Whenever high-purity or very corrosive media, or media containing solids in suspension, have to be conveyed and dosed in chemical processes, diaphragm valves should be the first choice, reports engineering company Omsa Valves & Instrumentation.

The greatest advantage of this valve design is that only the valve body and diaphragm come into contact with the medium. Any particles are safely held in place by the soft diaphragm and carried off when the valve is opened.

This innovation came from an engineer in the late 1920s.

The engineer was performing routine maintenance on a hose and realised that if the hose were dented, the flow of the medium would completely shut off, and if it were released, it would return to its original state without being damaged.

Based on this observation, the engineer developed a diaphragm valve. The valve consists only of three main components, namely the valve body, the diaphragm and the actuator or manual bonnet.

Usually the body is a 2/2-way body independent of the flow direction, and at its centre is a weir. The diaphragm is pushed onto the weir by a compressor which is connected to the actuator or bonnet through the valve spindle, thus closing the valve.

Correct material match
The valve body, as well as the compressor and actuator/bonnet are manufactured from cast iron, SG iron 40,3, or various stainless steels, depending on the application.

To increase the valve service life in applications with corrosive chemicals and abrasive media, bodies are lined with natural rubber and synthetic rubbers or chemically resistant plastic materials, such as polypropylene (PP), polytetrafluoroethylene (PTFE), ethylene chlorofrifluoro ethylene, paraformaldehyde (PFA), as well as glass.

Valves with thermoplastic bodies are used in special applications involving corrosive or high purity media. These bodies are mostly manufactured from PP, polyvinyl chloride, poly- vinylidene fluoride or PFA. Diaphragm materials are ethylene propylene diene monomer (EPDM), butyl, neoprene, hypalon, perbunan as well as fluoro- plastics, such as PTFE and FPM.

When designing diaphragm valves, the materials of lined or unlined valve bodies and the diaphragm must match. Only if the thermic, mechanical and chemical resistance of these materials is similar can a long service life be ensured.

Use with corrosive media
Diaphragm valves can be used in about 90% of all industrial applications.

Depending on their design, the Gem