Help needed with dual U-Tube overflow

[beapeams]

Anybody have any experience with a dual U-Tube overflow. I replaced my CPR earlier this week. The problem I am having with it is that When both tubes are passing flow, one of them accumilates air bubbles and eventually breaks suction. While they are both running they both have air bubbles, once one of them breaks suction, the other tube losses the bubbles and is completly filled with water. Also I checked to make sure the overflow was level.

It tends to be the tube on one side that has the issue. I checked the tube for any cracks, and see none and the tube does not have a leak of any kind when I test it. The overflow is rated at 1100GPH and my pump at 4 ft head puts out a little over that.

Could it be that the overflow is actually pulling water out quicker than the pump is pumping it back in?

Any Ideas?

 

[frenchie]

if you have micro bubbles in main tank they can accumulate in overflows and eventually it will stop had this problem also. i use dual u tube style overflows and i had to lower the 2 intake sections in the tank side lower in water and get the u tubes to a closer level to bottom in each compartment cause water flowing into the two compartment was causing bubbles in which was getting sucked up into u tubes on my overflow. I've been lucky so far and no more bubbles getting caught in tubes.

 

[BigMOCats]

That's what it sounds like to me. What's it do with only one tube?

 

[hagfish]

My dad came up with a good solution for this. Take a low GPH powerhead that has an air intake and put it near your overflow. Drill a hole in the top of your u-tube where air bubbles would collect so that you can insert some sort of connector to an air line. Make sure it seals well. Run the air line from the tube to the powerhead. This will suck any air bubbles out and put them back into the tank. He hasn't had any problems since doing this (before that, he'd had major problems).

 

[thatguy]

When both are running the flow through each tube is reduced from what it would be if just one tube was going. If one tube does 600gph, then with 2 each would do about 300gph.

This slower flow will allow air bubbles to accumulate in the tubes, or at least in the one with lower flow. With all the flow in one tube the water is moving fast enough to pull the bubbles with it.

I can't really think of an easy way to prevent this.

 

[beapeams]

I will try some of your suggestions. It actually works great with the one tube, but I want both going just for protection of a tank overflow. I don't think I will try drilling a whole in the one, that type of setup is what made me get rid of my CPR.

 

[sirreal63]

Use one tube...you do not have enough flow to keep the bubbles clear with 2 tubes. One tube and no bubbles prevents floods and 2 tubes and bubbles will make a flood. Watch it with one tube, if the water level in the display is getting higher then you may need to cut back on the flow to the display. In reality you do not need more than 5-600 gph flow through the sump.

 

[kipher]

A lesson in Fluid Dynamics

A lesson in Fluid Dynamics

I don't have a dual U-tube overflow....but I will share a recent experience I had with my single tube overflow. Recently I attempted to replace my stockman stand pipe in my outer overflow box with a durso style standpipe. However when I did the average water height in the outer box got higher than it was before. What this did was decreased the pressure head between the inner box and the outer box.....thus reducing the velocity at which water traveled through the u-tube. As the guys stated above, the slower the water goes through the u-tube the more likely you are to collect bubbles in the u-tube. So, the Durso I built was too tall. I had to remove bubbles from the U-tube everyday. After a week I got tired of this, I just put the stockman standpipe back in outer box and my problem was fixed. (I do plan to re-build a durso...but it will be shorter next time.) (Edit- I should also note that I had to reduce the flow via a ball valve in my return pipe while using the "too Tall" durso.)

Conclusion: if you can shorten the pipes in the outer box (without making the bottom of the u-tube higher then the top of the drain pipe!!! Do this and you will loose your siphon during power outages.) Then you will increase the speed at which water will travel through the U-tube. Although I'm not sure this will make enough difference in your case. (Edit- DISCLAIMER remember that each time you re-start your overflow...you may not get the u-tube perfectly vertical. When the u-tube is not vertical it creates a slight variation in how high the bottom of the u-tube is within the outter box. So if you cut the height of the drain pipes down...you need to allow some margin for error!)

Side note: I don’t know if this is the case for everyone, but on my U-tube the two ends are NOT equal lengths. One side is about ¼”-1/2” lower than the other. I can take better advantage of this by putting the longer end in the outside box. Thus, allowing me to drop the water level in the outside box even more.

 

[kipher]

<a href=showthread.php?s=&postid=11975842#post11975842 target=_blank>Originally posted</a> by sirreal63
Use one tube...you do not have enough flow to keep the bubbles clear with 2 tubes. One tube and no bubbles prevents floods and 2 tubes and bubbles will make a flood. Watch it with one tube, if the water level in the display is getting higher then you may need to cut back on the flow to the display. In reality you do not need more than 5-600 gph flow through the sump.

For the most part I agree with Jack here.

 

[beapeams]

I've played around with the flow into the tank, I can reduce it to about 700gph. This still does not help. I think I need to re adjust my power heads so that I have less surface agitation. I noticed that the side that does not collect an air bubble has less water agitation where the water comes into the overflow box, vs the problem U-Tube has major water agitation due to the power heads. This would account for a higher bubble count getting caught in one U-tube vs the other. I plan on adjusting power heads, overflow water heights, and U-tube lengths. Technically I can run on 1 U-tube without problems, but I want the redundancy of two.

 

[kipher]

leason in fluid dynamics 2

leason in fluid dynamics 2

I just thought of another factor that controls how high the drain in the outer box needs to be. You can't have the drain in the outer box lower than the bottom of the u-tube in the inner box. If you think about it, when you turn off the return pump the elevation of the water on the inner box and outer box will be the same in a properly constructed overflow unit. (no differnce in elevation = no preasure head = no flow) The outside box WILL drain to the elevation of the top of the drain in the outer box. All the while, the inner box will contiune to push water through until the elevation of the water in the two boxes are equal. If the drain in the outside box is below the end of the u-tube inside the inner box, the u-tube will suck air at the inner box before the water elevations are ever able to equalize. Thus breaking the siphon!

I just came to this realization today. Although I've never thought about it in this much detail before. Even if my blabering doesn't help solve your problem, I do appreciate the chance to think anylitically about your situation. (I guess that makes me a big engineering nerd to put this much thought into it. I'll admit it!) Maybe moving your pumps and such will help. I have noticed at times in my tank that the way the water falls into the inner box does cause an excesive amount of bubbles at times. Although I truely don't have a solution for that at this time.

 

[kipher]

Re: A lesson in Fluid Dynamics

Re: A lesson in Fluid Dynamics

<a href=showthread.php?s=&postid=11976345#post11976345 target=_blank>Originally posted</a> by kipher
Side note: I don’t know if this is the case for everyone, but on my U-tube the two ends are NOT equal lengths. One side is about ¼”-1/2” lower than the other. I can take better advantage of this by putting the longer end in the outside box. Thus, allowing me to drop the water level in the outside box even more.

With my realization just stated in my prevoius post, the most appropraite way to construct the u-tube is to have both ends of the u-tube exactly equal. And the drain in the outer box needs to be slightly above the end of the u-tube. Thus my above quote is really incorrect and my u-tube is simply improperly cut.

 

[BigMOCats]

<a href=showthread.php?s=&postid=11975530#post11975530 target=_blank>Originally posted</a> by beapeams
It actually works great with the one tube,

I'd just stick with it then. I have tanks running both types of overflows and have never had any trouble with the U-tube type. One tanks has been running over 3 years with out ever stopping. Knocks on wood!

 

[zeus_roush]

u tube

u tube

what type of return pump do you have? and what is it reated

 

[beapeams]

GEn-X 6000 rated at 1170GPH at 4ft of head.

 

[reefnut1]

I had this problem and ran a line from the air intake on a maxi jet 1200 up into the center of the each tube. If air bubbles get in there the power head will pull them out right away keeping your tubes primed.