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Smear the new impeller
with liquid dish soap or something equally slippery and water-soluble,
and push it onto the shaft. (The lubrication is important to keep the
impeller healthy until the pump primes, so use plenty.) Don’t worry
too much about deflecting the vanes in the proper direction; they’ll
sort themselves out on the first rotation. Replace the setscrew and hose,
if necessary, then replace the paper gasket under the faceplate with the
one that came with the new impeller. Don’t use gasket compound. When
you start the engine, watch for water to appear in the exhaust before
getting underway.
Diaphragm Pumps
Diaphragm pumps are less common onboard than centrifugal and impeller
pumps but frequently found in pressurized freshwater systems and serving
as fuel-lift pumps (bringing fuel from the tank to the engine) on diesel
engines. Manual bilge pumps–the kind with handles that rock back
and forth–are diaphragm pumps, too. Unlike either centrifugal or
impeller pumps, diaphragm pumps rely on one-way valves to control fluid
intake and exhaust as the diaphragm flexes in and out like a bellows.
When the pump misbehaves, chances are either the intake or exhaust valve
is clogged with debris. (That’s why small, electric diaphragm pumps
make poor bilge and sump pumps but are great for moving clean water and
fuel.) Eventually the diaphragm will split after being flexed a few million
times, but in my experience one diaphragm will outlive several sets of
valves.
Again, maintenance and
repair are simple, but read the directions first, as some diaphragm pumps
are more complex internally than others. Basically you open the pump body,
clean or replace the valves (making sure to install them so they operate
in the correct direction), check the diaphragm and replace it if necessary,
and reassemble. You don’t have to lubricate anything, and the pump
will prime itself quickly. Diaphragm pumps run dry without harm. Diesel-fuel
lift pumps of this type will live for literally thousands of hours of
operation, freshwater pumps for almost as long.
It’s daunting the
first time you have to repair any pump, just like the first time you do
anything involving tools and expensive bits of gear. But most folks with
opposable thumbs can handle the job easily by taking their time and reading
the directions. Knowing how to keep your pumps pumping will save you lots
of money, downtime, and aggravation, so it’s worth learning how ahead
of time…before you’re high and dry.
Mike Smith is a licensed
yacht- and commercial-boat captain living in Stamford, Connecticut.
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