Finding pin holes in a closed loop system

[loveless]

Cavitation and aeration are two different things. If the intake to your pump is blocked partially to fully cavitation will occur. If air is getting into your pump then airation is occurring. Im not sure if cavitation could cause microbubbles but checking the intake for restriction would be one to check on top of air leaks.

[my2rotties]

Thanks everybody I will check it out, just not tonight. If I touch anything this late Murphy's law will kick in... With well over 325g of water it could be ugly.

You guys are the best!!!

[golf nut]

Just curious, what kind of pump is it?

[my2rotties]

A Blueline 100. Not happy with it. A killer on power bug time. Will be changing it.

[midgetwaiter]

It's pretty unlikely that you have something like a pinhole in the side of a pipe, you just don't have enough pressure to rupture PVC. If you have a hole it will be somewhere at the edge of a fitting where the glue has a space in it. This space could theoretically allow air to be sucked in by the movement of the water through the pipe like the venturi on your skimmer works.

In practice this is pretty unusual in a return line, the back pressure would be more likely to force water out of the hole than draw air in. Due to the rise in your system I imagine you have a check valve on there that will keep the pipe full with the pump shut down. Turn off the pump and look for leaks either in the plumbing or around the pump volute.

[Buccaneer]

The answer to your question is cavitation

I had the same problem with a Iwaki return pump on my old 330G reeftank

Just put a ball valve or gate valve on the output side and throttle back the output a bit


bubbles gone

[sphelps]

Not necessarily cavitation but something similar. Could you describe what the plumbing looks like from the sump to the pump? Likely this part of the plumbing has too much restriction which results in a low pressure situation. If the pressure is low enough dissolved oxygen will actually be liberated from the water, a very common problem that most never figure out and usually blame it on a pin hole which is actually pretty ridiculous when you think about it.

A quick fix is restricting the output flow of the pump as already mentioned, this will in turn increased the pump intake pressure. A better fix is to plumb the pump properly.

[golf nut]

Restricting the output of the pump will reduce the cavitating, however if this system has been up and running for some time then this should not be the issue, and it sounds more like a restriction on the input side.