How far must a butterfly valve be rotated to open or close the valve?

A butterfly valve operates by using a disc that rotates on a central axis to either allow or stop the flow of fluid through a pipeline. When the valve is in the closed position, the disc is perpendicular to the flow, effectively sealing off the passage. To open the valve, the disc must be rotated from the closed position to a parallel position relative to the flow direction. This rotation is typically a quarter turn, or 90 degrees.

When the disc is turned 90 degrees, it creates a clear path for the fluid to flow, allowing for efficient and rapid opening and closing of the valve. This quarter turn mechanism is one of the key features that makes butterfly valves popular for applications that require reliable performance and compact design.

In contrast, opening or closing by half a turn or 180 degrees would not be necessary for a butterfly valve, as that would exceed the typical operational range. Similarly, 1/8 turn or 45 degrees is insufficient to fully open or close the valve, and a full turn or 360 degrees is unnecessary and inefficient for the butterfly valve's intended function. Thus, the appropriate answer regarding the degree of rotation needed to operate a butterfly valve is indeed a quarter turn or 90 degrees.