. The science of railways . their General Construction, is preventedin compound engines of the Richmond type bythe use of by-pass valves located in the castingof low-pressure cylinder, as shown in Fig. 151,and further showm in detail in their two positionsby Figs. 155 and 156. They work automaticallyby the oj)ening and closing of the engine throttle,their construction and operation being as follows:The outer ends of the two piston valves VV areconnected by the passages A A with the inductionloorts of the low-pressure cylinder and their innerends are connected by the passages 00 with the OPERAT
. The science of railways . their General Construction, is preventedin compound engines of the Richmond type bythe use of by-pass valves located in the castingof low-pressure cylinder, as shown in Fig. 151,and further showm in detail in their two positionsby Figs. 155 and 156. They work automaticallyby the oj)ening and closing of the engine throttle,their construction and operation being as follows:The outer ends of the two piston valves VV areconnected by the passages A A with the inductionloorts of the low-pressure cylinder and their innerends are connected by the passages 00 with the OPERATION OF COMPOUND LOCOMOTIVES. 253 steam x^orts. The pistons PP simply act in thecavities of the valves as dash-pots to prevent slam-ming of the valves. Open the engine throttle, and live steam fromthe induction ports through the passages AAdrives the valves VV toward each other againsttheir seats and communication ])etween thetwo steam ports 0 and 0 is closed, as in Fig. the throttle closed, the least vacuum in the. steam chest, acting at A A, is aided by compressionin the cylinder through ports 00, and the by-pass valves move outward to the position shownin Fig. 155. In this position the two steam ports00 are connected and air passes freely from oneside of the piston to the other—the purpose forwhich they are applied. The necessity for very large port openings forthe large low-pressure cylinders w^as mentionedunder the general discussion of compound loco- 254 ENGINEERS AND FIREMENS MANUAL. motives and it was there stated that auxiliaryported valves of the Allen type were used togive a double port opening to the cylinders in theearly part of the admission period. One llichmond design of slide valve employsthis auxiliary port not only for double early ad-mission, but also to give a double opening in theearly exhaust period. Fig. 157 shows the designand gives the dimensions. It will be noticed that
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