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Re: Eheim confusion

> Date: Tue, 01 Jan 2002 16:24:43 -0500
> From: Keith Brummett <brummett at ds_net>
> Subject: Re: More Eheim Confusion
>     > ... Every part number by part number, within each series,
>     > the xxx6 and the xxx8 are the same except that the media
>     > container is taller for the xxx8s.  ...
>     > Would anyone else care to stand up and defend the laws of
>     > physics against Eheim's specs?
>     Um, since the container is taller, wouldn't that mean it's
>     working against a shorter head?  Might be worth a few percent
>     of flow rate.  I dunno -- just guessing.
>     -- Keith
I think that's a good guess, Keith.  While the higher pump head has a
shorter output tube through which to push water, the siphon tube is
dropping the water equally low on either the xxx6 or the xxx8 (i.e.,
near the bottom of the media container).  Normally, the height of a
pump is irrelevant re head because however much push is needed to get
water up through the output tube, that much push is gained by the water
pressure of the siphon drop -- of course, a few other factors (like
friction) interfere with this simplified "perfect balance" picture.

But I think this is not the answer.  Eheim gives a 100 l/hr. higher
output for the xxx8 pump than the xxx6, exclusive of the filter (Ehiem
is one of the few pump/filter makers that tell you what the pump output
is when actually used on the filter, which is always lower than
"unfettered" conditons).  So it appears that Eheim's estimation of the
pump-only performance is better when it is merely contemplated for use
on an xxx8 than when contemplated for use on an xxx6.

Scott H.

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