Grundfos Constant Pressure System Issues--Fluctuating Pressure

[Alan Adamson]

Apologies in advance for long post, but I think background is necessary.

Had Grundfos SQE constant pressure system installed. First problem was one day a CPVC pipe broke at joint prior to expansion tank and pressure gauge. Dealer repaired and said it must have been damaged by someone banging into it. Second problem, a few months later, was that the expansion tank started leaking around weld at stem. Dealer again replaced under warranty and said tank was deficient. Third problem was another leak in CPVC at a joint in line before controls/tank, coupled with air in the water line. I also, for the first time, realize that there is a very bad water hammer in the line. I'm now suspicious of the first dealer and call another plumber. New plumber says that either there is no check valve installed just above the pump or it is defective. Pulls pump and lo and behold there is no check valve installed. He installs a check valve (and also runs copper from where the water line enters the house to the copper where the controls/tank are mounted--says first installer was lazy/cheap and should have done that in first place). There was a check valve installed horizontally just before the tank, so now I have 2. The plumber mentions that the check valve inside is not necessary but I can leave it. Magically all of my problems seem to be solved--no more air in line and water hammer disappears.

Two weeks later, a new problem appears. When I run water, the water pressure fluctuates drastically in a regular rhythm. For example, when a toilet tank is refilling you can hear the pressure fluctuating. When I look at the pressure gauge (set at 60 psi), the pressure rapidly fluctuates between 50 and 80 psi in about 1 second waves. If I open up multiple faucets and increase the demand significantly I can make the waves disappear and the pressure will stabilize to approximately 60 psi.

Well is 10 years old and yielded 10 gpm when drilled. 180 feet deep, static water level is 40 ft. We are in rainy/snowy season and have had plenty of moisture so I don't think I have any issues with sufficient water.

Before I call plumber again, I was hoping to get some ideas on direction for the plumber, particularly since it's so expensive to pull up the pump. One thought was that second expansion tank was damaged by water hammer before second check valve was installed and that I need to replace yet again. Any ideas? When the system works, I love it--but this is testing my patience!

Thanks!

[ballvalve]

I understand that you can remove all the electronic crap and run the pump with a normal switch and pressure tank. Its been discussed here before, in relation to adding a CSV.

[valveman]

My first guess would be that the tank is bad or has too much air in it. You only need about 45 PSI of air in that tank. If the bladder is busted, or if you have 60 PSI air in thr tank, it will cause the pressure to bounce.

If the tank and air pressure are OK, then you have a problem with the pressure transducer or the CU301 controller itself, as is usually the case. A Cycle Stop Valve set at 60 PSI will deliver the same 60 PSI constant pressure. But you would be able to completely remove the pressure transducer and CU301 box. You would only need to replace the pressure transducer with a standard 50/70 pressure switch, and wire the pump directly to the pressure switch without needing the CU301. See the following link for a picture and explanation of how to make the change.

You will still "love it", the constant pressure of the CSV I mean. But you will no longer have to temper that with "when it works". Do a search on this site for CU301 or SQE, and you will see that these problems are common to that type pump control. Even if you get the pressure problem solved for now, you will continue to have problems with that type system.

http://www.cyclestopvalves.com/csv-vs-vfd_17.html

[McB]

I don't normally log on to these forums, but this was one of the few that addressed my problem and offered solutions so here it is. After reading several other posts, I checked my O&M manual that came with the Grundfos system. I followed the instructions of Draining the system before checking the pressure in the 2gal tank. It had lots of pressure (over 60psi limit of my gauge). Reading the O&M manual further I noticed that the "Note" under the "Precharge pressure setting" on page 8 it indicated that excessive pressure would also make the system pressure fluctuate. I found a different gauge and to my surprise my P.T. had 102 psi in it. I don't believe this has always been the case as the system functioned fine for 3 years and this fluctuation condition only started after an earthquake, followed by a hurricane where electricity was on & off for three days, and then week of monsoon rains. For the life of me I don't know how it could increase pressure, but after releasing the pressure down to 64 psi (large drops occurred quickly since it's such a small tank so I stopped when I got close) and the system seems to be working fine once again. I'll post further should this not remain the case.

[valveman]

There are two things that had to happen for the air charge in your tank to have increased to 102 PSI by itself. First your CU301 controller apparently at some time did not shut off the pump at the correct pressure, and let the system pressure increase to at least 102 PSI. This probably busted the bladder in your tank and allowed water and pressure from the pump to get on top of the bladder and increase the pressure to 102 PSI. Now the busted bladder is covering the outlet hole of the tank, and not letting the excess pressure get out of the tank. That tank that should weigh about 5# will probably weigh about 30# now that it is too full of water. I don’t think you have solved your problem, just found the symptom.

[LLigetfa]

Sounds like neither the OP nor McB has a PRV installed which IMHO, is not optional on a SQE.

[valveman]

I agree. Pressure Relief Valves are mandatory on those systems.

[LLigetfa]

LOL... when I was shopping for a new pump, my supplier tried selling me on a SQE. When I asked him how many failures he'd seen, he said not that many, but when the go, they go they sure do with a bang. Apparently some of his customers had some catastrophic ruptures that did serious damage. His answer was to just use a PRV.