Diaphragm valve

A diaphragm valve, or membrane valve, consists of a valve body with two or more ports, a flexible diaphragm, and a weir, saddle, or seat upon which the diaphragm closes the valve. The valve body may be constructed from plastic, metal or other materials depending on the intended use.

Categories

There are two main categories of diaphragm valves: One type seals over a weir, or 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.

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 and throttling diaphragm valves, other types include the three-way zero-deadleg valve, the sterile access port, the block and bleed valve, the valbow and the 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.

Body materials

Brass Steel type: Cast Iron Ductile iron Carbon Steel Stainless Steel Alloy 20 Plastic type: ABS (Acrylonitrile butadiene styrene) PVC-U (Polyvinyl chloride, unplasticized) also known as PVCu or uPVC PVC-C (Polyvinyl chloride, post chlorinated) also known as PVCc or cPVC PP (Polypropylene) PE (Polyethylene) also known as LDPE, MDPE and HDPE (see note) PVDF (Polyvinylidene fluoride) PTFE PFA

Body lining materials

Depending on temperature, pressure and chemical resistance, one of the following is used:

Unlined type Rubber lined type: NR/Hard Rubber/Ebonite, BR/Soft rubber EPDM BUNA-N Neoprene Fluorine plastic lined type FEP PFA PO PP Tefzel KYNAR XYLON HALAR Glass Lined (Green Glass or Blue Glass)

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:

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

Markets Diaphragm valves have many applications in the following markets:

Water and Wastewater Power Pulp and Paper Chemical Cement Mining and Minerals Pharmaceutical and Bioprocessing

Diaphragm valve

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