Pump Runs Dry

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ThinkPad

ThinkPad

0
Jul 8, 2014
227
East Coast
I walked outside earlier to find the pump running dry. Fortunately, I walked out about 8 minutes after the pump started, and no damage has been done.

My pump has a small air leak somewhere. Normally, once the pump shuts off, I will hear air bubbles moving through the pump, and the water level in the pump will slowly decrease. The water level normally decreases to about halfway or at the bottom of the opening from the basket to the impeller. I noticed before the pump turned on, there was condensation on the pump lid, and the water level was below the impeller opening. I've seen it do that before, and last time there didn't seem to be an issue.

Is it possible that the water is evaporating and leaving through the air leak? Has anyone else had this issue? Like I mentioned above, the air leak is small, and the pump will run normally once it primes.

To add to that, the pump leaks when it is running. The pressure is also normally low (8 or 9 psi). The low pressure and water/air leak have been that way since I moved in.

For now, I'm manually priming and turning on the pump.
 
With an air leak, the water simply drains back to the pool. There is no evaporation involved or necessary. Air leaks typically occur in the pump lid gasket or drain plugs. A little pool lube should solve the problem.


To add to that, the pump leaks when it is running.
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That could be damage caused by running dry. It might be either a seal leak or other gasket leak. You can usually fix that with a new seal kit.
 
When the pump is turned off after running/pumping, listen around your plumbing and equipment...you may be able to hear the hissing of the leak.

I have had a number of air leaks, and have always been able to use my ear to identify the source....with the exception of...

My pump has two threaded plugs on it at the bottom of one side, which I believe act as vacuum breakers to make it easier to get the top off the pump basket...do you have anything similar? If so, are they tight? If tight, unscrew them, is the rubber gasket intact?
 
Yes, the water does drain back in the pool. Normally, it will obviously stop draining once it reaches the bottom of the suction side opening in the pump basket. But today (and a handful of times before), the water level will go below both the suction side and impeller side openings. Once the water has gone down below the suction side opening, the bubbling noise stops. That's why I'm questioning evaporation.

The water leak has been there since I moved in, this was not a result of the pump running dry. I caught the pump dry right after it turned on, and there appears to be no damage.
 
I don't hear a hissing sound, just the ticking of the bubbles from the air leak. The leak could be really small. It's probably where the water leaks out of the pump housing when it's running. If there is a water leak when it runs, there is probably an air leak when it doesn't. My next suspect would be the o-ring, because it looks like a little water comes out of that, also.
 
ThinkPad said:
Yes, I can hear the air leaking, it makes a bubbling noise. Is it likely to be evaporation causing the excess water loss?
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No, it is not evaporation. It has to do with a siphon.

What you have is an air leak. The pump basket is above water level so when the pump is off, the pressure in the pump basket is lower than atmospheric pressure so the atmosphere tries to push air into the pump basket. If there is a small leak in the pump lid gasket or drain plug, air enters the pump basket and displaces the water which then runs out of both the suction and return plumbing.

You just need to fix the air leak.
 

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I know there is an air leak. But what I'm asking is when the water level in the pump basket gets below both the suction and impeller side openings, is that due to evaporation? Normally, due to the air leak, the water level gets right at the bottom of the suction side hole in the pump basket. Sometimes, the water level will go below the openings in the pump basket, and I'm wondering if this is due to evaporation.
 
ThinkPad said:
It's probably where the water leaks out of the pump housing when it's running. If there is a water leak when it runs, there is probably an air leak when it doesn't. My next suspect would be the o-ring, because it looks like a little water comes out of that, also.
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Those 2 air leaks should be your priority. Losing water to evaporation from within the pump is highly unlikely. Finding the 3rd leak location causing the drop with those 2 leaking is also highly unlikely.
 
ThinkPad said:
I know there is an air leak. But what I'm asking is when the water level in the pump basket gets below both the suction and impeller side openings, is that due to evaporation?
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What you are seeing is a siphon effect out of the return side. The water level drops below the suction port because it is being sucked (actually pushed) out of the return side and does not stop until the siphon is broken which means that air needs to enter the pump chamber and part of the return side plumbing before the siphon is broken so the water level can drop well below the suction side port and as low as the impeller inlet.
 
mas985 said:
What you are seeing is a siphon effect out of the return side. The water level drops below the suction port because it is being sucked out of the return side and does not stop until the siphon is broken which means that air needs to enter the pump chamber and part of the return side plumbing before the siphon is broken so the water level can drop well below the suction side port and as low as the impeller inlet.
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The water level in the pump will go below the return side opening in the basket, also. It will then continue to drain, but eventually stops.

I was bored, and was just looking at a picture of my pump while reading the reviews, and I noticed a small drain plug. I went out and felt mine, and mine was loose. I tightened it, and it appears to no longer leak while running, and leak air when off. It's been holding the prime for about 15 minutes now, which is longer than usual. I will wait until later and see if the prime is still held, and then see if it leaks when ran longer. I will post an update. I'm guessing my low filter pressure was caused by the missing parts in my filter (another whole issue).

Someone mentioned earlier to check the drain plug, I thought that person meant on the filter.

Thanks everyone for your input!
 
ThinkPad said:
The water level in the pump will go below the return side opening in the basket, also. It will then continue to drain, but eventually stops.
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Yes, that is not unusual. The siphon is broken when it stops and it can be below the impeller inlet.
 
Oh, so the water is being pulled through the return opening in the basket, then flows back to the pool? That makes sense, because when I take the lid off to empty the basket, I will hear a gurgling noise, and feel the pipe from the pump to the filter vibrating. I always just thought that the vibrations and noise were from the filter losing the water. Learned something new today! :D
 

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