Pump losing prime ONLY in filter mode.

[robertmee]

Going to try and be as thorough with the info, so we don't go down the rabbit hole of Pump Lid seals, suction leaks etc.

Variable Speed Pump
Sand Filter with Hayward Multiport
Two main Drains into one intake line (valved), One Skimmer in other intake (valved)
Three Returns in three separate lines (two inground in one valved line, three fountains in one valved line , six jets in one valved line)

Symptoms:

Pump loses prime on Filter position ONLY. No loss of prime or bubbles on Circulation, Backwash, or Waste.

Actions and Info:

Changing from Main Drain to Skimmer to Both makes no difference. Water level in Pool is fine.
Changing Pump Lid Seal makes no difference (no air in other modes). Greased and New.
Rebuilt Pump Seals and Changed Impeller, no difference.
Swapping between fountain, main returns or jets, makes no difference on returns....These are three separate pipes, so not likely any kind of underground leak
No water loss in pool
No dirt in pool
At 1800 RPM Pump PSI is about 12. At 2400 RPM it is around 18. At 3200 RPM it is around 30. Normal operating range is 1800 RPM.
Have backwashed filter multiple times. Pressure drops a few PSI but nothing major.
Have done deep clean of Sand Filter multiple times.
Have changed Filter Sand.
Have changed laterals.

None of the above resolves the issue....Pump loses prime in about 4 hours. Only way I can run is to program multiple timers which on the Vari-pump starts a Prime at 3400 RPM. But even that doesn't fill the basket, only raises the pressure and partially refills pump basket.

Everything to me points to a blocked filter, so the last thing I have to change I suppose is the multiport valve. Would seem odd that only the Filter port would be blocked and none of the others, but maybe? Since both backwash and filter uses the stand pipe, I don't think it could be full of sand causing an issue? Especially since backwash goes down the pipe and out the laterals? I would think that would be harder to push through.

I'm at my wits end on this one. I'm about to the point of emptying the filter of all sand and seeing what happens, or buying a new valve. Please help!

 

[Texas Splash]

Sounds like you've done your due diligence in troubleshooting. A partial clog somewhere might otherwise seem like a reasonable thought, but then you seem to pull water fine in other settings. Can you post a pic or two of the equipment pad and plumbing just so we can relate better to what you described above? Was your pool closed all winter? If so, when did this start happening?

 

[robertmee]

Sounds like you've done your due diligence in troubleshooting. A partial clog somewhere might otherwise seem like a reasonable thought, but then you seem to pull water fine in other settings. Can you post a pic or two of the equipment pad and plumbing just so we can relate better to what you described above? Was your pool closed all winter? If so, when did this start happening?

Thanks for the response. No, I don't close the pool. Started happening about a month ago, progressively getting worse. Just did another Deep Clean this past weekend and didn't help. I had a different problem last summer where the basket never filled, and at that time, thought I had resolved with a new pump rebuild, new sand and new laterals. But I think I just delayed the problem until now.

EDIT: Additional Info, Pool is 8 years old now, all equipment original/rebuilt.

Not home to take picture, but I quickly drew this to show flow diagram:

 

[robertmee]

Also additional info, the valves are just standard PVC Ball Valves....No fancy Jandy or Pentair valves. However, it doesn't seem to make a difference which return valve I open/close, as far as prime. Obviously opening more than one return valve causes a pressure drop, but doesn't hurt/help the prime situation that I can tell. Same for intake valves. For the first 6 years or so, I ran with just the main partially open and the skimmer fully open to draw as much suction on the skimmer. I thought maybe I was starving skimmer, so now I'm running both full open. No differenece.

 

[Texas Splash]

I'm currently only seeing two scenarios:
1 - There's still a problem in the filter confirmed by everything working fine when in recirculate and waste, essentially bypassing the filter.
2 - (Probably a stretch here) - There's a partial clog between the suction ball valves and the pump that is restricting water flow. Unlikely, but we're taking about water flow.

Unless I'm missing something else. Maybe others will see another possibility.

 

[robertmee]

I'm currently only seeing two scenarios:
1 - There's still a problem in the filter confirmed by everything working fine when in recirculate and waste, essentially bypassing the filter.
2 - (Probably a stretch here) - There's a partial clog between the suction ball valves and the pump that is restricting water flow. Unlikely, but we're taking about water flow.

Unless I'm missing something else. Maybe others will see another possibility.

Maybe a combination of the two? Partial clog after the two valves on the suction side, which gets exasperated by the restriction of the filter only in that mode....not enough of a blockage to affect waste/recirc.

Trying to remember if there is a union before the pump that I can take it apart and run my camera scope in there to see.

 

[robertmee]

Just realized, I've never tried it in Rinse. Rinse is the same as Filter, correct, it just goes out the waste pipe instead of the returns? But the water flow is the same? So, if the pump doesn't fill up quickly in rinse like backwash or waste, then that would point more and more to the filter. If it fills up quickly, then that would point to something with the pipe after the filter? I only have done Rinse right after backwash, so the pump basket is always full at that point. Next time I lose prime, I'll try Rinse first.

 

[oldprophet]

Did you check the male pvc fitting going into the pump suction port. They can come loose

 

[robertmee]

Did you check the male pvc fitting going into the pump suction port. They can come loose

All fittings appear tight with no leaks....ive used soapy water techniques and no air suction leaks on inlet side that I can find. In that pump has no issue when filter is bypassed would think that there isn't an issue with any leak, especially small and not obvious, on the suction side.

 

[robertmee]

Not sure why, but installing a new multi port valve seems to have resolved my issue. 2 weeks of 24/7 running now and no loss of prime. Thanks for everyone's help.

 

[Texas Splash]

Not sure why, but installing a new multi port valve seems to have resolved my issue. 2 weeks of 24/7 running now and no loss of prime.

Didn't expect that one, but glad to hear you got it resolved. Now you can enjoy the weekend.