pool pump suction fades

[Larrrrry]

Hi there!

I have a pool pump problem I need some advice on. When I turn my pump on, the suction at the skimmer is fine for about a minute or so and then quickly fades off and the skimmer float just bobs up and down (no suction). When I pull the backwash valve, the suction is very strong. close the backwash valve and suction dies again. Pool filter is clean
Video of the issue here:

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Any help would be appreciated

Larrrrry

 

[Texas Splash]

Hi Larrrrry! Welcome to TFP. I see that when you lift-up on that plunger valve, there's no doubt the pump was starved for water. I suspect for the first 30-60 seconds, the pump is pulling every last bit of water out of the suction line before it goes dry - until you open the plunger valve. Even though you note the filter is clean, it sure sounds like there's a water restriction in there somewhere. Maybe something got sucked-up into that valve to a point where water flow is being impeded in filter mode? It must be something significant to block water flow like that. I'd be inclined to open the filter and look again, or maybe pull the plunger vale if needed.

Maybe someone else will comment soon with other thoughts. Let us know. I'm curious now.

 

[simon SPRAGG]

Can you do a skimmer pressure test?
Is the pipe from skimmer to plant room rigid or flexible. If flexible and chlorine tablets have been used in skimmer it is very likely the pipe has rotten... Common problem.
Run with vac valve alone. Allow pressure to build up. Slowly open skimmer, if it reduces pressure overall and pumps fills with air then the skimmer pipe is damaged... Sadly this means digging up the skimmer pipe and replacing...

 

[Brett S]

In looking at this, I don’t think this is a problem on the suction line or the skimmer line at all. There is no suction when the pump is running normally, but as soon as the backwash valve is open then suction seems normal at the skimmer. That tells me that the skimmer line is just fine.

Instead, I think the pressure side is clogged somewhere. When the pump is running normally it will suck water through through the skimmer for a short time until enough pressure builds up against the clog that it can’t move any more water. As soon as the backwash valve is open the pump is no longer trying to push against the clog and things operate as expected.

Do you have a pressure gauge on your system? Is it indicating a lot of pressure? Is there any water coming out of the returns at all? Even for the first 30 seconds or minute when the pump first starts up and there is suction at the skimmer?

 

[simon SPRAGG]

Maybe the problem is in the multivalve. Or maybe you need a really deep backwash.
If you decide to check out the multivalve do so carefully and slowly... I suspect backwash heavily first, and agree with above the pressure on the fikter guage will give you a clue..