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injection piping/problems

STEVEusaPA Member Posts: 5,692
Hello everyone, long time reader, first time poster.  I'm having a problem with the injection  piping supplying the radiant heat zones.  The problem appears when only one radiant zone calls for heat.  The injection supply gets very hot, the injection return gets very hot, and the both sides of the closely spaced tees (supply/return to/from circs) stays cold.  Then the supply sloooooowly warms.  If more then one zone calls, everything works like it should.  I think the problem is the injection piping and the supply/return to/from radiant circs, are both 3/4".  My opinion is the injection circ is ramping up and blocking flow (or reversing flow through the closely spaced tees) and returning right back to the primary loop.  If I turn the radiant circs up to 'high', its less of a problem, but I end up with lots (and loud) expansion noise of the pex.  Should I repipe the supply/return to/from the radiant circs to  1 1/4 copper, then reduce to 1 1/4x 3/4 tees to the circs?  I (hopefully) attached a picture showing the main components.  Any input would be greatly appreciated.



  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Sounds to me as though the Grundfos circulators...

    supplying the radiant mainifolds are not running, or there is no flow through the radiant zones. Because otherwise, to the extent that there is flow between the supply and return manifolds there would be a reduction of flow directly between the supply and return T.
  • Ironman
    Ironman Member Posts: 6,877
    Injection Bridge Too Large


    It looks as though you have correctly diagnosed the problem. The injection bridge must be at least one pipe diameter smaller than the loop.

    You didn't post any btu loads, so I don't know if you could decrease the pipe size of the bridge or if you'll need to increase the loop size. You should also put a valve in the return of the bridge that can be used for throttling. You could also install a bypass in the bridge with a balancing valve.

    I can't get the file that I wanted to attach. Go to Tekmar's site and see their "essays" on injection pumping and balancing.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,692
    thanks for your reply ironman

    Thanks for your reply.  I did find the tekmar essay.  I wish the installer found it first :).  I apologize for making an incomplete drawing.  There are flow checks, iso valves, etc., I just put in the pipes/sizes, and circs.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited May 2011
    Piping Is Not

    An injection loop. Just a zone loop being pulled off the seconday. Take a look at this for some help direct from our friend John Barba.

    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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