Finding pin holes in a closed loop system

my2rotties · #1 02-25-2009, 05:21 AM

The sump is full. The water gets sucked into the return pump from the bottom of the sump not the top. The water would have to be drained right out for it to be sucking air. I feel that the pump is cavitating and on it's way, out but the LFS INSISTS there is a pin hole in my system. I don't know much abut how the system works but I cannot see how it is possible to have a pin hole to be honest. Sorry about my lack of knowledge on the set up. I watched it get built but do not know the technical names of all of it. I just take care fo the entire system except for broken things.

Quote:

Originally Posted by Mr OM

Then it isn't a closed loop but a standard return.
It could be a number of things, but based on the fact that hubby is out playing hockey I would think that your sump may be running dry and air is being sucked in.

golf nut · #2 02-25-2009, 05:27 AM

Make sure the inlet to the pump is clear.

loveless · #3 02-25-2009, 05:37 AM

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 · #4 02-25-2009, 05:55 AM

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 · #5 02-25-2009, 06:04 AM

Just curious, what kind of pump is it?

my2rotties · #6 02-25-2009, 06:40 AM

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

midgetwaiter · #7 02-25-2009, 06:41 AM

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 · #8 02-25-2009, 06:50 AM

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 · #9 02-25-2009, 03:38 PM

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.