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Reg. 294, Reg. 295, Reg. 296

Over pressure of Safety Valves

 
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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