Diaphragm Check Valve
Water treatment, petrochemical, food and chemical processing, power generation, medical and plumbing industries are all highly reliant on diaphragm check valves, which prevent flooding, pressure surges and cross contamination. Unlike hydraulic, electric, manual or even
pneumatic diaphragm valves, this particular type of
diaphragm valve operates entirely off of the pressure flows of the process streams and therefore requires no external activation or actuation device. As with other check valve styles, this makes for easy installation into pre-existing pipelines and cisterns. The function is equally easy. The valve body is placed in the tubing where needed, dividing the plumbing into an upstream portion before the valve and a downstream portion behind it. In the cross section of the body is what is known as the seat, a ring that extends inward toward the centerline of the pipe, but does not fully close. A diaphragm or membrane is located downstream from the seat with a spring or rod just behind it. When the valve is closed, the rod or spring pushes the membrane into the seat creating an hermetic seal. An influx of pressure moving downstream pushes the diaphragm back from the seat creating a gap through which process liquids, gases and slurries may flow freely downstream. When this pressure subsides, or if reverse flow occurs, the diaphragm is pushed back into place closing the valve and preventing the possibility of backflow.
A number of different materials may be used in the construction of a diaphragm check valve. Often the chemical composition determines the necessary materials used. Because process streams can include anything from water to toxic waste, durable materials are most often required. Metals such as stainless steel, copper, brass, iron and aluminum are commonly extruded or cast to form the main cavity of the valve, though plastics such as PVC and polypropylene are also used. These same materials are commonly cold rolled to form the supportive rod as well. The diaphragm itself is an elastomer or rubber film. Plastics such as polyethylene, polycarbonate, polystyrene and PVC among others can be wound, cast or extruded into precise thickness for use in diaphragm check valves, though molding and blown extrusion are the most commonly used techniques. These materials must be compatible with the process stream, but also have small enough pores to prohibit any materials from permeating the valve. Additional considerations for diaphragm check valves are similar to all other check valves and include maximum operating temperature ratings, valve flow coefficient, overall size and diameter, pressure rating and cracking pressure, or the minimum pressure that will operate or open the valve. Manufacturers can provide helpful insight into the proper diaphragm check valve for a specific application and should be consulted in cases of uncertainty.
