Unexplained Air Bubbles in Hang-On Filter

**tetrakid** · 10th Aug 2012, 15:20

I am a big fan of hang-on filters. Recently I installed a double-chambered "Super HOF (Oceon Free), which is the most powerful HOF I ever used. The water flow is superb, and on account of this alone, I will definitely won't hesitate to buy another one.

But when the filter was finally up and running, there is a big rush of air bubbles coming it seems from the right-angled bend of the inlet pipe.

I thought there's a leak in the joint, but even after I have carefully sealed the joints with several layers of transparent nail polish, the bubbles still occur. Since the joint is sealed and air-tight, this phenomenon is rather puzzling.

Does anyone have any explanation for that?

**Cyberkinetic** · 10th Aug 2012, 20:52

Is there any water leakage? On my Fluval C3 the part where the impeller is located can be opened with a twist. If air can get in, gotta be from that joint only i think...

**tetrakid** · 11th Aug 2012, 06:14

For my case, I don't think the bubbles are due to any air leak. If it is an air leak, there won't be so much bubbles but only a single stream of bubbles. What I have is a big rush of bubbles right at the inner right-angled portion of the plastic inlet pipe joint, which I am 100% sure has no air leak hole or gap in it in the joint or at the bend.

I think it may have something to do with the right-angled structure of the plastic pipe which gives rise to this phenomenon, something like eddy currents in water. Anyway, I will try fitting a replacement pipe assembly next week and see if the same thing occurs.

Originally Posted by Cyberkinetic

Is there any water leakage? On my Fluval C3 the part where the impeller is located can be opened with a twist. If air can get in, gotta be from that joint only i think...

**KeIgO86** · 12th Aug 2012, 22:56

Highly unlikely... But just maybe.

http://en.wikipedia.org/wiki/Cavitation

**tetrakid** · 15th Aug 2012, 20:36

Thank you for the article's link.

As the bubbling effect occurs at the inside of the RIGHT-ANGLE BEND of the suction tube, and there's no air leak, I tend to want to accept what is explained in that article, since I already had some inkling that it has to be something like what is described.

Thanks again.

Originally Posted by KeIgO86

Highly unlikely... But just maybe.

http://en.wikipedia.org/wiki/Cavitation

**xXXXx13** · 15th Aug 2012, 23:36

Maybe you can try adjusting the height of the intake tube?.

**tetrakid** · 16th Aug 2012, 09:56

Adjusting the tube seating (not height) at the impellor housing works in making the bubbling stop, but the bubbling returns after a while.

At this moment of writing, there has been no air bubbles for two days already. But I suspect the bubbling can return anytime because it is not due to any air leak in the plastic tubings itself.

Originally Posted by xXXXx13

Maybe you can try adjusting the height of the intake tube?.