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Regulation 12. Safety valves.



                                   P.U.(A) 5/70
FACTORIES AND MACHINERY (STEAM BOILER AND         
                 UNFIRED PRESSURE VESSEL)
                            REGULATIONS, 1970
                     PART II - STEAM BOILERS

Regulation 12. Safety valves.

(1) Every safety valve fitted to a steam boiler shall-
(i) be so constructed and adjusted that it will open when the authorised safe working
pressure of such steam boiler is reached. The area of such valve or valves shall be
sufficient to ensure that the maximum peak load evaporation of the steam boiler is
completely discharged with a rise in pressure of not more than ten per centum of such
authorised safe working pressure:

Provided that an Inspector may in his discretion permit any safety valve to be adjusted so
as to open at a pressure greater than the authorised safe working pressure by an amount
not greater than five per centum thereof;  

(ii) have a diameter of not less than-
(a) three quarters of one inch if the heating surface is thirty square feet or less, or

(b) one inch if the heating surface is greater than thirty square feet;
(iii) be so constructed that breakage of any part will not obstruct the free and full
discharge of steam from the steam boiler;

(iv) have the lid and spindle effectively guided and means provided to prevent such lid
and spindle lifting out of the guide;

(v) have no stuffing box fitted to the spindle;

(vi) in the case of the lever type safety valve, have either the pin or the bush of every
bearing thereof made of a non-ferrous or corrosion resistant metal;

(vii) be fitted with a spring which shall be so constructed that-
(a) the unloaded length thereof shall not be greater than four times its external
diameter;

(b) in the case of a compression spring the compression required to load the
valve to the authorised safe working pressure of the steam boiler to which it is
fitted shall not be less than one-quarter of the diameter of the valve, and the
distance between the coils of such loaded spring when the valve is lifted onequarter
of its diameter shall not be
less than one-sixteenth of an inch; or

(c) in the case of a tension spring the extension required to load the valve to the
authorised safe working pressure of the steam boiler to which it is fitted shall not
be less than one-quarter of the diameter of the valve, and provision shall be
made to prevent the extension of the spring beyond the amount corresponding to
a valve lift of one-quarter of the diameter of the valve;
(viii) be mounted as close as practicable to the steam boiler shell and in a position where
the steam shall have direct access to such safety valve without passing through any
valve cock or internal pipe;

(ix) have its axis vertical;

(x) be provided with a device whereby the adjustment of the valve may be locked or
sealed so that it is not possible to alter the setting of the valve except by unlocking or
breaking the seal;

(xi) be so arrange that the valve can be lifted off its seat when under pressure by easing
gear from a safe and convenient position; and

(xii) be clearly marked with the manufacturer's or maker's name, the diameter and
designed lift in inches and the pressure to which the valve has been set.
(2) All the safety valves fitted to a steam boiler may be located in one chest but such chest shall
be separate from any other valve chest or steam connection:

Provided that where the cylinder casting of an overhead engine is mounted directly on the steam
boiler shell, such safety valve may be fitted to the cylinder casting.

(3) Every safety valve chest shall-
(i) be connected to the seating pad on the steam boiler by a strong branch, the passage
through which shall have a cross-sectional area not less than the aggregate area of the
safety valves;


(ii) where a waste steam pipe is fitted thereto, have the cross-sectional area of such pipe
not less than the aggregate area of the safety valves:

Provided that where safety valves of the full-lift type are fitted, the area of such waste
steam pipe shall be twice the aggregate area of such valves; and

(iii) be provided with means of drainage that cannot be closed.



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