What is a butterfly check valve?
A butterfly check valve is a type of valve that is used to prevent reverse fluid flow in different applications. These valves employ a seating arrangement similar to that used in butterfly valves. Butterfly check valve flow characteristics are similar to the flow characteristics in butterfly valves. As such, these valves are often used in piping systems that use butterfly valves. Butterfly check valves operate automatically through the principle of pressure difference. This is the principle in which the valve disc opens when the suction pressure is more than the outlet pressure. The valve closes when the suction pressure reduces or when there is backflow or when the pump stops. The closing of a butterfly check valve helps to prevent the fluid from flowing in the reverse direction. Fluid flow in the reverse direction can contaminate the fluid especially in water supply and in food applications. Also, reverse fluid flow can cause damage to piping equipment like pumps and boilers. Butterfly check valve manufacturers produce different types of these valves for use in various industrial applications ranging from corrosive to non-corrosive, low to high pressure, and temperature. The material used by the butterfly check valve manufacturer to construct the valve dictates the area of application.
Figure: Butterfly check valve.
Construction and components of a butterfly check valve
Butterfly check valve manufacturers construct these valves with sufficient space to allow free movement of the valve disc. The valve disc consists of two plates that tilt about a hinge. This valve does not need valve spaces. The design of a butterfly check valve uses a flexible sealing member with the valve bore oriented at around 45o degrees. Such design helps to shorten the distance the disc moves from fully open to fully close which helps to reduce the slamming effect frequent in other check valves. These valves are simple in design which allows butterfly check valve manufacturers to produce them in large sizes up to around 72 inches. Some of the most common components of butterfly check valves include the following.
Valve body
This is the part of a butterfly check valve used to house internal components. The valve body is made very strong against impact damage and high pressure. Such high strength is enhanced by the use of strong metallic materials such as cast iron, ductile iron, stainless steel, and carbon steel among others. The valve body also contains the valve ports that connect the valve to the pipe.
Valve disc
This is the part of a butterfly check valve used to open fluid flow and also used to prevent reverse fluid flow. The valve disc works with help of a spring.
Spring
This is the component of the butterfly check valve which helps the valve disc to flap allowing fluid flow. The spring maintains its stretched position due to suction pressure until when the pressure reduces where it reverts back allowing the disc back to its seating position.
Seat
This is the part of a butterfly check valve placed between the valve body and the valve disc to prevent fluid leakage as well as provide the surface where the valve disc seats.
Gasket
This is the part placed between the mating faces of the valve and the pipe to enhance a tight seal free from fluid leakage.
Figure: Parts of a butterfly check valve.
How does a butterfly check valve work?
A butterfly check valve operates based on pressure differential. This is the case where the valve employs suction pressure to open and close automatically. Butterfly check valve manufacturer design these valves without actuators or handwheel. These valves open the valve disc when the suction pressure is more than the outlet fluid pressure. The suction pressure provides the energy to force the spring and disc to flap. As such, the disc creates space for the fluid to flow through the valve. The valve disc remains open and fluid flows through the butterfly check valve until a time when the pump is stopped or when there is backflow. In such an instance, the valve spring gets relieved to stretch back allowing the disc to return to its seating position.
Figure: Working of a butterfly check valve.
Types of butterfly check valves
Butterfly check valves with counterweights
As the name suggests, this is a butterfly check valve designed with a counterweight mechanism. This type of butterfly check valve enhances reliability in regulating the time needed to close the valve. This mechanism has a lever that facilitates an anti-hammer system and an oil cylinder slows down the closing movement reducing slam and noise. Butterfly check valve manufacturers use this damping system to prevent water hammer effects via reduced damping time. Butterfly check valves with counterweights open in the forward direction and close when there is backflow or suction pressure drop.
Figure: Butterfly check valve with counter weight.
Flanged end butterfly check valve
This is a butterfly check valve that is designed with flanges at the ports. The flanges have holes. The holes are used to hold bolts that connect the valve to the pipe. Also, the pipe is produced with flanged ends of the same size and holes as the butterfly check valve. Flanged end butterfly check valve manufacturers produce these valves for use in high-pressure applications since these valves can withstand high pressure due to their tight connection. The tight connection is enhanced by the use of several bolts and nuts and a gasket placed between the mating surfaces of the valve and pipe. Depending on the material used to make internal parts this valve be used in both low and high temperatures. Flanged end butterfly check valves are easy to install and disconnect from the pipe. However, these valves are heavy relative to the welded and threaded end types. The high weight arises from the use of the bolts and nuts as well as the flanged ends.
Figure: Flanged end butterfly check valve.
Threaded end butterfly check valve
This is a butterfly check valve that is connected to the pipe using threads. This type of valve comes from the butterfly check valve manufacturer with the threads having been machined. The threads are either male or female. If the butterfly check valve manufacturer produced the valve with male threads the pipe end needs to have female threads and vice versa. Threaded end butterfly check valves are used in low and medium-pressure applications. However, depending on the material used to make the valve, it can be used from low to high temperatures. This type of valve occupies less space and is light in weight relative to bolted type.
Welded end butterfly check valve
This is a butterfly check valve that is connected to the pipe using the welding method. Both the valve end and the pipe are welded together. This ensures that there is no possibility of fluid leakage through the valve-pipe connection joint. Butterfly check valve manufacturers recommend the use of this valve where frequent repair and inspection are not required. Also, such valves are used where hazardous media is transported such as oil, gas, and acids in which any slight leakage can cause huge losses. This type of valve is suitable for use in high-pressure applications since high pressure will not cause fluid leakage. However, welded end butterfly check valves cannot be repaired while in the piping system. When the valve develops a mechanical problem the weld has to be removed first. Such valves are also not meant for use in sanitary applications such as foods and pharmaceuticals because the valve has to be cleaned frequently.
Applications of butterfly check valves
Advantages of butterfly check valves
Disadvantages of butterfly check valves
Troubleshooting butterfly check valves
No fluid flows through the valve
The butterfly check valve does not close
Internal fluid leakage
External fluid leakage
Summary
A butterfly check valve is a type of check valve used in various industrial applications to prevent reverse fluid flow. This type of valve has flow characteristics similar to those of butterfly valves and thus it is often used in piping systems together with butterfly valves. This type of valve is manufactured to operate automatically by using pressure difference. The valve opens fluid flow when there is high suction pressure than the outlet pressure. The valve disc is made of two plates that flap allowing fluid flow through the valve. Once the valve is opened, fluid keeps flowing through the valve unless the pump is stopped or there is backflow. Butterfly check valve manufacturers use different types of materials to make these valves. The type of material used to make the valve determines the area of application. Butterfly check valve manufacturers produce various types of valves which include butterfly check valve with counterweights, threaded end butterfly check valves, flanged end butterfly check valves, and welded end butterfly check valves. Applications of these valves include oil and gas, chemicals, foods and beverages, wastewater treatment, boiler applications, and pharmaceuticals among others. Using a butterfly check valve is advantageous in a number of ways such as automatic operation, high efficiency, versatility, durability, free from fluid leakage, maintaining working pressure, and fast operation.
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