Bubbles, lots of bubbles.

[novice150]

Ok everyone. I'm at wits end trying to get rid of the bubbles in my tank. I feel that I have tried everything, short of tearing out my plumbing, and starting over.
Here's the deal. The 1650 is up and running, nearing the end of its cycle. I have 2 pumps on this tank. Each of them are 5000 gph lifegard sea horse models. One of the pumps is on a closed loop, the other runs my sump via 2 4" overflows. The water is returned to the tank via 1.5" bulkheads, 2 on each pump.
I have bubbles coming from all 4 of the returns in the tank. I could understand if I only had bubbles from the pump on the open loop, maybe my bubble baffles in the sump aren't right, or maybe the water is low. But this is not the case. The pump on the closed loop has an equal amount of bubbles as the open loop pump.
The closed loop pump draws water from about 2 ft below water line, so I know its not drawing in air there. I am sure that the pump running the sump is not drawing air from the sump. The baffles are working (visual) and it is not low on water.
I've come to the conclusion that the pumps must be drawing in air on the intake side. But I cannot figure out where. I have shut down the pumps for up to 3hrs, in hopes of finding a small leak that would allow the pumps to draw air when operational. I have found none.
Any idea's or suggestions? I really hate these bubbles.
I will post a pic of the bubbles later today, the wife has the camera
Thanks

 

[10k]

What are the chances, that these 5000 gallon p/hr pumps, are creating so much vacume on the inlet side, that they are actually sucking the O2 out of sulution. I've seen it happen before, but not in an aquarium...just a thought

 

[rsd]

I'm assuming your plumbing is PVC.
With out a diagram I'm a little lost on your discription of whats happening... but that doesn't change much.
Two options.
1. Air is being sucked in to your intake by the pump... You said no way for that to happen...
2. PVC is notorious for having hair line cracks or bad seals at the joints. This happened to me. Even if you shut off the pump you might not see a leak because the pressure for the water to escape is too little to "push" through the seal. Also with this theory you know that the crack/bad seal is before (on the intake) side of your pump. We know this because if it were on the pressurised side you would have a drip or a small spray... not bubbles.
You may have to shut off the pump and reseal all your joints (any of them threaded joints?) or worse yet you may have installed a peice of PVC pipe with a small crack mid body.
Heres how it works.
When a pump is on you have changed the pressure on both sides of the pump with in the plumbing. On the outlet side of the pump you are creating an atmosphere of +10 (just for a number... you may also call it gallons per minute (GPM) inside of the pipe... on the intake side of the pump you have created a -10(GPM) atmosphere... Water in your sump is at 0(GPM) since it has no "force acting upon it until the pump is turned on. Therefore it is drawn into the pump to try and equal out the pressure. When there is a leak on the outlet side you might see that +1(GPM) is leaking onto the floor and a value of +9(GPM) is entering the tank... while + 10(GPM) is leaving the sump.
When a leak is on the intake side of the plumbing (anywhere between the pump and the plumbing's opening) You see +10GPM (air/water mix) leaving the pump to your tank. +1 GPM air (from the leak) and +9gpm water from the sump. A vacuum is a vacuum. If it could pull at +10 from the leak (like when water level is low) it will.
If I can help you track it down let me know.

 

[rsd]

Imagine drinking pop through a straw that has a crack above the "water line". You suck air even though the bottom of the straw is in water.
You may have to back pressure the plumbing to find the leak.

 

[sal t. nutz]

How close to the water surface are your returns? I found that my 1500 GPH pump, split into 2 returns, just below the water surface, causes a whirlpool at the surface just above the return. It eventually sucks air right from the waters surface and spits millions of bubbles.

 

[novice150]

10K: I have given that theory some serious thought. I'm moving some serious water. But I just can see how its enough in this case. I mean, these are essentially swimming pool pumps. They work in that application, so they should here. Right? I'm still not 100% on this one.
RSD: Option #1, your right, the intake is just too far below water line for it to pull air in.
Option #2, I worry your right again. But what the heck do I do? I knew this was the case, and that's why I shut off the pumps. If it's drawing air when on (creating vacuum) then it should leak when off. But its not
The pvc is flexible tubing. The same stuff used on hot tubs. I'm relatively sure it does not have any cracks. But, there are alot of joints back there, and some are threaded.
There is no easy way for me to back pressure the plumbing. So I will follow your advice and re seal every joint. But wait, what if I reversed the polarity on my pumps? Wouldn't that cause them to run backwards, and pressurize the intake side? Im not sure if this would work due to the design of the impeller, since it's designed to pull water in one direction.
I've come up with one other option, and I'd like to hear everyone's input. Maybe its the pumps themselves. By this I mean, maybe the internals seals on the pumps are not strong enough to handle the vacuum, but strong enough to handle the pressure when the pumps are powered down. They have a pot/strainer attached to the intake for pre filtration of large debris. This pot is sealed by O rings, maybe they're leaking?
Sal T: I checked on that as well. I even got in the tank to look for a funneling effect near the bulkheads when powered up. All checked out OK. Good idea though.

 

[glazer]

I agree with what RSD is saying... but by common sense, law of averages and plain logic I would think that it was highly unlikely that BOTH pump setups have leaks somewhere on the intake sides.
Sooo if the impeller isn't drawing air then the source, in my opinion is blade cavitation. The trailing edges of the impeller create low pressure zones. Since the impeller speed is dictated by the motor, which is in turn dictated by the frequency of household current there really isn't a practical way to change the speed on the pump.
So following along the lines of RSD's explanation for pressure differentials I would try adjusting the flow rate. You may have to restrict the flow slightly on the input OR the output side of the pumps by way of ball valves and make adjustments till ya find the "sweet spot" so to speak.
OH, and also... if the impeller housing is such that you can open it and inspect the the blade(s) look for any sharp or rough edges.. and gently file them down smooth if they exist.

 

[oceanjumper]

Are your return lines translucent? If Glazer is right (and it certainly makes sense), you might be able to see where the bubbles originate. If nothing else, you might want to replace them with translucent ones just to look at it..... Or, test you pumps with shorter feed & return lines in your bath tub. See if it causes bubbles there as well. If so, Glazer might be right and your PVC lines might be okay. If not, it could be the PVS pipes or something else....
I had another thought (far-sought perhaps). A lot (if not all) return lines have an "air hole" to break the siphon in case of power failures. Normally this air hole is under the water surface. In your situation this hole would not be directly exposed to air, right? Not even occasionally because of water turbulence?
Man, I like to see what caused it. Nice case to resolve though....

 

[rsd]

I found that my threaded pipes were incredibly hard to seal air-tight. Did you use any teflon tape or pipe tape?
If your lines are clear you may try and turn the pump on... then block the intake side of the plumbing.... forcing the pump to suck air through the hole... then you might see it. (unfortunately I've found that clear hoses tend to build up algea in them....may be a cause for concern later.... you could always wrap the hoses in something like foam pipe raps or something to block the light later.)
You can also try shutting off the pump and sealing all your joints with silicone. Let it cure for 24 hours and restart the pump.
I wouldn't recommend disassembling your pump unless you have to. I'm never one to mess with a "machine" seal... or one that a machine sealed... it's just me.
Good luck and keep us informed of what you find.

 

[novice150]

Well, unfortunately my lines are not clear. They are 1.5" flexible pvc, white in color.
My sump is 180 gal.
I have a question about the cavitation. If the blades are cavitating, where are they getting the air from? I've had problems with cavitation on my boat and jet ski's before. But I was under the impression that the air came from the surface of the water. How would that work on a closed loop?
I agree that the threaded joints are hard to seal. In the beginning, I found that when the pumps were off, 2 of the threaded joints had a slow drip. I took the whole system apart and resealed them. The leaks stopped, but the bubbles didn't.
I several layers of teflon tape on all of the threaded joints.
I plan to try the easy things tonight. I'm going to silicone the threaded seals, and also the O ring seals on the strainer pots. I also have ball valves on both of the pumps, intake and outlet. So I'll try playing with those and see if it makes a difference.
Thanks everyone for the help These have all been some really good ideas.

 

[glazer]

http://www.mcnallyinstitute.com/CDweb/c-html/c021.htm
Novice, don't mean to be lazy but check this link.... excellent explanation of the whole thing. I just wimped out... I started typing and couldn't seem to stop and then I was getting too anal I thought in trying to explain it all. My cavitation experience stems from 4 years as a construction mechanic working on extremely HIGH output pumps and then another 5 years as a marine mechanic servicing OB and IO high performance motors. Like, I KNOW what cavitation is...my stoopid fingers weren't workin' with the brain.... gawd I love them things called search engines...mah fingers can handle a "point 'n click" thing no prob...lol

 

[rsd]

Just curious.... did we stop the bubbles?!?

 

[novice150]

Sorry I haven't replied sooner. I have been testing/trying all of the suggestions and ideas everyone posted. The good news is that I'm making progress!
First I shut off all of my pumps again, and waited a few hours for leaks just in case I somehow missed one before. Nothing.
Then I siliconed all of the suspect joints on the intake side of the pumps. This did not help one bit.
Next I removed the lids on the strainer pots of the pumps, and siliconed the area that should be sealed by an O ring. This helped a little on the open loop pump, but not at all on the closed loop.
After that, I decided to bite the bullet and remove/replace most of the plumbing on the intake side of the pumps. This turned out to be a waste of time.
The last thing I did (I know, I should have tried this first, LOL!!!) was cut back the flow on the pumps with ball valves. 1/8 of a turn was all it took, and the closed loop stopped making bubbles. Cavitation? I think so. On the flip side, this really did not help the open loop at all. I tried reducing the flow on the intake, and outlet of this pump and it didn't do much. I think the bubbles may be coming from the sump, so I plan to work on that this weekend.
Hopefully that will "clear" this problem up
Thanks again everyone!

 

[rsd]

Just a thought.
I was having trouble with my intake sucking up too much loose stuff from my sump so I distributed the intake over a wider surface.... like a reverse spray bar.
On the intake I added 8 inches of pvc pipe the same diameter of the intake pipe and this addidtion has a cap on the end. The addition also has ALOT of 1/4 inch holes dilled everywhere with them closer together as you reach the very end of the pipe (including the cap.)
What this does is take an opening that is say 3/4" across and flat and expands it out to @40 openings 1/4" over 8". or an opening that is equal to 10" across. No one point has THAT much suction. Also none of the holes are on the bottom 1/3 of the pipe.... alows it to suc in alot less detritus.
Again... just a thought.

 

[pmauro]

Can you email me the address for the place you got the sand my computer crashed and I lost all of my emails thanks

 

[baddboyzz]

wow 10k
man you got a nice tank going man i like that,good job on it.