A reciprocating pump of any type would have to be specially built for pumping sewage not carefully screened or otherwise treated, as the valves, ordinarily used in such pumps for lifting water, would clog. The vertical triple-expansion pumping engine with special valves and for large installations, and the centrifugal pump for large or small installations are the only suitable types for pumping sewage. With steam turbine or electric drive the centrifugal has the field to itself. [Illustration: FIG. 70.—Expectancy Curves for Pumping Engines Working against a Pressure of 100 Pounds per Square Inch. J. N. Chester, Journal Am. Water Works Ass’n, Vol. 3, 1916, p. 493. ] =87. Costs of Pumping Machinery.=—The cost of pumping machinery can not be stated accurately as the many factors involved vary with the fluctuations in the prices of raw materials, transportation, labor, etc. The actual purchase price of machinery can be found accurately only from the seller. The costs given in this chapter are useful principally for comparative purposes and for exercise in the making of estimates. The costs of complete pumping stations are shown in Table 31.[48] These figures represent costs in 1911. TABLE 31 COSTS OF COMPLETE PUMPING STATIONS These costs include the best type of triple-expansion engines, high-pressure boilers, brick or inexpensive stone building with slate roof, chimney and intake. Cost of land is not included. ─────────────────┬─────────────────┬─────────────────┬───────────────── Discharge │ Horse-power per │ │ Pressure, Lbs. │ Million Gals. │Cost, Dollars per│Cost, Dollars per per Sq. In. │ Pumped │ Horse-power │ Million Gallons ─────────────────┼─────────────────┼─────────────────┼───────────────── 30│ 12│ 562│ 6,750 40│ 16│ 438│ 7,000 50│ 20│ 362│ 7,250 60│ 24│ 312│ 7,500 70│ 28│ 277│ 7,750 80│ 32│ 250│ 8,000 90│ 36│ 229│ 8,250 100│ 40│ 213│ 8,500 110│ 44│ 200│ 8,750 120│ 48│ 187│ 9,000 130│ 52│ 192│ 10,000 │ │ │ ─────────────────┴─────────────────┴─────────────────┴─────────────────