Re: [APD] Re: Aquatic-Plants Digest, Vol 11, Issue 8

["S. Hieber" <shieber at yahoo_com>]

--- Ann Viverette <annv777 at houston_rr.com> wrote:
> 
> Because this is a pressure problem, the sequence of
> closing valves and
> turning off the pump matters a lot.
> 
> The impeller pushes, with suction on the canister side.
> So as the IN valve
> is closed, what had been low pressure inside the canister
> becomes even lower
> pressure. Then the OUT valve is closed, sealing that
> slight vacuum in the
> unit.

The vacuum would very very slight. At best, the pump can
develop only a few psi, maybe as much as 5, and that's it.
So I don't think vacuum matters at all.

> Then power off and disconnect the IN and OUT lines
> at the valves
> attached to the tank side of the lines. The canister side
> has some sort of
> auto shut-off that is operated by the handle.

Don't think so. Once the tubes are removed the in/out
spouts are open -- except that the ball valve in the outlet
spout imperfectly closes off that spout.
The pump head should lift off easily once the tubes are
disconnected.
> 
> If you do it the "normal way", turning off the power,
> then closing the
> valves, the canister is sealed with a much higher
> pressure inside, greater
> than atmospheric pressure, equal to the head of the water
> column.
> Apparently, a slight vacuum will allow air to enter as
> the lever is rotated,
> while a positive pressure keeps that from happening. This
> positive pressure
> makes the lever hard to move, making the cam slip,
> leading to forcing it
> open with a screwdriver.

Just the opposite, positive pressure would tend to push the
pump head up and out of the canister. It's a vacuum that
makes it want to stay inside the canister.

> 
> >When you shoult off the pump with
> > the hoses still open, the water has nowhere to go. Just
> > disconnect the hoses after shutting the valves and you
> > shouldn't have any problem.
> 
> But this is the scenario that gives so much trouble. It
> is quite
> counter-intuitive. It seems that one ought to turn off
> the pump, then
> disconnect the hoses. 

You can do it that way. It won't hurt anything. Or you can
turn off the outlet valve and let the pump 24/7. It won't
filter but it won't hurt the pump either. Centrifugal pumps
don't care if the outlet is blocked -- they happily just
spin the imeller around in the water that's in the volute.
It might cause cavitation in the water and so be noiser
than when the outlet is unblocked, but it won't hurt
anything.

> Closing the valves while the pump
> is running seems so
> very wrong! 

With a positive displacement pump, yes, but not with a
centrifugal pump.

> But that is exactly how the ECCO must be shut
> down in order to
> open easily. If the ECCO is shut down following the
> instructions, it works
> terrifically well! Just like a highly engineered, very
> expensive,
> German-built machine...

Once the tubes are off, the canister is at atmospheric
pressure -- open to the air.

> 
> Well, first, if the valves are closed it does not matter
> whether the hoses
> are connected or not. 

The valves are on the hoses and are removed formthe pump
when the hoses are disconnected. ONce disconnected the
valves only matter in terms of whether you want to siphon
water from your tank onto the floor. I've done this
unintentionally but it's not a preferred practice ;-)


> Second, the pump head will come out
> just fine as long
> as there is a vacuum that draws air into the canister as
> the lever is
> rotated.

Okay, when I get home, I'll play around with the thing some
more.

> 
> A vacuum is created when you close the valves in the
> right sequence, so that
> as you operate the lever to roll the cam-locks and open
> the canister you are
> allowing air in, drawn by the vacuum. Doing it the way
> one would intuitively
> do it (pump off, then close valves) leaves a positive
> pressure in the filter
> that the cam lever cannot overcome. I suspect there is a
> one-way valve
> operated by the lever that will not open if there is high
> pressure inside
> the unit relative to atmospheric pressure.

There is on the output side -- it's the ball valve that
allows the priming to work. I'll look for one on the other
side. But as I recall, one can run a brush right through
the inlet spout.


> Yes, of course. I'm not admitting to having done that,
> however.

Then keep up the good work. I think mMost of us have
drained our tanks in many undesirable ways at one time or
another ;-) 

> 
> > If after removing the hoses, you still need something
> to
> > pry the pump head off the canister, then something is
> wrong
> > -- probably the Oring needs a little petroleum jelly
> and
> > nothing more than that.
> 
> Although, Eheim does say to lubricate all seals any time
> you open the unit,
> that has nothing to do with this issue.


It would only matter regarding the Oring aorund the pump
head. But he amount of lubrication needed is very small.
> 
> 
> Yes. If the tank is nearly full, with the output line
> above the water level
> and only an inch or two from the water to the rim, the
> lever will prime with
> one pull or less. The Eheim instructions never actually
> mention that you
> want to wait until the tank is nearly full before you try
> to prime the
> units, but it works better that way (the pictures show
> the set- up with
> output line just above water). The priming units can only
> provide so much
> suction, about 4 inches of head seems to be the max, IME.
> 


> When I clean a canister, after I disconnect the filter I
> open both the
> tank-side valves and drain some water into a bucket to
> clean the hoses of
> some of that build up. That leaves the output line empty,
> full of air, and
> the input line is full of water, no air. When I restart,
> the output line is
> still empty and above water level so all air in the
> canister has no choice
> but to follow the path of least resistance... up the
> output line.
> 

> 
> >
> > Anyone wonder why lfss sell beginners backfilters? ;-)
> 
> Yeah, they are for folks who won't read instructions. ;-)


=====
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