Engineers and uber smart folks..put on your thinking caps...

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mr_X

Aquarium Advice Addict
Joined
Apr 27, 2008
Messages
17,895
Location
Fairless Hills, Pa.
A friend is having a problem. It has stumped me.
He has his system hard plumbed. No leaks, and it's drive is a Blue Line 70 external pump.
Just for "poops" and giggles, it's a 120 in-wall display and a 30 breeder frag tank with a 20 long refugium and a 100 gallon stock tank used as a sump.
Everything is hard (pvc pipes) plumbed and herd is the problem-

The system has been running fine for a month now, until today when he had a power outage. The sump filled and stopped, then the power was restored and the pump did not push water like it was supposed to. It basically sat idle but heated up so much that the outer casing was barely touchable.
Then after unplugging and plugging back in for a while, it fired back up.

He was so distraught, he went to "Champion lighting and supply" who just happens to be close enough, and bought another blue line 70.
He hooked it up and the exact same problem happened.


The guys at Champion said it was airlocked...that it back drained air into the pump and it could not self-prime. I find this ridiculous since the pump is below the sump and no way would it drain air below the water line inside the sump.
Can you give us any fresh ideas on why both of these pumps are not restarting?
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But wouldn't the water that's below it, inside the pump move the air back out? I mean, in every system I ever had when you fire the pump back up it blows all the air into the tank before the water.
 
I know the those pumps are not self priming ( I have one ) so as long as there's a solid water feed to the pump with no air pocket it should run,...I remember when I first bought mine I was outside trying to see how it would work and I had a heck of a time trying to get it primed using the garden hose etc before it would work as intended... Somehow I bet there's an air pocket in the " impeller" section , how it got there who knows but those pumps are designed to use centrifugal force to throw the water outward into the outflow pipe,.if there's any air in there it's just going to spin creating heat.
Just my two cents.
 
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He doesn't have any section of the plumbing that could be an air "trap", does he? (Think a p-trap, but upside down).
 
Ok...another piece of info- If we choke the pump at the exhaust port to about half, it will start every time. We are thinking that it's the 90 before the pump intake that might be restricting a little flow, but enough to make a difference.
Do you think plumbing this pump straight in front of that hole might be the solution?
How about a length of spa flex instead of an elbow?
 
IMO the least amount of restrictions the better...it might just be starving for enough water to keep it primed and going ,..... That's a pretty powerful pump and needs a lot of water to make it work,..... Question,..once you restricted the " output" and it started did it continue to pump water or did it die out? If it continued to pump water could you slowly open up that valve to increase to flow to normal? At this point I'd say you got nothing to lose by running a straight line into its input side
 
Yes, that's exactly what happened. We opened the valve all the way and it ran fine. Ok. Thanks. I'll keep you posted.
 
Is the diameter of the pump inlet larger than the supply line? It sounds like its cavitating. If the impeller were locked up, the magnetic drive wouldn't heat up that much but if the impeller were spinning with no water flow, it will eventually fail for good.

If there is any leak on the supply line, air could be getting trapped. The pump won't pump air, it needs water flow to purge the air in the system. The back force on the outlet could be causing a bubble to get trapped right at the impeller. Moving the plumbing around a bit may cure it.

How does air enter the system anyway? If the inlet is always below water, and the outlet doesn't drain the pump when it's off, it shouldn't ever loose it's prime. If that's the case install a one way back flow valve that will hold the water column in the pipe.
 
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Well, at this point he's installed a check valve on the return, and this seems to have cured the problem. All the systems I put together and none of them had a check valve, and they all functioned fine. Crazy.
 
Engineering in general can get crazy. I'm at Motorola headquarters now working on a interesting project. Did a fluidics project in school that gave me some insight to pumping fluids around. Strange things can happen.
 
Well, at this point he's installed a check valve on the return, and this seems to have cured the problem. All the systems I put together and none of them had a check valve, and they all functioned fine. Crazy.


I was just going to ask you that ! :)
 
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