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The development of diaphragm valve [2009-07-21]

A diaphragm valve is a shutoff or control valve with a flexible membrane, or diaphragm, which seals the valve completely or partially once the valve is engaged. Once the actuator is engaged, a stem within the valve pushes a plug or compressor against the diaphragm. The diaphragm is pushed against a raised section of the valve, creating a seal. This seal stops the flow of liquid, gas or other material through the valve. Diaphragm valves are able to seal more tightly than other types of valves due to their flexible membrane.
The diaphragm valve traces its origins back to the ancient Roman and Greek times, where it was used to control the water and temperature of the hot baths. With a crude leather diaphragm, which was manually closed over a weir, it was a primitive but effective control valve. In the early 1900s, a South African mining engineer by the name of P. K. Saunders was charged with the project to cut the costly power losses due to faulty, leaking seats and stuffing boxes of the valves used to supply air and water in the underground mines. Saunders was interested in ancient history and archaeology as a hobby, and stumbled upon the use of the control valves used in the baths. He utilized this concept to develop the first modern diaphragm valve.
Originally, the diaphragm valve was developed for use in non-hygienic applications. Later on the design was adapted for use in the bio-pharmaceutical industry by using compliant materials that can withstand sanitizing and sterilizing methods.
Diaphragm valves (or membrane valves) consists of a valve body with two or more ports, a diaphragm, and a "saddle" or seat upon which the diaphragm closes the valve. The valve is constructed from either plastic or steel.Diaphragm valves are available in two basic forms: weir type and straight through types. The weir design is best for general use applications or for tough corrosive and abrasive services. The straight through type can be used in situations where the flow direction changes within the system. They are excellent for use with sludge, slurries and other viscous fluids. Both styles provide a streamlined path for fluid flow that yields minimal pressure drop across the valve. In addition to the well known, two way shut off diaphragm valve, other types include: three way zero dead leg valve, sterile access port, block and bleed, Val bow and tank bottom valve just to name a few.
The advantages provided by diaphragm valves are many. They are extremely clean, and can form a nearly leak-proof seal for tight shut-off. The diaphragm design provides for easy maintenance and repair as it can be replaced without disturbing the piping line. However, they are limited they are limited to moderate temperature (-60 to 450°F) and pressure service (approximately 300 psi) by the mechanical properties of most common diaphragm materials. They cannot be used in multi-turn operations.
The diaphragm valves are mainly used in water treatment plants, fertilizer & petrochemicals industries, chemical industries, refineries, thermal power stations, and other process industries. Equally suited to on and off, or flow control applications, a diaphragm valve will handle positive pressures or high vacuum. Due to the wide range of material options it will handle almost all applications within its temperature and pressure ranges (175°C max. and 16 bar max.) and as such is used in almost every industry on both corrosive and abrasive applications. All working parts are isolated from the line media which enhances its reliability. Maintenance is a simple task with the body remaining in the pipe, the valve thus being field serviceable. It has linear flow characteristics which makes it well suited to throttling or modulating duties. On/off and control automation is possible with the use of modern compact actuators and accessories.

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