PROPORTIONING PARTS OF HEATING BOILERS.-STEAM HEATERS.

SPECIFICATIONS FOR HORIZONTAL TUBULAR BOILERS.

H. P. rating

Radiation rating
(120 sq. ft. per H.
P.)...

1,800 2,400 3,000 3,600 4,200 4,800 5,400 6,000 7,200 8,400 9,600 12,000 15,000 18,000

Diam. of stack, in.]
Length of stack, ft.
Approx. weight of
boiler.

16

28 35 35

22

999

60

60 66

14

16

16

76

76

94

116 116

60

60

50

76

50 60

24

24 26

28 28

2,700 3,200 4,250 4,650 5,200 6,300 7,150 7,750 9,150 10,480 11,900 14,400 16,600 17,900

2,000 2,700 3,250 3,450 3,700 4,100 4,250 4,450 4,850 5,120 5,600 6,2007,400 7,700

SAFETY-VALVE AREAS, IN SQUARE INCHES PER SQUARE FOOT OF GRATE SURFACE.

Boilers used for heating buildings of moderate size usually have what is termed a portable setting; i. e., they are mounted, without brickwork, on cast-iron bases that may be extended to accommodate any increase of capacity of the boiler, made by adding other sections, when the demand for steam becomes greater than the original size of the boiler may have been designed to supply. Vertical cast-iron boilers having slab sections require no outer casing, although they are sometimes set in brickwork to prevent loss of heat, or to utilize the extreme outer surfaces of the sections as indirect heating surface. As a rule, however, an external covering of some non-conducting covering, such as magnesia and asbestos, is used in place of a brickwork setting, effectively preventing serious loss of heat from the exterior surfaces of the boiler.

The setting of a 60-in., return-tubular boiler with a half-arch front, as designed by the Hartford Steam Boiler Inspection and Insurance Company, is shown in the accompanying illustration. The foundation is heavy stonework laid to a depth of 3 or 4 ft. below the surface. On top of this is laid the brickwork. The side and rear walls are double, with a 2-in. air space between the inner and outer parts. The inside

wall i, next to the furnace, is faced with firebrick, as is also the bridge and all portions in direct contact with the flames.

The boiler is supported by cast-iron lugs / riveted to the shell; these lugs rest on iron plates m placed on the top of

the side walls. The front lugs rest directly on the plates, but the back lugs rest on rollers o of 1-in. round iron. The boiler is thus free to expand and contract. The rear wall is 24 in. from the rear head of the boiler, so as to allow the gases an opportunity to enter the tubes; above the tubes, however, the wall is built in to meet the head, and forms a roof for the chamber. The rear wall is provided with a door d for removal of the dirt and soot that collects back of the bridge and to provide a means of inspection.

The grate g is placed 24 in. below the shell; this is a sufficient distance for anthracite, but for bituminous coal it might better be 30 to 36 in. The grate has a fall of 3 in. from front to rear, which facilitates the admission of air to the rear of the grate and makes it somewhat easier to clear the spaces between the grate bars from below. The back end of the boiler should be set about 1 in. lower than the front end; this insures a thorough draining of the boiler when the blow-off is open.

The brick work is closed into contact with the shell at the level of the center of the upper row of tubes; this prevents the gases coming in contact with the plates above the waterline. Some boilermakers prefer to make a brickwork arch over the top of the boiler and to allow the gases to pass back to the rear through the flue thus formed. The practice is risky, as it may lead to the overheating of the upper plates. A safe rule is "Never expose to fire or gases of combustion any part of the shell not completely covered with water." This rule applies to the blow-off pipe as well; in order to prevent its destruction by the gases of combustion and the heat, it should always be protected either by being covered with a larger pipe or by a cast-iron sleeve, or by being bricked in. The last method has the serious objection that it interferes with the examination of the pipe, which may corrode badly, when bricked in, without it being discovered.

The brickwork is strengthened by buckstaves b held together by tie-rods t. The buckstaves are best made of wrought-iron channel or angle irons. It will be noticed that in the present case the flue pipe p is rectangular, but the