What does a diaphragm do in a valve?

Flow control device

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Diaphragm valves (or membrane valves) consists of a valve body with two or more ports, a flexible diaphragm, and a "weir or 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" (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 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[1] However, most non-diaphragm valves used in industrial applications are built to the ANSI/ASME B16.10 standard.[2] 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

Body lining materials

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

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:

See also

References

What are Diaphragm Valves: Description, Common Uses and Specifications

Overview

Diaphragm valves are flow control or pressure moderation plumbing valves. They are fitted with an internal diaphragm made of resistant thermoplastic materials that can be adjusted according to application demands. The innovative and adjustable design of diaphragm valves allows their internal diaphragm to be set for differing levels of flow or pressure. This in turn offers detailed control of system operation by restricting or maximizing plumbing flow rates as needed. 

Pressure relief type diaphragm valves are engineered to accommodate individual pressure maximums. When internal plumbing pressures reach these valve's set level it triggers valve operation and effectively relieves excess pressure within the system. Diaphragm valves are well suited for process systems that need precise flow control and ones that develop operation pressure or back pressure due to system fluctuations.

Application

Diaphragm valves are frequently used due to their ability to be finely tuned and the compatibility of the diaphragm material with commodity fluids. These valves are often employed within chemical synthesis and dosing operations, oil and gas injection scenarios, water and wastewater treatment, chlorination systems of large pools and waterparks, pulp and paper production, metal finishing and electro plating, healthcare, as well as food and beverage processing.

Specifications

Manufacture

Our diaphragm valves are US made by Hayward Industries. The valve bodies are manufactured from either PVC or CPVC thermoplastic materials with the option for PP or PVDF. PVC diaphragm valves are made from Cell Class PVC. CPVC diaphragm valves are made from Cell Class CPVC. Our diaphragm valves meet ASTM D design standards and receive ANSI / NSF 61 and 372 certifications for lead-free, potable water use.

Sizes

Diaphragm sizes are available from 1/4" to 6"' plumbing diameters. Full valve sizes are 1/4", 3/8", 1/2", 3/4", 1", 1-1/4", 1-1/2", 2", 2-1/2", 3", 4", and 6". Only DAB series flange type are offered standard from 2" to 6". Additional sizes to suit application needs can be provided on request.

Connections

Diaphragm valves come in FPT x threaded, flange style, or socket and threaded connection types. DAB series valves come with flange or True Union socket and thread connections. RPV and PBV valves are fitted with FPT x threaded type connections and are suitable for horizontal or vertical installation.

Seals

Socket and threaded True Union type diaphragm valves feature double EPDM material o-rings at each union port.

Diaphragm Valve Series

Diaphragm valves are offered in DAB series flow control, PBV back pressure and RPV pressure relief series models. The individual valve performance specifications will vary by series type.

DAB Series | Flow Control

DAB Series | Flow Control

DAB series diaphragm valves are also known as flow control valves. They are rated for 150 PSI (10.3 bar) @ 70˚F (21˚C) for 1/4in valves up to 5in valves and rated to 75 PSI (5.17 bar) @ 70˚F (21˚C) for 6in flanged type only. DAB models feature sure grip handwheels and high visibility, beacon position indicators for precision diaphragm control. DAB type valves can be fitted with EPDM, FPM or PTFE diaphragm materials. DAB series valves are also suitable for actuator installation.

RPV Series | Pressure Relief Valve

RPV Series | Pressure Relief Valve

The RPV series diaphragm valve is also known as a pressure relief valve. They feature PTFE/EPDM diaphragms and are rated to 250 PSI (17.2 bar) @ 70°F (21°C). RPV series valves have been engineered to protect systems from over-pressurization by retaining total pressures beneath a certain level. The valves are designed to release excess pressure build up from the relief port when internal pressures increase past the set level. This function is controlled by an adjustable diaphragm spring with an operation range between 10 to 150 PSI. The springs come set at 50 PSI and can be easily changed via the adjustment screw slot. These are Hayward pressure relief valves.

PBV Series | Back Pressure Valve

PBV Series | Back Pressure Valve

The PBV series diaphragm valves is also known as a back pressure valve. Similar to RPV models, they feature PTFE/EPDM diaphragms and are rated to 250 PSI (17.2 bar) @ 70°F (21°C). Back pressure RPV valves are anti siphon devices that promote stable fluid / dosing rates by eliminating fluctuating back pressures. RPV diaphragm valves are set to specific pressure limits. When pressures increase past the threshold, it causes the diaphragm to raise from the seat and allows fluid to flow until pressure returns. PBV diaphragm springs are preset to 50 PSI and are easily field adjusted between 10 to 150 PSI with the adjustment screw. These valves are Hayward back pressure valves. 

Diaphragm Valve Options

All diaphragm valves are also available in polypropylene (PP) or PVDF body materials. Internal diaphragm options are available in EPDM, FPM, PTFE (Teflon') or PTFE/EPDM. Valves with EPDM or PTFE diaphragms can be fitted with PVDF material vapor barriers.

Diaphragm Valves are Right for You if....

Diaphragm valves are the right choice if you need to relieve pressure in a contained process system, need to prevent the build up of back pressure, need to prevent fluid siphoning or need to control flow to an injection point. Check out PVC Pipe Supplies Diaphragm Valves for Sale.

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