What is diaphragm valve and it’s Applications

Diaphragm valves (or membrane valves) consists of a valve body with two or more ports, an elastomeric diaphragm, and a “weir or saddle” or seat upon which the diaphragm closes the valve. The valve body may be constructed from plastic, metal, wood or other materials depending on the intended use.

There are two main categories of diaphragm valves: one type seals over a “weir” (saddle) and the other (sometimes called a “full bore or straight-through” valve) seals over a seat. In general, straight-through diaphragm valves are used in on-off applications and weir-type diaphragm valves are used for control or throttling applications. While diaphragm valves usually come in two-port forms (2/2-way diaphragm valve), they can also come with three ports (3/2-way diaphragm valves also called T-valves) and more (so called block-valves). When more than three ports are included, they generally require more than one diaphragm seat; however, special dual actuators can handle more ports with one membrane.

For high purity applications, the design of the basic weir-style diaphragm valve seal presents a number of issues for process engineers working in the biotechnology and pharmaceutical industry. In typical configurations, a weir in the valve body rises in a fluid path and when the valve is closed, the diaphragm meets the weir to shut off the flow. While the technology is intended to reduce turbulence and shear, weir-style valves present a number of issues, for example in upstream processing applications they can be difficult to install, prone to leaks, and increase the potential of product contamination. As such, a weirless diaphragm valve technology was developed by ASEPCO valves, part of the Watson-Marlow Fluid Technology Group.

Diaphragm valves can be manual or automated. Automated diaphragm valves may use pneumatic, hydraulic or electric actuators along with accessories such as solenoid valves, limit switches and positioners.

In addition to the well known, two way shut off or throttling diaphragm valve, other types include: Three way zero deadleg valve, sterile access port, block and bleed, valbow and tank bottom valve.

Valve body
Many di­aphragm valve body di­men­sions fol­low the Man­u­fac­tur­ers Stan­dard­iza­tion So­ci­ety MSS SP-88 How­ever, most non-di­aphragm valves used in in­dus­trial ap­pli­ca­tions are built to the ANSI/ASME B16.10 standard. stan­dard. The dif­fer­ent stan­dards makes it dif­fi­cult to use di­aphragm valves as an al­ter­na­tive to most other in­dus­trial valves. Some man­u­fac­tur­ers offer di­aphragm valves that con­form to ANSI B16.10 stan­dards thereby mak­ing these di­aphragm valves in­ter­change­able with most solid wedge, dou­ble disc, and re­silient wedge gate valves as well as short pat­tern plug and ball valves.

Actuators
Di­aphragm valves can be con­trolled by var­i­ous types of ac­tu­a­tors e.g. man­ual, pneu­matic, hy­draulic, elec­tric etc. The most com­mon di­aphragm valves use pneu­matic ac­tu­a­tors; in this type of valve, air pres­sure is ap­plied through a pilot valve into the ac­tu­a­tor which in turn raises the di­aphragm and opens the valve. This type of valve is one of the more com­mon valves used in op­er­a­tions where valve speed is a ne­ces­sity.

Hy­draulic di­aphragm valves also exist for higher pres­sure and lower speed op­er­a­tions. Many di­aphragm valves are also con­trolled man­u­ally.

Diaphragm materials
Unlined or Rubber Lined Type:
NR/Natural Rubber
NBR/Nitrile/Buna-N
EPDM
FKM/Viton
BUNA-N
SI/Silicone rubber
Leather
Fluorine Plastic Type:
FEP, with EPDM backing
PTFE, with EPDM backing
PFA, with EPDM backing

Applications
Di­aphragm Valves are ide­ally suited for:

1.Corrosive applications, where the body and diaphragm materials can be chosen for chemical compatibility. (E.G. Acids, Bases etc.)
2.Abrasive applications, where the body lining can be designed to withstand abrasion and the diaphragm can be easily replaced once worn out
3.Solids entrained liquids, since the diaphragm can seal around any entrained solids and provide positive seal
4.Slurries, since the diaphragm can seal around entrained solids and provide positive seal