Grundfos CP system pressure tank issuse

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tracgray

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My CU301 system calls for a 2 gal PT. I did not know this until my PT failed, a 4.4 gal PT had been installed originally and also replaced with a 4.4 gal. The book says use a 2 gal PT at 70% psi of system psi setting. Thus, 60psi=42psi pre charged setting on PT tank. Can I use the 4.4 gal PT on this system? If so, what would the pre charge psi be? In other words 2gal PT= 42psi so 4.4 gal PT= ?psi. Or do I just have the 2 gal installed? Thanks for any advice.
 

tracgray

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The new 4.4 gal was set at 44psi, system then wanted to cycle at 50/70 at low flow. I played with it and got it to stop cycling at 17psi. I was told this system should not cycle, even at low flow it should be a constant pressure via the pump running. Any advice? Thanks
 

Valveman

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Do a search on this forum for the “CU301” control box you have. You will see that lots of other people have had problems with these systems. The cycling on and off you mentioned means your CU301 box has lost contact with the electronics in the SQE motor. When this happens, the CU301 reverts to cycling the pump on and off like a pressure switch. I think the latest version number 7 of the CU301 will cycle like this 1000 times before it shows a fault that says, “lost connection”. This cycling is WHY your bladder in the tank failed. Cycling does the same thing to the bladder, as bending a wire back and forth until it breaks.

Your best fix is to replace the CU301 with a standard 40/60 pressure switch, and use a CSV to regulate constant pressure. The CSV will also work with any size tank, 2.2 gallon, 4.4 gallon, or 20 gallon. I recommend the 4.4 gallon since it is going to need replacement anyway. See how to replace a SQE or CU301 with a CSV at this link.
http://www.cyclestopvalves.com/csv-vs-vfd_17.html

[video=youtube;djYEdL6an5g]http://www.youtube.com/watch?v=djYEdL6an5g[/video]
 
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tracgray

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After reading your reply I played with this some more. What I don't understand is why if the control and SQE motor lost contact why can I make the system work properly by lowering the psi in the oversized pressure tank ?
 

Valveman

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With only 17# air in the tank, it is not taking very much water. And you are stretching the heck out of the bladder. Lost connection is not the only problem. Those computerized controllers can have lots of other glitches. Could also just be the transducer or pressure sensor, they also give lots of problems.
 

tracgray

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Should my pump man be able to trouble shoot this fairly easy? From what your telling me this is over my head but I do appreciate your advice. Thanks
 

Valveman

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It will be over your pump mans head as well. All anybody can do with those type systems is replace the controller and/or pressure sensor, and see if that solves the problem. There is no repairing anything on that type system. Which is exactly the point. They are designed to cost a lot, not last very long, and are not repairable, so you have to replace the controller, sensor, and/or the pump itself on a regular basis. This is “planned obsolescence” at it’s finest.

Many don’t make it through the warranty period. So they may have to replace the controller a time or two for free. But your warranty period doesn’t start over until you purchase a new unit. So as soon as the warranty is over and you have to purchase a new unit, it covers any expense the manufacturer had with warranties.

The installer is the one who loses out on the warranties, as his labor is generally not covered. However, I recently heard from an installer who was paid $30,000 for a years worth of warranties on that particular system. He must be a really good customer, because they usually don’t pay labor for warranties. But it gives you some indication of how many warranties a single installer can have.

This installer said he spent 1 month out of 12 last year doing warranties. He is experiencing 30-40 callbacks each month, instead of 2 as he had before switching to that style pump system.

Of course all of this is paid for by the consumer. Even if you get a free warranty service or two, you still have to purchase new equipment about every 5 years instead of every 20 years. So you end up paying many times more for that kind of equipment, than if you had a pump system that would last.
 
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