“Return Air System”
This is a method of lifting water by compressed air that is a modification of the pneumatic displacement pump and is put out by the Ingersoll Rand Company, New York. The system comprises a closed circuit in which by a regular cycle of operations, one air volume is compressed, expanded and recompressed and re-expanded indefinitely, each cycle of compression and expansion corresponding with a discharge of one of the pump tanks. As will be noted by the illustration, the essentials of the system are an air compressor, a reversing switch in the compressor room, two air lines, each leading from the compressor through the switch to one pump tank and two tanks submerged in the water supply or within easy range of siphon action. Compressed air is admitted to a tank full of water, forcing the latter out through the discharge pipe equipped with a check valve: the air that has displaced the liquid is then expanded back through the air line and switch to the compressor until equilibrium is secured throughout the system which then contains a charge at a certain pressure. Phis equalizing operation is little more than momentary during which the compressor operates at “no load,” pressures being balanced on either side of the piston. As soon as equilibrium is reached, the compressor again takes up the load, compressing the air in the second tank and drawing its intake, already at high pressure, from the first tank and pipe line. As the pressure increases in Tank No. 2. the water is displaced. while as it diminishes in Tank No. 1. the latter again refills with water.