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Thread: Change pump motor from 2 hp to 1 hp - any problems?

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    Change pump motor from 2 hp to 1 hp - any problems?

    I have a 2 hp Sta-Rite Dura-Glas II pump (model P4RA6G-188L). I'd like to lower the output on the pump and am considering replacing the 2 hp motor with a 1 hp motor, the A.O. Smith USQ1102 for example. My thought is to replace the seal and o-rings but reuse the impeller. Are there potential problems with doing something like this, such as overloading the new motor?

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    Mod Squad jblizzle's Avatar
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    Re: Change pump motor from 2 hp to 1 hp - any problems?

    Yes. You can not downsize the motor without also downsizing the impeller ... which may or may not also require additional hardware changes, like the diffuser in the pump

    {You can oversize the motor for an impeller though without problem.}
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    Re: Change pump motor from 2 hp to 1 hp - any problems?

    Looking at my owner's manual the 1.5 and 2 hp Dura-Glas II pumps both have the same impeller (#C105-238PDBA). Based on this I should be able to drop down to a 1.5 hp motor without any problems, correct?

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    Re: Change pump motor from 2 hp to 1 hp - any problems?

    Quote Originally Posted by Silverhawk
    Looking at my owner's manual the 1.5 and 2 hp Dura-Glas II pumps both have the same impeller (#C105-238PDBA). Based on this I should be able to drop down to a 1.5 hp motor without any problems, correct?
    I would be careful about this. As far as I know (and I may be wrong), they are not the same impellers. That said, you need to compare the service factors on the old motor, with the service factor on the proposed new motor.
    In other words Service Factor (SF) x HP = real HP, so a 2HP motor with a SF of 1.1 = 2.2 HP. A 1.5 HP motor with a SF of 1.65 = 2.475 HP.
    Why do you want to do this? If it's to reduce flow, you need to reduce the impeller size. If it's to reduce energy consumption, reducing the motor size will have virtually no impact, and may lead to excessive wear and tear on the motor.
    You're probably better served by doing more research and going to a two speed pump motor with the proper impeller.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Mod Squad Bama Rambler's Avatar
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    Re: Change pump motor from 2 hp to 1 hp - any problems?

    I just went back and reread what you're wanting to do. Changing the motor won't do what you want. The wet end (and plumbing) is the determining factor in how much a pump works. In order to lower the output (GPM) of the pump you'll have to change the impeller and possibly the diffuser. Even keeping the same motor and changing the wet end will accomplish what you're wanting to do.

    If you keep the same impeller and went to a 1 hp motor the current draw will be the same.
    Dave J. TFP Moderator
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    Senior Member mas985's Avatar
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    Re: Change pump motor from 2 hp to 1 hp - any problems?

    Quote Originally Posted by Silverhawk
    Looking at my owner's manual the 1.5 and 2 hp Dura-Glas II pumps both have the same impeller (#C105-238PDBA). Based on this I should be able to drop down to a 1.5 hp motor without any problems, correct?
    The reason they have the same impeller is because they actually use the same size (Label HP * Service Factor = total HP) motor. One is full rated and one is up rated.

    If your goal is to reduce energy costs, what you really want to do is drop the impeller by one or more sizes. The motor does not need to be changed.
    Mark
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