Water Booster Pump, check valve missing?

[doug jabor]

Hi all. I have a question about a symptom i am seeing on an aqauboost II controller and water booster pump system that is for the most part configured exactly like you see in the attached drawing, with the exception that there is no check valve on the suction side of the pump.... This system is 8 years old, and I never remember seeing this problem before, but here is what happened.

The first problem that is new was that the pump was never shutting down under no load conditions. Xylem techs told me to check the pressure in the V6P diaphragm tank as a starting point 9 see diagram). I replaced it instead and found that after I took the old tank off, and tested the pressure, it was at zero. The new one ( and the old one) comes pre charged at 38 psi. I run the system at 60 psi.

Now what is happening is that under no load conditions, the pump runs to like 62 , comes down to 60 and the pump shuts off... for about 4 seconds, then I see the pressure on the discharge drop to about 58, the pump kicks back on and goes to 60, then 62, then comes back down to 60 and shuts off... then repeats this cycle. When I close the valve to the suction side under no load , the pump stops and stays there. When i shut the valve on the discharge side, the pump just targets around 60 and does no shut off.

Is the problem that there is no check valve on the suction, so after the pump reaches 60 psi and shuts off., some of the 60 psi discharge pressure sneaks past the impeller to the suction side, and when it hits 58 psi, the pump kicks back on and so on?? It can't be a leaking bypass check ( see diagram) correct? otherwise, when I shut the suction side valve off, the pump would keep running.

Does this make sense?? IF so, can you recommend the correct type of check valve to install on the suction side of this system so the pump,p actually stays off under no load conditions??


Thank you!

 

[Valveman]

There has to be a check valve some where. Water doesn't just "sneak back" through an impeller, it would gush back and the pump would be on in a second. Eight years is already twice the average life of those variable speed type pumps. They are made to sell and make money for the installer and manufacturer, not last a long time and benefit the homeowner. The Goulds corporate jet needs fuel, so it is probably time to buy a new pump.

The check valve or lack there of is not even in play when the pump just sits at 60 and won't shut off. I suspect the pump is shutting off on low amperage thinking it is running dry, which it is running dry when you close the valve on the suction side. The pump should at least shut off when you close a valve on the discharge side, and it is not, which makes me think controller problem, not a check valve.

Also this has probalby been happening for quite a while, which is why the bladder in the little tank is bad.

 

[Sponsor]

 

[doug jabor]

There has to be a check valve some where. Water doesn't just "sneak back" through an impeller, it would gush back and the pump would be on in a second. Eight years is already twice the average life of those variable speed type pumps. They are made to sell and make money for the installer and manufacturer, not last a long time and benefit the homeowner. The Goulds corporate jet needs fuel, so it is probably time to buy a new pump.

The check valve or lack there of is not even in play when the pump just sits at 60 and won't shut off. I suspect the pump is shutting off on low amperage thinking it is running dry, which it is running dry when you close the valve on the suction side. The pump should at least shut off when you close a valve on the discharge side, and it is not, which makes me think controller problem, not a check valve.

Also this has probalby been happening for quite a while, which is why the bladder in the little tank is bad.

Great points, Thank you again! I think it started after a new boiler was installed last year with a new DHW mixing valve board with lots of check valves... or, maybe just coincidental with age... not sure. Under load, is it normal to swing a few psi? Like from 58 to 62 with a set point of 60? I am trying to determine how fast I may need to change the pump out because the pressure changes are impacting the mixing valve. We are using a honeywell MX series that has a delta P limitation of 7 PSI between the hot and cold side. When the pump is in, the temp swings enough for it to be noticed in the shower. When the pump is off and I am straight street pressure of 35 psi... the temp holds pretty steady.

 

[Valveman]

There are lots of possible problems with those variable speed type pumps. But there shouldn't be any difference in pressure on the hot or cold water. The pump feeds the cold water to the water heater at the same pressure as it feeds the cold water supply. So only if you have pressure loss in the water heater would the hot water pressure be different than the cold water pressure.

 

[doug jabor]

yes i agree that the pressure should be at least close, so either the pressure gauges are bad , or there is something wacky going on because believe it or not, the pressure in the hot water from the coil is showing about 8 psi higher than my cold side under water use and standby conditions.... If that is real (can't be now that I think about it) AND the pressure is swinging from the pump 4 or 5 psi, that is probably enough to change materially the flow through the mixing valve causing temperature output issues ( i.e., pressure impacting flow through the mixing valve thereby changing the temperature out). In any event, I can actually see the temperature out of the mixing valve fluctuate with changes in the pressure out of the pump... If these mixing valves are all that pressure sensitive , it may make sense to put a pressure regulating valve in to limit the output to 50 psi with a pump set point of 60...

I may change the check valve in the bypass around the pump in the picture above....just since it is a swing valve and has been there for at least 8 years. I mean, there is a possibility that there is pressure leaking from the 60 psi side to the 35 psi side of the check valve. Do you have a preference for check valves that are the best in this application? Ball, Swing? Ball spring? Thanks for your expertise...

 

[Reach4]

Ball spring?

That.