Butterfly Valves

What are butterfly valves?

A Butterfly valve is used to stop, control and start the flow of fluids. The handle will open or close the valve through a 90° turn. There are many different types of butterfly valves including wafer, double & triple offset and lug valves. They are used for pipeline isolation and modulation and are suitable for water applications

Butterfly Vale principle of operation

Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favoured because they cost less than other valve designs, and are lighter weight so they need less support. The disc is positioned in the centre of the pipe. A rod passes through the disc to a lever on the outside of the valve. Rotating the lever turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow, so it induces a pressure drop, even when open

A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The “butterfly” is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway

When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to throttle flow

There are different kinds of butterfly valves, each adapted for different pressures and different usage. The zero-offset butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high-performance double offset butterfly valve, used in slightly higher-pressure systems, is offset from the centre line of the disc seat and body seal (offset one), and the centre line of the bore (offset two). This creates a cam action during operation to lift the seat out of the seal resulting in less friction than is created in the zero offset design and this then decreases its tendency to wear

The valve best suited for high-pressure systems is the triple offset butterfly valve. In this valve, the disc seat contact axis is offset, which acts to virtually eliminate sliding contact between disc and seat. In the case of triple offset valves, the seat is made of metal so that it can be machined such as to achieve a bubble-tight shut-off when in contact with the disc