Fig. 68 is a compact vertical engine, as built by R. Hoe & Co., of this city.  It is intended to drive printing presses, but is adapted to any kind of work, and is especially suited to such places as require economy of space.  Although the value of expansion has been called in question by some of the engineers of the United States Navy, and under an appropriation from Congress is now to be made the subject of experiment; yet, in almost all the manufactories and workshops of the United States, no matter what the form of steam engine, or the purposes to which it is applied, whether stationary, locomotive, or marine, some form of cut-off, by which expansion of the steam can be availed of, is considered indispensable.  Many varieties are in use, but those engines are most popular in which the cut-off is applied directly to the valves on the cylinder, opening them quickly and shutting off almost instantly, avoiding all wire drawing of the steam at the ports, and regulating the speed of the engine promptly.  Of this class of engines, those manufactured by the Corliss Steam Engine Company, of Providence, R.I., are perhaps the widest known, not only for their extensive introduction, but also from having, by a long and successful litigation, established the claims of the patentee, Mr. George H. Corliss.

[Illustration:  Fig. 70.]

Fig. 70 is a section of the cylinder and valve chests of a horizontal Corliss engine. S is the steam connection, and E the exhaust; there are two distinct sets of valves, the steam s, s’, and the exhaust e, e’, operated independently of each other.  In their construction the valves may be considered cylindrical plugs, of which portions near the ports are cut away to admit the steam and reduce the bearing surface; the valves are fitted on the lathe and the seats by boring.  The motion given to the valves is rocking, but it will be observed that the valves are not firmly connected to the rocking shaft or cylinder; in the figure the valves are shown shade lined, and the shaft or stem plain; in this way the valves are not affected by the packing of the valve stem, but always rest upon the face of the ports.  In the figure the piston is just about to commence its outstroke, the movement of the steam is supposed to be represented by the arrows; the inner steam valve s, and the outer exhaust e’, are just beginning to open.  It will be observed that the outer steam s’ is fully closed, whilst the inner exhaust valve e is but barely so, showing that there has been a cut-off on the steam valve, but no lead to the exhaust, that it was left fully open till the completion of the stroke.

[Illustration:  Fig. 71.]