Question about Grundfos MQ3-45 1 HP Pressure Booster Pump

1 Answer

When I turn on the tap, the water does not come right away

Posted by Anonymous on

  • Anonymous May 18, 2010

    The type of booster pump we have used does not require a tank. It senses either a pressure drop or flow to activate the pump and holds the pressure steady until the demand is gone. I failed to mention that the pump is pushing water about 300 feet to the house and also has to achieve about a 20' head. I talk with Grunfos and they think that perhaps the long pipe to the house acts like a tank in and of itself and so when a toilet is flushed there is not enough movement of water in the pipe to activate the pump. I am still puzzled as to why the water is not right at the tap when I turn it on though - is it back draining some how? Grunfos has recommended that I install another pump to bring the water into a holding tank in the house and then use the booster pump to supply pressure for the house. Your thoughts on this? Thanks

  • Anonymous May 19, 2010

    Thanks for the insight - I never thought about moving that mass of water in order to activate the pump. No wonder it doesnt work properly. What we are planning is a non pressurized water storage in the house which will feed a whole house booster pump to supply adequate pressure. The holding tank will have a float and be filled from the pump in the pump house - two pumps in total...but I dont have a lot of choice as I really like the idea of constant pressure as provided by the Grunfos booster pump vs a bladder tank and fluctuating water pressure.
    Again, thanks for all you help




1 Answer

Al Kupchella

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Sounds like the pressure tank isn't working right. The pressure tank should have air in it that is compressed by the water, so that when you open the tap, the air pressure should immediately begin pushing the water. Water is virtually incompressible, so you need that air to give you some volume to be compressed. After the air pushes the water for a moment, the pressure drops enough so that the pump kicks in to maintain and restore that pressure. If you don't have such a tank, that's the problem. If you do have such a tank, then it may be full of water and you will have to find a way to fill it with air. Or, perhaps the tank is not piped correctly. I hope you found this helpful. Good luck.

Posted on May 17, 2010

  • Al Kupchella
    Al Kupchella May 18, 2010

    I'm very puzzled by the two-thumbs rating. Give me some more information and I can probably help.
    Al K

  • Al Kupchella
    Al Kupchella May 18, 2010

    That's a very different scenario from what I was left to imagine. I agree that the long pipe will act like a tank, as pipe will stretch a little under pressure. But unlike a tank, unless that pipe has a pretty large diameter your tap can't respond until all of the water in the pipe starts moving - that's a lot of mass to accelerate. Putting an air bladder tank at the house would definitely help the response at the tap. Maybe that's what you meant by "holding tank". Good luck.

    Al K



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