Reg. 307 B, Reg. 308, Reg. 309
|Torsion bars shall
be manufactured from steel which shall have a yield point
of not less than 141 kg./mm² (90 tons/in2.).
Note.-Special steels developed by individual Manufacturers
may be accepted by the Chief Inspector of Boilers at their
|For ordinary lift
valves, the compression or extension of safety valve springs
required to load the valves to the set pressure shall
not be less than one quarter of the diameter of the valve
due consideration being given in the case of spring loaded
lever safety valves to the ratio of leverage. The proportion
of unloaded length to external diameter of the spring
shall not exceed 4:1.
These requirements do not apply to full lift and high
lift safety valves.
Determination of Working Pressure
||The maximum working
pressure to be allowed for steel springs of round, square
or rectangular section shall be determined from the following
For Springs in Extension.
(a) Round section: -
(b) Square section: -
(c) Rectangular section: -
||160,000 B² H²
where all dimensions in inches
For Springs in Compression.- The working pressure calculated
by the above equation may be increased by 25 per cent.