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3 way valve stopping flow?

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Mikeymike
Mikeymike Member Posts: 2
in Radiant Heating

Hey guys,

We're piping a mixed temp system, 4 baseboard zones & 3 in floor heat zones. The in-floor zones have 1" S&R to the manifold with 3/8" pex loops. We piped in a Caleffi 520616AC mixing valve with internal checks to control the temp to these zones. When we went to fire up the system there is very minimal if any flow to these 3 low temp zones. I'm thinking the higher temp return water from the baseboards zones is closing the mixing valve, stopping the flow.

Check out the photos of the set up and the drawing of how I plan to re-pipe in a couple days. I was going to add a check valve separating the high temp and low temp returns.

What do you think? Any other insights or critiques?

Boiler piping 1.jpg mixing valve 1.jpeg low temp side 1.jpeg low temp side repipe 1.jpeg

Comments

  • hot_rod
    hot_rod Member Posts: 26,575

    I would pull the checks and strainers out, leave them out

    Any idea of the gpm of those 3 radiant pumps ?

    That 520 valve is a 2 cv, so 4 gpm would be about all it could handle without some higher head circs

    Remove the checks, put 3 pumps on speed 3 and report back

    Checks in all the pumps or just downstream is important

    Header piping for all those zone circs may be small

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    bjohnhy
  • HomerJSmith
    HomerJSmith Member Posts: 2,710
    edited December 24

    @Mikeymike, I think you may be right. Put a check valve before the left three low temp returns and the higher baseboard returns on the right. that would prevent hotter return water from mixing with the return water from the three radiant zones. Not the mixing valve that I would have chosen. A high flow Cv valve, I think would have been better. Merry Christmas to one and all.

  • Mikeymike
    Mikeymike Member Posts: 2

    I don't know the gpm of the pumps… 4 gpm doesn't sound great when all zones are calling.

    I'm not seeing a high flow in stock for Friday, I'll have to look some more. Either way we'll add that check between the returns. I'll let you guys know how this shakes out on Friday.

    Thanks and Merry Christmas.

  • HomerJSmith
    HomerJSmith Member Posts: 2,710

    This may explain it.

    image.png
  • bjohnhy
    bjohnhy Member Posts: 142
    edited 5:10AM

    @hot_rod advice is spot on, as usual.

    Putting an additional check where you suggest will not make any difference IMHO. There is no flow in that direction anyways if you have a check on mixing valve hot side.

    Do you have this problem when all pumps are off on the high temp zones?

    1" header supplying all those zones is probably not big enough when 2 or more of the high temp zones are circulating, especially with a cV 2 mixing valve that the low temp circs have to work against.

    In addition to turning the low temp circulators on high (level 3), you can try turning the high temp pumps to level 1 (but this very well may not be enough flow through those); maybe they already are?

    If all that doesn't help, I would consider the 3/4 iSeries ODR mixing valve cV 3.3. Or consider repiping with 3 separate mixing valves, 1 for each of those zones. Those mixing valves can be surprisingly restrictive. Repiping three in parallel will effectively triple the cV? Also triples the failure rate?

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