Atypical well system in Mexico

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by seaweeds, May 22, 2009.

  1. seaweeds

    seaweeds New Member

    May 22, 2009
    Hi. I live in Mexico in a small, seasonal beach-front community that uses a old-fashioned hand dug well (typical here) about 30 feet deep x 3' wide. We have a system that is not typical for the US, but works fairly well for us.

    It is: 1/2 hp 10-12 gpm Sub, 1 1/2"pvc running about 250 feet to a holding tank that gravity feeds several houses. Total lift is maybe 125 feet.

    Another resident installed the system years ago, originally with a pressure tank but those tanks and pressure switches rusted out and/or failed repeatedly over the years (we are right on the coast ) so he switched to a small (1100 liters) black poly tank.

    So it's a small elevated storage tank, fitted with a float switch going down to a relay for the pump box. There is also a float switch in the well, to cut off the pump when the water drops. Some years it's better than others.

    The water used to be good, but in recent dry years, it turns salty. Nobody drinks it, we have purified water delivery, but we bathe etc with it, some watering of our salt tolerant plants.

    That uphill storage tank feeds a dozen low water usage houses. All dry toilets here on the coast saves a lot. We have water meters and the total water pumped last year was 1500 cubic meters.

    So, that's our system. It works fine for us. Power goes out frequently enough but the small storage tank will buffer us for a few hours to a day, depending on how many homes are occupied at the moment. The pumps, typically Flowtecs (I know, I know) tend to last about 3 years here.

    I'm writing because our newest pump just failed after only 18 months of use. It's an Evans/Franklin, 1/2 hp 10GPM 3-wire, bought locally. The motor is obviously fried - the motor shaft won't turn and armature is shorted to ground. Motor bearings look very good and the pump turns. It has some rust and corrosion at the top of the motor and around the wiring harness, but not a lot. When I opened the motor up I found that the metal cylinder that houses the armature was slightly cracked and expanded, stopping the stator from moving.

    So, what might have caused this? My two best ideas are brownouts and chattering contacts on the float relay. I doubt it's working too hard, and from what I can figure, it's staying on longer than two minutes, as the float switch probably has about a 50 gal range from on to off, and typical flow out is 1-3 gpm from a water faucet, depending that each houses' piping/distance/elevation . Of course many faucets could be open at once, though typically not full blast.

    Anyway, I wonder if the symptoms of the motor failure suggest anything should be corrected in our system, and I wonder if we should be considering flow control to reduce pump cycling in any case. Since there is no pressure at the top of the pipe, it appears that we are pumping on the lower side of any 10-12 gpm curve....

    Any thoughts or suggestions? I don't think we'll go back to a pressure tank no matter what, but sure would like our pumps to last longer. Perhaps a bigger tank, to further increase the run time when the pump is triggered, and also considering a CSV.

    Or maybe we are fine and just had bad luck with this motor...

  2. valveman

    valveman Cary Austin Staff Member

    Mar 15, 2006
    Pump Controls Technician
    Lubbock, Texas
    Heat is what causes the stator to swell and crack. Heat can be from several causes. The bouncing float switch is certainly not a good thing. Maybe you could put the switch in a stilling well inside the tank. Stilling well is just a perforated pipe that stops wave action.

    Low or no water in the well will also cause excess heat. The float switch in the well should catch this, just make sure it is working. A Cycle Sensor will also catch a dry well with low amperage, and will also shut down on short cycling if the float switch is bouncing.

    A top feeding well will also cause a hot motor. The motor is on the bottom and a top feeding well does not cool the motor. A simple shroud on the pump/motor can make sure the motor gets proper cooling from a top feeding well.

    They also now make motors really short so they run hot and don't last long, (planned obsolescence). You can put a 3/4 HP or 1 HP motor on a ½ HP pump. This is more the way they use to be made when they were designed to last, it makes the motor run cooler.

    A Cycle Stop Valve will work with an elevated tank. It just needs to be adjusted to a pressure that you see just before the elevated tank is full. A pressure tank would give you better pressure but, would not help during power outages. If the pressure switch corrosion is the only problem, Square D now makes a sealed pressure switch. And a small generator would give you much more water for longer periods during power outages.
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