How Do Butterfly Valves Work?

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Butterfly valves are one of the most utilised valves available in today’s market because they’re low cost, quick to operate and easy to install. The butterfly valve is a quarter-turn rotational motion valve, similar to a ball valve. It operates by rotating a circular disc through an external handle to stop, regulate and start fluid flow. In this article, we explain what a butterfly valve is, its main components and answer, “how do butterfly valves work?”.

What is a butterfly valve?

Butterfly valves have a short circular shaped body that is available in either Wafer, Lug or Double Flange configurations. A thin circular disc sits inside the body and is connected to a stem which projects through the body. This allows the disc to be rotated through an external handle or operating mechanism. The disc sits flush in the valve seat, perpendicular to the flow, when the valve is closed, stopping the fluid flow. When the disc is rotated by turning the external handle, it opens allowing flow to pass through the valve. The design of the butterfly valve allows the disc to be positioned between the fully open and closed positions to control the flow of the fluid to the desired volume and velocity.

The short body design of the butterfly valve provides the benefits of fitting into tight spaces, being lightweight and subsequently cost-effective. It’s popular because of its isolation capabilities and the ability to be opened and closed quickly. Butterfly valves suit applications that are required to handle high flow rates at relatively low-pressures and fluids with small particles.

How do butterfly valves work?

Before we can answer “how do butterfly valves work?” we need to identify the main components of their construction.

Butterfly valve components

Here are the main components used in all butterfly valves:

  • The body connects the two sections of the pipe and protects the internal parts of the valve.
  • The seat is located on the inside diameter periphery of the body and seals the disc. The most common type of butterfly is the ‘concentric’ type where the seat is manufactured from an elastomeric material that fully envelopes the internal surfaces of the body. 
  • The disc is a thin circular piece of metal that sits in the middle of the valve.
  • The stem connects the disc to an exterior handle and is responsible for turning the disc.

Working principle

So now we know the main components that make up the valve, but how do butterfly valves work? The disc is responsible for the main functionality. The disc sits flush in the seat to isolate fluids in the pipe. When opened, the disc turns away from the seat and towards the centerline of the adjacent piping so that fluid can flow through. The disc is connected to an external handle by the stem. When an operator turns the handle, they are operating the valve by turning the stem, and therefore the disc.

Valve operation can be performed manually, pneumatically or electrically, depending on the size and type of butterfly valve, and the specific application requirements.

Smaller size manually operated valves incorporate a notched locking plate. This means the handle can be suitably positioned between the fully open and closed positions to control the required flow rate through the valve. For larger manually operated valves, the stem and disc are rotated through a worm type gearbox and handwheel. The gearbox is sized and selected to ensure that only reasonable effort is required by the operator to open and close the valve regardless of the valve’s size and operating pressure. 

When fitted with a pneumatic actuator, electronic switch mechanisms provide the air pressure needed to open and close the valve. Pneumatic actuators can be of the double acting type where air is used to both open and close the valve. They are also available with an internal spring that will automatically open or close the valve should a loss of air pressure to the pneumatic actuator occur.

The fitting of an actuator automates the operation of the valve so that it can be opened and closed from a remote control room.

Final thoughts

Butterfly valves are robust, cost-effective and easy to use valve for the isolation and control of fluid flow. They can include pneumatic and electrical actuators to assist in opening and closing the valve for more demanding applications. The large range of applications that butterfly valves are suited for makes them a common choice for many industrial applications. Ready to find the right butterfly valve for your system? John Valves can help.

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