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Thread: Pump Too Large?

  1. #1
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    Pump Too Large?

    Several years ago, our old pump died (I don't recall the size - it was new in 1998 - died in 2006). We ran it 24 hr/day from May through Sept. The pool service company suggested we get a larger pump - they installed a 2.4 hp Jacuzzi Magnum with a Centurion motor Model B836 (2 hp, but listed as 2.4 on the housing).

    Ever since the new pump was installed, we've had problems with overheating. The longer it runs, the more frequently it shuts down (it automatically turns back on). That is, when we first start it, it will run well for 10-15 minutes. However, after it runs that long, it will start to shut down for 30-60 seconds, then restart itself. After it gets "warmed up" it only runs about 30 seconds before it trips.

    The pool people are blaming the electricians, and the electricians have verified correct wiring multiple times. It overheats even if I bypass the sand filter completely, so that tells me the sand is not the problem.

    Our pool is roughly 30,000 gallons. There are three intakes from the pool: two skimmers and a drain in the deep end. There are two "inputs" to the pool.

    I haven't measured the "head" using pressure gauges, but the pipe lengths from each intake are estimated to be 25ft (deep skimmer), 45 ft (shallow skimmer), and 15 ft (deep drain). The pipes are 1 1/2" PVC. The total pipe length to the two jets is an estimated 60 feet (15 feet to the first, and 45 feet to the second). Would the "head" be the total length of all the intake paths, or an average of the three intake paths, or ??

    While I am not a pool expert, the one thing that changed is the size of the motor (and presumably the expected flow rate).

    So the question is, if the pump is too large for the size of the intake pipes, could that cause the motor to overheat? If not that, what else? The pool guy said he verified through each line that there were not obstructions in the intake lines.

    Pump-less in Omaha.....
    30,000 Gal, Sand Filter, IG Vinyl Liner, Jacuzzi Magnum Force 2.4hp

  2. #2
    Administrator JasonLion's Avatar
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    Re: Pump Too Large?

    There is no question that that pump is too large for that pool. However that doesn't explain why it is overheating. Even with your fairly small pipes the pump should still work, just using more electricity than you need to be using.

    Calculating total dynamic head is complex. If you can tell us what your filter pressure is when the pump is running we can estimate it for you.

    There are three common causes for overheating, pipes blocked, incorrect wiring, and defective motor. From what you said, a defective motor seem most likely. Regardless of what the actual reason is, I would use this problem to pressure the pool company to replace the pump with a smaller pump. From your description, you would be fine with a 1 HP full rated pump. Better still would be to get a two speed pump.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  3. #3
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    Re: Pump Too Large?

    Thank you for your quick response.

    I spoke to an online pool supply place. I've ordered a Pentair WFDS-26, a dual speed 1.5 hp pump and I will install it myself.

    I've lost faith in the local pool company - we've been fighting this for 3 years with no resolution.

    I will also purchase a pressure gauge so I can explicitly calculate the pressure losses.

    A couple of other data points that might be helpful.

    1) There is a single "return" pipe from the pump that must split underground going to the two inbound jets. This is a 1.5" ID pipe too. When its running, there seems to be a significant and even amount of water flowing from each.
    2) The 3 inbound pipes, each 1.5" are consolidated to a single 1.5" pipe going to the pump inlet. There is a reducer between the 1.5" pipe and the 2" opening in the pump.
    3) The pump is no more than 3 feet above the water surface.
    4) My wife mentioned that the Autoshut-down behavior seemed less intense when she partially closes the ball valves on all three of the inbound pipes. Seems to imply perhaps the issue is with the size of the outbound pipes compared to the amount the pump expects to move.
    5) The "hammer" action each time the pump shuts off has caused two of the joints on the inbound side to separate. Once the pump restarts, the suction pulls the joints back together again. Not sure if this provides any diagnostic data or not, but thought I'd share it.

    One additional question/clarification: if a blocked pipe could cause a motor to overheat, wouldn't a too-small-diameter pipe have essentially the same effect?

    I will study the excellent information on this site and determine next steps.

    Thank you for your help!
    30,000 Gal, Sand Filter, IG Vinyl Liner, Jacuzzi Magnum Force 2.4hp

  4. #4
    Senior Member spishex's Avatar
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    Re: Pump Too Large?

    Once you've got the old pump off, open it up and take a look at the part number on the impeller. If the motor is undersized (2hp motor with a 3hp impeller) it would overheat and the problem would be less frequent if you cut down the water flow to it. Not likely that that's the case, especially if they pulled it new from the box, but you never know with those pool people...

  5. #5
    Administrator JasonLion's Avatar
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    Re: Pump Too Large?

    Restricted water flow can cause a pump to overheat and the overheating sensor will turn it off till it cools down. But the restriction has to be fairly dramatic. A normal 1.5" pipe shouldn't be enough to overheat a 2 HP motor.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  6. #6
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    Re: Pump Too Large?

    Only having two return inlets to the pool seems somewhat on the small side. Our pool is slightly smaller than yours, but we have 4 returns (and a ridiculously large 2.5HP high head pump!)
    26,000 Gallon Gunnite IGP
    2 HP Challenger High Head Pump
    60sf Nautilus DE filter
    Polaris 280

  7. #7
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    Re: Pump Too Large?

    My pool has some similarity to yours except I have 2" PVC piping. I replaced my 1.5 HP Whisperflow with a 0.75 HP Tristar EE. Been very happy. Still have a 2HP Whisperflow running my spa jets.

    Before changing my pump, I installed a flow meter on the system to measure flow and used that on the old Whisperflow pump curve to get my total dynamic head.

    If you want to go through the calculations yourself there is a worksheet by Hayward here that you can apply to any pump for which you can get a pump curve for.

    http://www.haywardnet.com/pdfs/Pump_filter_sizing.pdf

    I think you will enjoy your 2 speed pump and the 1.5 HP Whisperflow is a much more appropriate pump for your pool.

    Good luck

    Lee
    IG 24k plaster with overflow spa. Goldline PS-8 SWG. Tristar 0.75 HP filter pump, Polaris 280 with SELF-PRIMING pump, large cartridge filter, 400k BTU NG LAARS, DelOzone 1gm CD ozonator, Life Saver pool fence, ORP managed.

  8. #8
    Senior Member Ohm_Boy's Avatar
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    Re: Pump Too Large?

    If you can get your hands on a clamp-on amp meter, you can take a quick current reading on your new motor and get a fairly instant idea of what it is doing. It should be within the nameplate rating for the motor. If it's high, there is definitely something going on.
    Any installer should always take a current reading on any motor installation or repair and verify that it's within specs before leaving the jobsite, whether it's a pool pump, compressor, conveyor, or whatever.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

  9. #9
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    Re: Pump Too Large?

    Here is a quick update.

    A smaller replacement pump has been ordered.

    In the meantime, we needed to drain the pool to adjust the liner. Initially, we were having the same "shut-down" problems as before.

    However, when I shut off 2 of the input valves, and almost totally closed the third input valve, the pump has now run continuously (water going to "waste") for the past 12 hours without shutting down. The pump "surges" with about a 4 second "cycle" (waves of water being pumped) but it does not shut down. What does this tell you about the nature of the pump issue?
    30,000 Gal, Sand Filter, IG Vinyl Liner, Jacuzzi Magnum Force 2.4hp

  10. #10
    Administrator JasonLion's Avatar
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    Re: Pump Too Large?

    Have you let all the air out of the filter? Do you see a lot of air in the pump strainer basket?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  11. #11
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    Re: Pump Too Large?

    There is air in the filter basket. Also - and this may be a stupid question - how would I know if there is air in the filter? Our filter is a large spherical device with sand in the bottom half. There is a valve on the top that used to have a pressure gauge. That was removed when they replaced the pump originally (and now has a bunch of what looks like "putty" on it).

    I took the top off the filter about a week ago to check if it was clogged - looked OK to me).

    Sorry if these are pool novice/rookie questions. But that's what I am....
    30,000 Gal, Sand Filter, IG Vinyl Liner, Jacuzzi Magnum Force 2.4hp

  12. #12
    Administrator JasonLion's Avatar
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    Re: Pump Too Large?

    You open the valve on the top and let all the air out until water runs out. As soon as water comes out steadily, all the air is out.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  13. #13
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    Re: Pump Too Large?

    We installed the new, smaller pump a few weeks ago. Everything is working great now!

    Thanks for your help!
    30,000 Gal, Sand Filter, IG Vinyl Liner, Jacuzzi Magnum Force 2.4hp

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