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