The New Twelve-Million-Gallon Engine.
The big, new 12,000,000-gallon pumping engine erected in the pumping station at Harrisburg, Pa., when officially tested, fully answered all expectations. It is of the vertical, triple-expansion, crank and flywheel type, with three outside-packed water plungers. The diameter of the high-pressure is twenty-eight inches; of the intermediate cylinder, forty-eight; of the low-pressure, seventy-two; each of the water-plungers, twenty-six and one-half; stroke of the engine, common to all pistons and plungers, forty-two. The main pumps are of the annular pattern, with each plunger-barrel and set of valve-chambers combined within one construction. The pump bodies rest upon suitable foundations in the basement of the building, and the main bed-plates of the engine are substantially supported at the level of the engine room floor upon brick piers. Struts, or distance-pieces, are attached to, and extend from the engine bed-plates to the main power holes—thus rigidly securing the water and steam ends of the machinery in the centre line of transmission. The steam end of the engine is of the usual type, with the induction and exhaustvalves for the steam distribution placed across the cylinder-heads so as to reduce the waste room. The main cross-heads are of forged steel, and, with the distance rods, also of steel, connecting the cross-heads directly with the pump-plungers, are very substantial and effective in operation. The main cranks, one for the high-pressure cylinder, one for the low-pressure cylinder, and two at the middle bed-plate for the intermediate cylinder, together with the two main shafts and the three connecting rods, are also of forged steel: the connecting rods, cross-heads, plunger rods, cranks, and main shafts, are all finished and polished. The valve gear is driven by means of eccentrics upon the main shafts: one for the highpressure cylinder, one for the intermediate cylinder, and two for the low-pressure cylinder, the exhaust-valves of the low-pessure being driven by an independent eccentric. The bed plates arc deep, massive and strong; and contain the pillowblocks for the main shafts, the shafts carrying the two flywheels, fifteen feet in diameter, and weighing about fifteen tons each. The framing of the engine, of the double A type, is heavy and in good proportion, supporting the cross-head guides, and bearing for the valve gear rock shafts. The engine takes steam at 140 pounds gauge-pressure into the high-pressure cylinder, thence exhausts it into the first receiver, after expanding it in a ratio of about three and one-third to one. From the first receiver the steam enters the intermediate cylinder at thirty-five pounds absolute pressure, thence exhausting into the second receiver, after expanding in a ratio of two and threetenths to one. From the second receiver the steam enters the low-pressure at 14.2 pounds absolute pressure, thence sending it to the condenser, after exp mding in a ratio of two and fifteenhundredths to one. The counter pressure in the low-pressure cylinder was 2.7 pounds absolute, giving a net effect of the vacuum equal to twelve pounds absolute pressure, which, of course, is a realisation in the cylinder ranging very high for the vacuum shown by the gauge. The actual ratio of total expansion, as shown by the indicator cards, is just about twenty-three to one. The condenser is of the surface type. The condensing water was a part of the water flowing to the main pumps through the suction-pipe from the well, the condenser being placed in a side circuit and the quantity of water utilised controled by means of a suitable gate-valve. The air-pump is attached to. and driven by the main engine by means of an extension arm on the low-pressure plunger-head; the boiler-feed pump, also, driven from this extension arm. A feed-water heater is located in the line of the main exhaust-pipe between the low-pressure cylinder and the condenser, and very materially adds to the general economy of the plant. Altogether, the pumping engine is heavy, strong, and substantial; and well calculated and proportioned for the work to he done. The resuts of the official tests show that the engine is capable of pumping more than the prescribed 12,000.000 gallons of water against the prescribed load, with a steam pressure not exceeding 140 pounds per square inch at the throttlevalve; and. while pumping this water, showed an economic duty equal to the rasing of otic 132,179.112 pounds of water one foot high for each 1.000.000 British thermal units consumed by the engine—the contract specifying 130,000,000 pounds of water to be so raised.