A Practical Treatise on Compressed Air and Pneumatic Machinery (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 Excerpt: ...whether the reheating of the air at the motor cannot be dispensed with. We will use a slide-valve engine, cutting off at % stroke, which would likely be the earliest admissible cut-off as regards exhaust temperature. The amount of air necessary to develop 48.3 H. P. is: 1.13 lbs. per second, or 67.8 lbs. per minute. If we were at the sea level, 1 lb. of air at 60 degrees Fahr. would represent 13.1 cubic feet. Sixty-seven and eight-tenths pounds represent, therefore: 67.8X13.1=888.2 cubic feet. If we use a single stage compressor, the I. H. P. required for 80 lbs. gauge receiver pressure will be: 15.18x8.882=134.83. But the Table of columns and powers at various altitudes shows that the power required to compress and deliver the same volume of air at the same pressure, but at 3500 feet altitude, is (Cols. 5 and 6): 89xi5-j=I-67 times greater than at the sea level. And as the temperature is 50 degrees Fahr., this figure should be reduced in the ratio of the absolute temperature (at 60 degrees and 50 degrees Fahr.) and becomes 1.046. The power actually required will therefore be: 134.83X1.046=141 I. H. P. in the compressor. And if we allow it mechanical efficiency, the brake power on the wheel is: =155 B. H. P. Whilst we have only 70 B. H. P. at our disposal. The air cannot therefore be used cold in the motor; in other words, we have not yet a sufficient margin of power between the wheel and the mill to permit the use of cold air; reheating must necessarily be resorted to. We have 70 B. H. P. on the compressor shaft, and 70X0.9= 63 I. H. P. in the air cylinder. From the above calculations, we know that the compression and delivery of 100 cubic feet of free air per minute at 80 lbs. receiver pressure, and at the given altitude and temperature require...