Diaphragm Control Valve
Industries such as food and chemical processing, biopharmaceutical, medical, petrochemical, irrigation, refrigeration, heating and cooling, pula and paper, mining and energy production rely on the adjustable precision capabilities of diaphragm control valves for day to day operations. While other configurations are widely available, diaphragm valves provide many additional benefits such as easy maintenance and replacement as well as a near leak proof seal because the elastomeric diaphragm compresses when in contact with the adjacent valve wall. As process streams are extremely variable, however, it is important to select chemically compatible materials for valve components as failure to do so could lead to contaminated materials and valve failure. To avoid such costly and potentially dangerous malfunctions, a number of materials are used in the construction of diaphragm control valves. Metals such as stainless steel, copper, brass, iron and aluminum are commonly cast, extruded or die cut into valve body components, though plastics such as PVC and polypropylene may also be used. The diaphragm is any of various polymers that have the elastic properties of natural rubber. Examples include polyethylene, polycarbonate, polystyrene and PVC which can be wound, cast, molded or extruded to the exact thickness needed for the valve. The materials must be compatible with the process stream, as well as impermeable.
In addition to material concerns, manufacturers should consider several other specifications include maximum operating temperatures, pressure ratings, valve flow coefficient, and overall size and diameter. Each of these aspects can vary considerably, but are integral to the success and functionality of a diaphragm control valve. Unlike diaphragm check valves, control models require an activation device. Hydraulic, electrical, manual and pneumatic systems are widely available. The general operation of each is the same. The valve body, a cylindrical element is installed in the pipeline or cistern. One wall is slightly raised towards the opposite wall where the diaphragm is located. When engaged, one of the aforementioned actuating devices presses down upon the diaphragm causing it to stretch until it meets the desired depth. In shut-off applications it extends fully to make contact with the raised wall and completely block the path of the process stream. In regulatory applications it may be only partially extended to decrease flow rates or increase pressure. To open the valve the pressure need only be removed and the elastic membrane will return to its original position. Often diaphragm control valves are computer programmed to automatically start, stop or modify process stream flow rates and pressures. Manufacturers can provide helpful insight into the proper diaphragm valve for a specific application and should be consulted in cases of uncertainty to ensure workplace and equipment security.
