Forced Cooling of Exhaust Valves
Page 78
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WITH the present trend towards VY increasing the power of engines, by supercharging or otherwise, the heating of the exhaust valves is becoming the limiting factor in power output. A scheme for positively air-cooling the valves forms the subject of patent No. 885,985. (Caterpillar Tractor Company, 800 Davis Street, San Leandro, California, U.S.A.)
The drawing shows a cylinder head as would be used on a supercharged engine. In addition to water-cooling passages (1 and 2) the exhaust valve-stem is surrounded by an annular space (3). This is connected to the compressed air in the inlet port (4) by an upward passage (5) and a downward one (6). A continuous current of cold air is thus applied to the valve stem, the air departing through the clearance (7) into the exhaust stream.
A flap-valve (8) is provided at the top of the two passages; the object of this is to prevent back-flow if the inlet pressure should be less than that of the exhaust. A second scheme shows the air-cooling sleeve extending almost to the head of the valve.
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