162 ENGINE TESTS. 



Engine No. 41 is a vertical cross-compound unjacketed high- 

 speed engine, having unpacked piston valves, one for each 

 cylinder, and controlled by a shaft governor operating on the 

 cut-off of the high-pressure cylinder. A jet condenser is used, 

 operated by an independent air-pump driven by steam taken 

 from the main pipe. The quantity of steam used by the con- 

 denser was determined by an independent test and allowed for. 

 Allowance was also made for steam condensed in the large ser- 

 vice main, which was designed for supplying several other 

 engines besides the one tested. Steam was furnished by hori- 

 zontal return tubular boilers, and a calorimeter test showed that 

 it contained T % of 1% of moisture. The valve of the high- 

 pressure cylinder was found to leak quite badly. That of the 

 low-pressure cylinder was reasonably tight. The leakage of 

 the valves interfered with a determination of the condition of 

 the pistons. The load consisted of dynamos furnishing cur- 

 rent for electric lighting. The tests were made with two differ- 

 ent loads, other conditions remaining the same. 



If the results of this test are compared with those made on 

 a four- valve engine such as No. 36, which showed a much more 

 economical performance, the effect of various features in the 

 design of the engine are apparent. Engine No. 41 had a single 

 valve, which secured less perfect distribution of steam than the 

 four valves of the other engine. It had larger percentages of 

 clearance space, and finally, the type of valve used permitted a 

 much larger amount of leakage than occurred in the other 

 engine. Engine No. 41, however, had the advantage of more 

 rapid reciprocations ; but this, it appears, did not have sufficient 

 effect to overcome the losses due to the causes mentioned. 



