Variable speed well pump?

Discussion in 'Shop Talk' started by DJ in WA, Sep 30, 2005.

  1. DJ in WA

    DJ in WA Well-Known Member Supporter

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    Had to have a new well drilled and we’re trying to determine what kind of pump to put in. 340 ft well has plenty of water (25+ gpm).

    We can use up to 15 to 20 gallons per minute irrigating lawn/pasture and garden. Problem is, the 3 hp pump needed for that cycles on/off when using less water. I should add more pressure tanks to reduce the cycling.

    My pump man says there’s a variable speed pump that maintains constant pressure (50 psi) that’s been used in domestic wells about the past 5 years. It would adjust to the flow needed for different volumes of watering. My concern was that when not irrigating, it would have to come on more often with regular household use (e.g. flushing toilet). He says it comes on every half a psi drop in pressure, but it is a soft start, versus the high amp start of a standard pump.

    With all the plumbing, trench digging, and new pump and 500 ft of wire, and new pipe down the well, etc, the variable speed system is about $3700 vs $3300 for standard pump system. The variable speed needs smaller wire. It would reduce pressure tank replacement costs down the road. Hopefully it would lengthen pump life by reducing hard start cycling.

    I’m wondering if anyone knows of this system and has any comments. The concept sounds good, but is there something I’m missing? The pump guy says it’s too early to know longevity, but they seem to work. He says he hasn’t pushed it too hard because of the extra expense – often a thousand bucks more. My long wire run helps make the cost gap smaller. Pumpman said I could read about it at Franklinelectric.com, which I will, but hoping someone has experience or perspective.

    I’ve thought of having a storage tank with separate pump for irrigating, supplied by a 1-1/2 hp standard well pump system. But I’d have to re-plumb to get that water from the tank to where it’s needed. I’d like to keep things simple.

    Anyway, thanks for any comments.
     
  2. fordy

    fordy Well-Known Member

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    ................Simplify , Simplify !! You surely don't need a 3hp pump . I would think 2 hp at the most . 340 feet not that deep , just find a 500 or 1000 gallon P.tank which won't cost any 3300 dollars . Well man can calculate friction loss easily . I'd leave that variable speed deal alone . fordy.. :)
     

  3. BobK

    BobK Well-Known Member

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    I agree with fordy...why go that route? Why not plan a irrigation plan that allows the well to discharge a bit less than maximum capacity thus preventing cycling of thepump?
     
  4. agmantoo

    agmantoo agmantoo Supporter

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    What is the water table depth? At most you only need a 1 HP pump. If you want to irrigate just run the system longer. Why pay for a pump that will be supplying less than 5 GPM the majority of its life? Not only will the utlility be more for a higher HP unit, the replacement costs, should lightning hit it, would be higher. I get by just dandy with a 3/4 HP pump set at 220 ft and it supplies the geothermal heatpump 8 GPM water in addition to the the household. I strongly suggest that you put as much storage [bladder tank(s)] as the budget can tolerate. This will add longivity to the pump while reducing utility costs.
     
  5. DJ in WA

    DJ in WA Well-Known Member Supporter

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    Okay, from your replies and poking around the net, looks like variable speed pump not the way to go. Computerized, stuff can go wrong.

    Yes, 3 hp is clearly oversized, though that is what was installed here before we bought the place. We often used it’s max output in the summer in the garden with my homemade drip system (holey pvc conduit), or when running many sprinklers on lawn/pasture. Most the time, though, didn’t need that much water.

    I’m thinking of a 1-1/2 or 2 hp and just make it work, and add another pressure tank. My static water level is 260 feet – pump man says 1-1/2 will do 10 gpm, 2 hp will do 11-12 gpm.

    I was hoping the variable speed would allow the pump to adjust to our needs rather than us having to plan around the pump. I water lawn/pasture only when it’s starts to dry, which varies with weather. If I get too small a pump, with the area we have, there won’t be enough time in the day to get it all done. I use 4+gpm impact sprinklers on hoses. It took four to keep 3 hp from cycling, most of the time we need 2 to 3 sprinklers running.

    In reading, many talk about Cycle Stop Valves which maintain constant pressure. They claim to be better than variable speed pumps for much less cost (about $75). Anyone have an opinion on them? Supposedly need less pressure tank, and less wear and tear on pump and plumbing. www.cyclestopvalves.com

    If no consensus that these things help, I’ll just go with the standard system. Thanks.