What is causing my skimmer to "burp"? Too much turbulence?

[shelburn61]

I can't get stable foam production because a big bubble bursts from underneath every few seconds. What causes this? Too much water/air flow?

How do I fix it? What if I switch to 6" diameter pipe of the same height? Does the swirling action from the tangental injection help or hurt?

Skimmer body is 4" x 20" pvc
Oceanrunner 2700 needlewheel recirculating pump.
Gravity feed ~100 gph (does not produce bubbles).

http://reefcentral.com/gallery/data/500/73441my_skimmer2.jpg

[eameres]

Just picturing other recirculating skimmers in my head, Could it be that the output of the pump is too high up on the body? can you get inside there and put a fitting on it to redirect the output down?

Just brainstorming...

[grim]

Gravity feed from your overflows? If so, it's likely that your gravity feed is somehow introducing the large bubbles. It's really the only place they can come from. In other poor skimmer designs, you might see a similar problem when bubbles collect under flat areas like riser transitions & box to tube transitions, but your skimmer doesn't look like it has those. Have you tried feeding the skimmer with a small powerhead. The only other possibility, and this is a big longshot here, is that airbubbles are collecting in your recirculation injection pipe. This would be the case if you had a fitting inside the reaction chamber aimed downwards, but didn't have enough flow to ensure that section of pipe flowed at a high enough velocity to keep bubbles from collecting there..

jb

[eameres]

Just to clarify, you said "Gravity feed ~100 gph (does not produce bubbles)." Did you test this by just allowing the skimmer to recirculate without any feed?

[Alfalfameister]

In my experience, the problem is that it is gravity fed AND backpressure (gravity fed by itself is not a problem).

If water from overflow (I assume, since it's gravity fed) goes into the input side of your skimmer which is below the water level of the skimmer, then there's backpressure. Enough to make it burp/fluctuate.

EDIT: Another possibility, though I discounted it at first, is there may be too much air-flow in the Ocean Runner. I know that with a Resun 6000 pump, it kinda cavitated, and instead of a constant bubble-producing/chopping pump, it went in small "bursts"... That doesn't happen to the Rio 2500, and since everyone uses the Ocean Runner, I discounted that possibility, but you could check into it. (try restricting the air flow somehow, and then post back here the results).

[shelburn61]

So the pump isn't too big?

I added a 45 tee on the output from the pump to point it down but this seemed to do little.

Grim,
Are you calling my design poor! ;)
I have already tried looking inside the skimmer with the pump turned off and gravity feed running. There are no bubbles at all!
Though I hadn't thought about bubbles getting trapped in the overflow. It seems that the gravity feed might not be enough to push them out? Why would running it with a feed pump help?

Alfalfa,
I don't quite understand the the backpressure burping theory. The flow should be pretty constant b/c I only have a about 100gph coming down a 1" flex pipe. The slack in the tube forms a "U' that goes down and then back up to the skimmer. Would this be a problem?

[Alfalfameister]

Shelburn61:

You have 100 gph coming down, but with the backpressure, it may be going 90 gph for one second, then 110 gph for the next second... hence the burping...

Kinda like some people who are having problems with burping/fluctuating durso overflows and the like.

Also, the flow may slow down a bit, then the siphon pulls the water faster, then it slows down again, then the siphon pulls... ad infinitum -- fluctuating and possible "burping".

Anyway, good luck, and hope you can sort it out.

P.S. Try this: disconnect your skimmer or something, then with ANOTHER pump (not the re-circulating pump), pump saltwater into the intake side of the skimmer. The pump should provide a CONSTANT flow of water. If it still burps, then maybe the recirculating pump is drawing too much water and cavitating from time to time. If it doesn't burp anymore, then the source of the problem lies in the overflow-into-skimmer intake.

[grim]

No! I'm definately *not* calling it poor! What I mean by poor are the skimmers that go from a 12" reaction chamber body to a 4" neck by using a flat piece of acrylic to form the transition. This huge flat area causes all sorts of bubble build up and 'burp'..

jb

[grim]

Another possible issue I've noticed on my other designs that leads to a cycling water level in the reaction chamber is an undersized hartford loop. What happens is the skimmer drain plumbing forms a siphon once in a while and sucks the skimmer level down a bit further than the hartford height. What this does is 'tears' foam head that is in contact with the riser, making it very difficult for a good foam column to form.

jb

[shelburn61]

I will try feeding it with a pump tonight. The hartford siphon thing doesn't seem to be happening here. wouldn't have thought of that. The pulsing of the oceanrunner is something else to check?