How Does A Butterfly Valve Work

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 seat is the primary sealing agent together with the disc. The disc lodges to the seat when the valve is in the closed position.

The disc is the thin, waferlike contraption 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, allowing a certain amount 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 MFVALVE?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 disc is attached to the stem, either through the former or the stem 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, electronically or pneumatically. If electronically 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 pneumatically-driven, a piston is attached to the side of the body. This will provide the air pressure needed to open the valve. This type of actuation operates the quickest according to many 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 the passage of the medium in full force. 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 parallel position of the disc moves to the perpendicular position and as it does, it positions itself to the seats for an even sealing. This is the fully closed position.?

Throttling happens when the closed valve disc slightly changes position to a certain degree 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,?should be installed in the open position. If the valve was installed in its closed position, there is a good chance that the soft seat will wedge against the disc, making the opening of the valve difficult.