CHAPTER XV. 

 TESTS FOR LEAKS. 



The cylinder rings and the valve should be occa- 

 sionally tested to see that they are steam tight. 

 Should the piston or valve leak very much steam the 

 economy or efficiency of the engine will be considera- 

 bly lessened. The steam that leaks through, besides 

 being wasted, interferes with the free working of the 

 engine by choking the ports and exhaust, thus causing 

 high back pressure. If an engine is allowed to do 

 much leaking the results are far reaching. The ports 

 and exhaust being unduly filled, the engine has to do 

 more work to overcome the back pressure on the 

 piston and this, of course, means that the governor is 

 admitting an extra supply of steam to keep up the 

 speed. ,We thus have a double loss the steam 

 leaking through, and the steam used in excess of the 

 normal to overcome the resistance. This excess of 

 steam calls for an extra amount of feed water to be 

 forced into the boiler, an extra amount of fuel to be 

 burned, and an extra high temperature to which the 

 fire-box and plate are subjected. The engine and 

 boiler are thus required to dp an extra amount of 

 work, which in some old, worn engines may be nearly 

 fifty per cent of the actual work performed. 



The piston and valve may be easily tested as 



H7 



