The upper part of it is hollow, to receive a small rod, that is attached by a cross pin to a brass sliding socket, which is connected with the governor arms by two small links, and partakes of the motion communicated to them by the movement of the balls. The small rod has a communication with the throttle-valves, by means of the levers fixed to the ceiling of the engine-house.
The kind of boiler attached to this engine is of the waggon-shaped kind, a full description of which has already been given at page 198 of the first volume of this work.
The steam cylinder and its casing are cast together in one piece; the space betwixt them is constantly filled with steam, which prevents any condensation taking place within the cylinder, and serves also as a conducting-pipe for the steam to the boxes E, containing the sliding valves, (which are generally called D valves, from their resemblance in form to that letter,) through two separate openings for that purpose, in each of which is placed a throttle-valve, and on their spindles are levers, communicating by a rod with the governor, for regulating the speed of the engine.
The sliding-valves are packed on their circular sides with a soft substance of hemp or flax, and in consequence of the steam being admitted to the under side of the top valve, and the upper side of the bottom valve, they of course require no more force to move them than what is necessary to overcome the friction of the packing, and the surface over which they slide. The weight of the valves and their rods are accurately counterbalanced by a movable weight or a lever under the cylinder, and are moved by an eccentric circle, on the fly-wheel shaft. By the arrangement of having two throttle valves, the least difference in weight between those parts of the engine that are attached to the opposite ends of the working beam can be regulated, by allowing a little more steam to pass in the same time through either of the valves, as may be found necessary, - thereby equalising, as much as possible, the action of the engine. One pipe, G, only is required in front of the cylinder, and that for the purpose of conducting the steam from the upper side of the piston to the condenser.
H, a vessel in which the condensation of the steam is effected after its escape from the cylinder, by admitting a quantity of cold water out of the condensing cistern I, through an injection cock, the opening of which is regulated by hand. The condensing cistern is supplied with water by the cold water pump K. L is the hot water pump, used for raising water to supply the boiler; which water passes through a small valve, and down the same pipe that contains the damper-float. This valve is connected with a lever, having one of its ends connected by a rod passing through a pipe with a stone float, that rises and falls with the surface of the water in the boiler, and thereby admitting a smaller or larger quantity of water, as may be requisite. This pipe, for the rod to pass through, has several advantages over the method of passing it through a stuffing-box on the boiler top; as, in case the hot water pump by any accident should cease to act, and the water get low in the boiler, the steam would make its escape before any serious injury could happen, - showing instantly that such was the fact, the moment it got below the end of the pipe. The friction between the rod and the water being so trifling, insures an almost uniform regularity of action.
N, a small cistern, containing the blow-valve, for the purpose of allowing the air to escape from the cylinder, etc, previous to the engine being set to work. We shall now give an example of a common arrangement of the high pressure engine; in which, as no air pump is required, the beam is dispensed with.
h, the steam-pipe leading from the boiler, in which is the throttle-valve i; j, the side-pipe, in which work the slide-valves k k, moved by the rod l, attached to the eccentric m, on the shaft of the fly-wheel n. o o o are brass stuffing-boxes; p, the upper steam entrance to the cylinder; q r, the piston-rod working through the bridge s, and communicating with the crank t by the side-rods u u, - forming a very simple parallel motion; v v, pedestals supporting the main shaft, the revolution of which gives motion to a pair of bevel wheels, and thereby to the governor w, the expanding or contracting of the arms of which raises or depresses the collar z, and acts on the valve i through the medium of the lever 1 and handle 2; 4 is the pump for supplying the boiler through a feed-pipe (not shown) worked by the rod 5, and eccentric 6; 7 7 are the metal cheeks of the frame; 8, the metal foundation plate, under which is a small cistern, (not shown,) containing a day's consumption for the boiler. At the bottom of the side-pipe is an eduction-pipe, (not shown,) from which the steam is discharged into the cistern, to heat the water for supplying the boiler after the steam has performed its office in the cylinder.
The periphery of the fly-wheel is round in its transverse section, and of cast iron; the arms or radii are of wrought iron, and are inserted into the former while casting. The subjoined figure represents an arrangement which is frequently adopted for engines of small power; the cylinder is suspended upon axes or gudgeons, and vibrates to and fro during the revolution of the crank, and hence these engines are commonly called vibrating engines. The gudgeons are hollow, and form the steam and eduction pipes; a is the steam cylinder, b the hollow gudgeon at which the steam enters, and whence it passes by the channel c to the slide case d; and a channel similar to c connects the eduction passage with the other gudgeon, which opens into the condenser. The gudgeons project beyond the bearings in which they work; and their extremities pass through stuffing-boxes in the steam pipe and condensers; no connecting rod is required, but the piston rod is connected directly with the crank pin, and during the revolution of the crank the cylinder vibrates upon its gudgeons through an arc proportioned to the length of the crank.