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Why aren't pump stations "Pumping Away"?

waderbern Member Posts: 1
I've noticed that when picking up a pump station for solar installation, that the circulators are not pumping away from the expansion tank (point of no pressure change), but rather pumping directly into the connection.  Can someone tell me why?


  • Bob Gagnon plumbing and heating
    Pumping Away

    A lot of people just haven't caught on yet, old habits die hard. years ago when I was younger a worried customer called, the gas company told him that I piped the boiler all wrong, and I would never be able to get the air out of the system, the customer told me the boiler has never been that quiet since I replaced the boiler, with pumping away piping, but it still took him about 5 years until he was not worried anymore, this situation was repeated last year on another boiler replacement. Doing things different than the norm is always controversial

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,333
    Doing things right

    should not cause so much controversy.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Karl_Northwind
    Karl_Northwind Member Posts: 139
    pumping toward

    The theory is that the PRV and expansion tank are non-isolatable from the heat source (solar panels) and the circulators in these small systems aren't monsters, there is no new fluid to introduce dissolved gasses and any installer who knows their stuff will be eliminating nearly all the air from the system at the get-go.

    these systems also typically run at 45 PSI (compared to boiler 12 PSI) and that helps keep the gasses dissolved as well.

    not Pumping Away in this case isn't a big deal.

    still good practice, and our custom built systems all do that.

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Yeah... And ANOTHER thing....

    I LOVE Viessmann. I think it is some of the finest equipment to grace the face of the Earth. But....

    Why don't they follow the "Pumping Away" standards followed by us North Americaners? Most of their Vitodens drawings don't comply in one way or another.

    When Siggy ,Bill Shady and myself and were in Germany touring the Wilo Facilities, I mentioned the PONPC to some of their upper pump engineers, and they looked at me like I was from another planet...

    I tried explaining my position to them, but they didn't want to hear it.

    Funny how some things don't translate well across the different countries...

    The Germans have their way of doing things, and the rest of the world has their way of doing things...

    In general, if you are not dealing with a high head pump, it doesn't make a big difference pumping towards the PONPC, other than air binding. If you have a high head pump, with a high pressure drop, it becomes a REAL problem.


    There was an error rendering this rich post.

  • Fortunat
    Fortunat Member Posts: 103
    I have the same complaint

    I agree...I don't love that we pump into the expansion tank on most solar pump stations.

    I think the reason they do it that way is just practical...for the solar system to go to stagnation gracefully in case of a power failure or overtemperature condition, steam has to be able to leave the collector from both supply and return ports and push down to the expansion tank.

    For fluid to be able to move to the expansion tank from both collector ports, the expansion tank has to be downstream of any check valves in the system. Since most pump stations have a check valve right by the pump, the expansion tank ends up downstream of the pump by default.

    For more information about the importance of expansion tank placement (and sizing) during stagnation, google for the many good articles by 'Hausner and Fink et al' on the topic.


  • hot_rod
    hot_rod Member Posts: 22,467
    a couple reasons

    convenience being one of them.

    The "safety group" is a fitting that serves multiple purposes. It has the relief valve, pressure gauge, and expansion tank fitting all in one assembly. The expansion tank and relief valve must be above the isolation valves, should someone turn them off and forget the collector would see extreme pressure in full sun.

    That safety group fits right up against the check/ isolation valve assembly.

    They also want the expansion tank on the return side so it sees the coolest fluid when running, when located up top like that.

    I agree closed loop glycol solar systems should run higher pressures than hydronics.

    5 bar, 72 psi is a common fill pressure over there. Notice the relief valves are 6 bar, 87 psi for that reason on solar pump stations. 72 psi keeps the boiling point of the glycol around 320F, to prevent the collectors from flashing to steam under stagnation conditions.

    Here is a pic of a triple duty solar valve I cut in half. It shows a gauge well, check valve, and isolation valve. When turned to a 45, the edge of the ball holds the check open so you can drain down the collectors. It can also allow thermosiphoning when held open to serve as over-heat protection, when the owners are gone on vacation.

    The other picture shows the safety group mounted above the triple duty valve.

    Combining all these functions into two valves, or groups, allows for a small package and the least amount of fittings and connections. It also keeps the cost down also as opposed to all individual components.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    you know

    I really love this place.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • burky1957
    burky1957 Member Posts: 10
    Solar Webinars

    Hot Rod has done some very good webinars on Solar DHW. They should be available on the Caleffi website. I think he covered this in one of the recent ones.
  • burky1957
    burky1957 Member Posts: 10
    edited September 2010
    Duplicate post.

This discussion has been closed.