200

MODERN STEAM PRACTICE.

have to be studied, they may be beneficially used for pumping waterfrom moderate depths and forcing or lifting it to moderate heights.

For moderate depths horizontal high-pressure pumping engineshave been used, connected to two bell cranks, directly from the piston-rod crosshead, with long links, one on each side, taking the longarm of the bell crank nearest the engine; and the two bellcranks are connected to each other with wooden connecting linksstrapped with wrought iron, the pins for carrying these linksbeing nearer the centre of Vibration of the bell cranks; thus thestroke of the engine is somewhat longer than that of the pumps.The bell cranks are so arranged that the one goes up and theother down alternately, the steam being admitted into each endof the cylinder as in ordinary high-pressure engines. The valvemechanism is worked in a similar manner to that of the Cornishengine, with tappets, cataracts, and all the necessary starting handles.One useful feature in this dass of engine is that it can be driven ata higher or lower rate of speed, or more or fewer strokes given, asthe increased or diminished quantity of water in the pit may require.The exhaust steam is made to pass through a series of tubes, aroundwhich there is a constant circulation of cold water; thus the steamis partially Condensed, and the water pumped into the boilers again,as in surface-condensing engines. A jet of steam, however, escapesinto the atmosphere at each stroke, which is due to the tube surfacenot being of sufficient area, and to give the condensing vessel therequisite area would make it too bulky and expensive. By thismethod of allowing the exhaust steam to pass through the tubesthe water around them is heated to a high degree, and it can bepumped into the boiler separately, or mixed with the water collectingin the receiver; but in either case the tube surface acts as a feed-water heater.

Horizontal high-pressure engines with slide valves and eccentricmotion are sometimes used for pumping water out of coal and othermines. The valve gear is of the simplest description, consisting ofa rocking lever, fitted with a link for the valve rod, and a pin fortaking the gab end on the eccentric rod, which is made to throwout of gear when required. The cylinder is securely bolted to oneend and the pillow block for the crank shaft to the other end of thebed plate, which consists of a heavy box casting placed on eachside of the cylinder, running the entire length of the foundations,and secured at the ends with cross pieces all cast together, and