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.
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.