276 ENGINE TESTS. 



As the economy of non-condensing compound engines is greatly 

 affected by the boiler pressure, the single-valve engine in this 

 case has an undoubted advantage, which more than makes up 

 for the difference produced by the valve. The superior econ- 

 omy of the 4- valve type is evidently due in part to the better 

 distribution of the steam in the cylinders, as revealed by mor^ 

 perfectly formed diagrams; and, in some cases to the tighter 

 condition of the valves and pistons. 



One test is given that shows the loss in economy due to the 

 variable load produced in electric railway service. This is 

 Engine No. 58 B, which is a Corliss compound condensing 

 engine. Compared with test No. 58 A, which was made 

 with the same engine working under a steady load, the loss is 

 only 2.5%. On the test with the variable load, the average 

 power was 843.4 II. P., while that with the Meadv load was 

 1030.1 H. P. It is evident that the difference in economy 

 shown was caused to a considerable extent, if not \\holh. bv 

 the fact that in the variable load the engine is at times under- 

 loaded, and not working to its best economical advantage. 

 This was probably an unusually favorable showing for a varia- 

 ble load in the service mentioned, for the reason that the ran^e 

 of variation was less than occurs in much work of this kind. 

 An examination of the indicator diagrams gives some idea of 

 the extent of the variation. 



One method of reducing the loss of steam where compound 

 engines are used, is to exhaust the air-pump into the receiver 

 of the engine. This virtually converts the air-pump from a 

 simple engine to a compound engine. The effect of thus util- 

 izing the exhaust steam of the air-pump is seen in test No. .">7. 

 The effect is shown by the large increase of the amount of 

 steam accounted for in the low-pressure cylinder, as compared 

 with that in the high-pressure cylinder. The increase is from 

 .696 to .80, or .104. In Engine No 55, which is of similar 

 type except in this particular, the increase is only .013 ; and in 

 Engine No. 58 A, also similar in type, there is a falling off of 

 .08. In Engine No. 57, the steam used by the air-pump when 

 exhausting into the condenser amounted to .9 of a pound per 



