Main Drain - Can"t run pump off MD

[ellry99]

I opened my pool with a new company today. They could not prime pump off main drain as I usually do when I open pool. We could prime pump off spa line but not main drain. (skimmers were not tried as water level was not up yet)

Any idea of what could be the problem with Main Drain? We look at gate valve to MD and it seemed fine.

Thanks,
elle

In-ground gunite 20x40
sand filter
pool pump
booster pump
gas heater

[Poconos]

How far below the skimmers is the water level? If it's too low then the lift could easily be too much for a prime. With little or no water in the pump it basically turns into a very inefficient vacuum air pump.
Al

[ellry99]

The water level was about a foot and a half or so below the skimmers.

Had valves to skimmers off and only main drain on. I had a brand new company open my pool. So I dont know if he just wasnt familiar with my equip. He is telling me I might have a main drain leak or some place else.


I could not get strainer pot lid off to trouble shoot today - it was too tight.
So, today pool was full - all I could do was try to turn on valves slowing - But it would just shut down prime on pump. Pump will only run off spa.

[polyvue]

I could not get strainer pot lid off to trouble shoot today - it was too tight.
So, today pool was full - all I could do was try to turn on valves slowing - But it would just shut down prime on pump. Pump will only run off spa.

Will just respond to the issue you're having removing the pump pot lid. Try using a rubber mallet and be sure you're tapping it in the right direction... don't use too much force. I use a wooden stake (having run out of fang-toothed blood-loving nemeses) and start the lid with a few light taps. After it's off, clean the threads on both lid and pot thoroughly and apply some pool lube. Next time it's removed, it'll be much easier.

[ellry99]

Got strainer pump lid off with the mallet. Thanks!

Still cannot get prime running pump off main drain - I have 3 gate valves (main drain, pool skimmer, and spa skimmer) When I open the Ball Valve to the gate valves the pump loses prime immediately.

My pool guy says I have a leak somewhere and that he did not see any anti freeze from the pool close.

Any ideas where to go from here. ????

[polyvue]

Got strainer pump lid off with the mallet. Thanks!

Still cannot get prime running pump off main drain - I have 3 gate valves (main drain, pool skimmer, and spa skimmer) When I open the Ball Valve to the gate valves the pump loses prime immediately.

My pool guy says I have a leak somewhere and that he did not see any anti freeze from the pool close.

Any ideas where to go from here. ????

Happy to throw out a couple of half-baked ideas but I'm not the expert here.

A typical configuration would probably share suction between skimmer(s) and main drain (MD) and I assume that when both are open 50% this would not cause the pump to lose prime, and when you set suction at 100% skimmer or 100% spa there is likewise no issue. At 100% main drain, when the pump loses prime "immediately" do you observe a near total stoppage of water flow into the pump? Or is some water coming in? Do you see a lot of air bubbles and turbulence at this point?

Knowing the pressure reading (PSI) at the filter may help with the diagnosis or at least paint the larger picture. What is the reading at the pressure gauge --- normal and current PSI?

I've read enough about possible leaks to know that quite often a valve or a PVC connection or other fitting between the pump and the MD is faulty. I tend to lean toward surgery (replace the suspect valves between MD and pump, starting with those closest to the main drain); the approach is not especially clever but it may do the job. I wouldn't rule out an air leak at one of the valves, a distintegrated o-ring or 90 degree elbow that's come a bit loose, etc.

You could perform a bucket test to see if the main drain connection at the pool has been compromised - if the pool level is dropping that would indicate a water leak.

What else? An obstruction of some kind in the pipe. Might be able to reverse roto-rooter it back into the pool.

Worst case, you have some broken pipe connection beneath your deck or pool shell. Pick A) Employ leak detection company to pinpoint location and start digging; or B) Who needs a main drain, anyway?