FACTORIES AND MACHINERY (STEAM BOILER AND
UNFIRED PRESSURE VESSEL)
Regulation 48. Safety valves.
Every safety valve fitted to an unfired pressure vessel shall:
(i) be so designed and constructed and adjusted that it will open when the authorised
safe working pressure is reached;
(ii) have an effective valve area sufficient to ensure that under the conditions of maximum
supply of the working fluid the pressure in such unfired pressure vessel shall not exceed
the authorised safe working pressure assigned to such vessel by ten per centum of such
safe working pressure;
(iii) not be less than three-eighths of an inch;
(iv) be of the direct spring loaded type with a washer or ferrule fitted under the spring
adjusting screw so that the valve cannot be overloaded when under pressure;
(v) be so constructed as to allow the valve to be eased by hand from its seat when under
pressure, and of such material that it cannot seize on its seat on account of corrosion or
distortion of the valve body;
(vi) have a valve seat and valve made of non-ferrous material;
(vii) where such unfired pressure vessel contains a viscous liquid, have a plain valve disc.
No fin or web shall be in contact with such fluid and the passage to the valve disc shall be
as short as practicable;
(viii) be clearly marked with the manufacturer's or maker's name, the nominal diameter
and the designed lift of calculated relieving capacity at the pressure to which the valve
has been set.
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