Chap. XXI. STEAM CONSIDERED AS A MOVING POWER.

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the cylinder, which is securely fixed to the floor; a lid at e covers the top ; through thisslides the piston-rod in an air-tight stuffing-box ; the beam moves on its gudgeons, thebearings for which are properly sustained: a pump-rod carrying a counter-weight issuspended at the end of the beam at y, and both it and the piston rod k are connected bya parallel motion to the working beam, fg: at m is the condensing cistern, which con-

BOt’LTOS AND WATT’S SINGLE-ACTING ENGINE.

Fig. 1956.

tains the air-pump, w, the condenser and hot well, o. By the action of the cold waterpump, a continued supply is obtained, and all excess is carried away to the well by thewaste-pipe : r is the upper steam valve, s the lower one, t the exhausting valve ; thesearc all opened by the plug tree, v , and the lappets with which it is furnished. Water israised from the hot well, o, by the pump, to supply the boiler, and is carried by a pipe,tew, into a small cistern, x, on the top of the feed-pipe, which has a valve, acted onby a lever, attached to a wire passing through the stuffing-box to a stone float in theboiler, which opens the valve by its descent, and permits an additional quantity of water toflow in when required.

Xhe Single-acting Engine differs from the double in the arrangement of its pipes andvalves, as shown in fig. 1959. : the steam is condensed into the state of water : the movingforce equals the power of the steam : there are two cylinders; one admits the steam atthe top, and another, called the condenser, admits the steam at the bottom, from thelower part of which is the passage to the air-pump. The cylinder in which the pistonworks is shown at C, the condenser at B, and the air-pump at A : by the pipe S thesteam passes from the boiler through a valve at O, by which the piston, P, is forced down ;the steam which is beneath it passes into the condenser, the bucket, p, of the air-pumpdescending at the same time: the rod O receives a motion when the piston has arrived atthe bottom of the cylinder, which opens the valve 6, and shuts those of a and c. Thepipe E has then a communication with both the bottom and top of the cylinder: thejet is stopped, and the cylinder and condenser again filled with steam from the boiler;the piston is raised by a counterweight to the top of the cylinder ; this counterweight isay plied to the opposite end of the beam to that on which the piston-rod is fixed : whenthe cock is open, which allows the steam to pass from the boiler into the cylinder, thesteam in the condenser, and below the piston of the cylinder, is, by the playing of thejet of cold water into it, reduced to water; when the pressure on the top of the pistonbeing equal to the force of the steam in the boiler, and that below being small, the pistonis pressed down, and thus raises an equivalent weight at the opposite end of the beam.

The passage to the condenser is shut off when the piston reaches the bottom of thecylinder; a valve in the piston then opens, and allows the steam to pass through it:the piston rises by the action of the weight placed on the opposite end of the beam.