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Pump Away

bart flanzbaum
bart flanzbaum Member Posts: 2
in THE MAIN WALL
I know htis is old but could some one refresh me as to way having the pump on the supply is the preffered loction???

Comments

  • patrick linhardt
    patrick linhardt Member Posts: 134
    what 's old is new again

    Hi Bart,

    What you are pumping away from is the expansion tank. Where it is connected to the system determines the point of no pressure change. When the pump starts, it uses this as a reference. If it is pumping away from the point of no pressure change, the pump differential (head) is applied as positive pressure to the system. This keeps the air bubbles small and in solution, which results in very few air problems and almost no bleeding of radiation. If it is pumping towards the point of no pressure change, just the opposite can happen. The pump differential is applied as a negative to the system, allowing the air to come out of solution to create large air bubbles that can require lots of bleeding and stop circulation. The problem is worse on systems with high head pumps. The higher the head, the more likely problems will occur if pumping towards the point of no pressure change. Put the tank off the tapping on the boiler or better yet use an in-line air separator on the outlet side of the boiler. Connect the tank to the bottom of the air separator. The pump or pumps will then be next as we move away from the boiler.

    We can thank Dan Holohan for reminding us what Gil Carson of B&G told us about the point of no pressure change back in the 60's. What's old is new again.

    Any questions or clarifications are welcome.

    Best regards, Pat
  • Sweet_2
    Sweet_2 Member Posts: 143
    Great explanation

    another good practice would be to connect the fill valve P.R.V.) to the system at the point between the air seperator and expansion tank. This would eliminate any false readings of the fill valve(P.R.V ) from differential pressure fluctuations causing overfill.Point of No Pressure change Im a believer.
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    PONPC in living colors...

    Excellent dscription Patrick.

    Maybe this will help your minds eye.

    ME
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    Great explanation Pat,

    and the other thing I stress while teaching is that your also pumping into the system where the true resistances are.

    This comes in handy to remember when you're pumping into indirects and any kind of coil where feet of head must be overcome.

    Boilers essentially are just big pots, no resistance there.
  • patrick linhardt
    patrick linhardt Member Posts: 134
    you're right

    Hi Sweet,

    I left that part out. Thanks for mentioning it. You are right, the best place for the fill line is between the air separarot and the expansion tank.

    Best regards, Pat
  • patrick linhardt
    patrick linhardt Member Posts: 134
    nice pics

    Hi Mark,

    Thanks for the excellent diagrams, in living color no less. I am sure this will help someone out. I like the addition of the open tank.

    Best regards, Pat
  • .
    . Member Posts: 80


    Sounds good, but completely unscientific nonsense. It makes no difference whether you pump towards the region of greatest head loss or away from it. (Pumping away from the tank is still correct, of course.)
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    The open tank....

    and a student with an open mind is what turned the light on for me. I was speaking in one of my classes, and said that hydronics HAD to be good because water covered 75 % of the Earths surface, to which my student, a forced error contractor replied "Yeah, but it's 100% covered with AIR!"

    From the mouths of babes:-)

    ME
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