Micro bubbles driving me crazy

[SPotter]

I am getting a lot of micro bubbles entering the tank from the return lines and its driving me crazy. There are no bubbles in the return chamber of my sump and the bubbles dont always come out in an even flow. Every now and again there will be a burst of bubbles released from the return lines. I have checked all of the plumbing for leaks and nothing. I have zero salt creep building up on the fittings.

I am thinking that its one of two things.....return pump too big or how the return pump was plumbed to the sump.

Pump too big...I have a blueline 100hd on my 480g twv system. The pump feeds two 1" returns to the dt and also feeds a manifold. Currently the manifold is being used to feed my frag tank and a water change tank. I have a ball valve on the outlet from the pump and then 2 ball valves on the return lines. I have all three ball valves turned back because the flow is too strong in the dt and things get blown around. Could the flow restriction be causing the bubbles?

Too many 90's.....here is how the pump was plumbed to my sump. I have been reading that too many 90's between the sump and the inlet for the pump can cause bubbles as well. I need to add that I bought the sump used and it was already drilled for a 1.5" bulkhead and it is reduced to 1" after the ball valve. Also, the outlet on the pump is then expanded to 1.5" and then reduced to 1" when the lines are split for the manifold and return lines. I hired an installer to do all of the plumbing work so I am not sure why the outlet is opened to 1.5" and then reduced back to 1".

Here's pictures of my pump and return lines....

195920

195921

Any thoughts and feed back will be greatly appreciated!!!!

[Craig Borowski]

I have been reading that too many 90's between the sump and the inlet for the pump can cause bubbles as well.

That is a possibility. If the 90s restrict flow enough then the pump can create cavitation bubbles.

[sirreal63]

The pump may be cavitating from the reduction. They make the correct reducing bushing to prevent the reduction the way the plumber did it, which was a mistake, it is acting like a venturi on the intake, and that is not good.. The elbows are also hurting the flow to the pump. Restricting the flow out of the pump will not cause microbubbles.

[SPotter]

The pump may be cavitating from the reduction. They make the correct reducing bushing to prevent the reduction the way the plumber did it, which was a mistake, it is acting like a venturi on the intake, and that is not good.. The elbows are also hurting the flow to the pump. Restricting the flow out of the pump will not cause microbubbles.

Thanks Jack. Originally I wanted to just cap that bulkhead and drill a new hole for a 1" bulkhead but was told that wouldnt be necessary. Can you tell me where I can find that bushing? I will try to see if I can modify the plumbing and use the correct bushing and do away with the elbows.

[sirreal63]

A real plumbing store, sometimes a good Ace or True Value hardware store will keep them. Forget the big box blue and orange places, they probably wont have specialty reducing bushings that large. You want one that goes in one step from the 1-1/2" to the size of the pump inlet. No reductions along the way to the pump, you lose some volume with any fittings, as well as the ball valve and the length of the run. You cannot have too much available volume for the pump, but you can have too little. Next time you see your plumber, kick him in the sack. :D

[SPotter]

I know exactly what you are talking about one side 1.5" and the other is 1". Too bad they dont make a bulk head that 1.5" on one side and 1" on the other. The installer is supposed to come take a look at everything when he gets back from vaca.

[SPotter]

Here's a better picture of the intake line from the sump to the pump. I don't think I will have enough room and maybe thats why a bushing was used because of space. So, I will need to figure something else out.

http://i1129.photobucket.com/albums/m510/spotter10701/2012-07-11202416.jpg

[sirreal63]

The right bushing would make it about 2" shorter than it is now.

[SPotter]

Do you think I would be better off capping that bulkhead, put a new 1" bulkhead in and make the outlet line straight between the sump and pump?

[sirreal63]

Yes, it would be better, but I would still use 1-1/2" to feed the pump. It removes any possible cavitation issues. A straight run is always better than a run with elbows.

[SPotter]

ok then I can use the same opening since thats already drilled for 1.5" and then reduce it to 1" on a straight line for the inlet to the pump.

[sirreal63]

Just make the reduction to 1" as close to the pump as possible. The less work the pump has to do to pull water into the impeller the less chance there is of it cavitating.

[polleke]

Hi, are you sure the intake in the sump is not the problem? Are there enough holes or slits in the "filter" in front of it?
Do you still have bubbles if you remove it altogether and just have an open piece of PVC sticking into you sump?

[sirreal63]

Look at the first pic, the strainer should be more than adequate.

[Heliman]

These mag drive pumps absolutely hate being fed with turbulent water, they easily cavitate. Your pump is fed directly from an elbow and is getting a lot of turbulent intake flow.

Royal Exclusive (who make the superb Red Dragon Pumps) require that their pumps are fed with laminar flow water, achieved by having a straight length of intake pipe which is equal to or greater than 20 X the diameter of the intake piping....otherwise they advise that flow rates can fall 50% and cavitation/bubbles WILL happen.

Could well be a major part of your problem