Diaphragm valves (or membrane valves) consists 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. The valve is constructed from either plastic or metal.

There are two main categories of diaphragm valves: The A Type seals over a "weir" (saddle) and the KB Type (sometimes called a "full bore or straight-way" valve) seals over a seat. The A Type (Weir) is the most common in process applications and the KB Type is more commonly used in slurry applications to reduce blocking issues but exists also as a process valve.
Diaphragm valves can be manual or automated. Their application is generally as shut-off valves in process systems within the industrial, food and beverage, pharmaceutical and biotech industries.