IMPELLER Pumrs include the centrifu gal and the jet types.
Centrifugal pumps, in their simplest form, consist of a series of van e s, o• blades, mounted radially on an axis, and inclosed in a chamber. The centrifugal action of the revolving blades throws the w a t e r through the outlet pipe. The present ac cepted curved vanes tend to convert the machine into a screw pump, with displace ment due to pressure.
Centrifugal pumpS are generally confined to raising water to comparatively small elevations, but they may be employed for higher lifts, although not so economically as some form of displacement pump. Jet pumps make use of a jet of steam or water, which, be ing delivered at high velocity through a small throat, imparts some of its velocity to the water to be moved. The our lift has been classed by some as a displacement and by others as a jet pump. It seems more correct to say that its action depends upon the formation of a column of water and air, which, because of its lesser specific gravity or weight, is overbalanced, or raised, by a column of water. Two tubes are employed, the smaller of which is centered within the larger. The small inner pipe veys compressed air down into the volume of water to he lifted. The air and water together rise up through the outer and larger tube. This device is used oftentimes as a substitute for deep-well reciprocating piston pumps, which re quire the placing of a pump deep in the well and connecting it by means of a long piston, or pump rods with some sort of motive power at the sur face. Air-lift pumps are cheap in first construe
thin, simple in operation, and have no wearing parts, hut their fuel economy is low.
As steam lifts thousands of times more water than any other artificial agent, the term pump ing engine, and even the word pump alone, is often employed to denote the combination of a pump and a steam engine in one machine; while when a pump is driven by detached motive power, even if that power be steam itself, the pump is termed a power pump—that is, one operated by independent power. There is a tendency to con fine the term 'pumping engine' to more or less elaborate machines of large capacity, and to confine the use of the term 'steam pumps' to those of smaller capacity and simpler design, but there is no hard and fast line between the two. Other motive powers for pumps are electricity, gas, gasoline, and oil engines. With the excep tion of the steam pumping engine, the various motors employed to drive pumps will not he described further in this article, and most of the principles involved in the steam end of pumping engine will be explained under :STEAM ENGINE.