The simple slide valve, low-duty, non-condensing, throttling engine, is the lowest in first cost and the most expensive in the consumption of fuel. The triple-expansion Corliss, or the non-releasing Corliss, high-duty pumping engine is the most expensive in first cost but consumes less steam for the power delivered than any other form of reciprocating engine. For pumps of very small capacity the cost of fuel is not so important an item as the first cost of the machine. For this reason and because of the lower cost of attendance low-duty pumps are more frequently found in small pumping stations. [Illustration: FIG. 64.—Diagram Showing Rates of Steam Consumption for Different Size Units under Different Loads. ] TABLE 27 WATER RATES OF PRIME MOVERS AT FULL AND PART LOADS ───────────────────────────────┬──────┬─────────────────────────┬────── Type of Engine │ │ │Boiler │Power,│ │Press. │ K.W. │ Per Cent of Full Load │ Lbs. ───────────────────────────────┼──────┼────┬────┬────┬─────┬────┼────── │ │ 25 │ 50 │ 75 │ 100 │125 │ ───────────────────────────────┼──────┼────┼────┼────┼─────┼────┼────── Single cylinder, high speed, │ │ │ │ │ │ │100 to non-condensing │ 25│ 33│ 27│26.3│ 27.0│27.5│ 150 │ 250│ 42│37.5│ 35│ 34.0│34.0│ │ │ │ │ │ │ │ Automatic, flat four valve, │ │ │ │ │ │ │100 to high speed │ 150│ │ 32│ 30│ 26.5│29.0│ 125 │ 250│ │ 33│ 31│ 28│30.0│ │ │ │ │ │ │ │ Tandem compound condensing, │ │ │ │ │ │ │100 to high speed │ 125│ │ 23│ 19│ 17│ 18│ 150 │ │ │ 25│ 20│ 19.5│ 21│ │ │ │ │ │ │ │ Cross compound, condensing, │ │ │ │ │ │ │ 125 high speed │ │ 30│ 26│ 24│ 23│23.5│ │ │ │ │ │ │ │ Cross compound, non-condensing,│ │ │ │ │ │ │ 125 high speed │ │ 39│ 31│ 27│ 26│27.5│ │ │ │ │ │ │ │ Single cylinder Corliss, │ │ │ │ │ │ │ 100 condensing │ 120│23.7│20.4│ 19│ 18.5│19.0│ │ 500│26.3│22.8│21.3│ 20.8│21.3│ 125 │ │ │ │ │ │ │ Compound Corliss, condensing │ │16.5│ 14│12.5│ 12.1│12.5│ 100