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Thread: Slowing a Capacitor-Start pump motor

  1. #1
    DIY Junior Member nooboo's Avatar
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    Default Slowing a Capacitor-Start pump motor

    I bet someone here knows how to do this:

    Picture a water transfer pump, a Tsurumi LB480, submersible, 2/3hp, 230v, 1ph, 60 hz, capcitor-start...I want to slow the GPM it delivers and I am thinking that slowing the frequency will slow the motor and slow the GPM flow rate.

    I have checked around with my friend Google, but after writing the manufacturer reps, I am told they don't have a device. I asked at Davis for AC Drive / Frequency Inverter, 200-240 VAC single or three phase input with 3 phase output, 2.4 max. ; not suitable, 3 ph out..
    Well, I do agree that slowing down the frequency of the power will slow down the pump. I know that can be a problem when running 60hz equipment (like fans) internationally because they often only have 50Hz. But I don't have the right equipment to offer to do that with the pump you have
    Tsurumi says it is possible and OK to use a VFD on the pump, just not above 60hz. The VFD's I reviewed are not suitable for the capacitor-start.

    The motor has blk, wht, green wires, to be used in the US, 110/220/1ph,60hz.

    b

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Install a valve on the DISCHARGE pipe from the pump and you can throttle it to any GPM you want. It would not work on the inlet to a pump, even if there were a way to do it.
    Licensed residential and commercial plumber

  3. #3
    Electrician ActionDave's Avatar
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    It would need to be a permanent,split, capacitor motor to be slowed down. Cap start and other single phase motors need to reach full speed quite soon or the starting winding will fail.

    Hj has a good idea. An added benefit of clamping down on the water is the extra back pressure will be easier on the motor.

  4. #4
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by hj View Post
    Install a valve on the DISCHARGE pipe...
    +1
    A dole valve is a common and acceptable way to reduce the GPM output. Did you want to reduce the GPM or vary the GPM and why?

  5. #5
    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by hj View Post
    Install a valve on the DISCHARGE pipe from the pump and you can throttle it to any GPM you want. It would not work on the inlet to a pump, even if there were a way to do it.
    As long as it is a centrifugal pump, that would be fine. That could even reduce the current the motor will draw; less GPM transferred means more water just spiining around inside the pump body, using less work to get stationary water in motion.
    I am definitely not a pro plumber, but I am a pro crastinator

  6. #6
    Moderator & Master Plumber hj's Avatar
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    As long as there is some flow. Completely stopping the flow would cause the water to heat up and turn to steam, then cavitation would damage the impellers.
    Licensed residential and commercial plumber

  7. #7
    Electrician ActionDave's Avatar
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    Quote Originally Posted by hj View Post
    As long as there is some flow. Completely stopping the flow would cause the water to heat up and turn to steam, then cavitation would damage the impellers.
    That makes for a really bad day.

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