A diaphragm valves consist of a valve body with two or more ports, a diaphragm, and a "weir or saddle" or seat upon which the diaphragm closes the valve. Diaphragm valves are excellent for controlling the flow of fluids containing suspended solids. A diaphragm is a flexible, pressure responsive element that transmits force to open, close or control a valve.
Diaphragm valves are available in two basic forms:
Weir Type: The weir design is best for general use applications or for tough corrosive and abrasive services. They are best used to control small flows. The body of the weir-type has a raised lip that the diaphragm comes into contact with. Weir-type valves use a smaller diaphragm because the material does not have to stretch as far.
Straight Through Type: The straight through type can be used in situations where the flow direction changes within the system. The body of this design has a flat bottom that is parallel to the flow stream. This allows the flow to move uninhibited through the valve with no major obstructions. A flexible material is required for the diaphragm so that the mechanism can reach the bottom of the valve body; this can shorten the life span of the diaphragm. They are excellent for use with sludge, slurries and other viscous fluids but they are not well suited for high temperature fluids
Method of Control
Diaphragm valves use a flexible diaphragm connected to a compressor by a stud which is moulded into the diaphragm. Instead of pinching the liner closed to provide shut-off, the diaphragm is pushed into contact with the bottom of the valve body to provide shut-off. Manual diaphragm valves are ideal for flow control by offering a variable and precise opening for controlling pressure drop through the valve. The hand wheel is turned until the desired amount of media is flowing through the system. For start and stop applications, the hand wheel is turned until the compressor either pushes the diaphragm against the bottom of the valve body to stop flow or lifts off the bottom until flow is able to pass through.