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Reg. 220, Reg. 221, Reg. 222

FURNACES

Plain Furnaces of Horizontal Boilers

For plain furnaces or furnaces strengthened by Adamson or other joints or stiffeners of sufficient strength and for the semi-cylindrical tops of fire-boxes and bottom of combustion chambers where the sides are securely stayed, the working pressure shall not exceed the smaller of the values obtained from the following formulae :-
W. P. = C X (t - 1)2 Eqn.(57)
D ( L + 24 )

W. P. = C1 X {10 ( t - 1) - L ) Eqn.(58)
D

Where
d = the external diameter of the furnace or chamber top or bottom in inches

t = the thickness of the furnace plate in 32nds of an inch.

L = the length of the furnace or other part in inches measured between points of substantial support, i.e. centres of rows of rivets in end seams or commencement of curvature of flange, whichever is applicable.

C = 1450 where the longitudinal seams of steel furnaces are welded and 1300 where they are riveted,

C = 725 where the longitudinal seams of circular copper fireboxes or furnaces are fitted with double butt straps and 650 where they are lapped,

C1 = 50 where the longitudinal seams of steel furnaces are welded and 45 where they are riveted,

C1 = 25 where the longitudinal seams of circular copper fireboxes or furnaces are fitted with double butt straps and 22.5 where they are lapped.


Reg. 221

FURNACES

Corrugated Furnaces of Horizontal Boilers

The maximum working pressure to be allowed on corrugated furnaces shall be determined by the following formula -
W. P. = C ( t - 1 ) Eqn.(59)
D

where
D is the least external diameter in inches measured at the bottom of the corrugations on the water side.

t is the thickness of the furnace plate in 32nds of an inch measured at the bottom of the corrugation or chamber,

C = 480 for the Fox, Morrison, Deighton, Purves,, and other similar furnaces and 510 for the leeds Forge Bulb Suspension Furnace.


Reg. 222

FURNACES

Plain Furnaces of Vertical Boilers

The same formulae as for the plain furnaces of horizontal boilers shall be used, but where the furnaces are tapered the diameter to be taken for calculation purposes shall be the mean of that at the top and of that at the bottom where it meets the substantial support from flange or ring. The length for the same purpose shall be the distance from the centre of the row of rivets connecting the crown and the body of the furnace to the substantial support at the bottom of the furnace, or to a row of screwed stays connecting the furnace to the shell, provided that the pitch of stays at the furnace does not exceed 14 times the thickness of the furnace plate when the stays are riveted at their ends or 16 times when the stays are fitted with nuts. Such screwed stays shall be in diameter over the threads not less than twice the thickness of the furnace plate and in no case less than 3/4" diameter {See Reg.135 (d)}.
 
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