7 (ph. 79) shows in section and in per spective an improved surface-condenser combined with an independent air-pump and a circulating-pump. The exhaust steam entering from the engine at A is scattered to the perforated plate 0; it expands in the upper part of the case, then passes among the tubes, and leaves the case at B, going thence to the air-pump. The cooling water entering the circulat ing-pump passes into the compartment F, thence into the small tubes, which it traverses, then returns through the annular spaces between the wall and the large tubes, and empties into the compartment G. Thence it passes into the compartment II by the passage-way E. It next circu lates through the upper section of the condenser in the same way, and finally passes out through I). This type of condenser differs essentially from others in that it employs concentric tubes, and that each tube is free to expand and contract without requiring any ferules or special joints. It has extraordinary capacity and is very readily cleaned. Tests with a small experimental apparatus show iot.8 pounds of steam condensed per hour per square foot of condensing surface with vacuum, and 204.2 pounds without. In the first case the injection-water temperature was 36X° Lahr., discharge 98°, hot 138°, and average vacuum by the gauge inches. En the second the injection was 78;<°, discharge 139°, and hot well 2o1°.
The old jet-condenser has been transformed into what is now known as the siphon-condenser (pi. 79, jig. 4), in which no pump is necessary; the vacuum produced by the condensation of the steam by a jet being suf ficient to raise the water in a continuous current when the action of the apparatus is established.
It should be distinctly understood that a condensing engine may be either compound or non-compound, single or duplex, and that the air pump and circulating-pump of the condenser may be so arranged that they may be either driven by the main engine itself or operated as sepa rate pieces of mechanism. It is well to have the condenser so attached that it may be thrown out if it be desired to inspect, clean, or repair it, or if it be found that the engine is under]oaded. Examples of non-compound condensing engines are given in Figures 4 and 6 (A/. 82); of compound condensing in Figures 3 and 4 (pl. Si); and of triple-expansion condensing in Figure 4 (pk8s).
being in a very early cut-off and in an excessive amount of expansion in one cylinder certain disadvantages—for example, the chilling of the internal surfaces of the cylinder and passages by the low temperature of a low-pressure exhaust, and the great range of pres sures upon the piston and crank-pin during a single stroke—these disad vantages are lessened by what is known as " compounding;" that is, run ning one or more engines with the exhaust from another engine, thus requiring only a moderate degree of expansion in the first cylinder, and running the second cylinder by expansion only, both engines being con nected with the same crank-shaft, or, in the case of those direct-acting pumping-engines which have no crank, with the same pump-pllinger.
There may be between the high- and the low-pressure cylinder either direct communication by steam-passages or a receiver or intermediate vessel which permits the low-pressure piston or pistons to act upon the crank-shaft at right angles to the high-pressure cylinder.
"olf Compound the Wolff or receiver compound engine the cranks are at right angles, so that they pass through dead-points at dif ferent times. The steam from the small or high-pressure cylinder passes into the receiver before going into the large or low-pressure cylinder; the pressures being thus equalized, although there is some loss caused by con densation of steam in the receiver. The condenser, with air-pump and feed-pump moved by a rock-shaft, is on the front. (It should be noted in this connection that the Wolff compound engine has a receiver; the Woolf compound has none.) In Figure 4 (pl. Si) is represented Woolf's compound beam-engine. Figure 3 (pl. 8S) shows a Collmann compound engine in which the cranks are at right angles. Figure 4 shows a com pound engine on Woolf's plan, but there are one high-pressure cylinder and two low-pressure cylinders, which have equal functions.
the Woolf or receiverless compound engine the small or high-pressure and the large or low-pressure cylinder stand side by side under the same end of the beam, their pistons moving in the same direction at the same time; the exhaust passing from either end of the small to the opposite end of the large cylinder. McNaught's improve ment has the cylinders at opposite ends of the beam, the pistons moving different ways, and the steam passing from either end of the small cylinder to the nearest end of the large one. Elder's compound engine has the large and the small cylinder side by side in close contact, inclined at 45'; pistons moving oppositely and driving cranks projecting in opposite direc tions from the shaft; a similar pair of cylinders acting on the same pair of cranks and inclined the opposite way at the same angle. Craddock's compound type has the cylinders side by side, their pistons driving cranks nearly opposite and moving for the greater part of the course in the same direction; the stroke of the small piston being made a little in advance of that of the large one, to prevent stopping on the dead points.