water line a large amount of mud and other matter which is kept on the surface by the constant ebullition can be blown out.

A combination surface blow off, bottom blow off, and circulating system can be arranged by a connection such as illustrated in Fig. 9. By closing cock A and opening cocks' B and C the bottom blow off is put in operation; by closing B and opening A and C the surface blow off is started, and by closing C and leaving A and B open the device will act as a circulating system. The pipe should be of the same size throughout. Blow off pipes should be of ample size, never less than 14 in., and from that to 21⁄2 in., depending upon the size of the boiler.

Feed Pumps and Injectors. The belt driven power pump is the most economical boiler feeder, but is not

the most convenient nor the safest. When the engine stops, the pump stops also, and sometimes it happens that the belt gives way and the pump stops at just

the time when the boiler is being worked the hard

est.

The modern double acting steam pump, of which there are many different makes to choose from, is without doubt the most reliable boiler feeding appliance and the one best adapted to all circumstances and conditions, although it is not economical in the

use of steam, since the principle of expansion cannot be carried out with the pump as with the engine.

In selecting a feed pump care should be exercised to see that it is of the proper size and capacity to supply the maximum quantity of water that the boiler car evaporate. This may be ascertained by taking into consideration the amount of heating surface and the required consumption of coal per square foot of grate surface per hour. First, take the coal consumption. Assume the boiler to have 30 sq. ft. of grate surface,

and that it is desired to burn 15 lbs. of coal per square foot of grate per hour, which is a good average with the ordinary hand fired furnace using bituminous coa!.

O

SECTIONAL VIEW OF DIFFERENTIAL VALVE.

Suppose the boiler is capable of evaporating 8 lbs. of water per pound of coal consumed. Then 30 × 15 × 8 = 3,600 lbs. of water evaporated per hour. Dividing

3.600 by 62.4 (the weight of a cubic foot of water in pounds) gives 57.6 cu. ft. per hour, which, divided by 60. gives 0.96 cu. ft. per minute. This multiplied by

1,728 (number of cubic inches in a cubic foot) gives 1,659 cu. in. per minute which the pump is required to supply. Suppose the pump is to make forty strokes per minute, and the length of stroke is five inches. Then 1659 40 41.47 cu. in. per stroke, which, divided by 5 (length of stroke in inches) gives 8.294 sq. in. as the required area of water piston. 8.294 + .7854 = 10.56, which is the square of the corresponding diam

+

=

eter, and the square root of 10.56 3.25. So, theo. retically, the size of the water end of the pump would be 34 in. in diameter by 5 in. stroke; but as it is always safer to have a reserve of pumping capacity, the proper size of the pump would be 31⁄2 in. in diameter by 5 in. stroke, with a steam cylinder of 6 or 7 in. in diameter.

There is another rule for ascertaining the size of the

feed pump, by taking the number of quare feet of heating surface in the boiler and allow a pump capacity of 1 cu. ft. per hour for each 15 sq. ft of heating surface. Thus, let the total heating surface of the boiler be 786 sq. ft. Dividing this by 15 gives 52.4 as the number of cubic feet of water required per hour, from which the pump dimensions may be found in the same way as in the preceding case.

In figuring on the capacity of a feed pump for a battery of two or more boilers, the total quantity of wate required by all the boilers must be taken into consideration. All boiler-rooms should be supplied with at least two feed pumps, so that if one breaks down there may always be another one available.

But the disad

The injector is a reliable boiler feeder, and is in fact more economical than the steam pump, because the heat in the steam used is all returned to the boiler, excepting the losses by radiation. vantage attending the use of the injector is that it will not work well with the feed water at a temperature very much in excess of 100° F., while a good steam pump, fitted with hard rubber valves, will handle water at a temperature as high as 200° or 208° F., when the water flows to the pump by gravity from a heater, or it will raise water from a receiving tank on a short suction lift at a temperature of 150° or 160° F.

Feed Water Heaters.

One great source of economy