| | | | |
indicated H.P.H.-- | | | | | | | | | | |
Simple Lb.|42.76| 26.89| ... | 26 | ... | ... | ... | ... | ... | ... | ...
Compound Lb.| ... | ... |34.16| ... | 21.37| 20.35| 19.45| ... | 19.19| ... | ...
Triple Lb.| ... | ... | ... | ... | ... | ... | ... | 19.68| ... | 19.19| 18.45
Steam required theoretically | | | | | | | | | | |
per 1 H.P.H. Lb.|34.67| 19.24|19.86| 17.9 | 17.65| 16.25| 15.23| 15.16| 14.87| 14.9 | 14.36
Percentage efficiency |81.1 | 71.5 |82.2 | 68.8 | 82.5 | 80 | 78.3 | 77 | 77.4 | 77.6 | 77.8
------------------------------+-----+------+-----+------+------+------+------+------+------+------+------
Percentage of feed water | | | | | | | | | | |
missing at cut off in | | | | | | | | | | |
high pressure cylinder | ... | ... | ... | ... | ... | ... | ... | 5.33| ... | 6.84| 5.01
Ditto high pressure cylinder | ... | ... | 5 | ... | 9.5 | 11.7 | 15.1 | 14.84| 17 | 12.06| 15.33
Ditto low pressure cylinder |11.7 | 24.8 |15.2 | 29.56| 16.25| 19.1 | 20.6 | 22.12| 21.3 | 22.11| 24.21
Percentage of feed water | | | | | | | | | | |
missing at end of stroke | | | | | | | | | | |
in low pressure cylinder |10.4 | 18.83|14.25| 21.53| 16.59| 17.55| 20.69| 18.01| 19.55| 18.81| 19.25
------------------------------+-----+------+-----+------+------+------+------+------+------+------+------

The author compared a series of compound trials, at different powers,
with 130 lb. absolute pressure, and various ratios of expansion, with
a series giving approximately the same powers at a constant ratio of
expansion, but with varying pressures, being practically a trial of
automatic expansion against throttling. Starting with 40 indicated
horse power, 130 lb. absolute pressure, four expansions, and a
consumption of 20.75 lb. of water, the plan of varying the expansion,
as compared with throttling, showed a gain of about 7 per cent. at 30
indicated horse power, but of a very small percentage when below half
power. If the engine had an ordinary slide valve, the gre