SICCA
11
Gate valves with pressure seal therefore have to be equipped
with a body safety arrangement whenever there is a risk of
trapped liquid volumes heating up. This prevents excessive
loads on the valve body and potential deformation under all
operating conditions and thus ensures safety.
This aspect has been addressed in ASME B16.34 which
says……
ASME B 16.34 Cl 2.3.3 – Fluid Thermal Expansion. “…..
A certain circumstance in which the center cavity is filled
or partially filled with liquid and subjected to an increase in
temperature can result in an excessive buildup of pressure in
the center cavity that may lead to pressure boundary failure. An
example is a piping system in which liquid from the condensing,
cleaning, or testing fluids accumulates in the center cavity of a
closed valve. Such accumulation may result from leakage past
the upstream seat of the valve. If during subsequent start-up,
the valve is not relieved of the liquid by partial opening of the
valve or by some other method, the retained liquid may be
heated during warm-up of the system. Where such a condition
is possible, it is the responsibility of the user to provide, or
requires to provide, means in design, installation, or operation
procedure to ensure that the pressure in the valve will not
exceed that allowed by this standard for attained temperature.
In the view of above KSB has standardized pressure relief
arrangement by way of drilled hole on the upstream side disc
in the absence of customer specification. However, this makes
the Valve Uni-Directional.
The potential pressure rise depends on the
temperature and the degree to which the body is
filled and may rapidly reach unallowable values for
the body.
The problem of heat buildup of trapped liquid volumes is
particularly dangerous when the gate valve is fitted with a
pressure seal, as the cover seal will become even tighter as
the pressure rise.
On gate valve with flanged covers, unallowable pressure rises
are relieved through leaks developing at the cover gaskets.
Pressure relief arrangement may be provided either in Upstream
or down stream side based on the Service requirements.
The other pressure relieving options offered by KSB are
illustrated on page no. 10 (Identified by Execution Ref. No.
PR-01 to PR-08).
KSB advice the user to select a suitable pressure relieving
option and indicate the execution reference at the time of
ordering.
Important Note : KSB standard Valves is provided with
safety arrangement - internal relief through wedge disc
Execution Ref. No. PR-03. It is specifically stated the
valve is unidirectional.
The ‘RED DOT’ on the arrow plate indicates the location
(Upstream/Downstream) of pressure relief arrangement.
Caution plate indicating the above is tagged on the body.
Summary of Contents for SICCA GLS Series
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