Main Drain issue

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Tyrone Shuz

LifeTime Supporter
Jun 2, 2007
107
Bowie, MD
Hello:

I have a skimmer and a main drain, and one return line (another return had been abandoned before we took ownership 13 yrs ago). I have a pent air DE filter, with the pressure gauge on top, that you can bleed the air out of by twisting the cap underneath the gauge.

At the pump there are two lines, one for the skimmer, and one for the main drain. We just opened, and there's a good bit of stuff on the floor that the main drain should suck down. Right now I can't the main drain, I will in a day or so. Anyway, when I turn the skimmer off and have the main drain on full, the pressure drops to 0. Is this normal? I can't seem to bleed the air out of the filter when the skimmer is off and main drain is on. Maybe I'm not waiting long enough, but it doesn't seem like anything's happening. What am I up against?
 
The main drain line is probably clogged. It really isn't a good idea to use the main drain to try and get rid of debris unless it is just very fine dirt. You can try to flush the line backwards through the pump basket and see if you can loosen the clog.
 
Would a regular backwash go through the pump basket? We have a multiport thingie. There's "filter" which is normal operation, "waste", "rinse", "backwash" and maybe two more. I only use "fllter" and "backwash", but I'll use "waste" if the pool gets too full. I'm not sure what the others do.
 
No, that exits out of the backwash valve.

To back flush a main drain line, set the suction side valve to be on main drain only. Open the pump basket lid and put a hose into the pipe that comes into the pump basket. Wrap the hose with a wet rag and try to seal it inside the pipe as best you can. Then turn on the water for a few minutes.

To remove the debris from the bottom of the pool, you are best off using a leaf rake like one below and then vacuuming to waste the remainder of the debris. Try to avoid pushing anything other than fine dirt to the main drain.
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I tried your idea, but it's difficult with what we have. Coming from the pump there's a pipe that T's after 6" one side to skimmer, other side to main drain. They each go 6" then each go straight down into the ground. When I stuck the hose in, wrapped in a rag, I couldn't hold a seal, the water would find its way back out. Now, after two tries, it looks like it's sucking some water into the pump on the main drain side, but not enough to prime it, and I don't feel anything coming out of the jet return. Maybe it'll unclog itself eventually, but I'm no plumber, and I guess the only other way is to take apart the junction and snake it, perhaps?
 
You can also get a Drain King at a hardware store. It is self sealing and pulsates so it might dislodge the clog.
 
Well I got a drain bladder, and at first I couldn't get it to function, but with the water pressure ever so gradually increased, I got it to not back out of the pipe. There's not much clearance before the T junction. Yes, I have the skimmer side off, so eventually, the water all goes down the main drain pipe. I left it on 5 minutes or so. I couldn't see anything coming up from the main drain, I suppose I should have waited longer, but that seems like a long time, the line isn't all that long, 25-30ft or so.

I don't know if I'm imagining it or not, it seems the line works a little better, but it won't prime the pump.
 
You are better off priming with both the skimmer and main drain open. There may be too much head loss to prime with just the main drain. After the pump primes, then turn the valve to 100% main drain and watch the filter pressure. If it dips too much, the line is still probably clogged.
 

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Another thing to try, is to alternate the valve between skimmer/main drain on to main drain only on and see if you can loosen it up that way. Back and forth, back and forth many times over. Allow the pump to fully prime in between with both on. Maybe mix up with a Drain King session too. It just may take some time to get loose.

The only other option is to attack it at the main drain end but you would have to remove the cover to do so.
 
OK I don't know if this is related--my pump is (sta-rite I believe 3/4 HP maybe 1/2--I think 3/4) is running hot to the point where it shuts down. The main drain and skimmer are both open and the pump primes fine, or seems to. Do you think closing the main drain will make my pump run cooler?
 
Does it shut down on the skimmer too?

If it shuts down on both the skimmer and main drain, it could be the bearings are failing which is causing excess load. If it shuts down on main drain only, then it could be the lack of flow is overheating the motor.
 
I turned off the main drain last night, and it shut down today. I did notice the pump bucket had stuff in it, which I removed. I guess there's extra suction w/o the main drain open. But it shut down long after I cleared the pump bucket. Can this be fixed, or do I need a new pump?
 
Is the motor making any unusual noises? Normally, if a pump runs and then shuts down after some time, it is usual the bearings causing the problem. However, impeller restrictions can also cause the same type of problem but they are less common. It is usually worth it to take off the wet end and inspect the impeller and diffuser for any issues before embarking on a motor repair. Any of these issues can be repaired by yourself if you are handy or a service tech if not.
 
Motor sounds fine. I have had to un-freeze the impeller the last 2-3 seasons upon startup. But once it's unstuck it spins really smoothly. The service I use taught me how to take that end apart, and that sometimes the impellers freeze. There's gotta be a way to lube that somehow, but I guess that would be from the other side. But that's not my issue at this time. She's just running very hot.
 
That is usually a symptom of a failing bearings. The impeller should never "freeze" and the bearings are sealed so they cannot be lubed and must be replaced.
 
Well the pool guy that came to look at the pump told me to just crack the main drain, then open it up after a while, then try turning the skimmer off. It worked. I'm guessing between the drain king and the other things I've tried it all helped somewhat, and it was gonna break free eventually, and there was a nice gift in my pump basket. Now the pump primes w/just the main drain if I need it to, and of course I don't now!

As for the pump, it still runs hot and shuts off, then turns back on. The pool guys took the info off the pump and left, they weren't mechanics. They said they'll research the model and the symptoms and see if anything can be replaced, or if I need a new pump motor, or new pump. But at least I know the clogged line had nothing to do with the pump behaving as it is. That's probably bad news, now that I think of it.
 
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