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Thread: Increase hp motor-pump & no prime

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    Increase hp motor-pump & no prime

    My old pump motor was 1.5hp and finally broke. It was 14 years old according to the sticker year stamp on the side that was badly faded. For the previous three years it performed well even if it didn't make the returns spray forcefully or the drain pull very hard.

    So a friend sold me on using his 3hp motor & pump that he had been using for a couple years since he was upgrading. So I hooked up the new pump and now I can't get a prime no matter what I do. I tried pulling from just the drain, just the skimmer, both, putting the hose into the skimmer supply to the pump and nothing. The 1.5hp pump was working with the same plumbing just two weeks ago when it finally died so I am puzzled why an increase in hp would prevent me from getting a prime.

    My question then is is too much hp going to cause me to not be able to get a prime (I think that's the right term) where the basket fills with water almost entirely? If that isn't the case then everything I've read suggests leak that is allowing air in. Would a leak have to be on the supply side of the pump? And would it need to be massive?

    I filled the basket with water and let the hose run into the skimmer and drain lines for close to ten minutes to where there was almost no air coming from them and pulled the hose, put the cap on the basket, screwed it down, and turned on the power very quickly. The pump pulled all the water visibly from the basket very rapidly and then nothing but a trickle. The pump sounds very smooth and isn't struggling but the lack of water flow has me thinking something is amiss.

    I'm not sure if it is apparent but I'm not very savvy about pools and their workings though I like to think I can learn. Also I did a cursory search on this subject and did not find anything that jumped off the page at me. If this is answered elsewhere any redirect is greatly appreciated.

    Thank you.

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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Increase hp motor-pump & no prime

    Welcome to TFP!!!

    It could be that the 3HP pump is too powerful and pulling in air where your old pump was not. That behemoth of a pump is going to be a waste of electricity if you do get it working. Might be cheaper in the long run to buy an appropriately sized 2-speed pump (or even a smaller 2-speed motor and impeller to put on the pump you got from your friend).

    Double check that you do not have any valves closed on the return side as well. Can you try to run in waste mode? (not sure if you have that since you did not tell us anything about your setup.)

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