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with Kurt Küpper*
* Kurt Küpper is director of Aquavolt
Electric Boat Parts. Tel: 02 9417 8455
So what else would you like to know? You are welcome to send in questions about
boat electrics or suggestions for topics that you would like explained.
29E Babbage Rd, Roseville Chase 2069
Tel: 02 9417 8455
Fax 02 9417 8423
WHISPER QUIET FANS
While stocks last
3-speed white gimballed
fan with timer 12V
For full details see website
Electric macerator pumps are pumps
used on boats to pump waste from
toilets and holding tanks. The term
macerator refers to the action of the pump
that grinds the waste as it enters the inlet
of the pump. The matter to be discharged
passes through a bronze cutter which
shreds the waste to a small particle size,
which minimizes the danger of clogging
hoses and tanks.
The macerator cutter will usually not
handle rags, wet wipes, hard objects,
sanitary towels etc. It is thus vitally
important to ensure that everyone aboard
is made aware of these limitations, as
disassembling the pump to remove
offending materials is a most unpleasant
The waste is then pumped by an
integral flexible impeller, discharging
through a 25mm hose. Most macerator
pumps are self-priming, which means
that the pump can be mounted above the
pickup point for the waste, and the waste
will be lifted up to the inlet of the pump.
From the outlet of the pump the waste can
be further lifted to be discharged above
the pump into holding tanks or overboard.
It is essential to ensure your installation
complies fully with local regulations. Many
areas will heavily fine anyone caught
This means you need to install a
holding tank to empty into until you can
discharge into a dockside pump out station
or directly overboard further out to sea.
Less water is required for flushing
if a macerator pump is installed on the
input side of the holding tank. Macerator
pumps are very compact and thus lend
themselves to installations where space
is at a premium.
Most pumps are available with either
12 Volt or 24 Volt DC electric motors and
require up to 10 or 15 amps of power.
Typically, macerator pumps are
not designed to be run dry of liquids.
The impellers will wear and the pump’s
capacity to discharge the liquids will
be lessened. Some advanced macerator
pumps will automatically shut off if the
pump runs dry of liquids. The run dry
protection is not designed to be used as a
means to automatically shut off the pump.
A built in delay of typically 20 seconds on
such pumps means that there will still be
wear to the impeller of the pump, and run
dry events should therefore be avoided as
far as possible.
While it is tempting to use as little
water as possible to flush a toilet, adding
water at the end of the cycle to ensure that
most solid waste is purged from the hoses
into the holding tank reduces the chance
of bad odours from the system. Flushing
with fresh water is also advantageous in
this regard, as organic matter in sea water
can also result in a build up of unpleasant
While macerator pumps should ideally
always be fitted to reduce the size of solids
in toilet waste, and they can also be used
to pump out holding tanks, the use of
diaphragm pumps for the latter function
holds distinct advantages.
Diaphragm pumps are self-priming
even for relatively high suction heads. They
can pump fairly large solid particles and
they can be run dry almost indefinitely.
There are some black water tanks available
on the market that provide for an integral
mounting of a diaphragm pump for pump
For shower and wash basin grey water
waste, handy compact plastic tanks with
bilge type pumps and float switches are
available. They come with multiple inlet
ports of various diameters and incorporate
strainers to trap hair and other solids found
in grey water.
Installation of a waste pump is very
straightforward. Careful planning should
be made to ensure easy access for good
serviceability, as this will inevitably be
required sooner or later. Circuit protection,
either an inline fuse or a circuit breaker
should be used to protect the circuit. Inlet
hoses can be rigid lines such as PVC or
flexible hoses with wire reinforcement to
prevent kinking or collapsing from the
suction generated by the pump.
The pumps should not be connected
to any circuit that is providing power to
any other appliance, as damage to one or
both appliances might occur. h
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