HOW THE TESTS WERE CONDUCTED. 27 



readily blocked in certain positions by standing a piece of tim- 

 ber endwise, reaching from the end of the crank to the floor 

 or bed, or by putting in a number of wooden blocks laid flat, 

 and building up to the desired height. Here, again, the crank- 

 pin should be brought to the required position before the blocks 

 are put in, and filling-pieces should be applied to make up the 

 leeway, rather than move the engine and run the risk of injury 

 by bringing up solid against the blocks. 



Leakage tests of the valve in the case of single-valve engines 

 cannot be made as satisfactorily as those in four-valve engines, 

 for if the valve leaks excessively it is difficult to locate by these 

 methods the exact place of the leak. The best that can be 

 done is to place the valve on its center covering both ports, 

 and try it under a full steam pressure. The same course can 

 be followed in testing the piston as that described for the four- 

 valve engines. In a leaking engine of this type, it is usually 

 necessary to test the piston with the cylinder head removed 

 before the investigation is complete. 



It is needless to call attention, in more than a passing way, 

 to the test of piston leakage in an e-ngine which is single-acting. 

 In a Westinghouse engine, for example, the leakage of the 

 piston is revealed by simply swinging off the cover of the crank 

 case, and observing at once what escapes from the periphery 

 of the piston, the engine being blocked and steam pressure 

 admitted into the cylinder. 



The foregoing remarks on the subject of leakage apply to 

 simple engines. In the case of compound engines the work is 

 to some extent simplified. For example, in testing the leakage 

 of the high-pressure exhaust valves and piston, the escape of 

 steam is observed by opening the indicator-cock on the end of 

 the low-pressure cylinder which is taking steam, and observ- 

 ing what blows through. Again, in testing the low-pressure 

 exhaust valves and piston by the time method, steam is ad- 

 mitted into the receiver until the desired pressure is reached, 

 then, after the cylinder has been thoroughly warmed, and the 

 supply shut off, the drop in pressure is observed by reading the 

 receiver gauge and keeping a record of this. A similar course 

 is followed in testing the leakage of triple-expansion engines. 



