COMMERCIAL GRAVING DOCK AT BARRY.
503
pumping engines have discs, 5| feet in diameter, and 18-inch cylinders of
16 inches stroke, and they are fitted with variable expansion gear and steam
stop-valves. Each pump can make 160 revolutions a minute, discharging
17,000 gallons of water or about 1,000,000 per hour. The dock has been
completely emptied in three hours against a head increasing to 22 feet, but
both divisions can also be emptied in an hour and a half, by letting the water
flow into the sea and in forty minutes when the tide permits.
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Fig. 505. —Pumping Station, Barry Graving Dock.
The equipment consists of three hydraulic capstans, six bollards, and a
number of snatch heads and hooks. The last-named are for giving a slight
list to vessels after they have settled on the keel-bloeks. The blocks are of
cast iron with elm caps, 4 feet long, 3 feet high, and 12 inches wide. They
are spaced at 4 feet 6 inches centres and are in two parallel lines, each
division of the dock being able to accommodate two vessels side by side.
Vessels are supported by timber props from the altars of one side only.
They are so arranged that those whose repairs are first completed can leave
the dock with the least possible interference to the others. The dock is
lighted by electricity.
The entrance and passage are closed by a pair of interchangeable
caissons, 17 feet wide and 34 feet 6 inches deep, the top decks of which
are planked. A line of railway runs over the dock for locomotives and
waggons.