Disc Check Valve

What is a disc check valve? 

A disc check valve is a type of valve that uses a disc component to open and close fluid ensuring no fluid can flow in the reverse direction. This type of valve works based on pressure difference in which inlet pressure needs to be high enough to provide energy needed to open the valve. Disc check valve manufacturers employ different ideas to design and manufacture these valves for use in different applications with the main objective of preventing reverse fluid flow. Fluid in a piping system tends to flow backward when the pump is turned off or when suction pressure reduces. The fluid flowing backward can cause contamination for example, to fresh water meant for human consumption. Also, fluid flow in the reverse direction can cause damage to other plumping fixtures like pumps or boilers. So, a disc check valve, though it uses simple technology serves to prevent losses in different applications. There are different materials used to manufacture these valves and the properties of these materials dictate the operating pressure and temperature. Usually, disc check valve manufacturers provide a user manual with instructions about the installation, repair, and operating conditions.

Figure: Disc check valve.

How does a disc check valve work? 

A disc check valve works depending on the amount of suction pressure. When the suction pressure is high it results in sufficient energy needed to force the disc to open. When the disc opens, fluid keeps flowing until the time when inlet pressure starts reducing or when the pump turns off. When the suction pressure reduces, the fluid changes the direction of flow towards the inlet port of the valve. If the valves do not close the fluid can flow back to the piping system or to the storage tank or boiler which can result in contamination or damage. To close fluid flow, disc check valve manufacturer design these valves so that they have high sensitivity to pressure changes. This makes the valve disc close the valve preventing reverse fluid flow. 

Figure: Working of a disc check valve.

Types of disc check valves 

Spring loaded disc check valve 

This is a type of disc check valve that employs a spring to help in reverting the disc to the seating position when the valve closes. This type of valve is advantageous in that it can be installed in either vertical or horizontal orientation because it does not depend on gravitational force to close. The spring used is designed with a strength proportional to the expected fluid pressure. If the spring is very strong it would need a lot of pressure to open. The working of this disc check valve is such that the suction fluid pressure forces the spring to compress as it opens the valve. The disc is then kept open using the fluid flow pressure until when the pressure reduces. At this point, the spring stretches back to retain its length. This pulls the valve disc back to its seating position which helps to restrict any fluid from flowing backward due to low suction pressure. Two types of spring-loaded disc check valves are in-line spring-loaded and Y-shaped spring disc check valves. The difference between these two is that the in-line one has the valve spring collinear to the pipe axis while the Y-shaped type has the valve spring oriented at an angle of around 45^o degrees to the pipe axis. The Y-shaped spring-loaded disc check valve occupies more space relative to the in-line type. The Y-shaped spring loaded disc check valve also makes inspection, cleaning, and repair easy as it can be opened without disconnecting it from the pipeline. 

Figure: In-line spring-loaded disc check valve and Y-shaped spring-loaded disc check valve.

Lift disc check valve 

This is a disc check valve in which the fluid flows through the valve from the bottom of the disc. Just like other disc check valves, this valve employs high upstream pressure to lift the disc from its seat allowing space for fluid flow. When the upstream pressure reduces or the pump is turned off, the valve employs gravitational force or spring to lower the disc back to its seating position which prevents reverse fluid flow. Disc check valve manufacturer design these valves with short travel distance to attain their fully open position. Disc check valve manufacturers mostly use a guided path to ensure the disc lies exactly on the seating surface to avoid any leakage. However, the guides tend to be prone to dirt accumulation which reduces the valve’s efficiency or causes damage to the valve seat. The dirt can also make the valve disc stuck wide open allowing reverse fluid flow. Lift check valves are installed in vertical orientation making use of gravitational force when closing. 

Figure: Lift disc check valve.

Wafer disc check valve 

A wafer disc check valve is a check valve designed with a short take-out length. This valve uses two-half discs also known as plates. The plates pivot on a center post that is a hinge pin. The half-discs are held on their position using springs. The springs are also mounted on the hinge pin. Fluid pressure opens the valve by forcing the springs through the plates which cause the plate to open allowing fluid flow. Disc check valve manufacturers aim to make this valve open relative to the fluid pressure. As such, the plate’s degree of opening is directly proportional to the fluid pressure and volume of fluid that is the more the fluid the more the plates will open. One of the advantages of using a wafer check valve is that it is small in size which helps to reduce its weight. 

Figure: Wafer disc check valve.

Silent disc check valve 

This is a special type of disc check valve which is used to prevent water hammer and reverse fluid flow. Water hammer is a phenomenon that happens when a disc check valve closes abruptly. Water hammer can cause huge losses as it can impair the structural integrity of piping and other plumbing fixtures. Silent disc check valve manufacturers use a mechanism that allows the disc to start closing as soon as it senses suction pressure reduction. Silent check valve employ an in-line spring to help the disc in reverting to a seating position. Since these valves use a spring to close, they can be installed in either vertical or horizontal orientation since they do not rely on gravity to close. 

Figure: Silent disc check valve.

Factors to consider when purchasing a disc check valve 

Flow conditions 

This relates to fluid flow rate and pressure levels. For the valve disc to work well, it has to transmit the flow rate given by the disc check valve manufacturer. If the flow rate is very high, it may cause the valve to vibrate and make a lot of noise. If the operating pressure is lower than the rated valve pressure, the fluid may not be able to open the disc check valve. Also, excess fluid pressure is dangerous as it may cause fluid leakage through the valve-pipe connection or valve bonnet-body connections. 

Type of media 

Disc check valve manufacturers produce different varieties of these valves for use in different fluids. There are valves meant for use in low viscosity and those meant for use in high viscosity fluids. Other disc check valves are meant for use in corrosive media like acids in which if not used accordingly can damage the valve within a few days of usage. As such, the type of media needs to be known before purchasing the valve so that the disc check valve manufacturer or supplier can know the specific valve best for that application. 

Operating temperature 

The operating temperature of a disc check valve depends on the material used to construct that valve. Some valves have the disc or seat made of soft materials like rubber and plastic while others are made of metallic materials like steel. Soft seated disc check valves are not supposed to be used at temperatures above 60 ^oC since they cannot withstand thermal heat above this temperature. Metallic seated disc check valves work well at temperatures below or above 60 ^oC because they cannot be damaged by thermal heat. However, if the temperature goes above 200 ^oC it is important to consult a disc check valve manufacturer to advise on the best metallic seated disc check valve. This is because at temperatures above 200 ^oC some metallic materials react and can result in damage. 

Applications of disc check valves 

• Clean water supply as well as wastewater treatment. 
• They are used in food processing plants. 
• These valves are used in the manufacturing of chemicals.
• Mining applications.
• Steam applications like steam power plants to prevent steam or water backward flow. 
• Pharmaceutical applications. 

Advantages of disc check valves

• These valves have a low-pressure loss. 
• Can maintain design pressure levels. 
• Durable as they can be used for a long time without being replaced. 
• Need lubrication like plug valve. 
• Can be used in different industrial applications. 
• These valves do not have fluid leakage if used according to the disc check valve manufacturer’s instructions. 
• They operate automatically without the need for a valve operator or actuator. 
• Easy to install and repair. 

Disadvantages of disc check valves 

• These valves are not recommended for use in applications where the fluid flow has pulsations. 
• They are prone to causing water hammers. 
• They can stuck open causing damage and or contamination in the area of application. 

Troubleshooting disc check valve 

No fluid flow through disc check valve 

• Blockage inside the valve. Open the valve and remove any materials causing a blockage. Clean the valve seat, disc guide, and spring. 
• The valve was installed in the opposite direction. Remove the valve from the piping system and install it according to the instructions given by the disc check valve manufacturer. 
• The pipe connecting the valve is blocked. Inspect the pipe supplying fluid to the valve for any blockage and remove any blocking materials. 

Fluid leakage through pipe-valve connection 

• Connecting elements that are threads or bolts are loose. Tight the threads or bolts to the torque level instructed by the disc check valve manufacturer. 
• The gasket is damaged. Replace the gasket. 

Valve produces excess vibrations or noise 

• Excess fluid flow rate. Ensure the flow rate is within the range recommended by the disc check valve manufacturer. 

Internal fluid leakage

• Worn out O-rings. Replace them. 
• Foreign materials inside the valve. Remove the materials and clean the valve seat. 

Summary 

The disc check valve is a type of valve that uses a disc component to prevent reverse fluid flow. The valve operates by opening the valve disc when there is a certain amount of suction pressure and it closes when the suction pressure reduces or the pump is turned off. Disc check valve manufacturers design these valves with high sensitivity to pressure changes which makes them close immediately after there is pressure reduction.

Disc check valves operate automatically hence they do not need a handwheel or actuator for operation. Some of the disc check valves close by using gravitational force while others use the concept of spring mechanism or a combination of spring and gravity.  Factors to consider before purchasing a disc check valve are the type of media, operating temperature and flow rate, and pressure.