. A manual of marine engineering: comprising the design, construction, and working of marine machinery. Fig. 85.—The Trick Fig. 86.—Common Double-ported Valve. Double-ported Valve.—This valve (fig. 86) has a system of ports andpassages which is added to the locomotive slide-valve, to allow of admission Piston valves. 267 and emission of steam through a second port in the cylinder face, so thatwith the same travel as the common valve, there is double the area ofopening for steam, and double the area for exhaust. Tliis form of valve isvery generally adopted for both the medium-pressure a
. A manual of marine engineering: comprising the design, construction, and working of marine machinery. Fig. 85.—The Trick Fig. 86.—Common Double-ported Valve. Double-ported Valve.—This valve (fig. 86) has a system of ports andpassages which is added to the locomotive slide-valve, to allow of admission Piston valves. 267 and emission of steam through a second port in the cylinder face, so thatwith the same travel as the common valve, there is double the area ofopening for steam, and double the area for exhaust. Tliis form of valve isvery generally adopted for both the medium-pressure and low-pressurecylinders of compound engines of large size, and for the low-pressurecylinder of even very small engines. Oare must be taken in designing sucha valve, that there is the requisite area for steam to enter into the cavityleading to the steam port, and also that there is ample room at its back forthe exhaust steam to pass from the outer port of the cylinder. Treble-ported Valves.—To obtain still larger opening for steam, the lapof the double-ported valve is extended so as to cover a third port at eachend ; a
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