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Boats and yachts live
or die by the pump. There are freshwater pumps, saltwater pumps, washdown
pumps, bilge pumps, sump pumps, baitwell pumps, fuel pumps, oil pumps,
engine-cooling pumps, air-conditioner pumps–well, you get the idea.
And with so many pumps doing so many important tasks, knowing how they
work and how to maintain and repair them is an important part of a skipper’s
expertise.
Pumps are basically
simple machines, so it’s pretty easy to keep them working, or to
revive them when they die. Knowing how a pump works takes you a long way
to understanding how to treat it when it’s sick. Although pumps serve
many different functions onboard, there are only three basic designs.
Centrifugal Pumps
A
centrifugal pump has a solid impeller similar to a turbine rotor; when
the impeller is rotated at high speed, it discharges fluid through an
exhaust port. Because the rotor is not tightly enclosed in a housing,
the pump is not "self-priming" and cannot create suction and
draw fluid into itself, so an outside force, usually gravity, has to supply
it. This type of pump is most often found sitting in the fluid it’s
meant to move, usually water (centrifugal pumps make perfect submersible
bilge or shower sump pumps).
Centrifugal pumps demand
virtually no maintenance, rarely break down, are difficult to clog, and
can even run dry, sometimes for days, before their bearings seize up.
Their major shortcoming is the inability to self-prime, which limits their
use onboard. So how do you maintain a centrifugal pump? Mostly by keeping
them clear of debris that can clog them or get inside and break the impeller
vanes. Usually, submersible pumps are fitted with float switches to turn
them on automatically. In my experience you’re more likely to have
trouble with the switch than with the pump. Fussbudgets like to install
their submersible pumps and float switches inside "strum boxes,"
wire-mesh or perforated-fiberglass boxes that keep gurry away from both
components.
Most centrifugal pumps
are inexpensive, and it’ll usually cost more to fix a broken one
than to install a new one. Some builders install expensive, rebuildable
centrifugal pumps; these can be repaired using kits supplied by the pump
manufacturer. The job is simple, demands only basic tools and skills,
and is seldom necessary.
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Impeller Pumps > Page 1, 2,
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