The slide-valve engine is built in a great variety of forms. Fig. 244 represents a sectional view of the cylin-der of a very common type. At e, Fig. 245, we have a cross-section through the steam chest and exhaust port at AB, and at F, a cross-section at CD through the steam port.
When the cylinder is small - 10 inches or under in diameter - the pattern is usually built up solid, but if more than 10 or 12 inches in diameter it should be built of staves, as shown in Fig. 246. When the size is 30 inches or over, a loam mold is usually made, as is fully described in the section on Foundry Work. The size limit, however, varies greatly in different foundries.
Fig. 244. Section through Slide Valve Cylinder.
Fig. 245. Sections through Slide Valve Cylinder at AB and CD, Fig. 244.
The construction of the pattern is illustrated in Fig. 246 and needs no description here, it being the same as already given for Fig. 226. The flanges, however, should be built up of segments of two or three layers each, as shown in Fig. 247. After gluing up to the necessary thickness to make the flange, it is sawed in two halves, jointed, and carefully centered on a wooden chuck, and turned to the dimensions required. The centering must be done with accuracy, or one-half of the flange ring will be larger than the other.
Fig. 246. Section of Cylinder Pattern.
The steam chest is next built and fitted centrally on the upper half of the cylinder pattern, as in Fig. 248.
The projections aa, which give the extra width of metal for the bolts of the chest cover, are left loose, being kept in place by long wires or dowel pins, as shown at cc, so that they can be withdrawn separately from the mold after the main part of the pattern has been taken from the sand. These four strips should be recessed into the corners of the chest 1/4 inch, as shown by the dotted lines, to prevent them from being rammed out of place after the dowel pins are taken out. The boss i for the valve-rod stuffing box, and also the boss k around the steam-pipe opening, must be loose so as to be taken out of the mold after the pattern has been removed. The pieces oo at each end of the steam chest, which form a thickness of metal over the steam ports, are then fitted in place, as is also the exhaust passage n, which must be parted on the line of parting of the two halves of the cylinder pattern.
Fig. 247. Built-Up Flange for Cylinder.
Fig. 248. Two View, of Cylinder Pattern Including Steam Chert.