A diaphragm valve is used as an on-off valve and to regulate flow.  It consists of a flexible diapragm which seats on the valve body forming a seal. Diaphragm valves are particularly suitable for handling corrosive, viscous fluids and slurries. The diaphragm isolates the bonnet and valve operator from the fluid being handled.

Diaphragm valves are available in the following designs :

  • Straight-through flow Design
  • Weir type design
Diaphragm Valve

The Weir type design is preferred for throttling service. The straight-through design is preferred for handling viscous fluids and slurries. The weir type valve provides tight shut-off with comparatively low operating force. The weir valve also produces only a short diaphragm movement and is less maintenance intensive compared to the straight-through design which has longer diaphragm movement and requires more maintenance. At very low flow rates weir type design has very poor flow control.

The pressure temperature limits of diaphragm valves are limited by the diaphragm material. The pressure temperature chart from manufacturer must be used to ensure that the valve is suitable for operating conditions.

Industry Codes and Standards

  • BS 5156 - Specification for diaphragm valves
  • MSS SP 61 - Pressure testing of steel valves
  • MSS SP 25 - Standard marking system for valves, fittings, flanges & unions
  • MSS SP 45 - Bypass and drain connections

Operators for Diaphragm Valves

Due to limited sizes and ratings available diaphragm valves are generally provided with handwheel or pneumatic actuators