Fisher high performance butterfly valves are used in throttling applications requiring large flow capacities and small installed footprints.
Butterfly valves are a type of rotary valve that use a rotating disk to control flow through a pipe. The disk is generally operable through 90 degrees and provides a linear flow characteristic. For throttling control applications, one type of butterfly valve is now the industry standard: high performance butterfly valves (HPBVs) or double offset valves. Their advantages include a straight-through flow path, very high capacity, and ability to pass solids and viscous media.
High performance butterfly control valves are intended for general service applications not requiring precision throttling control.
They are frequently used in applications requiring large sizes and high temperatures due to their lower cost relative to other styles of control valves. Care is required in sizing and applying this style of valve to eliminate control problems associated with process load changes. They work quite well for constant process load applications. Designs using characterized contour are able to expand the control range to that of a segmented ball valve.
Available end connection styles include wafer, lugged, and double flange.
The double offset design swings the disk away from the valve seal immediately after opening, which helps reduce friction and seal wear to promote better control and seal life.
The control range for high performance butterfly valves is approximately 30 to 50% open, one third as large as ball or globe style valves.
Recently, butterfly valves became available that have contoured disks that provide an inherent equal percentage flow characteristic, which gives a linear installed characteristic.
A butterfly valve of this design delivers provides good control with an acceptable gain of 0.5 to 2.0 from about 10% open to 70%, a control range improvement of nearly threefold when compared to a typical HPBV of the same size. This expanded control range is equal to that of a segmented ball valve or globe valve.
