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Primary secondary piping.

cubbydogcubbydog Posts: 4Member
I’m trying to find out if I need flow check on the secondary circ in a primary secondary system?
Does anyone have any diagrams showing circuit piping including boiler in the primary and them secondary feeding all the zones? I would like to see a complete diagram, they seem to be elusive on the internet and in Dan’s books.


  • IronmanIronman Posts: 4,965Member
    It's generally a good idea to use them to prevent ghost flow. I'm referring to the ones that go in a circulator or in some brands of isolation flanges, not cast iron ones. They can easily be changed if necessary.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • STEVEusaPASTEVEusaPA Posts: 2,820Member
    Here's tons of info and diagrams. If you can't find it here, your piping is probably wrong.

    I'd start with Issue #19:

    You can also check with a K-type thermocouple on a meter to see if heat is migrating more than desired.

    Might be easier to show a pic of your boiler piping for comments.
  • hot_rodhot_rod Posts: 11,259Member
    There are a number of ways to pipe a primary secondary. With a separate loop method fig 5-8 Use a a check on both supply and return if they go up vertically from the loop. Vertical piping seems to encourage thermo-siphon or ghost flow.

    Fig 7-2b is another way to pipe primary secondary, eliminating that loop pump. It also seems to eliminates ghost flow up the returns as they are on a cold return leg, so just check the supply side.

    The checks in the circulators work ok as Bob mentioned. Ideally the check should be 6" or so away from the circulator discharge.
    Use only spring checks designed for hydronic use, conical, soft seat type checks, plenty brands available.

    This journals shows good piping practices, and the ones with X thru them, not so good :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • cubbydogcubbydog Posts: 4Member

    Any comments? Is it possible to get ghost flow without internal check? Will I be able to adequately purge the system the way I have it?
  • hot_rodhot_rod Posts: 11,259Member
    The purge cock needs to be upstream of the shut off valve
    Flow goes up from circ stops at valve to purge

    I would have a check on supply and return to assure no ghosts in the machine
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • SuperTechSuperTech Posts: 938Member
    When piping a supply manifold in primary secondary systems I like to pipe my zone branches downward from the manifold to prevent ghost flow. I believe I got this idea from one of Dan's books or Siggys articles.
  • cubbydogcubbydog Posts: 4Member
    The cir has a internal check, what would you use on the return.
  • SuperTechSuperTech Posts: 938Member
    Caleffi makes a wonderful check valve that uses the same thing as the flow check circulators, it's built into a union and is a breeze to install. I can't remember the part number at the moment.
  • cubbydogcubbydog Posts: 4Member
    I’m guessing hotrod knows the check part number.
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