About Central Boilers Board •Contents Chapter Wise • Contents Regulation WiseIndian Boilers Act 1923

Reg. 383

Measurement of heating surface

a) For the purpose of regulating the area of the safety valves and the amount of registration and inspection fees the “heating surface” of a boiler shall be the total surface of all plates and tubes exposed to heat on one side and in contact with water on the other measured on the water side or the fire side, whichever is larger.
b)

For Lancashire and Cornish boilers the total heating surface shall include the wetted surface of the furnaces between the end plates, the fire surface of cross tube where fitted, and the part of the external shell below the side flue covers. In estimating the areas furnaces shall be considered as plain cylinders the area of their wetted surface shall be taken as their mean external circumference x the length of the boiler between end plates. For the shell the width of that part of the circumference below the flue covers shall be taken as = 2 D, and this width + the length between end plates shall be taken as the area of shell heating surface. The part of the surface of the back-end plate exposed to heat shall be omitted from the calculation.

Example.- The formula for the total heating surface of a Lancashire boiler having plain furnaces without cross tubes is as follows:-

H.S. in square feet = 2L(3.14 d + D). L is the length of the boiler between end plates in feet and D is the internal diameter of the largest belt of shell in feet.

c) For steam and water drums of water tube boilers the heating surface of the drum shall be taken as half the external mean circumference multiplied by the clear length of drum between the outer brick walls or centres of cross boxes, as the case may be. The heating surface of the tubes shall be taken as the external surface of the tubes between the tube plates or heaters. The heating surface of the heaters shall be omitted from the calculation.
d) For marine boilers of the fire-tube type, the heating surface shall include the wetted surface of the furnaces between the tube plates (considered in the same way as for Lancashire boilers), the wetted surface of the combustion chambers (less the area of the tube holes) and the wetted surface of the tubes between tube plates. The parts of the front tube plate exposed to heat shall be omitted from the calculation.
e) For locomotive type boilers, the heating surface shall include the wetted surface of the fire-box above the foundation ring (less the area of the tube holes and the firehole and ring) and the wetted surface of the tubes between the tube plates. The smoke box tube-plate shall be omitted from the calculation.
f) For vertical boilers of ordinary type the heating surface shall include the wetted surface of the fire-box above the foundation ring (less the area of fire hole and ring and tube holes if any) and the surface of any cross or other tubes and uptake below the lowest water level shown in the gauge glass.
g) For Electrode boilers the heating surface shall be calculated as follows:

 Heating surface = E 6

where E = the equivalent evaporation at 212°F under normal load, which x  K.W.

K.W. the kilowatts absorbed at the stated voltage when the water in the boiler has a specific resistance of not less than 200 ohms per inch tube at 150oF and while the boiler is delivering its normal output of steam at its working pressure with the feed water temperature of 60°F,
h) No deduction shall be made for stays, etc., in calculating the heating surface.
i) For any other heating surface not provided for in the foregoing instructions the same general procedure shall be observed.

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