. The steam-engine and other heat-motors . d of time. Hence with a uniform load and good feed-water aneconomizer may pay for itself. The amount of feed-water required per horse-power variesfrom— 40 to 25 pounds for simple engines,25 to 15 pounds for compounds,20 to 11 pounds for triples. Each pump should be designed to supply to 2 times thetheoretical quantity of water required. This allows for slip orimperfect filling of the pump with water. 288 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. The velocity of the water in the suction-pipe should not exceed,normally, 450 feet per minute, that in th
. The steam-engine and other heat-motors . d of time. Hence with a uniform load and good feed-water aneconomizer may pay for itself. The amount of feed-water required per horse-power variesfrom— 40 to 25 pounds for simple engines,25 to 15 pounds for compounds,20 to 11 pounds for triples. Each pump should be designed to supply to 2 times thetheoretical quantity of water required. This allows for slip orimperfect filling of the pump with water. 288 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. The velocity of the water in the suction-pipe should not exceed,normally, 450 feet per minute, that in the discharge-pipe being600 feet per minute. The net area of the valve passagewayshould be calculated at 400 feet per minute. The diameter of thesteam-cylinder is to times that of the water-cylinder, thusaffording a pressure of 2 to times that of the boiler. In duplex pumps the steam-valve on one cylinder is driven bythe reciprocating motion of the other pump. In the simplexpumps it is necessary to employ an independent Suction Fig. 150. Reciprocating Circulating Pumps (Fig. 18).—The piston speed ofthese pumps may reach 475 feet a minute; their volume may beobtained by allowing— 9 to cubic feet per hour per for compound engines:7 to 9 cubic feet per hour per for triple- or quadruple-expansion engines. This allows 80% efficiency for the pump. The number of strokes per minute made by a steam-pun p isgenerally calculated on the basis of 100 feet of piston speed perminute. For continuous boiler feeding and running under heavy SMALL AUXILIARIES. 289 pressure the speed should not exceed 50 feet per minute. The de-livery is also frequently given in gallons. If the diameter of thewater-cylinder is squared and then multiplied by 4, the result isthe delivery of the pump in gallons per minute on the basis of100 feet of piston velocity. On most pumps it is deemed advisable to place an air-chamberon the delivery side of the pump. In most cases it is ev
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