Bubbles from sump return.

[phishead]

After setting up a 20 gal. long as a small fuge and sump, I am having problems getting the return to stop blowing micro bubbles. I have put a filter bag on the input, Checked my skimmer and there are not a lot of bubbles in the sump. If I turn the ball valve on the return more than 2/3 open, it blows millions of bubbles. I am using a rio 2500 so max 500 gall/hour. What gives? Is it the size of the return tube (3/4" sched 40 and clear tubing)? Are there too many bends? Do I need a stronger pump?

 

[Montwo]

did you allow the proper cure time for the tubes if you used pvc, the only thing other than leaky tubes I can think of is maybe your sump or inlet is too close to the surface of the water.

 

[midiman]

Could it be cavitation? Are there any restrictions to the intake of your return pump?

(This question born of physics, not experience with aquaria, as I am a SW newbie)

 

[phishead]

OK, I Don't know much about cavitation except that it can be high pitched and has to do something with a wolfman's Brother.

I did read a couple of internet articles after google searching, and it makes sense. Microbubbles could be caused by the return plumbing, to many corners when water is moving to fast. Or, the cheap clear tubing is causing water to slow too much during certain aspects of the return trip.

How do I fix it? is this why I am supposed to get a pump rated higher than what I really want. So I can run it at 2/3 flow?

It does not seem that any joints are leaking and very few bubbles in the sump. Please help.

 

[swissfish]

I have the same problem. Because I'm pumping 1500 gph through a 27G sump, and I am having a seaclone skimmer.
There are some things u can do:
Put some baffles in the sump
have a submerged discharge
make sure the skimmer is not suplying micro bubbles

Hope that helps, I know it is verry frustrating.

 

[midiman]

It would seem to me that cavitation is the result of water moving too FAST, not too slowly, especially around obstacles where rushing water creates a low pressure area, thus releasing air (like when you open a soda bottle). This is also consistent with your observation, i.e., the bubbles appear when your valve is open more than 2/3.

Perhaps larger diameter return pipe would do the trick. PVC is cheap enough so that you could experiment, if you have the time and inclination.

Maybe the problem is with the ball valve itself?

Again, I'm just rear-seat driving here, because my tank is still dry and I'm waiting for my toys to arrive in the mail. I will make sure that I have a bubble trap in my sump, though!!

 

[phishead]

I played with it a little last night,

-tried to get all of the clear tubing as straight as possible,
-re-re-re-checked the skimmer. I had no problems prev. with it when it was in the tank,
-Increased the water volume in the sump so less splashing is occuring,
-actually increased the flow through the ball valve, this raised the water level in the overflow giving less air sucking.

I have less bubbles in the sump. But a little more in the tank.

end result, not as good.

I would understand a little more if I was trying to get 1500 GPH, but I am barely getting 400 now!

I don't think it is a problem in the sump, but may add a baffle anyway.

I think my next step is to run 3/4 pvc stright to the tank with no bends until the inlet.

 

[tmcpeek]

What kind of overflow do you have? Is the tank drilled?

 

[midiman]

Here is a link dealing with preventing cavitation. It seems to say that slowing the flow rate would help, because the pressure drop would be lessened. To slow the flow rate, you may need a larger diameter pipe.

That's the best I could come with. Hope all works out. Let us know!!!!!

http://www.tpub.com/content/doe/h1018v1/css/h1018v1_106.htm

 

[swissfish]

I doubt that you have a cavitation problem. Cavitation only occures when there is not enough water suplyed to the suction side pump.