Pump loses prime

[sethz]

Some observations:
If I keep the pump running, it won't lose prime.
If I shutdown the pump for several hour, it loses prime.
There are lots of air in the filter, when I fill the water under the pump lid, all water goes to the filter.
When the pump is running, I see lots bubbles out of return constantly.

My system is relatively simple: skimmer->pump->DE filter->returns

One possible problem I found is the glue-like sealant on top of the pump is not sealing anymore. What is the name of the sealant? Where to find?
[attachment=1:26m21hk9]prime1.jpg[/attachment:26m21hk9]
[attachment=0:26m21hk9]prime2.jpg[/attachment:26m21hk9]



Another unrelated question, how to prime efficiently? I use a sump pump and connect the sump pump to skimmer line with a vacuum hose, because the hose doesn't fit on sump pump (garden hose connection), I need both hands to push them together. Then I need another person to turn on the sump pump, then run to turn on the pool pump. With current prime problem, last was a busy weekend.

 

[JohnT]

The sealant is on the outlet side of the pump, which wouldn't give you bubbles or priming issues. You undoubtedly have an air leak somewhere before the pump impeller. It looks like your strainer basket lid or the housing has been repaired with something, and is a good candidate for the source of the leak.

 

[sethz]

I repositioned the gasket under the pump lid, as well as the o-ring inside of the pipe union. Things seem better. The pump prime itself in 2 minutes.
I still see bubble in the return, and there is 3 inch air pocket right under the pump lid. Once I shut down the pump, the air pocket slowly getting bigger, seems coming from the suction side tube.
I suspect there is still small leak in the pipe union (the o-ring looks old, I can't find a replacement in home depot), or one of the pipe connection right before pump.
Is there a quick and easy way to check small leak around PVC pipes?

 

[JohnT]

I suspect there is still small leak in the pipe union (the o-ring looks old, I can't find a replacement in home depot), or one of the pipe connection right before pump.
Is there a quick and easy way to check small leak around PVC pipes?

Suction side leaks sometimes spurt a little water when the pump shuts off. You can also try covering the are with the stream from a hose. This will temporarily stop air from getting in and the bubbles should disappear.

 

[sethz]

Suction side leaks sometimes spurt a little water when the pump shuts off. You can also try covering the are with the stream from a hose. This will temporarily stop air from getting in and the bubbles should disappear.

Will look into, thanks John