Closed Loop Cavitation

[matts125]

First off I have had my closed loop running for a few months now with a constant flow of microbubbles. I have been clueless as to why untill I learned about cavitation, this is obviously my problem. so here are a couple pictures of my closed loop

Here it is now running fully stocked, you can see to the middle/right in the back that the intake is over 20'' under water.

so my question is this: how do I change the plumbing or what do I need to do to get the cavitaion to stop?

Thanks in advance for any help!!
Matt

 

[matts125]

Here is a link and a picture of cavitation with a explination of what causes it.
(just for those of you who dont already Know)

http://en.wikipedia.org/wiki/Cavitation

 

[ronj]

i used to open and close the ball valve to the outlets....i would close it for a few seconds and turn it back on and repeat...it seemed to help blow out the air that was trapped

 

[matts125]

i used to open and close the ball valve to the outlets....i would close it for a few seconds and turn it back on and repeat...it seemed to help blow out the air that was trapped

Ron, I dont believe my closed loop has any trapped air.. Cavitation is when the impellar collapses tiny voids of air in the water...

I hope some one has some advice as to how I can Modify my plumbing to fix this problem....

Thanks....

Matt

 

[Scooterman]

Is it cavitation or is it sucking in air & the pump is producing micro bubbles, which enough air would cavitate the pump & probably damage it by now?
First off, you can almost eliminate the outlet & the closed loop, if your getting micro-bubbles. The only way you could actually get fine micro bubbles is when air & the impeller mix together with water. Yea there is that vortex thing that if just right the outlet could suck in air but lets not go there just yet. You need to test each connection from just below the water line a about 6" to the suction of the pump. I have to remember how this is done but there is a neat trick to doing it, let me think about it some, maybe someone else will know.

Just how much micro bubbles are we talking about, lots like in skimmer or really a fine mist?

 

[matts125]

Is it cavitation or is it sucking in air & the pump is producing micro bubbles, which enough air would cavitate the pump & probably damage it by now?
First off, you can almost eliminate the outlet & the closed loop, if your getting micro-bubbles. The only way you could actually get fine micro bubbles is when air & the impeller mix together with water. Yea there is that vortex thing that if just right the outlet could suck in air but lets not go there just yet. You need to test each connection from just below the water line a about 6" to the suction of the pump. I have to remember how this is done but there is a neat trick to doing it, let me think about it some, maybe someone else will know.

Just how much micro bubbles are we talking about, lots like in skimmer or really a fine mist?

Scooty, I already took the whole closed loop off as siliconed all the joints and it didnt change it a bit.... I didnt check the unions by the pump though...

Matt

 

[Scooterman]

First off silicone doesn't seem to adhere to PVC well, take the PVC cement & wrap each joint. Suspect the threaded fittings & close to the pump for sure. When using Teflon make sure you wrap the fittings in the proper direction as the wrong way will unravel the tape & not seal well, I had to bury almost every fitting, be very careful threading into the Volute as it will crack under too much pressure.

 

[Scooterman]

Ahh better clarify the tape thing lets see if i get it right

hold fitting in left hand, with tape in right hand wrap clockwise, this should be against the direction you actually tread the fitting.

 

[matts125]

So Scooty you dont think that this is caused by pushing more water then the pump can pull or vise versa? for instence if you were to plumb the intake with 1'' and the outlet with 1 1/2'' ? I know mine is plumbed with 1 1/2'' on the intake and outlet.... so I guess that it should be pushing as much as it can pull....

Matt

 

[Scooterman]

It would get louder when you restrict the inlet, also overheat it & if too much burn it. I see unions also, I use a little Vaseline on the O-rings, even though they should be well sealed. You can try & use an air tank with compressed air & try to inject each connection with forced air, see it you get a sudden rush of bubbles. I can't remember who but think it was BigT that had a way of testing that was easy. maybe shoot DonW a pm. You can always go bigger on the outlet no harm, & to a point smaller but not smaller on the intake (suction) side.

 

[Scooterman]

Also check the Volute, (pump housing) it seals all the way around, check it for leaks of any kind, looks sorta wet.

 

[Llarian]

So Scooty you dont think that this is caused by pushing more water then the pump can pull or vise versa? for instence if you were to plumb the intake with 1'' and the outlet with 1 1/2'' ? I know mine is plumbed with 1 1/2'' on the intake and outlet.... so I guess that it should be pushing as much as it can pull....

Matt

I doubt it. (I'm not Scooty, but I'll answer)

I've never heard of a microbubble issue caused by cavitation in an aquarium pump. While you're not supposed to run a larger output than one is rated for, lots of people do, it basically just adds to the head pressure. (Pushing against more water)

Every microbubble issues I'd heard resolved has to do with a tiny air leak somewhere in the intake path.

-D

 

[DonW]

Matt,
Run over to the beer making supply store on 112th. Buy a bunch of rubber corks. Hook your shop vac to the closed loop. It will suck in pvc glue and seal any leak you may have.

Don

 

[twilliard]

but if you think about it, the leak would have to be substantial to cause cavitation.

Are you missing a fish matt??? JK

So I havent read, is the pump not pumping or is it making miro bubbles?

 

[krisfal]

Matt,
Did you ever resolve your microbubble problem? I am having the same problem and am looking for suggestions to resolve.

Thanks,

 

[matts125]

it just eventually dissapated and now I no longer have the problem anymore, I suspect my issue was a small air leak in the locline above the water with eventually plugged itself with saltcreep or something...

Matt

 

[krisfal]

Thanks for the reply Matt. I am glad your microbubble problem went away and can only hope I get as lucky.

Although I am not ruling out the above the water locline, I really suspect my problem is on the intake side as I can hear air in the plumbing on that side and the pump sounds like it is "grinding" air. I am going to try scootermans suggestion above and blow compressed air on all the joints to see if I can discover a leak (tonight's attempt to solve, or at least locate the problem). If I don't find anything I think I will work on getting all the locline submerged so I can eliminate that possibility.

Thanks again for your reply.