STATIONARY ENGINES.

183

outside cylinder or casing is covered over with feit or non-conductingmaterial, and then carefully lagged with wood, with four or moremetallic straps girding it all round; in some instances heated airhas been applied all round the steam cylinder, the annular spacebeing encircled with brick-work. The thorough protection of theinside or working cylinder so as to prevent surface condensation,and the covering of the steam pipes from the boiler with feit andcanvas to prevent radiation—combined with the high steam pressureused and the large measure of expansion obtained—have raisedthe duty performed by the Cornish engine far above that of theordinary dass of engine used for land purposes.

Figs. 116 and 117 give side and end elevations of an overhead-beampumping engine erected at a pit near Kilmarnock. The principaladvantage in the arrangement here is that it leaves the pit mouthclear, and in sinking a pit enables the rods to be easily lengthenedas required.

The cylinder is 84 inches in diameter, suited for a 12-feet strokein the pump. The piston rod is connected to a strong malleable-iron beam, made of two plates placed 15 inches apart. The pumprod is connected to one end of the beam, and the other end is sup-ported by vibrating columns oscillating on journals working in twobearings, which are bedded on the top of the stone pedestals for thefoundation, and secured with bolts and nuts passing down throughthe foundation, and having a cotter and wall plate at the bottom.

The parallel motion for the piston rod consists of two motionrods, one on each side of the beam, connected to cast-iron Standardsbolted to projecting flanges on the top of the cylinder. The plugrod for the valve mechanism is worked directly off the beam, fromthe same gudgeon as for the parallel-motion bars, and is guidedwith a bracket placed underneath the engine-room floor.

The engine is fitted with a blow-through condenser, on a planwhich works as follows:—Steam being admitted to the bottomof the cylinder, the piston is forced to the top of its stroke; thesteam valve is then shut by suitable gearing, and the steampasses from the bottom side of the cylinder to the top side, thepiston is then in equilibrium, and the weight of the pump rodscarries it to the bottom, but before it reaches this point the injectorvalve is opened with a tappet placed on the feed-pump rod, withlevers and rod carried along to the valve; water is thus admittedinto the condenser, and the valve remains open until the steam is