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Thread: Pump size selection help

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    DIY Junior Member Tykat11's Avatar
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    Default Pump size selection help

    Hello everyone, I am building a new house, bungalow with basement, 2 full baths up, 1 below. I have a 3000 gallon underground cistern to feed the house(well water is poor in area)and it is 12-14ft below where the 1.25" pipe enters the house and the pump needs to go. My plumbers suggests an on demand pump(variable speed Grundfos)over a jet pump and pressure tank. Any suggestions? I have heard jet pump and tank system are more reliable and can be made to have constant pressure.

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    Moderator valveman's Avatar
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    You don’t need a variable speed pump for the well. The well is a low producer, so you need a regular small submersible pump and a Dole valve to limit the flow to the production rate of the well. Then a float switch in the cistern will control that pump.

    I also like a submersible in the cistern instead of a jet pump, but either will work. With three baths you need about 15 GPM at 50 PSI to handle peak demands. Then a CSV would let it run all three showers at the same time or make it work like a smaller pump, even down to 1 GPM, when that is all the water you are using.

    The CSV will do the same thing as the variable speed pump. The CSV is just simpler, less expensive, and longer lasting than variable speed pumps. If you want to check up on that variable speed pump they are trying to sell you, just Google “CU301”. That is the controller for that variable speed pump, and you need to know how it has worked for others.

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    DIY Junior Member Tykat11's Avatar
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    Thanks for the reply,sounds like a good suggestion.The constant pressure system my plumber suggests is the grundfos mq3-45. What's the lowdown on this unit?

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    Moderator valveman's Avatar
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    In my opinion the electronics in the MQ are not any better than the CU301. You would be better off with a regular jet pump, pressure tank, and pressure switch. Then if you want constant pressure you add the CSV. The MQ is not really constant pressure, it just shuts off using a flow switch instead of a pressure switch, which means it runs at max pressure all the time, not actually constant pressure.

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    DIY Junior Member Tykat11's Avatar
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    Thanks for the input, I don't want to be replacing my pump for a long time so it looks like jet pump, pressure tank it is. Definitely interested in the CSV, will look more into it.

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