Page 91 - Valve Selection Handbook
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78 Valve Selection Handbook
When this has happened, the steam begins to boil off the condensate.
If no pressure-equalizing connection is provided, the expanding steam
will force the upstream and downstream discs into more intimate contact
with their seats, and raise the pressure in the valve chamber. The magni-
tude of the developing pressure is a function of the water temperature
and the degree of filling of the valve chamber with water, and may be
obtained from Figure 3-33.
The pressure-equalizing connection may be provided by a hole in the
upstream disc or by other internal or external means. Some makers of
parallel gate valves of the types shown in Figure 3-25 and Figure 3-26
combine the bypass line with a pressure-equalizing line if the valve is
intended for steam.
Figure 3-33. Pressure in Locked Valve Chamber as a Result of the Revaporation of
Trapped Water Condensate. (Courtesy of Sempell A.G.)
