Minimum Aggregate Area
of Safety Valves:- (a) Saturated steam:- The rated discharge
capacity of safety valve which discharges saturated steam
shall be calculated using the following equation:
E = rated discharge capacity of saturated steam (kg/hr):
F = highest pressure of any safety valve mounted on the
boiler (bar absolute);
A = area (mm2)
For the ordinary lift and high lift safety valves, A is
the area of the minimum bore of the body seat. For full
lift safety valves, A is the area of discharge described
in clause (c) of regulation
292 and its value can only be obtained from the safety
C is a constant taken from the following table, appropriate
to the type of the valve or as established by tests carried
out in accordance with Appendix L:
|Type of valve
||Value of the constant C
The rated discharge capacity of a safety valve which discharge
super heated steam shall be calculated using the following
Es is the rated discharge capacity of super heated steam
E is the rated discharge capacity of saturated steam calculated
using equation 78 (kg/hr).
Ts is the degree of superheat (oC)
Equation 79 may be used to determine the rated discharge
capacity of safety valves at super-critical steam pressure.
In these cases the saturation temperature of the steam
shall be taken as 375oC.
||The total peak load
evaporation of a boiler shall be calculated on the basis
of evaporation not less than 30 kg/hr./m2 of heating surface
(exclusive of superheater and non-steaming economiser).
In the case of Waste Heat Boilers however, when the evaporation
per square metre of the heating surface is certified by
the manufacturers to be less than 30 kg., the minimum
number of safety valves required may be calculated on
the basis of the actual maximum evaporation of the boiler.