All About Engines

The Modern Reciprocating Engine *4* less than 0-98 lb. per square inch available for lifting the valves. The degree of vacuum obtainable, moreover, depends upon the temperature of the cooling water ; the lower this is the higher will be the vacuum with a given pump and condenser. In this respect cold climates are more advantageous than hot ones, and the power station that can draw upon a plentiful supply of very cold water is better off than one which cannot do so. The Mersey Railway, for example, have to pump water continuously from the tunnel under the river, and even in the height of summer this is almost icy cold, so they use it in condensers. Mr. Charles Day, when President of the Man- chester Association of Engineers, quoted the following to illustrate the importance of workmen understanding the theory of engines they constructed. A man was sent out to erect an engine and set it to work. After putting it together, he got up steam and started it running. But the vacuum gauge indi- cated only 26 inches instead of 28. He took the pump and condenser to pieces, refitted the parts, and spent two days in searching for a leak by which air could enter and reduce the vacuum. Now, if he had measured the temperature of the condensing water he would have found that it was too high to give the vacuum he desired. Since an engine is only guaranteed to give its full power at minimum steam consumption with condensing water at a speci- fied temperature, the builders were not to blame. The cooling water required is from 20 to 25 lb.