Two Pumps in Parallel. Now a pressure problem....What could be issue?

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by doug jabor, Nov 29, 2017.

  1. doug jabor

    doug jabor New Member

    Joined:
    Nov 29, 2017
    Location:
    New York
    mixing valve board pic.jpeg

    pumps in line pic.jpeg
    Hi All. First time posting and looking forward to reading more on this valuable site.

    Here is my current problem. This 5 story 5 family building with 5 bathrooms, 5 kitchen sinks and dishwashers needed to have a Gould Aquaboost II installed 7 years ago because the City water pressure was only 32 psi. This 1HP HMS pump (model 2HM1E2D) variable speed constant pressure pump is set to give me 50 PSI at the pump outlet.

    We just changed our boiler out and have a new steam boiler with a power burner and a hot water coil. The attached drawing shows the domestic hot water board mixing panel. A circulator was installed as you can see in the pictures. It is a Bell and Gossett NBF-25 103418LF1M61. I can supply pump curves. The circulator pump has 3 speeds and it was left at speed two in the beginning. What we noticed was that for some reason, on some occasions ( which I am trying to pinpoint what is happening in the system when we see this) the pressure gauges around the mixing valve , p2, p4 and p5 ( but not p3...probablyt because of check valve. would go to 100psi on the gauges.... scary! since they looked pegged. When hot water was used the pressure would get immediately releaved and drop back down to 50 ish psi.

    The guy who built the board came in and dropped the speed to 1 on the circulator. Now I see it goes to around 70 is PSI on those three gauges.

    Can anyone see what in this system could be causing that?? Is the circulator the problem? Or how the system is piped? The guy who built the board would leave some of the valves cracked instead of open as you can see in the picture of the board.

    I am very concerned that this may open up some joints in the hot water system running up to the apartments.... any suggestions or ideas are very much appreciated!

    Thank you, Doug
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  2. kevink1955

    kevink1955 Member

    Joined:
    Nov 17, 2011
    Location:
    L.I. New York
    I think you have answered your own question, the gauge on the cold inlet does not increase because it is before the check valve. The check valve is trapping hot water in what is basically a closed loop (when no one is using water) This water is heated and expands, it has no place to go so the pressure goes up.

    Solution is to add a potable water expansion tank in the hot water loop. It's a common problem around here since the water co started requiring double check valves or RPZ devices on the water main after the meter. The way to prove it is to leave a hot water faucet running a slow drip, if pressure spikes go away add the tank
     
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  4. doug jabor

    doug jabor New Member

    Joined:
    Nov 29, 2017
    Location:
    New York
    Thank you Kevin, I am going to try this tomorrow. Good solution!
     
  5. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    A thermal expansion tank will probably solve the problem. But it could also be that Aquaboost controller. Those variable speed type systems are notorious for loosing control and just maxing out at deadhead pressure of the pump. Maybe a bad pressure transducer or even the controller itself. I would also have a pressure relief valve in this system for times when the variable speed controller goes haywire, because a expansion tank is not enough to help in that situation.
     
  6. doug jabor

    doug jabor New Member

    Joined:
    Nov 29, 2017
    Location:
    New York
    Thank you, that is a very good point and I think now I need to watch what is happening when the pressure spikes occur. My best bet is to watch the aqua boost pressure gauge and see if that is the culprit, or does this happen with aqua boost at set point of 50psi, and only when the mixing valve is modulating ( or closed..). I think I need more testing. I could also take the aqua boost out of the circuit in bypass as another test. I do like the idea of changing the pressure transducer out ( there is a relief valve on the pump at I think 75 psi relief, I need to get that tested too. This pump has been operating for 8 years with no (apparent) problem until this new hot water mixing board went in with several check valves and the mixing valve (and gauges that let me see pressure after the booster pump check valve). I also used to operate at 140 degrees on the hot water coil of the atmospheric boiler...now, this boiler/coil operates at 180 degrees. My concern is with a delta P of 50 psi ( 50 psi normal operating to at least this 100 psi condition since the gauge was pegged)...what size expansion tank do I need? I am thinking it would be pretty big.....
     
  7. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    If it is thermal expansion a 2.2 gallon size tank is plenty. If it is the VFD system failing to control the pressure, there is no tank large enough to keep the pressure from spiking. Yes it could be the pressure transducer, but it could also be the aquaboost controller itself failing. I don't think there is anyway you can bypass the VFD controller, as it is needed to convert single phase to three phase, as that should be a three phase motor on the pump. A 75 PSI relief valve should have been popping off like crazy, so it is not working either. You are right that you need to figure out what is causing the pressure to spike. Adding a tank won't help if the VFD controller is the problem. Replacing that expensive VFD controller and/or pressure transducer won't help if the problem is expansion.
     
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