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Thread: Pump won't prime on MD only -- Skimmers work okay

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    Pump won't prime on MD only -- Skimmers work okay

    Hoping one of the gurus here can help.

    I've got a system with 2 skimmer lines and a main drain line feeding into the pump intake. When I have the Jandy valves set so that the pump only pulls from one or both of the skimmers, I have no issues getting primed.

    However, once I switch the skimmers off and try to use just the main drain, I can't seem to maintain prime. It will churn for a while, some water will come out slowly at first and then flow rather quickly like it's about to fill the pump basket like normal, but before the bubbles and turbulence settle down and go normal, the water flow drops dramatically and then it churns and churns again. After about another 30 seconds to a minute, the whole cycle will start over and it will look like the pump is about to prime finally but then flow drops again. Oddly, if I have both skimmers and the MD turned on, then it can also maintain prime.

    Things I've tried:
    Replace the o-rings in the Jandy valve for the MD -- No luck
    Replaced the pump basket T-Seal -- No Luck
    Pump Drain Plugs checked and tightened -- No Luck
    PVC Connections -- Checked and no signs of cracking or leak. Wrapped all the visible, above-ground PVC connections from MD to Pump in Electrical Tape -- No Luck Also tried the running water over the junctions and no luck.


    Nothing seems to make a difference so I'm leaning towards it being a PVC leak somewhere under ground, but was curious given the cycle where MD almost primes then flow backs off, almost primes then flow backs off, etc. if that could be an indication of something else.



    Pump is a Northstar 2 1/2 HP variable speed.

    Thank you!

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Sounds like a clogged MD line. Try jamming a hose turned on into the line to see if you can free it. A plumber's snake or electrician's tape may also be useful.
    ----Chris----
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    Re: Pump won't prime on MD only -- Skimmers work okay

    but was curious given the cycle where MD almost primes then flow backs off, almost primes then flow backs off, etc. if that could be an indication of something else.
    Your description does not match this but a rhythmic surge in the pump basket is often because the pool water is too low. Again, unless your description is backwards (won't prime in skimmer only), that doesn't add up.

    It is almost NEVER an underground pipe. It certainly can be but almost never is.

    What happens when you prime with both MD and skimmers open and then slowly close off the skimmers with the pump running?
    Dave S.
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    Re: Pump won't prime on MD only -- Skimmers work okay

    Agent 99 -- Thank you. I'll try the clogged line items and let you know. I'll start with the hose with the plumber's drain bladder first. My electricians tape won't be long enough, but I do have a full size plumber's snake I will try also.

    Duraleigh -- Thank you too! Pool water was topped off this morning and skimmers work perfect. I'm sure hoping it's not an underground pipe and as I've read, that usually isn't the case so hoping. When I attempt to prime with both skimmers and the MD open, it primes with no issues. If I then slowly shut off the skimmers, the prime quits/stops and it goes into that cycle as mentioned in the original post of almost getting prime, but then dropping over and over again.

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Quote Originally Posted by smokey75 View Post
    Agent 99 -- Thank you. I'll try the clogged line items and let you know. I'll start with the hose with the plumber's drain bladder first. My electricians tape won't be long enough, but I do have a full size plumber's snake I will try also.

    Duraleigh -- Thank you too! Pool water was topped off this morning and skimmers work perfect. I'm sure hoping it's not an underground pipe and as I've read, that usually isn't the case so hoping. When I attempt to prime with both skimmers and the MD open, it primes with no issues. If I then slowly shut off the skimmers, the prime quits/stops and it goes into that cycle as mentioned in the original post of almost getting prime, but then dropping over and over again.
    So it is sucking air in the MD only position....pointing to an as yet undiscovered air leak somewhere between the MD selector valve and the point where the pipes go underground. (As before, it can be an underground suction leak but it is pretty rare when you think of the physics involved) Double check that section. I think it is getting narrowed down.

    This doesn't fit your scenario very well, either, but did you put your hands up onto the impeller to check for debris?

    Another long shot is some debris where agent99 is suspecting. Not sure why it would rhythmically surge but it is sure worth a shot.
    Dave S.
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    Re: Pump won't prime on MD only -- Skimmers work okay

    A stone in the main drain would do this: The pipe will fill up, the pump will draw it down. The pipe will fill up, the pump will draw it down. It has to be just the right stone and it would almost have to be moving back and forth like a check valve. Kinda like when you pump too much from a well point. It will refill and then the pump will get a slug of water to send up to the house.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Pump won't prime on MD only -- Skimmers work okay

    I tried running a snake down it but no luck there either. I went as far as it would take the line and when I pulled it out, I tracked how much snake had been down the drain. It looks like it should have gotten more or less right to the MD but no debris pulled out and no change in symptoms.

    Unfortunately, between the MD selector valve and the point where the pipes go underground there are only two connections -- a ninety degree that goes to the Jandy valve on one side and the main PVC coming out of the ground on the other. Both ends of this junction have been taped with electrical tape with no changes.

    Interesting thought on the stone in the main drain. I've got one of the MDX drains (Pic below of the config I BELIEVE I have) and it's a royal pain to take apart with security Torxes, etc. as well as it being in the 8-10' down deep end. I'll have to take a look at that later.

    MDX-Drain.jpg


    Any other ideas before I do multiple dives to get the drain itself apart?

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Update:

    I pulled the drain cover off over a series of dives and ran a snake about 6-8 feet down the line with nothing impeding it and nothing pulled out. Still same symptoms at the pump and no improvements.

    Starting to sound more and more like an underground leak somewhere, but curious if there are any additional opinions out there before I bite the bullet and call a pro.

    Also, if I have to go that route, any suggestions for good and inexpensive pool pros in the north Dallas, Allen Texas area?

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    Re: Pump won't prime on MD only -- Skimmers work okay

    What if you pushed air through the MD (of course with the cover off) to determine if anything comes flying out of the tubing. I have to agree with Duraleigh, the plumbing should all be in tact.

    Kind of reminds me of the central vacuum system. It is clogged once in a while and looses suction. I have actually used my Cyclone in the last month, and boy did this do the trick. It pushed everything (clumped up together from cereal, hair, etc.), all the way to the end. By no means am I suggesting this in the lines, but I believe this is a tactical approach.

    Maybe closing off all the lines with filter off and only pushing air through the main drain to see if any debris come out.
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    Re: Pump won't prime on MD only -- Skimmers work okay

    I'd wondered about blowing air through the MD line but just wasn't sure how to go about it. I have multiple compressors and various ends but nothing that would fit inside a 2" PVC pipe and seal it off so that the air all goes towards the opened drain. Any hints on how to go about that? Something like the plumbing bladder but for the compressor. My access is through the Jandy Valve if that helps. Also have a shop vac that could be used, but again not sure how to seal it.

    Thanks for all the help!

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Quote Originally Posted by smokey75 View Post
    I'd wondered about blowing air through the MD line but just wasn't sure how to go about it. I have multiple compressors and various ends but nothing that would fit inside a 2" PVC pipe and seal it off so that the air all goes towards the opened drain. Any hints on how to go about that? Something like the plumbing bladder but for the compressor. My access is through the Jandy Valve if that helps. Also have a shop vac that could be used, but again not sure how to seal it. Thanks for all the help!
    You should have drain plugs at the pump housing, If removed, you can place a fitting attached to an air compressor. Close everything off besides the main drain to have enough volume. Remove MD cover and maybe there is debris there.
    14,700 gallons IG Pool Vinyl Liner - Octal Circulation System
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    Re: Pump won't prime on MD only -- Skimmers work okay

    I will see what I can do with regards to the blowing it out. May need to buy a few parts. Will update once I've tried this.

    I did some searching on the Cyclone Vacuum and Blower and it looks interesting and easy to blow out the lines with it. Might not be a bad purchase in general for future use.

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Wanted to give an update. It's beginning to look like the issue is almost certainly debris in the main drain. I hooked up my 21 gallon HFT air compressor to the pump's drain plug this morning and let it run some air through the MD lines. While I didn't see any large debris come up from the MD, I did see some dirty water start to come out. This was odd since the water is crystal clear normally (thanks to all the pool chemistry lessons from here). I never actually saw air bubbles come up from the MD, but I think this was due to air pressure issues and incomplete seals on the air line connections.

    Either way, once I started the main pump again, I did get a lot of air out of the MD as well as a boatload more dirty water enough that the entire pool is pretty cloudy at this point. I let it run for a bit playing with the Jandy valves switching between skimmers and the MD then I checked the pump basket -- bingo-- there was a solid inch or more of dirt and small gravel in there. I emptied out and am going to let things run for a while until the water clears up, but this seems like a clear indication that there is a clog as everyone suspected.

    I'm debating going ahead and buying the Cyclone as I feel it will do a bit better job at blowing out the lines than the air compressor did, but I may just try a few more rounds of the air compressor first. Thanks for all the guidance so far!

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Smokey:

    If you have enough air through the MD, you will see a lot of bubbles (I mean a lot). You said that you had "a lot of air out of the MD"? Is that what you meant. Bubbles means a lot of air. The surface of the water at the MD will look like a fountain if you have enough Volume.

    Did you close everything else beside the MD? Also, as the MD cover off when you did this? If the compressor is not that sufficient, you may want to invest in a Cyclone. Try a few more rounds of blowing out the MD. Each time you move water out, LOCK the valve and create a small air lock. Then turn on compressor, and slowly open the valve up full and give it a another shot. You may want to slowly close while the compressor on, but if you hear backpressure then open the valve again slowly. Do not close the MD valve all the way with the compressor on as you will build back-pressure.
    14,700 gallons IG Pool Vinyl Liner - Octal Circulation System
    Hayward Pro-Series 350 LB. Sand Filter Model # S270T - 2" Plumping
    Hayward CL2002 Chlorinator - Hayward Super Pump 2 HP Model # k48m2n111
    Hayward AQR9 SWG 25K Salt Cell & TF-100 Test Kit + Speed Stir
    Gulfstream HE125RA - 117K BTU Heat Pump - Date of Build is 11-2013

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Yes, lots of bubbles but primarily after I restarted the pump. With just the air compressor hooked up, I wasn't getting enough pressure/volume it seems to push the air all the way through to the MD (or maybe I didn't wait long enough with the compressor running). Everything was closed except the MD at this point, but due to layout, the filter housing was also in the air compressor mix but the valve was shut off for the pressure side right after the filters to ensure no air leakage on that side. MD cover was off.

    I did go ahead and order a Cyclone yesterday as I need more volume/pressure than I seemed to be getting with the air compressor but it probably won't arrive until next week. I'm cautiously optimistic this will make the difference given all the small pea gravel that came out after the first round of air compressor work. I see a light at the end of the tunnel at least

    Will update after I get a chance to play with the new equipment when it arrives. Thanks again!

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Quote Originally Posted by smokey75 View Post
    Yes, lots of bubbles but primarily after I restarted the pump. With just the air compressor hooked up, I wasn't getting enough pressure/volume it seems to push the air all the way through to the MD (or maybe I didn't wait long enough with the compressor running). Everything was closed except the MD at this point, but due to layout, the filter housing was also in the air compressor mix but the valve was shut off for the pressure side right after the filters to ensure no air leakage on that side. MD cover was off. I did go ahead and order a Cyclone yesterday as I need more volume/pressure than I seemed to be getting with the air compressor but it probably won't arrive until next week. I'm cautiously optimistic this will make the difference given all the small pea gravel that came out after the first round of air compressor work. I see a light at the end of the tunnel at least

    Will update after I get a chance to play with the new equipment when it arrives. Thanks again!
    Take a look at my post. If you can not create something like what I did, then you can easily purchase fittings that adapt to your skimmer (if you have 2 skimmers, close off one of them) and then close off the multiport and you can push air through the skimmer and it will be forced back to the pump and out to the MD. If you are pushing air through returns, then you need to put multi-port to the recirculate. You will understand your plumbing better then me. All the parts are in the post. Also, I believe the thread should be the same size as the fitting. Thank you.


    Modified Cover for Hayward Super Pump for Closing Swimming Pool
    14,700 gallons IG Pool Vinyl Liner - Octal Circulation System
    Hayward Pro-Series 350 LB. Sand Filter Model # S270T - 2" Plumping
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    Hayward AQR9 SWG 25K Salt Cell & TF-100 Test Kit + Speed Stir
    Gulfstream HE125RA - 117K BTU Heat Pump - Date of Build is 11-2013

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Nice setup you built! I'm planning on using the skimmer approach this time and already built out the parts I need for this. Your approach though gives me more flexibility and I may end up with something like that in the future. Much appreciated.

    Cyclone gets here sometime next Tuesday. Can't wait.

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    Re: Pump won't prime on MD only -- Skimmers work okay

    I had hoped to be writing to the board with a success post, but unfortunately, it looks like I am one of those extremely rare situations where there is an undergound leak in the drain lines. The cyclone came today and I hooked it into the lines. However, instead of air coming out of the MD as I had expected, lots of muddy water and dirt started shooting up between my pool coping and the concrete pool decking. Looks like this will be a royal pain for me now complete with jack hammering, etc.

    Anyone know a trustworthy and inexpensive (but good) pool person in the north Dallas area?

    Thanks for all the help along the way.

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    Re: Pump won't prime on MD only -- Skimmers work okay

    There is a product that I have read about, that might work. It is put in the pipes and it seal leaks. I'll look to see if I can find the threads.

    It was for a service called Pipes down under. But no response of it actually worked.

    You could try a quick google search of -- Repair underground pool pipe.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Pump won't prime on MD only -- Skimmers work okay

    Quote Originally Posted by smokey75 View Post
    I had hoped to be writing to the board with a success post, but unfortunately, it looks like I am one of those extremely rare situations where there is an undergound leak in the drain lines. The cyclone came today and I hooked it into the lines. However, instead of air coming out of the MD as I had expected, lots of muddy water and dirt started shooting up between my pool coping and the concrete pool decking. Looks like this will be a royal pain for me now complete with jack hammering, etc. Anyone know a trustworthy and inexpensive (but good) pool person in the north Dallas area?

    Thanks for all the help along the way.
    Sorry to hear about this. If the leak is near the coping and underneath the concrete, maybe the mason can cut the concrete out where someone can dig down for the repair. Maybe the mason has a special way of putting it back with an expansion joint. Jack hammering near a coping and pool may now be too much vibration, but a skilled mason with the right saw can probably work wonders. Good luck and keep us posted!
    14,700 gallons IG Pool Vinyl Liner - Octal Circulation System
    Hayward Pro-Series 350 LB. Sand Filter Model # S270T - 2" Plumping
    Hayward CL2002 Chlorinator - Hayward Super Pump 2 HP Model # k48m2n111
    Hayward AQR9 SWG 25K Salt Cell & TF-100 Test Kit + Speed Stir
    Gulfstream HE125RA - 117K BTU Heat Pump - Date of Build is 11-2013

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