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Thread: Pump motor size and priming issue and pump sizing

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    Pump motor size and priming issue and pump sizing

    Hello!
    I've just started taking care of my first in-ground pool. It is shaped like a figure 8 or a guitar and I estimate the volume to be 18,000 gallons.
    I can't get all of the air out of the pump basket and when vacuuming it easily loses pressure and needs to be re-primed.
    I also cannot seem to vaccuum the sand and dirt off of the bottom very well.
    Also it seems that very little debris is being caught with the skimmer.
    I'm thinking the pump motor is too small. The guy I hired to take care of the pool before we moved in had to replace the motor and put in a 3/4HP motor.
    He then told me the motor was too small...

    Is this the source of my priming issues?

    The filter I currently have is a posiflow and is rated 70GPM (which he also said is too small for this size pool).
    The pump runs at about 8PSI and has been steady. It is a cartridge filter.
    I run the pump 5 hours per day which I feel should be enough (18,000gal / 70GMP = 258min or 4hrs 18 min).
    The chemical balance of the pool stays level only requiring 1 chlorine tab every 7-10 days (we're not swimming in it very much).
    There is only my wife and I to use the pool, so there will not be heavy traffic in the pool.

    Is the filter too small?

    There doesn't appear to be any air leaking into the system as the water level in the pump basket remains the same after it is primed and I only seem to need to re-prime when vacuuming.
    I blocked off one of the returns and it seemed to help a bit (there are 4 returns), but I cannot block any more off as the nozzles are cemented in (which will be a fun project - separate post about that later).

    Thanks for your expertise!!

  2. Back To Top    #2
    Mod Squad Bama Rambler's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    Welcome to TFP.

    What you're describing sounds like a suction air leak when the vacuum is hooked up.
    Can you give us some model numbers for the equip? (pump, filter, vacuum, etc.)

    Just because the filter is rated for 70 gpm doesn't mean that the pump is delivering 70 gpm.
    As long as there's an air leak your vacuum isn't going to operate properly.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Pump motor size and priming issue and pump sizing

    Thanks for the quick reply. I forgot to mention that I also get persistent bubbles when running the filter (not vacuuming). They are pretty minimal, but never seem to go away.
    I've replaced all of the O-rings and everything seems to be sealed as the water level never goes down in the pump basket until I use the vacuum.
    I've tried to find air leaks, but no success.
    The vaccuum hose is brand new, so I'll be a bit peeved if it has a leak in it.
    I'll try to check it this week.
    Any suggestions on how to do so?

    The pump is a Posi-Flo 70TXR
    The "public pool rate" is 26GPM and the max is 70.
    Would a larger motor increase the flow rate?
    I've got 2" pipes on it.
    The returns had very little pressure when I had all 4 open. Once I closed one I had more pressure and was able to operate the vacuum longer.
    Let me know if I can provide any more details.

    Thanks again!

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    UnderWaterVanya's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    Does this pool have more than one suction? Multiple skimmers, main drain(s), etc? If so reducing flow from each of the non-vac sources will increase suction.

    You can test for valve and joint and pump basket leaks by pouring water over the pipes while the system is running. You can do a similar test by using shaving cream (dry the pipes if wet) and looking for places where it seems sucked in by a leak.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Mod Squad Bama Rambler's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    getting bubbles when the pump is running is a sure sign of a suction side leak.
    You can try running water over the plumbing while the pump is running and watching the bubbles in the pump basket to see if they get less or go away when running it over a particular area or fitting.

    Closing some of the returns only masked the problem by creating positive head and making the pump work less hard by pumping less water. I'd suggest you open those returns back up, at least until you find this leak.

    Assuming you have a vacuum that you plug into the skimmer or a dedicated vacuum port, you can plug that in and then run the water over the plumbing. That should make finding the leak easier. Also, you don't to spray the water you want it flowing in a sheet over the parts.

    If you still have trouble, posting some pics might help us identify possible places to concentrate on.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Pump motor size and priming issue and pump sizing

    There's only one skimmer/vacuum line.

    I've been looking for the air leak but haven't found it. I'll try more this week.

    I'm imagining that more air is being drawn into the system when I'm using the vacuum and it is getting leaves in it which is reducing the flow of the water and sucking more air through.
    Really was hoping it wasn't an air leak...
    I'll bring in some pics so you guys can see the set up. I could benefit from refitting the whole pump assembly, but really don't want to do it

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    bobodaclown's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    It might be a pin size hole in the hose.
    17K Kidney Shaped Pool Concrete (Diamond Bright) Pool, 3/4 hp 2 speed 115V Sta-rite Duraglas PEA5D-180L/P2R5D-181L (Impeller C105-92PS Diffuser C1-216P), 1.5 piping, Pentair CC100 Filter , Heat Siphon 100K BTU Heat Pump Pool Heater, Flow meter Blue White Flowmeter Model No. F-30150P, Hayward Astrolight SP0581N, SWCG CalimarTitanium Edition TE45 , Dolphin Nautilus Plus with CleverClean, Lakeland Florida

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    Mod Squad Bama Rambler's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    It could be a pin hole in the hose as Bobo said or it could be a valve leaking around the stem or a drain plug or even the oring on the basket lid. Those things will sometimes be fine at normal suction head but leak under increased head such as when the vacuum is connected.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Pump motor size and priming issue and pump sizing

    OK so I spent a while running water over the various connections on the pump and couldn't see or hear any suction. I could probably spend a life time and not find anything. So I'm leaning more toward re-sealing the connections on the pump intake and discharge. But since that is a bit of a project, I'm open to suggestions of other things to try first.

    When I watch the pump prime and operate I notice that the water in the final horizontal run of the intake pipe is not much more than halfway filling the pipe. Not sure if this helps in diagnosis. All of the pipes are underground and some are under the cement decking of the pool, I really hope to avoid getting in to those.

    While working on my removing my return eyeball fittings (some smarty cemented them in...) I noticed that the return across from the skimmer near the ladder (see illustration) has nothing coming out of it. I put some debris in it to see if it would float back out and it didn't, so I'm assuming that line is closed off somewhere, but it may be that the pump simply can't supply any pressure to it. It looks like it would have the furthest distance from the pump.

    At any rate. Here's a link to the photos and illustration of the pool layout:
    https://picasaweb.google.com/1046136...eat=directlink
    I really appreciate the suggestions here.

    Thanks!!

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    Mod Squad Bama Rambler's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    Have you replaced the pump basket lid o-ring or just lubed it?

    Did you reseal the drain plug?

    There has to be an air leak somewhere. Describe how you hook the vacuum up?

    It looks like the fitting at the front of the pump basket is leaking but it's hard to tell from the pics.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    UnderWaterVanya's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    You aren't supposed to be listening for suction as I understand it. I thought you were supposed to look to see if the air in the basket is reduced when you pour water over a spot.

    Another method uses shaving cream - watch for areas that get sucked in.

    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: Pump motor size and priming issue and pump sizing

    The o-ring on the pump basket has been replaced and lubed. I also cleaned and lubed the impeller housing seal as it was looking mighty dirty.

    I've never opened the drain plug (I'm assuming you mean the one underneath the pump basket?) and noticed today that it is a bit corroded, but completely covered in blue sealant from my pool maintenance guy.
    I might try pulling it, cleaning it, and re-lubing it. The basket has a bit of sand in it, so it could use to be flushed out.

    The vacuum is simply connected to the skimmer with a standard hose and adapter. I'm thinking the air leak is elsewhere. I opened all 4 returns today and it just bubbles like crazy even after multiple bleeds.

    There are no water leaks, the water you see is left over from me trying to find the leak.

    When I was pouring water over it with the hose I also did not notice any points where the pump regained suction, but I wasn't paying attention to that so well.
    My misunderstanding. I'll try again tomorrow and probably the shaving cream.

    It's hard to tell if the air in the basket is reduced due to the turbulence / sloshing of the water in the basket.

    I need to make a run to the pool shop tomorrow to get some new eyeball outlets and a fitting set removal tool so I can replace some of the damaged returns.
    I'm also going to get a new filter since it is due for replacement.

    A side-question: I have a bit of sand in the bottom of the skimmer basket, the outlet to the pump goes out the side and there is a fitting at the bottom for a bottom mounted outlet that goes down a couple inches.
    Any suggestions on clearing that out? Its not a big deak and I hope to find something to plug it better, but all tricks and tips are appreciated.

    Thanks!

  13. Back To Top    #13
    UnderWaterVanya's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    Another idea that helped a neighbor, wrap any and all suction side joints with a couple of wraps of electrical tape. If that works you can start removing the tape one joint at a time. Valves are problem with this method.

    For cleaning out the skimmer you might try the hose to stir it up and push it out to the pool for vacuuming later or a wet dry vac.

    Sent via Tapatalk...
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: Pump motor size and priming issue and pump sizing

    The side outlet from the skimmer is unusual. The bottom outlet probably has a plug in it and a little sand won't matter. I am assuming that you do not have a main drain in the bottom of the pool?

    The best way to check the male adapter going into the pump for an air leak is to run a bead of silicone around the connection and keep pressing it in with your finger. If that temporarily stops the air leak you have found the problem.

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    Re: Pump motor size and priming issue and pump sizing

    Yeah, to clean the bottom outlet for the skimmer I've just been stirring up the sand so it will get sucked into the filter when I turn it on, but every time I vacuum the pool I get a load of sand in there again.
    I don't like that the skimmer uses the side port instead of the bottom one. It also has a port that points toward the pool, but I'm assuming it is sealed like the bottom, though I've not stuck anything other than my fingers in to verify.
    Why the heck does it have 3 outlets? Is that an equalizer line that comes from the main drain?

    There is a main drain at the bottom of the pool. I've no idea if it actually flows to the pump though. Judging by the little bit of sand and no leaves being drawn to it, I think it is not connected or clogged.
    I've no idea where it connects to the pump, if at all. I'm not losing any water out of the pool other than normal evaporation.

    I'll work on the suction air leak more tomorrow as time permits. I tried packing Magic Lube around the fitting at the front of the pump basket before because that fitting looks like it is in poor shape, but it changed nothing.

    Thanks for the suggestions. Back to work!!

  16. Back To Top    #16
    Mod Squad Bama Rambler's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    If you're constantly getting air out of the returns you have a suction side leak somewhere. It may be hard to find. In fact, looking at the setup closely, it may be underground.

    You say you have a main drain but there's no evidence of it at the pad. It's most likely connected to the other side of the skimmer since you say the bottom port is plugged.

    The first order of buisness is to find that leak.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Pump motor size and priming issue and pump sizing

    Well I've found some of the leak. It was around the inlet to the pump basket. The shaving cream method helped a lot as the leak was on the bottom.
    I still have some air coming in, but not sure where, maybe under ground, but I don't think it is bad enough to dig for it. The pump basket is filled to the brim now, just the cap seems to keep filled with air. Maybe there's a small leak around the lid. I'll keep tinkering with it.

    Now it's off to replace the eyeball returns I've broken and chip the cement off of them! I sure hope whoever installed them didn't cement the threads too...
    I'll report back sometime this weekend.

    Thanks for the tips. This has been helpful!

  18. Back To Top    #18
    Mod Squad Bama Rambler's Avatar
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    Re: Pump motor size and priming issue and pump sizing

    I'm glad you found that leak. Just watch the lid. Sometimes it takes a while for all the air to purge from the lid and you may always have a little bubble, Mine does most of the time.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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