Monday, September 3, 2012

Diaphragm Valve How it Works

what is a diaphragm valve

A diaphragm valve is a linear motion valve that is used to start, regulate, and stop fluid flow. The name is derived from its flexible disk, which mates with a seat located in the open area at the top of the valve body to form a seal.

Construction & Working Principle of Diaphragm valve

Working Principle of Diaphragm valves are, in fact, simple "pinch clamp" valves. A resilient, flexible diaphragm is connected to a compressor by a stud molded into the diaphragm. In valve diaphragm ,the compressor is moved up and down by the valve stem. Hence, the diaphragm lifts when the compressor is raised. As the compressor is lowered, the diaphragm is pressed against the contoured bottom in the straight through valve or the body weir in the weir-type.A straight through type diaphragm valve is shown below.
Diaphragm valve
Straight through type Diaphragm Valve
The weir-type diaphragm control valve is the better throttling valve but has a limited range. It uses a two-piece compressor component. Instead of the entire diaphragm lifting off the weir when the valve is opened, the first increments of stem travel raise an inner compressor component that causes only the central part of the diaphragm to lift. This creates a relatively small opening through the center of the valve. After the inner compressor is completely open, the outer compressor component is raised along with the inner compressor and the remainder of the throttling is similar to the throttling that takes place in a conventional valve.A weir type diaphragm valve is shown below.Diaphragm type valve has stem that does not rotate.
Diaphragm valve
Weir type Diaphragm Valve.
Some diaphragm valves use a quick-opening bonnet and lever operator. A 90° turn of the lever moves the diaphragm from full open to full close position of valve. Diaphragm valves may also be equipped with chain wheel operators, extended stems, bevel gear operators, air operators, and hydraulic operators.

Flexible Diaphragm material

There is a wide choice of available diaphragm materials. Diaphragm life depends upon the nature of the material handled,temperature, pressure, and frequency of operation.Some examples of diaphragm materials are rubber and elastomeric materials. Many of the diaphragm materials exhibit satisfactory corrosion resistance to certain corrodents up to a specific concentration and/or temperature. 

Advantages of Diaphragm Valve
  • Diaphragm valves can also be used for throttling service. Its throttling characteristics are essentially those of a quick opening valve because of the large shutoff area along the seat.
  • A weir-type diaphragm valve is available to control small flows.
  • Diaphragm valves are particularly suited for the handling of corrosive fluids, fibrous slurries, radioactive fluids, or other fluids that must remain free from contamination.
  • The operating mechanism of a diaphragm valve is not exposed to the media within the pipeline. Sticky or viscous fluids cannot get into the bonnet to interfere with the operating mechanism.
  • Many fluids that would clog , corrode, or gum up the working parts of most other types of valves will pass through a diaphragm valve without causing problems. Conversely, lubricants used for the operating mechanism cannot be allowed to contaminate the fluid being handled.
  • There are no packing glands to maintain and no possibility of stem leakage in valves.
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