Construction of a Diaphragm Valve
|Fig. A: Sketch of a weir-type of diaphragm valve in open and closed positions|
The valve body is available in two patterns: tee-pattern and angle pattern.
|Table 1: Typical Materials Used for Diaphragms|
When an actuator is required, it should be sized and tested by the valve manufacturer and furnished with the valve as an assembled unit with settings made and verified in the shop.
Types of Diaphragm Valves
Weir-Type Diaphragm Valves
Straight-Through Diaphragm Valves
|Fig. B: Straightway-type diaphragm valve|
|Fig. D: Full-bore-type diaphragm valve illustrating passage of ball-brush cleaner through valve|
The full-bore type of valve is most extensively used in the beverage industry. It permits ball-brush cleaning with either steam or caustic soda, without opening or removing the valve from the line.
Advantages of Diaphragm Valves
1. Can be used as on-off and throttling service valves.
2. Offer good chemical resistance due to variety of linings available.
3. Stem leakage is eliminated.
4. Provides bubble-tight service.
5. Does not have pockets to trap solids, slurries, and other impurities. It is suitable for slurries and viscous fluids.
6. These valves are particularly suitable for hazardous chemicals and radioactive fluids.
7. These valves do not permit contamination of flow medium, thus they are used extensively in food processing, pharmaceutical, brewing, and other applications which cannot tolerate any contamination.
Disadvantages of Diaphragm Valves
2. Working temperatures and pressures are limited by the diaphragm material. Generally the pressures are limited to 200 psi (1380 kPa) and temperatures up to 400 F (204 C).
3. The diaphragm may also limit the hydrostatic pressure.
4. The diaphragm may experience erosion when used extensively in severe throttling service containing impurities.
5. Diaphragm valves are available in limited sizes, usually NPS ¹⁄₂ to 12 (DN 15 to 300).
Typical Applications of Diaphragm Valves
2. De-mineralized water systems
3. Corrosive applications
4. Radwaste systems in nuclear facilities
5. Vacuum service
6. Food processing, pharmaceutical, and brewing systems