The annexed figure represents a longitudinal section. At a is the foundation-plate, on which the engines are erected; it is supported upon two deep sleepers of wood, which cross the floor-timbers of the vessel, to which they are firmly bolted. A portion of the bed-plate is formed into a channel, nearly as deep as the sleepers, part of which channel forms the bottom of the condenser, and another part receives the foot of the air-pump; b the cylinder; c the slide-case, which is formed of three vertical compartments, connected at top and bottom by the apertures dd; the middle compartment forms the steam-chamber, and the side compartments are the eduction passages; e is the steam inlet; fthe slide-valve, formed of two short slides, connected by a rod, which is found preferable to a single long slide for large engines, as the latter is liable to warp; the slides, which on the back form about one-third of a circle, are pressed up to the seats by screws at the back, acting upon a block of metal, faced with a thick sort of mat, made for the purpose;/the valve lever, working upon the shaft of the parallel motion as a fulcrum; the motion of the eccentric is communicated by the intermediate lever g; h the parallel bar; j the condenser, cast in one piece, with k the hot-well, and bolted to the foundation-plate; i the injection pipe.

A tube, or cylindrical passage, is cast in the condenser, through which pass the gudgeons I of the working beam; these gudgeons are very securely wedged into bosses, cast on the sides of the condenser, and the brass bearings are fixed in a boss in the centre of the beam; m the air-pump; n the foot-valve; o the blow-through valve, through which the air and water are blown out of the condenser at starting the engine; p the delivery valve, through which the water passes into the hot-well; q the passage leading to the feed-pump; r the connexion with the relief valve; s the passage by which the waste water is carried off into the sea; t an air-vessel; v the beam; w the connecting rod; y the crank; z the blow-through cock, connecting the steam-chamber of the slide-case with the eduction passage; this cock is opened previously to starting the engines, for the purpose of expelling the air from the engines, or, as it is termed, blowing through.

Beam Engine 541

The feed-pump and bilge-pump are worked from the cross-head of the air-pump, and could not be shown in the sketch. The annexed figure represents, on a larger scale, a section of the feed-pump, with its valves. a is the plunger, attached to the cross-head b, and working through a stuffing-box in the pump-barrel c; d is the valve-box attached to the side of the hot-well; e is the suction-valve, through which the water is drawn from the hot-well into the pump by the rise of the plunger. On the descent of the plunger the water is driven out at the valve f, along the feed-pipeg to the boiler, unless the regulating valves or cocks on the boiler should be quite closed, when it raises the loaded valve h, and returns to the hot-well by the aperture k. The load per square inch on the valve h must somewhat exceed the pressure per square inch of the steam in the boiler.

In addition to the bolts, by which the cylinder, condenser, and side-frames are screwed down to the foundation-plate, there are twelve strong bolts, called holding-down bolts, which are passed from the outside through the floor-timbers, sleepers, foundation-plate, and bosses on the cylinders, condensers and side-frames, and screwed as firmly as possible by strong nuts. These bolts are of copper, or iron tinned, in order to resist the corrosion of the sea-water.

Beam Engine 542

The arrangement of the Beam Engine is, perhaps, that which is best adapted for general use in steam-vessels, as all the parts admit of easy access; the weight of the moving parts on each side of the beam nearly counterbalance each other, and the requisite pumps are easily attached; but their weight and the space they occupy have, in the progress of the improvements which marine engines have undergone, been deemed very serious drawbacks; and, at present, opinion seems to be setting in favour of what are termed "direct-action" engines, most of the leading engineers having adopted each some particular arrangement for dispensing with the side-beams. Several of these deviations from the common form we shall now proceed to describe, commencing with one which may be considered as intermediate between the Beam and the Direct-action Engines; it is commonly termed a "Lever Engine," the action of the piston being transmitted to the crank by a lever, whose fulcrum is at the extremity.