This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 Excerpt: ...either from contracted ports or too much inside lap on a slide valve narrowing up the exhaust passage as the center of the stroke is reached, and where the piston, and consequently the steam, has the greatest velocity. The same effect may be produced upon a Corliss engine. It is also found where a pair of cylinders working on cranks set at 90 degrees exhaust into the same pipe, the release of one cylinder occurring practically in the middle of the stroke of the other and the efflux of steam into the pipe causing a rise of pressure. The end of the back-pressure line depends for its shape upon the amount of compression. At c in diagram B, Fig. 64, for instance, the exhaust-valve closes and the steam remaining in the cylinder is compressed, the pressure rising upon the curve shown. With no compression the back-pressure line would continue straight to the end of the diagram, and with a prompt admission we should have a square corner at the end. When the compression commences earlier in the stroke the compression curve runs proportionally higher, as is well shown at F, taken from an engine where the compression varies with the load, and showing the effect upon the counter-pressure line of closing the exhaust valve at different points in the stroke. It is even possible to carry the pressure, by compression above that in the steam chest, so that when the valve opens for the admission of steam, the pressure in the cylinder being greater than that in the steam chest, there is a drop instead of a rise to the line of realized pressure, as shown at Q. CHAPTER X THE COMPRESSION LINE Compression is the inverse or opposite of expansion. In making the expansion line the volume of steam admitted up to the point of cut-off is increased in volume, the pressure falling in an i...