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RE: [APD] Eheim advice (also Fluval canister)

suisoman Dirk writes (regarding his Eheim 2028 canister filter):

 "...priming the pump was a major pain . ( as expected a bit , canisters
are not made to have big height differences between suction and outlet side
and the priming system is definitely not designed for it.)..."

and "For some reason the manual priming pump can't get the canister to fill
totally and when restarting it still has air. I need to shake it, turn it
sideways etc.. to clear the air.  To make matters worse , one time I was
trying to clear the air , the sound of the motor suddenly changed and it
stopped pumping all together. Turns out the propeller magnetic core had
broken due to running dry too much when priming. ( and that was an
expensive piece, I do blame these hobby companies for excessive pricing of
spare parts )."

Regarding the first comment: I have a Fluval 404, not an Eheim, but these
symptoms/anoyances are the same for me. In using a canister filter on a
plant tank setup, I usually modify the return line so that it goes down and
exits a couple inches above the substrate rather than use the normal return
spout that comes with the filter which exits near the top of the tank. I do
this for better water circulation and to keep the CO2 enriched water coming
in at the bottom. This modification defectively causes the height
difference problem that Dirk mentions by creating an airlock in the return
line. The primer was not designed to push against this head pressure (if
that's the correct term here) and so can not remove the air pocket.

I have found that by assembling the canister empty (no water) that I can
get the air lock to move out by attaching a hose to the return spout (now a
90 degree PVC hose barb fitting near the bottom of the tank) and sucking on
it. This causes the canister to fill with water and, because of the
momentum of the water flowing into the empty canister, forces nearly all
the air out of the system as it fills up.

Regarding the second comment:  I inject CO2 into the intake of this
canister and it occasionally burps excess gas but I have never had it get
stuck cavitating with a large gas pocket. I used it this way for about a
year and then it went into storage for about a year. I have since returned
it to service and as luck would have it the impeller broke after a month or
so. The bottom (or is it the top?) round plastic disk that is on the end of
the magnet fell off and this caused an imbalance with a lot of noise. I had
to order an impeller from Hagen (800-724-2436) as no one stocks them. The
impeller cost $15.90 and the shipping was $3.95; Total cost for the
impeller: $19.85. The dealers and distributors don't stock them because
they just don't sell that many and its money tied up in inventory that
doesn't move.

Now the filter still makes noise and I think there is something wrong with
the shaft. It may be slightly worn. I can't tell without a micrometer, but
the plastic piece that is part of the shaft assembly fits loose in the
motor head. Fluval supplies a shaft removal tool which indicates that it
should fit snug but it will just fall out without the cover plate
installed. So, this probably needs to be replaced also. Upon further
inspection of the cover plate, I noticed that the shaft fits loose in it
also. So, Do I need to buy a new cover plate as well? Since the filter has
been used only for about 18 months I am wondering if I should just throw it
away and purchase a new filter (another brand) as these three repair parts
may cost about half of what a new filter costs.

I admit that modifying the filter as I have stated above and also running
CO2 through it may somehow cause undue stress on the impeller and
associated parts. I am not opposed to having to buy these repair parts. I
am unhappy to see that the manufacturers have made it a point to say that
these units DO have replaceable parts and that you CAN get all kinds of
parts for them (implying that they are a reputable manufacturer with a good
product and that purchasing this product is a smart choice because it is
easily repaired, thus saving you the cost of replacing the entire unit) but
don't tell you that they have priced these parts at a point that makes it
impractical for you to buy them; instead , economically forcing you to
either buy another complete unit or upgrade. Such is the unwritten and
unfortunate way of many products, sales, and service these days.


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