Page 149 - Valve Selection Handbook

136 Valve Selection Handbook

Diaphragm valves share a similar advantage with pinch valves; name-
ly, a flow passage that is not obstructed by moving parts and is free of
crevices. They may, therefore, be put to uses similar to pinch valves,
including the sanitary handling of foodstuffs and Pharmaceuticals.

Weir-Type Diaphragm Valves

The weir in the flow passage is designed to reduce flexing of the
diaphragm to a minimum, while still providing a smooth and streamlined
flow passage. The flexing stress in the diaphragm is therefore minimal,
resulting in a correspondingly long diaphragm life. The short stroke of
these valves also permits the use of plastics such as PTFE for the
diaphragm, which would be too inflexible for longer strokes. The back of
such diaphragms is lined with an elastomer, which promotes a uniform
seating stress upon valve closing.

Figure 3-95. Diaphragm Valve, Weir Type,
with Double-Bonnet Assembly in Connection
with Large Valve Sizes. (Courtesy of Sounders
Valve Company limited.)

Figure 3-96. Diaphragm Valve, Weir
Type, with T-Branch. (Courtesy of
Sounders Valve Company Limited.)