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ASME BPVC 2023 Section VI

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6.1.1 General
Pressure relief valves are used to relieve excessive pressure
generated within a boiler. The pressure relief valve
or valves is the final line of protection against overpressure
in the boiler. They discharge a volume of steam and
hot water when relieving see 6.4. This is the single most
important safety device on any boiler. These valves shall
bear the Certification Mark, as illustrated in Figure 6.1.1-1,
with HV or V designator to signify compliance with Section
IV, HG-402.
6.1.2 Safety Valves
A safety valve is an automatic pressure-relieving device
actuated by the pressure generated within the boiler and
characterized by fullopening pop action. It is used for
steam service. Valves are of the spring-loaded pop type
and are factory set and sealed. See Figure 6.1.2-1.
6.1.3 Safety Relief Valves
A safety relief valve is an automatic pressure-relieving
device actuated by the pressure generated within the
boiler. It is used primarily on water boilers. Valves of
this type are spring loaded without fullopening pop
action and have a factory-set, nonadjustable pressure
setting. See Figure 6.1.3-1.
6.1.4 Temperature and Pressure Safety Relief
A temperature and pressure safety relief valve is a
safety relief valve, as described in 6.1.3, that also incorporates
a thermal-sensing relief element that is actuated
by the upstream water temperature.
6.2.1 Safety Valve Requirements for Steam Boilers Each steam boiler shall have one or more officially
rated safety valves, identified with the Certification
Mark with HV or V designator, of the spring pop type
adjusted and sealed to discharge at a pressure not to
exceed 15 psi 100 kPa. No safety valve for a steam boiler shall be
smaller than NPS 12 DN 15.
No safety valve shall be larger than NPS 4 DN 100. The
inlet opening shall have an inside diameter equal to or
greater than the seat diameter. The minimum relieving capacity of a valve or
valves shall be governed by the capacity marking on
the boiler called for in Section IV, HG530. The minimum valve capacity in pounds per hour
kilograms per hour shall be determined by dividing the
maximum output in British thermal units per hour kilowatts

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at the boiler nozzle, obtained by the firing of any
fuel for which the unit is installed, by 1,000 0.646. The safety valve capacity for each steam boiler
shall be such that with the fuel-burning equipment
installed and operated at maximum capacity, the pressure
cannot rise more than 5 psi 35 kPa above the maximum
allowable working pressure. When operating conditions are changed, or
additional boiler heating surface is installed, the valve capacity
shall be increased, if necessary, to meet the new
conditions and to be in accordance with The additional
valves required, on account of changed conditions,
may be installed on the outlet piping, provided there is no
intervening valve.
Figure 6.1.1-1
Official Certification Mark