Steam is furnished to this engine by two horizontal cylindrical boilers, of the following proportions : Total area of grate surface, 66 sq. ft. Total heating surface, (about) 2,S66 sq. ft. Total area of cross-section of tubes, sq. ft. Total area of chimney flue, 8•33 sq. ft. Ratio of heating surface to grate surface, 43.42. Ratio of grate surface to area through tubes. 9.19. Ratio of grate surface to area of chimney flue, 7.92.
The following average values are obtained from the records of the test : Mean steam pressure in boilers, per gauge, 81.05 lbs. Mean steam pressure at engine, per gauge, 78.01 lbs. Mean steam pressure in jackets, per gauge, 70.075 lbs. Mean water pressure. per gauge, 99.565 lbs. Total mean pressure on pumps, corrected, 103.735 lbs. Mean vacuum, per gauge on condenser, in. Mean vacuum, per gauge ou engine, 27.87 in. Mean temperature of feed water, 203.55° F. Mean volume of water, at 51°, passing the meter per hour, cu. ft. Mean revolutions of engine, per minute, 17.04. Mean effective area of plunger, sq. in. Mean rate of coal consumption, per hour. 600 lbs. Mean rate of consumption per hour per square foot of grate, 9.091 lbs. Mean rate of evaporation in boilers, per minute, 96.135 lbs.
Substituting in the formula the values found, for the duty, 117,936,698 ft. lbs., on the basis of the assumed evaporation of 10 lbs. of water per pound of coal. this result exceeds the guaranteed duty. 105,000,000, by 12.32 per cent., or by nearly one-eighth. The duty, based upon the actual coal consumption, is 113,378,479 ft. lbs. This result is 7.98 per cent. greater than the duty guaranteed. The capacity of the pumps of the new Saratoga engine is 333.2 U. S. gallons per revolution, and the rate at which water was pumped during the period of the test of eighteen hours was, therefore, 8,175.928 gallons in 24 hours, at a piston speed of 113.6 ft. per minute. This rate is something more than 2 per cent. greater than required by the contract, while the pumps were operated against a pressure 3.73 per cent. greater than was required. The quantity of water actually pumped during 24 hours. against a pressure of 103.575 lbs., and at a piston speed of 115 ft. per minute, was 8,277,354 U. S. gallons ; exceeding the contract. capacity by 3.47 per cent. against a pressure 3.57 per cent. greater than was required by the terms of the contract.
The following facts have been deduced from the steam cards : Clearance of high-pressure cylinders equivalent to fraction of stroke, 0.027. Clearance, low-pressure cylinders, fraction
of stroke, 0.030. Mean pressure at end of stroke, both low-pressure cylinders, 7-7565. Mean expansions in high-pressure cylinders, 2.933. Mean expansions in low-pressure cylinders, 4.207. Mean expansion, total, by pressures, 12149 times. Pounds of steam entered cylin ders, per minute, 87.348. Of this, there is accounted for at cut-off, 73.95 per cent.; at the end of stroke in the high-pressure cylinders, 78-82 per cent., and at the end of the stroke in the low-pressure cylinders, 89.08 per cent.
Thus it appears that at the cut-off there was, in the high-pressure cylinders, water constituting 26'05 per cent. of the steam and water which entered the cylinders. At the end of the stroke in the high-pressure cylinders, there appears to have been water constituting 21.18 per cent, of the water and steam originally entering the cylinders, and at the end of the stroke in the low-pressure cylinders there was water constituting per cent. of the steam and water which originally entered the cylinders.
The Corlies Pumpihg-engive at Pawtucket, R Z —This engine, built in 1878, was described in Vol. II. of this work. Numerous tests of its working have shown that it has uniformly given a remarkably high record of economy. It is a horizontal cross compound en gine, steam-cylinders, 15 and 30h in. bore ; water cylinders, 10.52 in.; stroke of all pis tons, 30 in.; clear ance. high-pressure cylinder, 4 per cent.; low, 3.7 per cent. Diameter of rods, 21 in. Ratio of vol umes of cylinders, 4'085. Average cut off in high-pressure cylinders, one-fourth, and in low, one-third. Jackets envelop the barrels, but not the heads, of both cylin ders, and steam of full boiler pressure is used in each The heads are cot jack eted, but contain passages leading to and from the ports. The condensed steam from the jackets is pumped into the feed pipe at a point be. tween the boiler and hot well. The con densed s t e a tn col lected in the receiver is received in a trap, and continuously pumped through a heater placed in the chimney flue, and thence returned to the top of the receiver. Out of a total of about 155 lbs. thus circulated per hour, in actual work, one-third only is evaporated and returned to the receiver as steam ; the other two-thirds gradually accumulates in the receiver and is blown to waste every three hours.