Sanitary diaphragm valves are carefully regulated to ensure clean processing of materials in industries such as dairy, food and chemical processing, medical, pharmaceutical, agricultural, brewing, beverage production, cosmetics, semiconductor and bio-processing. The Food and Drug Administration (FDA) is one of several regulatory bodies that require many of these applications to employ valves which are drainable, cleanable and able to be sterilized.
Diaphragm valves offer each of these features in addition to being one of the most leak resistant valve models available. Zero static valves are often employed with sanitary applications as well to eliminate dead space, or valve recesses in which materials may accumulate and stagnate leading to potentially damaging and dangerous bacterial growth and contamination. Although seat valves can be sanitized, weir valves are more often used in hygienic valve applications as they ensure minimal product contact of surfaces, reduced hold-up volume and minimal entrapment areas.
The basic operating process of a diaphragm valve is fairly simple. The body of the valve, a cylindrical or spherical device is attached to the necessary pipeline or cistern. This component houses the actuating device and any connected hardware. Pneumatic, hydraulic, electrical and manual actuation may be used and so specific designs may vary significantly. The diaphragm is located in the center of the body, but in normal position is flush against the wall so as not to impede flow.
When the membrane is engaged, however, the diaphragm is stretched toward the opposite surface of the body to a specific depth. To completely halt the process stream, the membrane must cover the entire diameter, while slowing the flow means only extending the diaphragm partially. When the actuator relieves the pressure the diaphragm returns to its relaxed position and maximum flow resumes. As the diaphragm and the body of the valve come into contact with the process flow, they must be made of sterile materials in order for the valve to qualify as a sanitary diaphragm valve.
Common materials for each include stainless steel, copper, bronze, cast iron, PVC and CPVC among others. Forged, molded or die cast, each component is designed to prevent any foreign matter from collecting in the interior recesses of the valve. While the valve exterior is not strictly regulated, the internal surface which encounters the sterile materials should be smooth with no burrs that might dislodge in the process stream. Additional considerations for sanitary diaphragm valves include chemical resistance, clean room assembly, operational temperatures and pressures, diameter and overall dimensions.