[APD] APD] Re: Vol 11, Issue 8 -- Putting pressure on Eheim and Eccoing some conclusions

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

Well, Ann's convinced me of part of her conclusion. But not
quite all. I believe I understand why Eheim instructs
closing the inlet valve before the outlet and both before
turning off the pump.

Going back to the filter to check, I confirmed that the
handle/priming-lever does not have any connections to
anything inside the pump head assembly. It rides on pins
sitting on the outer canister casing and rides on cams on
the outer pumphead housing. The lever release button has no
function other than to block the handle from the fully open
position unless the button is pressed. No internal valves
are at play with the the exception of the one ball in the
outlet. So once you remove the inlet hose, the canister
goes to essentially the same pressure as the atmosphere
regardless what pressure/vacuum might have been present
before removing the tubes. I.e., if there was a vacuum or
positive pressure inside the canister before removing the
outlet tube, it's gone once one removes the tube.

Hypothetically, shutting off the inlet first will cause a
slight relative vacuum in the canister. But more
importantly, I suggest, it theoretically prevents the
weight of the water in the tubes from putting a slight
positive pressure in the canister. Closing the outlet first
would give the same result as turning off the pump before
closing any valves -- namely, as Ann described, the height
of the water column from tank top to canister top will
present a pressure in the canister. When you turn off the
inlet, you block the water in the inlet tubing from
pressing down on the water in the canister. The water in
the outlet tube, theoretically won't push down because of
the internal one-way ball valve in the pumphead outlet. So
shutting the valves before turning off the pump will result
in less pressure inside the canister. This won't happen if
the outlet is turned off first because the inlet doesn't
have any valve inside the pump to hold back the weight of
the water in the tube until you close the inlet tube's
valve.

I suspect that this benefit from closing the inlet first is
rather imperfect since it relies on the ball inside the
pumphead outlet to hold back the weight of the water until
you clsoe the manual valve on the outlet tube. The one way
ball in the inlet doesn't seal that perfectly, especially
after it's acquired a coating of gunk after the pump has
been in use for a few weeks or months.

So I don't think you get a slight vacuum but I think one
avoids higher positive pressure by doing it eheim's way.
Now what good is avoiding higher positive pressure? One
might suppose that a slight pressure would cause a small
amount of water to be pushed out of the filter when the
tubes are removed. A slight vacuum would avoid this, but I
don't think one gets down to less than an room air
pressuer. In either case, the water in the tubes's ball
valves (between the gate in the valve and the filter) is
going to come out of the valve as soon as the tube is
removed. Perhaps this is why I can't detect a significant
diff in the amount of spilled water (a teaspoon or so) when
I shut off the inlet or outlet first. Or perhaps my Eccos
have dirty balls inside the pumphead. But I haven't
actually tried to measure the amount of water spilled; I've
only guessed based on seeing it.

[It's worth noting in passing that the 2026/2028 models
deal with the water that spills from the valve by catching
it in the small cavity around the hose connections on the
pump head. A bit of elegance in that design :-)]

But the ease or difficulty of removing the pump from the
canister shouldn't depend on which tube valve is closed
first; there's no mechanical reason for it to be easier one
way than the other. Once you remove the tubes, the pressure
in the canister is the same 9equalized with the atmosphere)
regardless of what it was before you removed the tubes. So
any pressure in the cansiter before you removed the tubes
can't put any greater pressure on the cams when you rotate
the handle to remove the pumphead, given that you
disconnected the tubes before trying to remove the
pumphead. 

In practice, I don't usually pay much attention the the
order because, heck, what's a little water on the basement
floor? However, I just installed an Ecco upstairs, so maybe
I need to be more careful, more like Ann.

Scott H. 
--- Ann Viverette <annv777 at houston_rr.com> wrote:

> 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.



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