Water Lifted By Compressed Air
For Municipal, Manufacturing, Irrigation or Other Water Supply

be carried to any distance and at all angles, has no inherent friction, and enjoys the highest transmission efficiency. The system eliminates all trouble from freezing, since the air is used repeatedly and moisture once removed cannot be returned. "While it requires two pipe lines instead of one, the pipe cost is often less because of the smaller pipe size permitted. The pump cylinders will be smaller because of the higher M. E. P., and the losses in clearance, often enormous, are entirely eliminated. But the greatest economy is secured in compres- sion, the system being based upon the well-known fact that the great- est losses in compi’ession occur at the lower pressures. For instance, 8.46 H. P. are required to compress 100 cubic feet of free air from atmosphere to 30 pounds pressure. But if the initial pressure was 30 pounds the same amount of power would produce a pressure of 90 pounds. Now suppose this air at 90 pounds was applied to a pump exhausting at 30 pounds, the exhaust being piped back to the compressor, where the exhaust pressure became the initial press- ure of compression. The available effective pressure at the pump would thus be 90 minus 30, or 60 pounds, and the power required in compression would be 8.46 II. P. On the other hand, suppose 100 cubic feet of free air was delivered to the pump at 60 pounds pressure exhausting at atmosphere. This would give the same available, effect- ive pressure at the pump and the same volume of free air, but it would be secured at the expenditure of 13.42 II. P. The return pipe system, therefore, of which the first instance is an example, in this case secures a saving in compression alone of 4.96 II. P. Take an example of the working of the principle at higher press- ures: 13.42 II. P. will compress 100 cubic feet of free air to 60 pounds pressure, starting at atmosphere. Starting with this air at 60 pounds the same power will compress it to 350 pounds, giving on the return pipe system 290 pounds available pressure with 60 pounds back pressure, all with the same amount of power required to secure 60 pounds available pressure with the open system. These examples illustrate the principle and possibilities of the closed pipe system. A reheater at the pump will secure additional economy. Losses through leakage in transmission will be supplied by a small 11 booster” compressor. Or where a limited amount of air is used from the system for purposes other than pumping, it wil] be withdrawn from the low pressure pipe and exhausted direct, the “booster” in this case being increased in capacity to supply this volume withdrawn from the circuit. A\hen pumps are only one, and perhaps a minor, application of the air of a plant, the return pipe system is not the best to adopt. In such cases high economy can be secured by the use of compound or triple pumps, reheating the air after each expansion. This may reduce the air consumption to one-half or one-third its value in a 5i