Strange Suction side leak.

[fjz]

Hi all, I hope you can help me out here with me little problem

I have a 1 Hp Northstar pump. (03 model) This year, I developed a suction side leak. I replaced ALL the o-rings on the pump to include the pump motor seal. (was leaking) Normally this would indicate a leak in the line up stream.

Now, what is confusing to me is I have a shut off valve down stream of my filter that I use to divert water to my pressure side pool cleaner. When the cleaner is properly adjusted, the filter pressure indicates about 20LBS and there is NO air bubbles in the water. When the valve is wide open the filter pressure is about 10LBS and there is a lot of bubbles in the return. I don't understand how a change in pressure would stop an air leak if it was in the supply line so this seems to indicate I have a air leak in the pump that goes away with higher water pressure. ( If I open the filter and run the pump there is a lot of bubbles in the water more so that at 10 LB as stated above.

Since I also replaced the impeller and motor seal, could this be creating the problem. Installed incorrectly, wrong parts. There is no water leaks under the pump.

PS. I did not change the strainer lid cover but the o ring was replaced. That is going to be next.

 

[Bama Rambler]

What you describe makes perfect sense. When you raise the pressure by closing a discharge valve you actually lessen the suction head so it leaks less. The more flow the pump produces (i.e. lower discharge pressure) the higher the suction head and the more air into the system.

You have a suction side leak somewhere.

Check the skimmer for a vortex and make sure the weir is working correctly and is not sticking.
Check the pump strainer basket lid for a leak.
Check the pump drains for a leak.

The shaft seal is on the pressure side of the pump so it's not the suspect here.

 

[duraleigh]

Hey,

Double ditto what bama said.....

Look for the air leak between the pump and the skimmer....since you have air in the lines, that is where you will find it.

Check that the o-ring is seated CORRECTLY on top of the pump strainer basket. Make sure that the drain plug in the basket body is screwed in correctly. check ALL the valves, joints and unions.

 

[fjz]

What is a weir???? Can you explain the vortex issue.

AS I indicated in my first posting, all possible entry points on the pump are 0 ringed and or teflon taped except for the strainer basket lid itself. I noticed it's not a tight as it was when it was new. (required a rubber mallet to remove) So maybe it's not pushing down on the 0 ring hard enough..... wishful thinking.

I talked to the Hayward tech rep and he thought my problem was cavitation. It's a high head pump and he thinks I don't have enough pipe volume and getting cavitation. I did replace the impeller when I replace the motor seal. His recommendation was to go to a smaller impeller and that MIGHT fix the problem... if its cavitation. Since the pipes are underneath 4 inches of concrete I'm hoping for a above ground fix. That said, is there any way to fix a pipe leak short of replacing it all. Does that chemical sealer work?? Understand you would have to pressurize the lines for it to work, Another problem.

 

[Bama Rambler]

The weir is the door in the skimmer that flaps down when the water is flowing. It should operate freely.

If the weir isn't working correctly or if the water gets a little low the suction will create a vortex (whirlpool) in the water and suck air down the middle of it.

You need to find the suction leak. I highly doubt it's cavitation. If it was you'd be complaining about how your pump sounds like it's about to come apart. Besides, you can't see cavitation in those pumps.

You can run a water hose over the pump basket and plumbing while it's running and see if the bubbles stop getting in.

 

[fjz]

Ok, I figured it out. After installing the o-rings that came with my pump rebuild kit and then spending $26.00 on a "new" o-ring for the basket it did not work. I installed the old o-ring I previously had and the leak stopped. I'm going to get a new lid and see if that finally fixes the problem and I maybe I can use the three "other" o-rings I have laying around here that are suppose to work. Some times it's the simple stuff the messes you up. Know what i mean. Thank to all who answered this post and provided guidance. It's been a frustrating couple of weeks working on the problem.... and costly to.