How does a Butterfly Valve Work?

 

The butterfly valve is one of the most useful valves installed in relative service. It covers three major functions. It can start, stop and control the flow of media. This article guides you to better understand the butterfly valve by knowing how it works, understanding the different kinds of butterfly valves as well as its applications.

What is a Butterfly Valve and Its Function?

A butterfly valve is from a family of valves called quarter-turn valves. It is different from ball valve in many ways. The thin disc of the butterfly valve is perpendicular to the flow of the media. A 90-degree turn of the actuator or lever moves the disc parallel to the flow of media.

The butterfly valve allows for quick opening. It can not only control media flow but has isolation capabilities. The valve disc is made of high-grade metal with a seat made of soft elastomeric material or another metal.

This valve has a simple design, which is advantageous because it is lightweight, cost-effective and can fit in tight spaces. That valve is also well-suited for applications that handle high volume but low-pressure liquids and gases. It is also suitable for handling media with small particles.

How does a Butterfly Valve Work?
 

 

 

Before delving deeply into the butterfly valve working mechanism, you need to understand different valve parts related to its working mechanism. There are four parts that directly affect how the butterfly valve works and those are the body, seat, disc, and stem.

The body covers and protects the internal parts of the butterfly valve. The seat covers the inner edge of the walls of the valve. It can be made of metal or elastomeric materials. The disc lodges in the seat when the valve is closed.

The disc is a wafer-like device in the middle of the valve. Together with the seat, it seals off the flow of media when the butterfly valve is used for isolation. For the control of flow, the disc moves to partially open or close the valve, allowing a certain amount of fluid to pass through. The stem is what connects the disc to the lever or actuator. The force from the actuator is passed to the stem to allow the valve to open.

The butterfly valve is one of the few industrial valves that are both efficient in isolating and regulating the flow of media. Like most quarter-turn valves, the butterfly valve is also quick to open. The valve disc is attached to the stem which either pass through the disc or is at the back of the disc. The stem is attached to the handle that is either placed on top of the body or at its side.

Valve operation can be done manually, electrically or pneumatically. If the valve is electrically opened, a signal from a remote source tells the gearbox located on top of the valve body to turn the stem so the disc also moves. If the valve is pneumatically-driven, a piston is attached to the side of the body, which will provide the air pressure needed to open the valve. This type of actuation operates the quickest according to many China butterfly valve manufacturers.

To open the valve, a handle is turned a quarter-turn. Inside the valve body, the disc changes position from being perpendicular to the flow of the media to being parallel to it. The disc moves away from the seat and towards the centerline of the valve. If the valve is opened in a full quarter turn, the valve allows an almost unrestricted passage of the fluid. There is a slight pressure drop when the valve opens. 

To close the valve, make another quarter turn in the opposite direction. In this sense, the disc changes position from being parallel to the flow of the media to being perpendicular to it and the disc positions itself to the seats for an even sealing. This is the fully closed position of the disc. 

Throttling happens when the closed valve disc slightly changes position to allow media to pass through but not fully. The amount of media that can pass through is determined by the angle created by the disc in relation to the valve centerline.

Ideally, butterfly valve should be installed in the open position. If the valve was installed in its closed position, there is a good chance that the disc will wedge against the soft seat, making the opening of the valve difficult.

Different Types of Butterfly Valves

The vast applications and pressure ranges have created different kinds of butterfly valves. All in all, butterfly valves can be categorized based on the disc configuration, and the type of connection ends.

Butterfly Valves Based on the Configuration of the Disc
 

Concentric 

This is the most basic kind of butterfly valve. Sometimes called the centric valve or the zero offset butterfly valve. The stem passes through the centerline of the disc and through the center of the pipe. This kind of valve is also known as the resilient-seated butterfly valve and its sealing depends on the efficiency of the seat when the valve is closed. This kind of butterfly valve is used for low-pressure applications.

Eccentric

The stem of the eccentric type does not pass through the centerline of the valve. Rather, it is placed behind the face of the disc which is opposite of the flow direction. 

#1 Single Offset

The single offset only has the stem attached at the back of the disc. This allows the disc make less contact with the seal before the valve is fully closed, which is to ensure a longer service life of the disc.

#2 Double Offset

A double offset type has the stem located at the back of the disc. There is an offset on the other side of the disc. This further limits the contact of the disc and the seat to about 1-3 degrees. The double offset butterfly valve is suitable for the high-pressure application that need a bubble-tight seal.

#3 Triple Offset

The triple offset butterfly valve has an additional offset located at the axis of the disc and seat, apart from the ones already mentioned in the double offset design. This creates a valve with a slightly tilting disc and seat. TOVs are often used for highly critical applications. It often has a metal-to-metal seat design. Knowing the difference between double offset and triple offset valve also help to choose a better valve for your projects.

Butterfly Valves Classified according to Its Connection Ends

How the butterfly valve is connected to the pipes is also one of the ways to classify this valve.

Wafer Style 

This type is attached between two flanges using bolts that lock the entire valve body

Lug Style

This type has lugs outside of the valve body. Bolts connect the valve to the pipe system. The kind of valve is commonly low-pressure rating and is usually attached to dead-end services.

Applications of Butterfly Valves

Butterfly valves are often used for food industries, pharmaceutical and chemical industries. This valve can also be used for wastewater treatment facilities, fire protection services, and fuel handling systems. Generally speaking, the butterfly valve can handle large volumes and slurries.

Conclusion

Butterfly valves have a very simple working mechanism that is extremely advantageous to the applications it services. If you need to learn more about butterfly valves, you can contact the reputable butterfly valve manufacturer UNIQUE at any time.