Monday, July 6, 2015

Valve Selection - When to Choose a Butterfly Valve

Industrial process control valves are available in a staggering array of materials, types, and configurations. An initial step of the selection procedure for a valve application should be choosing the valve type, thus narrowing the selection field to a more manageable level. Valve "types" are generally defined by the closing mechanism of the valve.

butterfly valve
Butterfly Valve
Courtesy Crane CPE
A butterfly valve has a disc that is positioned in the fluid flow path. It rotates around a central axis, the stem, through a 90 degree arc from a position parallel to the flow direction (open) to perpendicular (closed). A variety of materials are used in the valve body construction, and it is common to line the valve with another material to provide special properties related to the process media.

What might make a butterfly valve a beneficial selection over another valve type?

  • The closure arrangement allows for a comparatively small size and weight. This can reduce the cost, space, and support requirements for the valve assembly.
  • Generally low torque requirements for valve operation allow for manual operation, or automation with an array of electric, pneumatic, or hydraulic actuators.
  • Low pressure drop associated with the closure mechanism. The disc in the flow path is generally thin. In the fully open position, the disc presents its narrow edge to the direction of flow.
  • Quarter turn operation allows for fast valve operation from fully closed to fully open.
  • Some throttling capability is provided at partially open positions.
  • Small parts count, low maintenance requirements.
What may be some reasons to consider other valve types?
Butterfly Valve
Courtesy Crane CPE
  • Butterfly valve throttling capability is generally limited to low pressure drop applications
  • Cavitation can be a concern.
  • Some sources mention the possibility of choked flow as a concern under certain conditions.
Butterfly valves, like other valve types, have applications where they outperform. Careful consideration and consultation with a valve expert is a first step toward making a good selection.