DEVELOPMENT.
The Pelton wheel is not quite as efficient theoretically as a turbine, wasting from 5 to 7 per cent more water; a Francis turbine will deliver more water for the same diameter than a Pelton. But the turbines are more compli cated and more costly, and not so well adapted to receive the enormous pressures to which Peltons are subjected under a high head. For many years a three-foot Pelton wheel was run at the California and Consolidated Virginia mine in Nevada, under a 2,100-foot head with a little half-inch stream of water, making 1,150 revolutions per minute, or the equivalent of 240 miles an hour, and delivering 100 horse power. They are built in sizes up to 10,000 or more horse power, and use from one to four nozzles distributed around the periphery, the tendency being to employ one nozzle. Some of the larger nozzles deliver a stream of 9 or 10 inches diameter. This flow is regulated by a central uneed10 which can be advanced to par tially close the aperture of the nozzle. Deflec tors are also employed to turn aside the flow of water should the °load" be suddenly re duced. Both turbines and Peltons are now commonly coupled directly to dynamos for gen erating electricity, that the power may be sent out on wires, or the current used for electric lighting, etc.
Pumps.— To comprehend the action of pumps the reader must understand that water always seeks the lowest possible level. If a garden hose is nearly filled with water and the two ends are held up, it may be demon strated that the level of the water in one end is the same as the other end; this crude device is sometimes used in making grades for drains. It must also be borne in mind that water is under atmospheric pressure. The air weighs 14.7 pounds per square inch (at sea-level), and if the lower end of a pipe of one inch cross section be placed in water, and the air be pumped out or otherwise removed from the pipe, the water, being relieved of 14.7 pounds pressure, at once rises in the pipe until the col umn of water in the pipe equals the weight of the atmosphere removed, which in theory is about 32 feet, or in practice a little less.
The hand pump is made in almost an infi nite variety of forms and styles. The common
suction pump (see Fig. 1) has a pipe whose lower end rests in the water; the pump proper is a barrel A of larger diameter than the water pipe. A piston B with valves CC is recipro cated in this pump barrel A, by moving the pump handle up and down. As the piston moves upward the valves CC are automatically closed, and the valve D opens, when the tend ency to create a vacuum below sucks up the water, which may thus he raised to a height not exceeding 32 feet. In other words the up stroke of the piston causes the water below to rise because of the atmospheric pressure. To force water higher than 32 feet with a piston movement, the force-pump is employed. This has a solid piston, moving tip and down in a cylinder, hut the valves are both in the lower part of the cylinder, as shown in Fig. 2. When the piston is rising, as illustrated, the lower valve A opens and water is drawn into the pump barrel, the valve B being closed. When the piston reaches the top and starts its return downward stroke, the pressure closes the valve A and opens the valve B, and the water in the cylinder or pump barrel is forced into the pipe leading upward which may extend to a con siderable height. As described, the action of the force-pump is intermittent, but it may be made to deliver water continuously by attach ing an air-chamber to the eduction pipe. The air in this chamber is compressed while the pis ton is forcing water up the eduction pipe, and on the return movement of the piston, its pres sure being removed for an instant, the com pressed air acts as a spring and pushes up some water. The force-pump, it is apparent, raises the water as far as the pump barrel on the same principle as the suction pump, atmospheric pressure being the raising force in both case:, but above that point the action of the force pump is that of the downward force exerted by the pump handle on the confined water in the pump barrel, so that it is free to raise more water on every stroke regardless of its per haps having already raised a column of water 32 feet up to the barrel.