Setting up Knop Excalibur Series Protein Skimmer - Venturi Effect Question

[JavaJones]

I recently bought a used Knop Excalibur-series protein skimmer (see its advert - http://www.aquadirect.com/store/catalog/KNOP___Excalibur_Protein_Skimmer_p_483.html). Unfortunately it has two deficiencies: (1) it came without a manual and (2) the connection between its powerhead and the skimmer unit + the venturi valve seem to have been jerry-rigged by the (or a) previous owner. I can't seem to get bubbles into the skimmer. I replaced the powerhead with a spare Penguin 660 and then a Maxijet 1200; in both cases I left the Venturi tube and valve in place and connected the powerhead output to the skimmer. In both cases, water shot out of both the powerhead and the Venturi tube. Both powerheads work normally and don't shoot water out of the Venturi inlet when used to spray water into the tank; in those cases, the Venturi's valve can be used to control the amount of air bubbles. Clearly, I am missing something fundamental here. When the powerheads are connected to the skimmer (and water shoots out of the Venturi), the powerheads are pumping water, up, above their height into the skimmer's inlet, so I can see why the Venturi valve becomes just another pressure release system for the water, rather than an inlet for air sucked in by the water rushing out of the powerhead. Any ideas how I get the Venturi effect when the powerhead acts as a pump? I suppose the the Venturi tube should be connected to where the powerhead sucks in the water, but am not sure how that is accomplished.

 

[denvig]

You may be able to get some info here.
http://www.customaquatic.com/customaquatic/questionsearch.asp?question=EXCALIBER&Submit2=go

 

[nitrofish]

are you able to blow into the verturi (im guessing theres air line) and get bubbles? im having that problem with my powerhead, im soaking it in vinagar right now to clean out the calcium. other than that, im as lost as you are

 

[NateHanson]

I think you've got the right idea of what's causing the problem. There's too much back pressure on the pump for it to suck air through the venturi. Can you plumb it so the powerhead is closer to the water surface in the sump? That should help. Or just jury rig some adapters to attach the venturi to the inlet side of the pump. That way the bubbles get shredded by the impeller before they're injected into the skimmer. That's how I've set mine up.

Nate

 

[JavaJones]

I have explored the question a little more and checked the setup again (following Denvig's helpful link and Nitrofish's suggestion). However, I think Nate has it right: my Seaclone 100 skimmer has an air tube that enters from the input side through a modified inlet on its Maxijet. So my next step is to replicate the modified inlet on the Maxijet 1200...and indeed have the impeller shred the bubbles. Thanks for the leads! As usual, this board is most helpful.