Data Sheet

Bulletin 71.2:92B
8
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Installation of the Type 92B is dependent on the
application. As a minimum, a typical steam pressure
reducing station must include a 3-valve bypass, inlet drip
leg, inlet strainer (and steam separator if required) and
relief valve per ASME Section VIII code. A safety override
pressure reducing station can be installed in the event
a relief valve is not practical as per ASME B16.122.14
standards, subject to local codes and regulations.
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The Type 92B regulators are intended to be installed
with their diaphragm case above the pipeline so that
condensate will not collect in the cases. In order to
obtain the performance given in this bulletin, connect
the downstream end of the control line into a straight
run of pipe. The connection should be located at
least 6 pipe diameters from the valve body outlet in
an unswaged pipeline or 10 pipe diameters from the
swage in a swaged pipeline.
The Type 92B pilot should also be installed with the
adjusting screw pointing up and the control line should
be sloped with a downward pitch to ensure drainage of
condensate. The body should be installed so the flow
is in the same direction as the arrow on the body.
Note that the Type 92B pilot may be installed on either
side of the body.
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Overpressure protection is required when piping
and components downstream of a steam regulating
valve have a maximum allowable working pressure
(MAWP) that is lower than the upstream supply
pressure to the regulating valve. In some cases,
the regulating valve itself may have a lower outlet
pressure rating than its inlet pressure rating, which
will require overpressure protection.
Governing codes and standards dene the type
and design of overpressure protection. When full
flow relief valves are specied, they must relieve a
maximum specied flow at a pressure not to exceed
that specied by applicable codes. In North America,
the governing code for most steam regulating valve
installations is ASME Boiler Code, Section VIII, which
may be amended by local codes or variances.
The issue in sizing stream relief valves is quantifying
its maximum flow rate. Maximum flow conditions may
occur under many conditions, so the entire steam
system must be analyzed to make sure the maximum
relief valve flow is accurate. Failure to do so may
cause overpressure.
In applications where it is determined that the steam
regulating valve creates maximum flow to the relief
valve, several issues must be resolved prior to
quantifying the flow to the relief valve.
1. There must be general agreement on the failure
mode of the regulating valve. The Emerson
Process Management Regulator Technologies,
Inc. (Emerson™) provides wide-open regulating
coefcients to assist with sizing steam relief
valves. The coefcients assume that the valve
plug is at maximum travel and still in its normal
orientation. Contact your local Sales Ofce prior
to relief valve sizing in the event that there is
disagreement with the mode of failure.
2. Maximum steam flow must be calculated at the
pressure obtained at the relief valve’s full-open
condition. This pressure is typically larger than a
relief valve’s set pressure. This pressure must be
used as the outlet pressure of the steam regulating
valve when calculating the maximum flow through
the regulating valve.
3. Maximum steam flow should be calculated from
the manufacturer’s recommended procedure. The
Emerson recommends using either the Fisher
®
steam sizing equation or IEC sizing procedure.