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Reg. 294, Reg. 295, Reg.
296
Over pressure of Safety Valves
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| The safety valves
shall be so designed that they attain rated discharge
capacity with the over pressure not greater than that
given in regulation
292; provided that the safety valves which have a
discharge area less than 80% of the flow area, the over
pressure at which the design lift is attained shall not
exceed 10% of the set pressure. For safety valves having
discharge area 80% or more of the flow area, the over
pressure at which the design lift is attained shall not
exceed 5% of the set pressure. |
Reg. 295
Pressure Drop
| The safety valves
shall be reset at a pressure at least 2.5% below, but
not more than 5% below the safety valve set pressure.
The 5% limit is increased to 10% for valves having a body
seat bore less than 32 mm and/or having a set pressure
of 2 bar gauge or less. |
Reg. 296
Attachment to Boiler
| a) |
Safety Valves shall
be mounted, without any intervening valve, on pads or
branches used for no other purpose. The axis of the valve
shall be vertical. The cross-sectional area of the bore
of each pad or branch shall be at least equal to the area
of the bore at the inlet of the safety valve, or where
two or more safety valves are mounted on the same pad
or branch, at least equal to the sum of the areas of the
inlet bores of all the safety valves. |
| b) |
Branches shall be
as short as possible so as not to impair the proper action
of the safety valves or impose any undue stress on the
branches at their point of attachment to the safety valve.
Branches, particularly when full lift safety valves are
mounted on them, should be radiused at the inlet. The
inlet and outlet flanges shall be drilled in accordance
with the approximate table in Appendix E, for the diameter
of flanges adopted.
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