Closed loop / uv / microbubbles help needed.

[Biff0rz]

Ok so I have a dino issue and I decided to run my uv closed loop over the top of the tank down to the uv then pump back into the tank. I did this because I really do not want a pump in the tank. I am trying to have the pump pull water through the uv then back to the display. When I made the U shaped pipes that go over the tank I tapped them with a tapper and added rodi fittings on them. I've attached rodi line and valves on the ends. I did this because if I need to service the unit or break the siphon I easily can. So I've got it all running but one slight issue. I've got microbubbles. That means on the intake side I either have a small air leak or the way I did this just doesn't work. I'll go with leak for now (but I can't find it).

Left side, intake side

Right side, pump out to the display

These are the U shaped pipes with rodi fittings

Now, I start the siphon by sucking on one of the valves (intake). This fills the pipes. I then suck on the other side to draw more water in and create a seal. I start the pump and pump all air and water out. I stop the pump. This let's a few bubbles out. I start it again and there are noticeably less bubbles. Repeat and all bubbles gone. I then let it run for a while and come back and see micro bubbles. I keep inspecting all the pipes, there are no water leaks anywhere. My only guess is the rodi fitting on the intake side has a small small air leak. I plan to seal with some silicone.

When I view the water coming down from the intake side (looking through the UV window) I see bubbles dropping down.

Thoughts on next steps? I was going to try and reverse the pump but that'll take some pvc work (and parts) as the intake and put are different sizes.

 

[laverda]

My guess is it is because the intake side to the pump is too restrictive creating a vacuum, hence no visible leaks. This causes the pump to cavitate. Also most seals are designed to keep water in and do not work well in a vacuum situation. The pump intake plumbing needs to be at least as big as the pump intake. Bigger would be ideal due to the length and number of Benda and fittings. Put the uv on the output side of the pump.

 

[Biff0rz]

My guess is it is because the intake side to the pump is too restrictive creating a vacuum, hence no visible leaks. This causes the pump to cavitate. Also most seals are designed to keep water in and do not work well in a vacuum situation. The pump intake plumbing needs to be at least as big as the pump intake. Bigger would be ideal due to the length and number of Benda and fittings. Put the uv on the output side of the pump.

Ok, yea, this is exactly what's happening. Couldn't I add a valve on the output side and close it halfway? Wouldn't that do something similar to reducing the exit lip size?

I'll eventually re-do it but I want something to get me by for now.

 

[laverda]

Restricting the return flow should help. Looks like a DC pump. If so turn down the flow directly.

 

[Biff0rz]

Restricting the return flow should help. Looks like a DC pump. If so turn down the flow directly.

It is a DC pump and it was doing this on the lowest setting. I installed a ball valve on the exist side and closed it a little, no more microbubbles! Thanks!

 

[laverda]

That is telling you your intake is very restricted. Glad the valve fixed it.

 

[Biff0rz]

That is telling you your intake is very restricted. Glad the valve fixed it.

Yea when I piped it it, I did all the same size. This will get me by for now. I'll redo the exist 1/4" smaller eventually and reverse the pump.