Valves
DOE-HDBK-1018/2-93
TYPES OF VALVES
All elastomeric materials operate best below 150F. Some will function at higher temperatures.
Viton, for example, is noted for its excellent chemical resistance and stability at high
temperatures. However, when fabricated into a diaphragm, Viton is subject to lowered tensile
strength just as any other elastomeric material would be at elevated temperatures. Fabric
bonding strength is also lowered at elevated temperatures, and in the case of Viton, temperatures
may be reached where the bond strength could become critical.
Fluid concentrations is also a consideration for diaphragm selection. Many of the diaphragm
materials exhibit satisfactory corrosion resistance to certain corrodents up to a specific
concentration and/or temperature. The elastomer may also have a maximum temperature
limitation based on mechanical properties which could be in excess of the allowable operating
temperature depending upon its corrosion resistance. This should be checked from a corrosion
table.
Diaphragm Valve Stem Assemblies
Diaphragm valves have stems that do not rotate. The valves are available with indicating and
nonindicating stems. The indicating stem valve is identical to the nonindicating stem valve
except that a longer stem is provided to extend up through the handwheel. For the nonindicating
stem design, the handwheel rotates a stem bushing that engages the stem threads and moves the
stem up and down. As the stem moves, so does the compressor that is pinned to the stem. The
diaphragm, in turn, is secured to the compressor.
Diaphragm Valve Bonnet Assemblies
Some diaphragm valves use a quick-opening bonnet and lever operator. This bonnet is
interchangeable with the standard bonnet on conventional weir-type bodies. A 90 turn of the
lever moves the diaphragm from full open to full closed. Diaphragm valves may also be
equipped with chain wheel operators, extended stems, bevel gear operators, air operators, and
hydraulic operators.
Many diaphragm valves are used in vacuum service. Standard bonnet construction can be
employed in vacuum service through 4 inches in size. On valves 4 inches and larger, a sealed,
evacuated, bonnet should be employed. This is recommended to guard against premature
diaphragm failure.
Sealed bonnets are supplied with a seal bushing on the nonindicating types and a seal bushing
plus O-ring on the indicating types. Construction of the bonnet assembly of a diaphragm valve
is illustrated in Figure 15. This design is recommended for valves that are handling dangerous
liquids and gases. In the event of a diaphragm failure, the hazardous materials will not be
released to the atmosphere. If the materials being handled are extremely hazardous, it is
recommended that a means be provided to permit a safe disposal of the corrodents from the
bonnet.
Rev. 0
ME-04
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