462
Molesworth’s pocket-book
_ RELATIVE VALUE OF HEATING SUBFACE.
Horizontal surfaces above the flame = 1 • 00
Vertical .......................— .50
Horizontal beneath the flame ’ .. = -00
lubes and flues ............. ]i of their diam.
Convex surfaces above the flame.. li diameter
Boilers—Land.
RULES FOR HEATING AND GRATE SUBFACES.
G = Fire-grate surface in square feet.
1 ’ — Number of nominal horse-power.
h = Heating surface in square yards.
I' = \/ ll Gr,
I PS P2
G U h
For each nominal horse-power a boiler requires.*
1 cubic foot of water per hour.
1 square yard of heating surface.
1 square foot of fire-grate surface.
1 cube yard capacity.
5 28 square inches flue area; 18" over bridge.
lor cylindrical double-flued boilers, an approxi-
mate rule is:—•
Length x diameter .
---------—----------= nominal liorse-power.
Mountings for a Nominal 30-horse Boiler.
Man-hole, oval..........18 in. x 15 in
Vacuum-valve............2f in. diam. in seat
Spring-balance safety-valve .. 2i in. „
Weighted safety-valve .. 5 in. „
Escape-valve ...............2$ in. ",
Damper, area of opening .. .. 4 ft. X 13} In.
Damper weight...............8 in. x lo’x 4.
Blow-off cock ..............3 in. bore.
Kange of glass gauge........10 in.
Length of dead-plate........... 10 in.
Fire-doors................ .. loin. X13ia.