in which a and b show the wrong location for a slide valve and piston valve, respectively, while c and d give the correct position of the same as to drainage. In most Corliss engine cylinders the drainage is perfect at least as far as the cylinder proper is concerned, but in some designs water will collect in the steam chest, which may cause trouble if it is thrown over in a body by an abnormal rush of steam. Fig. 12 shows two cross-sectional views of Corliss cylinders of which the design FIG. 13.-Corliss cylinder with valves in heads. shown in B is to be preferred, since it is self draining, while the pockets shown in A will fill with water. In order to reduce the clearance space in cylinders the valves are sometimes placed in the heads, this we find in many engines of the Corliss type, for which a claim of high economy is made. If the exhaust ports are located, as shown in Fig. 13, there is very little chance for water that accumulates in the bottom of the cylinder to drain off; it will have to be forced out by the piston. A very troublesome feature of this construction is that the only way to get at the inside of the cylinder and at the piston and packing rings is to remove the back head including the valves, bonnets and everything connected with them; the valve gear must be disconnected and very likely the end of the cylinder must be propped up. This is even in large plants with plenty of help and lifting facilities quite a job for the engineer to undertake, the consequence is that cylinders of this design are not examined as often as would be desirable. It is advisable to steer clear of such troublesome designs even if the economy is a shade better than with the ordinary kind. FIG. 14.-Complicated cylinder design with poppet valves. The acine of complicity is shown in Fig. 14, representing a cylinder construction for high pressure and superheated steam. This design was originated several years ago in Europe and has been copied by engine builders in the United States. The poppet valves which are used are located in the cylinder heads, part of the valve gear is also attached to the latter. The cylinder proper consists of a simple cylindrical casting of symmetrical shape which is free to expand and contract. The inside of this cylinder is even less accessible than the one described previously. After removing the lagging, a part of the non-conducting material around the rear flange of the cylinder barrel must be knocked off in order to get at the nuts, steam and exhaust flanges must be disconnected, part of the valve gear taken off and the back head with the valves moved back on the foundation plates. If there is no spare engine to take the load, this work will throw the plant out of commission for the best part of a day, before everything is in running order again. FIG. 15.-Cylinder and heads with ground joints. The joints between the cylinder and heads will give trouble by getting leaky, which may be due to several causes. On some engines the joints are ground very carefully, obviating the use of gaskets. These ground surfaces are very apt to be damaged in handling of the heads, which, of course, will make them leak; if the leak is not stopped immediately the out-rushing steam will very likely damage the surface to such an extent that the surfaces have to be reground, which is a tedious and expensive job since often all the studs have to be removed and later put in again. Fig. 15 shows a design in which the difficulty about regrinding has been successfully overcome, the heads are made without the customary flange, they are both inserted from the back; the front head is drawn onto its seat by bolts while the back head is held in place by a plate bolted to the rear end of the cylinder. The ground surfaces are very narrow, if a leak should develop a copper ring made of wire could be used for quick repair. The construction is rather expensive and has, therefore, not found much favor with engine builders. The design commonly used is shown in Fig. 16, in this the head is made a good fit a short distance into the cylinder, the depth varying from 1 to 1 in. according to the size of the cylinder; the balance of the head is relieved COPPER GASKET about CYLINDER HEAD RELIEVED FIG. 16.-Regular joint between cylinder and head. in. all round, in order to make it enter freely. It is important to make the space as small as possible to prevent continuous condensation in the same. The inner surface of the head should be highly polished, also for the sake of avoiding condensation. The best material for the joint is a plain ring of soft copper not over in thick and from 2 to 1 in. wide according to size. Formerly corrugated copper rings were much used, but they are easily damaged, in which condition they will not make a tight joint. Attempts have been made to make gaskets of a combination of corrugated copper and asbestos, they may be used for cylinders of small bore but not for the medium and larger sizes. CHAPTER II VALVES Common slide valve. Partly balanced valves. Balancing rings. Influence of the angularity of the connecting rod. Equalization of cut-off. Valves for automatic engines. Prof. Sweet's valve. Piston valves. Adjustable valve seats. Adjustable piston-valve ring. Corliss valves. Port boring rig. Singleported Corliss valves. Double-ported valves. Corliss valves which wear leaky. Steam valves must lift. Water in cylinder. Porter-Allen valves. Multiported valves. Gridiron valves, Effect of high-pressure steam and superheat. Poppet valves. NOTHING is of greater importance on an engine than the valve or valves, on the operation of which depends, to a large extent, the success of the machine. The ingenuity of designers and engine builders has been taxed to the limit to make valves which will remain tight, are easily moved and give long service. The common slide valve has been used more than any other valve; it is, however, gradually being abandoned for the reason that it is so extraordinarily wasteful in the use of steam and subject to many other evils. Its simplest form is shown in Fig. 17; the principal trouble with it is due to the steam pressure acting on its large surface, causing excessive wear of valve and seat. Insufficient lubrication or hard spots in the valve or its seat are very often responsible for uneven wear and leaks. Leaky valves must be refitted and if the wear is uneven a slight cut should be taken off valve and seat and both of them scraped to a perfect fit. One of the things to look out for on valves of the older type is |
