How do Diaphragm Valves work?

Diaphragm valves constrict the flow path for fluid by pressing a flexible sheet against the border of a solid dam. Their operation is similar to pinching a flexible hose to control the flow of water through it. These valves are ideal for flows including solid particle matter, such as slurries, albeit exact throttling may be problematic due to the elasticity of the material.

Diaphragm valves (also known as membrane valves) are made up of a valve body having two or more ports, a diaphragm, and a “weir or saddle” or seat where the diaphragm closes the valve. Depending on the intended function, the valve body might be made of plastic, metal, wood, or other materials.

Diaphragm valves are divided into two types: one seal over a “weir” (saddle) and the other (also known as a “full bore or straight-way” valve) seals over a seat. The weir or saddle type is the most frequent in-process applications, while the seat type is more commonly employed in slurry applications to prevent blocking, but it can also be used as a process valve.

While most diaphragm valves have two ports (2/2-way diaphragm valve), they can also have three ports (3/2-way diaphragm valves, often known as T-valves) and other configurations (so-called block-valves). When there are more than three ports, more than one diaphragm seat is usually required; however, special dual actuators may handle more ports with just one membrane.

A diaphragm valve controlled by an electric motor is shown in this shot, which is used to control the flow of treated sewage:

The external shape of the valve body reveals the “dam” structure against which the flexible diaphragm is forced to establish a leak-tight seal when closed in the following photograph:

Pneumatically operated diaphragm valves use pressurized air on one side of the diaphragm to press it against the dam (on the other side) to close the valve.

The following illustration shows a small air-actuated diaphragm valve controlling water flow through a 1-inch pipe:

An electronic solenoid valve provides the actuating air for this particular diaphragm valve. In this photo, the solenoid valve has a brass body and a green-painted solenoid coil.

Advantages of Diaphragm Valves

• Throttling can also be done with diaphragm valves.
  Because of the huge shutdown region along with the seat, it has throttling characteristics similar to a quick opening valve.
• To manage minor flows, a weir-type diaphragm valve is available.
• Diaphragm valves are ideal for handling caustic fluids, fibrous slurries, radioactive fluids, and other fluids that must be redirected.
• A diaphragm valve’s functioning mechanism is not exposed to the media in the pipeline. Fluids that are sticky or viscous cannot enter the bonnet and obstruct the functioning mechanism.
• Many fluids that would clog, corrode, or gum up the functioning portions of most other types of valves pass through a diaphragm valve without issue. The lubricants employed in the operating mechanism, on the other hand, must not contaminate the fluid being handled.
• There are no packing glands to maintain, and there is no risk of valve stem leaking.

Disadvantages of Diaphragm Valves

• The valve transition has been set, stopping the pipeline from discharging completely.
• Depending on the diaphragm material, the operating temperature and pressure have restrictions. Typically, they are employed at a pressure of 200 psi (14 bar) at a temperature of 204 degrees Fahrenheit.
• The diaphragm can only withstand a certain amount of hydrostatic pressure.
• Diaphragm valves come in a variety of sizes. They are available in sizes ranging from DN15 to DN300.