STATION AR Y ENGINES.

173

allowed to fall by gravitation into the cistern or metallic box. Inanother example, where refinement of construction is a desideratum,the cistern is dispensed with, and the oil isejected through a valve fitted to the pistonon the down stroke, and passes through thesame valve on the up stroke, it being forcedthrough by suitable mechanism in thedown stroke, and the ascent of the pistonis acted on by the weight, as in the formerexamples. This plan of cataract necessi-tates a hollow piston rod, with stuffing boxon the pump cover, fitted with an internalrod attached to the valve, passing up to thecrosshead, for taking the disengaging rod;this hollow rod is fitted with a stuffing box,and the internal rod has a thumb screw atthe top for regulating the lift of the valve.

Thus this valve allows of the oil passingfrom the bottom to the top of the piston,and also regulates the flow of the oil fromthe top of the piston to the under side ofit, forming a self-contained and handsomecataract pump.

j /t-'* __\ r ,1 /-« *i Fie. 106.—Cataract without Cistern.

1 he condenser (rig. 107) for the Cornish

. . ... 1 , a, Cylinder. b, Cupped leather pis-

engme is generally a separate vessel, worked t0 n with valve. c, Hoiiow rod.on the injection principle. As the exhaust D ’ T , Stu ? ng box , and gIand -

J 1 1 e, Thumb screw and gland.

pipe from the steam cylinder is of large

diameter and of considerable length, it is obvious that the cubicalcontents of the condenser need not be so large as for ordinaryengines, the exhaust pipe acting as a receiver, and the steam beingCondensed in a vessel placed at the extreme end.

The airpump is of the ordinary kind, with metallic liead and footvalves, the bücket being open, with a metallic valve placed on thetop, and it is made tight with ordinary hemp packing plaited, or whatis termed a gasket. In another example (Fig. 108) the air pump andcondensing vessel are placed inside of a cast-iron tank, which is keptconstantly full by means of a pump termed the cold-water pump.When this arrangement is adopted the condensing vessel is kept quitecool by the surrounding water, and to a certain extent acts as a surfacecondenser, in combination with the injection System. The tank