Grundfos SQFlex 1.2-3 running continuously even if tank is empty.

sebax82sebax82 Registered Users Posts: 3
Hello to everyone,

I am writing here looking for some help regarding a water pumping plant installed in Haiti 5 years ago.

We, as volunteers, have 10 solar water pumps (model Grundfos SQFlex 1.2-3 installed in parallel within a tank, all connected to the same pipe which goes up to the Mare Rouge town, 140meters above the tank. They are all powered with solar panels, each one of them with an independent string of PV panels.

At the latest and recent visit, we found that all those 10 pumps keep running even if the tank becomes empty, meaning they run even when the dry-run sensor should stop them.

We have no way to explain how they can ALL 10 be continuously working:
- it should not be a defect, as it's unlikely that all 10 pumps have the same defect;
- it should not be due to aging: consider that 1 of them was replaced last year and it also has the issue;
- may it be a short circuit of the dry-run sensor due to environmental conditions? Consider that the tank is closed and water comes in via a pipe connected to the source of water, a few meters above.

Any help would be appreciated. 

Consider that we have only 36 hours to provide a solution as our tech person there will have to leave then. We are in a hurry!

Here is a video showing the plant to give you an idea:



  • AguarancherAguarancher Solar Expert Posts: 312 ✭✭✭
     I assume the run-dry sensor is external of the pump. If they are all connected to one sensor that is a recipe for disaster. sensors do fail on a regular basis. It might be better to have your pumps on a stand alone basis each with their own run-dry sensor. Looks like an excellent project and much appreciated by all,

  • jonrjonr Solar Expert Posts: 1,384 ✭✭✭✭
    edited September 2018 #3
    Is something incorrectly keeping the dry run sensor wet (splashing, wrong location?) or dirty?   Note that Grundfos writes:

    The dry-running protection is activated by a water level electrode placed on the motor cable 0.3 - 0.6 m above the pump depending on the pump type. When the water level falls below the electrode the pump will be cut out, the pump will automatically restart 5 minutes after water covers the electrode.  Note: Horizontal installation requires the water level electrode to be placed min. 0.3 to 0.6 m above the pump to ensure the dry-running protection.

    When pumping from a tank, this means that the pumps should be horizontal, the power wires must go directly upwards from each pump and the bottom .3m of the tank water cannot be used.  I suspect that the power wires may be laying on the bottom of the tank.

    I am available for custom hardware/firmware development

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,699 ✭✭✭✭✭
    Hard to believe that all 10 would do this as each has a sensor, I agree. How do you know all 10 are on?  Why are you letting the level get so low? 

    If the controllers were lightning damaged there might be a failure mode that could cause this. I would get the Grundfos folks on the phone before your technical talent leaves. Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • sebax82sebax82 Registered Users Posts: 3
    Hello thanks for your help.

    The installation is vertical. All 10 pumps are vertically instslled. At the same exact level.

    All of them have an individual dry run sensor.

    We did some tests. It seems that after 5 years of operations, some water entered the cable of the dry run sensor generating a false negative from the dry run system.

    Very odd, as these things are designed to work in these conditions and seeing so many failing... Is not normal.
  • sebax82sebax82 Registered Users Posts: 3
    Davide, level is low as the source of water is seasonal. Lightning may have been one reason.

    It's hard to troubleshoot as we never have timely information and only see the plant once every year.
  • jonrjonr Solar Expert Posts: 1,384 ✭✭✭✭
    A really wild guess, but is chlorine ever added to the tank water?

    I am available for custom hardware/firmware development

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,699 ✭✭✭✭✭
    It sounds like you are running from 120vac or 240vac and not solar direct? Either way there should be surge protection.
    I would still call grundfos Monday AM and get their advice.
    If there was a lightning strike near by this could easily cause this problem,  EASILY !
    A picture would help here and for Grundfos tomorrow!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

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