These are made both horizontal and vertical; the prime consideration
being in all cases the amount of floor space the pump will require.
This is especially true in reference to small steam vessels, pleasure
craft, etc.
Owing to the unusual corrosion, caused by galvanic action, salt and
various impurities, marine pumps are built of iron with brass linings,
but frequently with the entire water ends of bronze.
The arrangement of the water valves in the most approved forms of
vertical pumps is such that the pistons are always submerged, and
the water valves sealed, thereby securing immediate lift of water
through the suction pipe, and steady, quiet operation of the pump;
many horizontal pumps of the ordinary duplex design are also used on
shipboard.
_The ship’s pump_ is common to all vessels and used to keep the
“hold” free from water. It is usually worked by hand but it is the
law in certain countries that the “ship’s pump,” aside from steam
vessels—shall be driven by windmill power; it is said to be an odd
sight to see the practical working of these at sea.
[Illustration: FIG. 447.]
The illustration on page 156 shows a marine vertical pump of the
Davidson pattern, designed to work against a pressure of 250 pounds per
square inch. The table given herewith will show the sizes and principal
details of these pumps.