A butterfly valve is a valve that isolates or regulates the flow of
a fluid. The closing mechanism is a disk that rotates.
Operation is similar to that of a ball valve, which allows for
quick shut off. Butterfly valves are generally favored because they
cost less than other valve design, and are lighter weight so they
need less support. The disc is positioned in the center of the
pipe. A rod passes through the disc to an actuator on the outside
of the valve. Rotating the actuator 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
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 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.
Wafer type Butterfly Valve
Face to Face:
ISO 5752;API 609;DIN 3202
ISO 7005-2 PN10/PN16;ASME B16.1;DIN 2501PN10/16;
2.Main Parts and Materials