PUMPS AND PUMPING. 543 PUMPS AND PUMPING. the power wasted by the continual acceleration connecting it by means of a long piston, or pump and retardation of the ascending column, various rods with some sort of motive power at the sur- methods have been used for that purpose. The face. Air-lift pumps are cheap in first construe- most common is the air chamber, which is an air- tion, simple in operation, and have no wearing tiglit receptacle fixed vertically on the discharge parts, but their fuel economy is low- pipe ; the water forced into the pipe by the down stroke compresses this air, which, acting as a spring, returns this force to the ascending column during the period of the up stroke, and so, by taking the blow of the entering water, and return- ing it gradually, equalizes the pressure, and ren- ders the discharge uniform. If in place of a piston, which fits the pump cylinder tightly, a plunger rod smaller than the cylinder be used, working in a water-tight packing or stuffing box and discharging through an outward opening valve at the other end, we 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 wlien 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 eon- 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 have a simple force pump, which may at the same those of smaller capacity and simpler design, but time be made very powerful. It will be under- there is no hard and ftst line between the two. stood that the pistons or plungers may work in Other motive powers for pumps are electricity, either a horizontal or vertical direction, giving gas, gasoline, and oil engines. With the excep- rise to the terms horizontal and vertical pumps, tion of the steam pumping engine, the various and that, as already mentioned, a great major- motors employed to drive pumps will not be described further in this article, and most of the principles involved in the steam end of pumping engine will be explained under .Steam Engine. ity of the large displacement pumps have a number of small inlet and outlet valves, instead of one large one. Impeller Pumps include the centrifu- gal and the jet types. Centrifugal pumps, in their simplest form, consist of a series of vanes, or blades, mounted radially on an axis, and inclosed in a chamber. The centrifugal action of the revolving blades throws the water through the outlet pipe. The present ac- cepted curved vanes tend to convert the machine into a screw Cylinder pump, with displace- ment due to pressure. Centrifugal pumps are generally confined to raising water to comparatively small elevations, but they Chamber Pump DiSiharcfe Head "•-Pump Inlet may be employed for 5+eam End 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 air 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 con- veys compressed air down into the volume of water to be 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 Wa-t-er End BECTIO-V TUitOrGH 8MITH-VA1LE STEAM PUMP. Ste.m Pumping Engines. The simplest of these machines consists of a single steam and a single water cylinder, with a common piston, but this type did not come into use until ponder- ous beam engines had been employed for scores of years. All steam pumping engines have pumps of the displacement type. The steam end of the pump may use the steam at its initial pressure through the whole length of the stroke, when it falls in the simple, high-pressure type. If now the steam, after having done all possible work in the first cylinder, is admitted to a second one, still further service may be secured and the machine becomes compound. A third, or even a fourth cylinder may be used, in w-liich case the terms triple and quadruple expansion are em- ployed. If it is desirable to obtain still higher degrees of expansion, cut-offs are employed, so the steam is shut off when the stroke of the pis-
