STEAM 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 lamps 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, o• even a fourth cylinder may be used, in which 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 IAA ton is but partially completed. The balance of the stroke is due to the expansion of the steam in the cylinder and is a gradually decreasing pressure. (See STEAM ENGINE.) In the direct-act ing pumps the piston speed is maintained through the whole stroke by means of a compensating device. One of the best known of these, the Worthington high-duty attachment, employs an accumulator for this purpose, consisting of an oscillating piston. During the first part of the stroke the forward end of the pump piston forces the oscillating piston against water pressure. When the steam is cut off this pressure is auto matically released, and, through proper mechan ism, is utilized during the completion of the stroke, while the steam is expanding. In place of this device another manufacturer employs a portion of the high pressure of one side of a duplex engine to aid the expanding steam on the other side. Where a, flywheel is employed it affords all necessary compensation, exactly as in the steam engine. The Ilolly-Gaskill is the best known type of a horizontal fly-wheel pumping engine and the Leavitt and Allis engines illus trate the vertical type. The object of these various devices is to secure greater economy in the use of fuel, to which end an increased first cost of construction, or capital outlay, is under gone. Such engines are classed as high duty.
The duty of a pumping engine was formerly expressed in millions of pounds of water lifted one foot high by the consumption of 100 pounds of coal. Since coal is variable in quality, there was substituted for it as a basis the work done by 1000 pounds of dry steam; and as a further refinement, the work done by 1,000,000 British thermal units (B.T.U.). The two last give results that are fairly comparable for ordinary conditions, but, whereas 1000 pounds of dry steam, in a high-grade pumping engine. have yielded about 150.000,000 foot-pounds, the duty of the same engine, based on 100 pounds of coal, was about 168,000,000 foot-pounds. On the coal basis the duty of pumping engines has increased, in round numbers, from 6,000,000 foot-pounds for the Newcomen atmospheric pumping engine of 1760 to 178,000,000 foot-pounds for the best crank-and-tly-wheel triple-expansion pump of the present day. The wide range of efficiency of various types of pumps now used is shown by the following figures from Turneaure's Water Supply, based on the duty per 1000 pounds of steam: High duty, 168-100 millions; ordinary pumping engines, 100-75 millions; steam pumps, 40-10 millions; direct-acting deep-well pumps, 6-2 millions; vacuum pumps, 8-2 millions; jet-pumps, 4-1 million foot-pounds. Power pumps, with direct connecting engines, the pumps alone having an efficiency of 75 per cent., are ranked at 114 to 37 millions according to the type of engines. The air lift pumps, with a pump efficiency of 25 per cent., are figured to give duties of 31.000,1)00 to 6,000, 000 foot-pounds per 1000 pounds of steam, with various styles of air compressors. The theoretical efficiencies of the above three classes of pumping apparatus (i.e. pump and motive power com bined) range from 20.t per cent. for the high duty engines to 0.13 per cent. for the jet pumps, 14.7 per cent. for the triple-expansion condensing engines and power pumps, 4.8 per cent. for shn ple high-speed condensing engines and power pumps. and 4 to 0.77 per cent, for air-lift pumps.