PLATE IV. Fig. 1. is a section of the parts of a high pressure engine with a four passaged cock. The engine is supposed to be partly within the boiler, of which D B. is the top plate. P is the steam piston, and R the piston rod, A is the four passaged cock; the steam enters from the boiler at S, and passes through t to the top of the piston, and the steam below escapes through the passage b, and pipe a and E, to the atmosphere; the pipe E is surrounded by water which the escaping steam: warms ready for the boiler. By turning the cock the motions are reversed, but it is obvious we cannot in this engine employ the expanding force of the steam. The motion is regulated by a throttle valve V. (See art. 356–361.) Fig. 2. and 3. shew a section and plan of a similar engine, with a dee-slide instead of a cock; the steam enters from the boiler at S, and by the passages being shut and opened close to the extremities of the cylinder, there is no loss by the communicating pipes being filled with strong steam. (See art. 364.) This engine will not work expansively unless the construction of the slide be altered. (See art. 371.) Contrary to the usual practice, the packing of the slide is on the sliding part; the advantage of this plan is obvious, but the practical difficulty of boring a semicylinder is incurred. Fig. 4. is a simple arrangement of the high pressure engine by which the expanding power of the steam may be used; it is the invention of Messrs. Taylor and Martineau. The passages are opened and closed by pistons sliding in a pipe: the steam enters this pipe at S, and the steam is supposed to be just shut off by the upper piston, so that by the expansion of that in the cylinder the rest of the stroke is completed, the passage E to the atmosphere being still open, (see art. 371-380.) The slide would be improved by making it of the form of a dee-slide. The construction of the pistons of the slide is a suggestion which may perhaps answer better than the common ones, (art. 450 and note.) Fig. 5. is an arrangement to illustrate the action of a high pressure engine to work expansively by means of combined cylinders. (See art. 381-383.) PLATE V. Fig. 1. is a section of a double acting condensing engine, with a slide adapted for working by the expand ng force of steam; the slide being, in Fig. 1, in the position for letting the steam on at the top. Fig. 2 shews the steam shut off and the passage to the condenser still open, and Fig. 3, the position when the steam is let on at the bottom. (See art. 448.) The steam enters at S, and a pipe of communication between the steam pipe and the condenser is necessary, to allow steam to enter the condenser when the engine is about to be set to work, (art. 414.) Fig. 4. is a section of a single acting condensing engine, with valves to the passages, (see art. 406;) and Fig. 5, a different arrangement of the valves for a single engine. In all these figures the same letters indicate the same parts. C is the steam cylinder, P the steam piston, R the piston rod, B the condenser, with a jet of water playing into it from I the injection cock; A is the air pump, and p its piston; G is the foot valve between the condenser and air pump; M the air pump, and Q the discharge valve of the air pump, through which the air and hot water are forced into the hot well K, from whence a part is raised by a small force pump to the boiler feed head, and the rest runs off by a waste pipe. H is the blow valve to the condenser, (art. 566.) The condenser and air pump are placed in a cistern which is constantly supplied with cold water by a pipe N. The jet should be made through a rose on the end of the pipe; for to produce speedy and perfect condensation, the cold fluid should present the greatest possible surface to the steam it is to condense, (see art. 280;) and it should be impelled into the condenser with greater force than the ordinary head in the cistern admits of. In large engines the connecting eduction pipe E, Fig. 1, may be on the outside of the steam pipe S, and the parts of the slide connected only by a rod, as mentioned in (art. 447.) |