valve: This type of check valve has a ball that is pushed out of its seat by the fluid flow and allows it to pass through. When flow stops, a spring pushes the ball back into its seat, preventing backflow.
• Butterfly Check Valve: This type of check valve has a disc mounted on a shaft that is rotated by a lever to open or close the valve.
• Double Plate Check Valve: This type of check valve has two spring plates that are hinged together and open and close with fluid flow.
• Non-Return Check Valve: This type of check valve is also known as a one-way valve or check valve. It allows fluid to flow through it in only one direction and is often used to prevent backflow in systems using pumps or compressors.
• Poppet Check Valve: This type of check valve has a piston-like disc that allows fluid to be pushed through its seat by its flow. When flow stops, a spring pushes the disc back into its seat, preventing backflow.

Each type of check valve has its own unique design and features and is suitable for specific applications. The type of check valve used in a particular system will depend on factors such as the type and pressure of the fluid being conveyed, the size of the pipe and the required flow rate.

What are the Points to Consider When Choosing a Check Valve?

• Material compatibility with the environment
• Correct selection of max pressure and separation pressure
• Pipeline size for assembly
• Mounting Orientation (Horizontal or Vertical)
• Temperature
• Availability for maintenance and repair

What are the Problems and Solutions in Check Valves?

Commonly, noise, water hammer, vibration, reverse flow, abrasions, leaks can be seen. In order to eliminate these problems, it would be appropriate to make the correct selections and installations, and to choose quick-closing check valves to prevent reverse flow and water hammers. Shock fluctuations can be prevented in fast closing.

What is Separation (Cracking) Pressure?

The pressure at which the valve opening occurs is called the separation (cracking) pressure. This pressure varies according to design, size and diameter. When choosing the check valve, you must confirm that your system can create this pressure.

How Is the Check Valve Closed?

The check valve will close if the inlet pressure falls below the separation pressure or if there is a back pressure.

What are the Considerations for Check Valve Installation?

Check valve bodies have an arrow indicating the flow direction. After the assembly, the flow direction should be checked and the damages that may arise in this way should be avoided.

What are the Advantages of Wafer Type Swing Check Valves?

Spring wafer check valve offers the advantage of providing full closure as it is a spring design. This provides ease of assembly in all directions, as well as advantages such as minimum pressure loss. Sealing can be metal-to-metal as well as offers alternatives such as soft sealing. The use of different sealing (ptfe, epdm, etc.) elements provides a quiet operation.

Compact design, lightness, minimum pressure loss, ease of assembly, easy accessibility, low cost, horizontal and vertical mounting are the main advantages.