Venturi Effect

[ShinySideUp]

I bought a power head just to move the water about and it has a venturi bubble effect. Unfortunately the bubbles don't form if I put the power head any deeper than surface level. I have a smaller power head from a Aquael 120 filter that produces bubbles even when the power head is very deep (air is sucked in to the motor rather than using venturi so the comparison is unfair) and I want the same effect from my larger power head. Is there any way I can get the bubbles to form with deeper immersion? I have a funny feeling a physics site would be an additional place for this post.

 

[Juggler75]

Just checking there is an airline attached and valve is open when you move powerhead is lower in the water

 

[OldMan47]

Attach an air line to the venturi side opening and extend the other end above the water's surface. Bubbles will appear on a scale that might amaze you.
Yep, physics is definitely involved.

 

[ShinySideUp]

Attach an air line to the venturi side opening and extend the other end above the water's surface. Bubbles will appear on a scale that might amaze you.
Yep, physics is definitely involved.

Did that but thought I'd missed something, but I've rechecked, and unless the pump is very near the surface there are no bubbles coming out of the pump. It's possible there is a bit missing as these things work by water passing across an orifice and dragging air in so either my orifice (ooh er missus) is not big enough or the design of the pump outlet is no good. Having read a review on Charterhouse Aquatics by someone with the same problem I lean in favour of the design problem. BTW it's a MaxiJet MP400 powerhead