Diaphragm Valve

Diaphragm Valves

Diaphragm Valves

Diaphragm Valves use a ‘pinching’ method to stop the valve flow using a flexible diaphragm. They are available in two types: weir and straight-way. The most commonly seen of the two is the weir-type. This is because the straight-way type requires additional stretching of the diaphragm, which can shorten the diaphragm’s life-span.

One of the major advantages of using diaphragm valves is that the valve components can be isolated from the process fluid. Similarly, this construction helps prevent leakage of the fluid without the use of a gland seal (packing) as seen in other types of valves.

On the other hand, the diaphragm becomes worn more easily and regular maintenance is necessary if the valve is used on a regular basis. These types of valves are generally not suited for very high-temperature fluids and are mainly used on liquid systems.

Diaphragm valves are used on shut-off and throttling service for liquids, slurries and vacuum/gas.

The seal is achieved by a flexible membrane, usually elastomer, and possibly reinforced with a metal part. The membrane is tensed by the effect of a stem/compressor with linear movement until contact is made against the seal of the body.

The operating parts of the diaphragm valve are isolated from the flow. This makes this valve suitable for viscous flows and also hazardous, abrasive and corrosive flows as its sealing system avoids any contamination towards or from the environment.

Diaphragm valves are available in a wide variety of metals, solid plastics, plastic, rubber and glass linings. They are well suited to the handling of multiple chemical applications both clear fluids as well as slurries.

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The diaphragm valve has an extended use for applications at low pressures and slurry fluid where most other kinds of valves corrode or become obstructed.

There are two types of diaphragm valves:

1- Weir

  • The Weir Diaphragm valve can be used for either off/on and throttling services

 

 

 

 

2-Straightway

  • named also Straight-Thru is only used for on/off services.

Advantages of Diaphragm Valve

  • Can be used as on-off and throttling service valves.
  • Offer good chemical resistance due to a variety of linings available.
  • Stem leakage is eliminated.
  • Provides bubble-tight service.
  • Does not have pockets to trap solids, slurries, and other impurities. It is suitable for slurries and viscous fluids.
  • These valves are particularly suitable for hazardous chemicals and radioactive fluids.
  • These valves do not permit contamination of flow medium, thus they are used extensively in food processing, pharmaceutical, brewing, and other applications which cannot tolerate any contamination.

Disadvantages of Diaphragm Valve

  • The weir may prevent full drainage of piping.
  • Working temperatures and pressures are limited by the diaphragm material. Generally, the pressures are limited to 200 psi (1380 kPa) and temperatures up to 400 F (204 C).
  • The diaphragm may also limit the hydrostatic pressure.
  • The diaphragm may experience erosion when used extensively in severe throttling service containing impurities.
  • Diaphragm valves are available in limited sizes, usually NPS ¹⁄₂ to 12 (DN 15 to 300).

Typical Application of Diaphragm Valves

  • Clean or dirty water and air service applications
  • De-mineralized water systems
  • Corrosive applications
  • Radwaste systems in nuclear facilities
  • Vacuum service
  • Food processing, pharmaceutical, and brewing systems
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