Flapper Check Valve

What is a flapper check valve? 

This is a check valve that uses a tilting disk to open and close the fluid flow. The fluid flows from the inlet through the disk and leaves the valve through the outlet valve. The disk is fixed at one end and the other end is free. The fluid pressure forces the free end making the disk open allowing fluid flow. Flapper check valve manufacturers employ gravity or spring force to close the valve when fluid pressure starts reducing. The vertical plane and the seat are oriented at a seating angle of between 0^o to 45^o degrees. Flapper check valves are automatic and hence they do not need control mechanisms like an actuator or handwheel. Flapper check valve manufacturers produce different varieties of these valves targeting different pressure and temperature levels. Other flapper check valves are suitable for corrosive applications like controlling the flow of acids. The materials used to make the valve determines the best application. Flapper check valve manufacturers provide a user manual regarding the installation and application of the valve. 

Figure: Flapper check valve.

Components of a flapper check valve 

Valve body 

The valve body is one of the external parts of a flapper check valve. This part is responsible for housing internal parts of the valve. Flapper check valve manufacturer constructs the valve body using strong metallic materials like steel, ductile, and cast iron. These strong metallic materials are meant to help transfer their high strength to the flapper check valve so that it can be able to withstand high pressure, and temperature and be resistant to impact damage from falling objects. 

Valve bonnet 

This is another external part of a flapper check valve. This part is placed on top of the valve body. The body and bonnet are connected using bolts and nuts or screws to help in enhancing a strong connection free from leakage. The body and bonnet are made of the same material to ensure one part does not break when the bolts are tightened. The bonnet is also meant to complete the valve body as well as serve as a pressure barrier. 

Disk 

The disk is the component used to open and close the valve to allow and block fluid flow respectively. The disk has one end pivoted and the other end is free. The free end is where the fluid presses to open the valve. 

Seat 

This is part of a flapper check valve where disc seats to close the valve. The seat also helps to prevent fluid leakage between the disc and the interior of the body. The seat is a very important component is it determines the operating temperature of the flapper check valve based on the material of construction.

Spring

Flapper check valve manufacturers also design some of these valves with springs. The spring is used to help in reverting the disc to its seating position once suction fluid pressure reduces. 

Figure: Components of a flapper check valve.

How does a flapper check valve work? 

A flapper check valve employs the differential pressure principle. This is where the valve disk opens based on the suction pressure level. The inlet pressure needs to be high to provide enough force needed to force the disc wide open. The suction pressure is provided by the pump. Once the valve opens, the fluid keeps flowing through the flapper check valve until when the pump pressure starts reducing. At the moment the fluid pressure reduces or the pump is stopped, the valve disc reverts to the seating position where it ensures no reverse fluid flow. Backward fluid flow can cause damage to the piping equipment like pumps or boilers as well as cause contamination to fluids like water and beverages. 

Figure: Working of a flapper check valve.

Types of flapper check valves 

Straight flapper check valve 

This is a flapper check valve with a circular disk and hinge pin where the disk flaps to open and close the fluid flow. The straight flapper check valve is mounted in horizontal orientation. The fluid flows from the inlet through the disk to the outlet port until when the suction pressure reduces making the disk return to its closing position. Straight flapper check valve manufacturer design this valve with a seat ring to help the disk rest on it when it closes enhancing a tight and uniform seal. The seating surface is oriented at a slight angle so that it can open at low pressure, create a positive seal and reduce valve shock when it closes. 

Figure: Straight flapper check valve.

Tilting disk flapper check valve 

This is a flapper check valve designed with a disk-like closing element. This disc flaps about a pivot between the edge and center of the disk. The flapper check valve is designed such that the disk can lift from the seat when the tilting disc check valve opens and it can drop into the seat when it closes. These valves operate very fast relative to other valves because the disk center of gravity has a short path between the open and closed states. These valves are more difficult to repair and expensive relative to the straight type. Flapper check valve manufacturers recommended these valves for use in areas where other flapper check valves cannot be used. 

Figure: Tilting disk flapper check valve.

Y-shaped flapper check valve 

This is a flapper check valve designed with a Y shape to make it easy to access and inspect internal parts of the valve without disconnecting the valve from the pipe. Despite this valve having a Y-shape, fluid flows through the valve straight similar to how it flows through the straight flapper check valve. The part of the valve with an opening where the valve is opened for inspection is oriented at an angle of around 45^o degrees to the pipe axis. The top part of this oblique part is connected using either bolts or threads. The inspection of the internal valve parts is done by opening this part. The Y-shaped flapper check valve occupies a larger space relative to other valves. 

Figure: Y-shaped flapper check valve.

Flanged end flapper check valve 

This is a flapper check valve manufactured with flanges at the ends. The flanges are meant to help connect the valve with the pipe. The flanges are at both ports of the valve and they have holes. These valves are connected to the pipes using bolts and nuts. The end of the pipe connected to the flanged end flapper check valve needs to have a flange with holes. Between the flanges of the pipe and the flanged check valve is a gasket used to enhance a tight seal free from leakage. Flanged end flapper check valve manufacturers recommend these valves for use in high-pressure applications because their connections are very tight due to the number of bolts and nuts used as well as the gasket. Because of the bolts and nuts as well as flanged ends used in these valves, they end up being heavy relative to other valves. 

Figure: Flanged end flapper check valve.

Threaded end flapper check valve 

This is a flapper check valve that is connected to the pipe using threads. Flapper check valve manufacturers produce this valve with male or female threads. The pipe end to be connected to the valve also has threads. If the threaded end flapper checks valve female threads then the pipe ought to have male threads and vice versa. Threaded end flapper check valves are smaller in size relative to the flanged end types. Also, these valves are light in weight compared to the flanged ones. Threaded end flapper check valve manufacturers recommend these valves for use in medium pressure applications. However, depending on the internal materials used on parts like disc and seat, the valve can be used for both low to high-temperature applications. 

Figure: Threaded end flapper check valve

Applications of flapper check valves 

• Used in sewage and wastewater treatment. 
• They are used in household and commercial fresh water supply systems. 
• Firefighting applications. 
• Foods processing plants. 
• These valves are used in the manufacturing of different types of chemicals. 
• Pharmaceutical applications. 
• Open and close fluid flow in steam power generation plants. 
• Boiler systems to control the flow of steam and feed water. 
• They are used in mining applications.

Advantages of flapper check valves 

• They are automatically operated by employing pressure differences to open and close. As such, they help to cut down the cost of having valve actuator or valve operator. 
• Used in different industrial applications making them one of the most versatile industrial valves. 
• Durable considering they can be repaired for reuse when they break down. 
• Free from fluid leakage making them suitable for use in hazardous fluids like acids. 
• They do not need lubrication. 
• It can maintain the required pressure level in their areas of application. 
• These valves have low-pressure drop which assists in enhancing pumping efficiency. 
• Made of different materials suitable for use in either low or high-temperature applications. 
• Operate faster relative to other valves like globe valve or gate valves. 
• Do not allow reverse fluid flow. 
• Easy to install and repair.

Disadvantages of flapper check valve 

• Prone to water hammer. 
• Flapper check valve manufacturers do not recommend these valves for use where there is pulsating fluid flow. 
• Cannot allow fluid flow in both directions. 

Troubleshooting flapper check valves 

Fluid leakage through the valve connections 

• Damaged gasket. Replace the gasket. 
• Worn out O-rings. Replace the O-rings. 
• Loose bolts or threads. Tighten the bolts or screws to the torque level recommended by the flapper check valve manufacturer. 

No fluid flow through the flapper check valve 

• The pipe feeding the flapper check valve is blocked. Check the pipe and remove any materials causing blockage. 
• The flapper check valve is clogged and closed. Open the valve and remove any material causing a blockage. 
• The suction pressure is low. Increase suction pressure. 
• Downstream valve is closed. Ensure downstream valve is open. 
• The valve was installed in the wrong direction. Install the valve according to the flow direction given by the flapper check valve manufacturer. This arrow is indicated on the valve and on the user manual. 

The flapper check valve does not close 

• Debris has stuck the disc wide open. Open the valve and remove any material making the valve open. 

Summary 

The flapper check valve is a type of valve that uses a disc that “flaps” at a certain angle to open and close the fluid flow. These valves are used in different industrial applications without a valve actuator or valve operator since they operate automatically using pressure difference. When the suction pressure is high enough it forces the free end of the valve disk to open. Because the disc is pivoted at one end using a pin, the free end needs some slight force for the fluid to pass through the valve.

Flapper check valve manufacturers produce these valves for use in different levels of temperature and pressure. There are valves meant for use in low and those for use in high temperatures. If the valve is used according to the flapper check valve manufacturer’s instructions it lasts longer and has low maintenance costs.