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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