All About Engines
Forfatter: Edward Cressy
År: 1918
Forlag: Cassell and Company, LTD
Sted: London, New York, Toronto and Melbourne
Sider: 352
UDK: 621 1
With a coloured Frontispiece, and 182 halftone Illustrations and Diagrams.
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Engines for Ships 291
the main valve. At the same time, it admits steam
through f to the right-hand end of the main valve,
causing it to be forced to the left against the
cushion formed by the exhaust steam. The port c
is now open to exhaust, and the port d is open
to steam. The same action takes place on the
down stroke.
Under certain conditions the piston will not com-
plete its stroke by the expansion of the steam from
three-quarter stroke—for example, if the pump is cold
on starting, much of the steam will be condensed
and the piston will come to rest. This difficulty
is provided against by the by-passes 1 and j in Fig.
162, which can be operated by hand. What excites
admiration about this pump is the amount of thought
which must have been necessary in order to design
the valves and ports by which the distribution of
the steam is so delicately controlled. The sea-going
engineer, however, would say that what he admired
most was its efficiency and reliability. He is less
interested in pretty devices than in results. And,
after all, this is the main test.
Although the steam used by the main engines
and auxiliary apparatus is condensed and returned
to the boilers, there is a small loss of from 4 per cent,
to 8 per cent, daily, which has to be made up; and to
carry this amount of fresh water would be impos-
sible. For suppose a 10,000 horse-power vessel to
evaporate 12 lb. of water per horse-power per hour,
the total evaporation per hour will be 120,000 lb.,
and for twenty-four hours it will be 2,880,000 lb.