[mbllanby] efficiencies OF MULTIPLE-EXPANSION ENGINES 13S 



A B. If to the left it shows that the cushion steam at admission pressure 

 would more than fill the clearance space, if to the right, that the cushion 

 steam at admission pressure is insufficient to occupy the whole of the 

 clearance. The weight of the hotwell discharge Avas then found, and 

 divided by the total number of strokes made by the engine during the 

 trial. This gives the weight of steam passing through the cylinder 

 at each stroke, assuming as stated above that an equal amount of cylinder 

 feed is taken by either end of the cylinder. The volume that this weight 

 of saturated steam would occupy at admission pressure is then foand and 

 set off to the right of A B. A curve is then drawn, showing the volume 

 of this steam, plus the amount of cushion steam at different pressures. 

 This gives us for any pressure the volume that the weight of steam in 

 the cylinder would occupy if it were dry and saturated. The volume 

 that this steam does occupy at any pressure after cut off, is given by the 

 indicator card, and the ratio of these two volumes gives us the dryness 

 fraction of the steam for any particular point. A slight complication 

 enters into these particular diagrams on account of the clearance space 

 of any cylinder not being constant throughout the stroke. Thus during 

 expansion the clearance is greater than during compression by the volume 

 of the admission port in the main valve. The distance between A B and 

 the line E F on the L.P. cylinder represents the clearance volume during 

 expansion, and in obtaining the dryness fraction of this cylinder the line 

 BJ F has been taken as the ordinate of no volume. The extra amount of 

 steam represented by the space between C D and E B" has of course been 

 taken into account. 



The indicator diagrams of the jacketed and unjacketed quadruple 

 expansion trials, working at 90 revolutions per minute, have, in addition 

 to being shown as combined cards, been transferred to the temperature- 

 entropy chart. In order to form a more ready means of comparing the 

 action of the steam during expansion, in the two cases, both sets of cards 

 have been shown on one diagi'am. The results of the experiments are 

 given in three tables. Table No. 1 gives the record of the compound and 

 triple series, working at 155 lbs. absolute intended mean admission pres- 

 sure, with cylinder No. 2 used as the II. P. cylinder and No. 3 as the M.P. 

 cylinder in the triple trials, and No. 4 as the L.P. 



Table No. 2 gives the recoi'd of the compound and triple series work- 

 ing at the same admission pressure, and Avith the same number of 

 expansions as tho.se in table No. 1, but using cylinder No. 1 as the IIP., 

 and with fii-st 3 and 4, and then 2 and 4 as the M.P. andX^-P- cylinders. 

 Table No. 3 gives the resulls of the triple and quadruple series, 

 working with an intended absolute mean admission pressure of 205 lbs., 

 using cylinder No. 1 as the II. P. and 2 and 4 as the M.P. and L.P. 

 cylinders for the triple trials. 



The various efficiencies have been worked out on the assumption 

 that the steam enters the steam chest dry and saturated. A sepai-ator 



