, or equal to seven
atmospheres. If it were boldly accepted that eleven atmospheres, or 165
lb., were to be the standard working pressure, the result would be a
gain of 14.55 per cent., provided no counteracting influence came into
play. Of course, there are forces which war against the attainment of
the full extent of this advantage, viz., the greater condensation in the
cylinders and loss in the receiver or passages.
In regard to the former, it may be questioned whether by steamjacketing
the high pressure cylinder, correctly proportioning the steam passages,
and giving a due amount of compression in both cylinders, this may not
be reduced far below the generally received notion; and the latter cause
of loss may be considerably reduced in its effect by a more carefully
chosen cylinder ratio. The ratio usually adopted, between 3.5 and 4 to
1, whether the pressure be 70 lb. or 90 lb., may well be questioned.
With a cylinder ratio of 2.95 to 1, the economic performance is very
good, and equal to any with the higher ratio. A lower cylinder ratio has
another advantage of considerable value, viz., that the working pressure
can be much reduced as the boilers get older, while by giving a greater
amount of steam the power may be maintained--at an extra cost of steam,
of course, but not so great a cost as with higher ratios.
Pages:
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46