Constant pressure Grundfos system question

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by Cornucopia72, Dec 3, 2017.

  1. Cornucopia72

    Cornucopia72 New Member

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    I have a grundfos constant pressure system that was installed about 2 years ago. Two months ago I noticed the pump was running constantly even when the main valve was shut. I replaced the check valve and that took care of that problem but now the pump runs full speed and then shuts off every few seconds. The pressure oscillates between 90 and 50. Replacing the pressure sensor would solve the problem? I do not want to spend $175 on a sensor if that isn't the problem. Thanks
     
  2. nakopf

    nakopf Nailed it.

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    By "main valve", do you mean the shut off at the house, or an isolation valve immediately down stream at the pump?
     
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  4. valveman

    valveman Cary Austin Staff Member

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    A bad check valve should have nothing to do with a pump running all the time. A bad check valve will cause the pump to come right back on and it has shut off, but won't keep it from shutting off.

    That is a very common problem with the SQE/CU301 type system. They use the same wires the power goes down to the motor to send a radio signal back up to the controller. It is constantly losing the radio connection to the controller. Generation 1,2,3,4 all moved up the number of signal loss events before it even shows a fault. I think the new generation 8 or 9 versions now let it cycle 1000 times like a regular pressure switch before they even show a fault for loss of signal connection.

    Those SQE pumps will work fine without the CU301 controller. We just use a Cycle Stop Valve to make them deliver constant pressure and replace the CU301 with a normal 40/60 pressure switch. Like in upper drawing of this link.
    http://www.cyclestopvalves.com/csv-vs-vfd_1.html
     
  5. Cornucopia72

    Cornucopia72 New Member

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    My system's brand is Goulds and not Grundfos as I misstated above.

    nakopf,
    I meant the main valve right after the pump. I should have given more details. I have a submersible pump that fills a 5,000 gallons above ground tank. The pressure buster pump is the one acting up.

    Valveman,
    Are you sure a bad check valve between the storage tank and the buster pump will not make the buster pump run constantly? It makes sense that it would and when I replaced the check valve it stop doing it.

    I was able to borrow the pressure switch (9K518 Goulds transducer) from another system in the area that has been working great for five years and discovered that my problem isn't the pressure switch. In the system that has been working great, the pump engages on water demand and then adjusts the rpms to the water demand and runs smoothly until the demand stops. I the system that is acting up, the pump comes on harder on water demand and then the pressure and pump rpms keep oscillating even if the demand is constant
     
  6. Reach4

    Reach4 Well-Known Member

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    You have two pumps, and the one that is having the problem is pumping from an atmospheric tank? You sure did not give clear information initially.

    I think you mean booster pump.

    Have you replaced the pressure tank? At least check it.
     
    Last edited: Dec 6, 2017
  7. valveman

    valveman Cary Austin Staff Member

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    Yes I am sure! Check valves only work when the pump goes off. If the check valve is not working, the pump will come right back on, even though you are not using any water, but it won't keep it running all the time.

    If your sure you have a good pressure transducer, the problem is most likely the VFD controller. It is either not getting a steady signal from the transducer, (which a bad tank could also cause) or the VFD controller is not acting correctly according to the signal it is getting. Seven years is a long time for a VFD system. There main purpose is to cost you more money every 5 years or so.

    As long as they are working correctly the pressure from a VFD system is great as it is exactly the same constant pressure you can get with a Cycle Stop Valve. The difference is the Cycle Stop Valve only cost 174 bucks and will last 30+ years. The VFD transducer and the controller are expensive and designed to only last a short time.
     
  8. valveman

    valveman Cary Austin Staff Member

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    I forgot to say, the motor on the Goulds VFD system will be three phase instead of single phase. In other words you cannot easily change to Cycle Stop Valve without changing the pump/motor to single phase power. You need the VFD controller to convert single phase to three phase to power the three phase motor. That is how they lock you into at least a couple of VFD replacement controllers before you figure out you've been hooked.
     
  9. Cornucopia72

    Cornucopia72 New Member

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    Valveman, you are right. My buster pump has a 1/2 hp 3 phase motor. Crap! How can I test the pressure tank?
     
  10. valveman

    valveman Cary Austin Staff Member

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    The pump does not have to be working to test the pressure tank. With zero pressure on the water pressure gauge, you should still have maybe 30 PSI air in the tank. If not air the tank up to 30 PSI and see if it holds that for a few hours or a day. If the air doesn't get out, the tank is most likely still good. Plus nothing the tank could do would cause the pump to run continuously. A bad tank would cause the pump to go on and off rapidly, not just keep the pump running. Sounds like a bad VFD controller. Now is the time to see if it is more expensive to keep the VFD system or switch to a normal single phase motor where you have some control choices that can make the pump last 30 years.
     
  11. Cornucopia72

    Cornucopia72 New Member

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    I tested the pressure tank and it is OK. So the controller is most likely bad. I checked and they run $750 and up
     
  12. ThirdGenPump

    ThirdGenPump In the Trades

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    They have a 3 year warranty. Any Gould's installer can normally get credit up to 5 years on them
     
  13. valveman

    valveman Cary Austin Staff Member

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    Get a warranty if you can. If not you can do a lot for $750 toward switching to a normal single phase pump/motor that will last a long time.
     
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  14. nakopf

    nakopf Nailed it.

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    For the cost of that repair, I'd look at a Scala2...
     
  15. valveman

    valveman Cary Austin Staff Member

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    That one is the same concept as the Goulds, or any other VFD. The Scala2 replaced the MQ, which isn't available anymore for a lot of reasons. Reasons that the Scala2 isn't going to fix. Just remember they aren't trying to fix the problems. They just want to offer something that sounds so cool you don't mind replacing it every 2-3 years instead of every 20-30 years.
     
  16. Cornucopia72

    Cornucopia72 New Member

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    The guy that installed my system came by yesterday to check if the controller needed replacement. It turned out that the problem was low pressure in the the air tank. He said that it needed to be 50 or 55 psi for the system to operate properly. It was reading only about 30 psi. We increased the pressure to 55 psi and started the system and it worked fine afterwards.
     
  17. valveman

    valveman Cary Austin Staff Member

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    Glad you got it working. But that tank should not have lost any air. Probably still something wrong, I would keep an eye on it.
     
  18. Cornucopia72

    Cornucopia72 New Member

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    The system worked fine for two weeks and now the old symptoms are coming back. I suspect a bad tank. It currently has a Hydro Pro 205746-002 that looks about 5 gallon capacity. The pump is 1.5HP. DO you recommend changing the tank? If so which tank would be a good fit?
     
  19. valveman

    valveman Cary Austin Staff Member

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  20. Cornucopia72

    Cornucopia72 New Member

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  21. valveman

    valveman Cary Austin Staff Member

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