24 ENGINE TESTS. 



matter is to make the examination when the engine is at rest, 

 for certainly no thorough inspection can be made when it is in 

 motion. If it is found that there is practically no leakage at 

 rest, it seems reasonable to conclude that the engine is tight in 

 motion. If, however, there is leakage at rest, we can certainly 

 say that there is a probability of leakage in motion, although it 

 may not be possible to judge of its degree. 



The leakage tests here referred to are not quantitative ; that 

 is, they do not determine the exact amount of leakage, but 

 rather the fact as to whether leakage does or does not exist. 

 They are intended simply to give the observer a fair idea as to 

 the general condition of the engine. 



Turning to the methods employed in testing for leakage, the 

 steam-valves are readily disposed of. In a Corliss engine, it is 

 necessary simply to close the two admission valves, open the 

 two indicator-cocks, and with the starting-bar move the exhaust 

 valves first one way and then the other, the throttle valve be- 

 ing open, and a full pressure of steam being admitted into the 

 chest. When the starting-bar is moved so as to close the ex- 

 haust valve at the head of the cylinder, any leakage of steam 

 through the steam valve at that end will be made to escape at 

 the indicator-cock, and thus become visible. Likewise when 

 the starting-bar is moved so as to close the exhaust valve at the 

 crank end, the steam which leaks through the crank-end ad- 

 mission valve will show itself at the open cock. In making 

 these movements of the starting-bar, care is taken that the 

 steam valves are held unhooked. The quantity of leakage is 

 judged by the force of the current of steam blowing out of the 

 cock. If the valves are tight there is simply a breath of steam, 

 or an entire absence of vapor. If they leak badly, the cur- 

 rent will blow out of the indicator-cock with much force and 

 noise, and rise to a height of several feet. 



In testing the exhaust valves and pistons for leakage, the 

 best method is to block the fly-wheel in such a position that the 

 engine is taking steam with the piston at a short distance from 

 the end of the stroke, open the throttle valve, and observe what 

 blows through. It is well to try this if possible with the 



