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Zone Valve too close to circulator?

leafsfan Member Posts: 1
Hey guy's

I am replacing an old chromolax electric boiler as well as pump, expansion tank and zone valves.  I am going to guess and the say the system is 20 yrs old.  The way it is piped up now has the pump on the return and the 2 zone valves on the supply. (perimeter loop, 1 up, 1 down)  I would rather pump away from the expansion tank when I do my retrofit.  The problem is this...  The two return lines join somewhere is the finished ceiling and come back to the mech room as one pipe.  I would like to have put my zone valves on the returns and have my pump on the supply pumping away from the expansion tank.  What I want to know is if I put my pump and expansion tank on the supply, can I still put my 2 zone valves there as well.  What I am worried about is that the slow closing zone valves will be too close to the pump and when they close will cause water hammer.  I thought about installing the new boiler the same set up as the old, which would have the pump pumping into the expansion tank to avoid water hammer problems.  Any comments or ideas??



  • lchmb
    lchmb Member Posts: 2,997
    How about

    Why not put your air scoop on the return prior to the circulator and then you are pumping away and dont have to worry about spacing...:) If you use a taco control the circulator should be off prior to the zone closing so you shouldnt have any water hammer issues...
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Air scoop location...

    I thought you wanted the air scoop in the hottest part of the system, which would be on the supply side, and at the lowest pressure part of the system, which would be on the input side of the circulator. Putting these things on the return side will lower the efficacy of the air scoop.
  • lchmb
    lchmb Member Posts: 2,997

    Most systems offer alternate forms of piping. If you read through them they allow for the circulator and air scoop to be on the return to the boiler so that you can still "pump away". I have never heard that you want an air scoop in the hottest part of the system so I'll wait to see if other's offer info on that one...

    Then again, I have hundreds (at least) of system's running with the circulator on the return and have never had an issue with them. Some being in service for 20 plus years..."shrug" the old saying come's to mind, if it's not broke, dont fix it...
  • Jason_13
    Jason_13 Member Posts: 299
    air elimiation

    The air separator/expansion tank with the pump pumping away on the return will still add pressure to the system and will work OK. It is better on the supply due to heating the water in the boiler. When you raise the water temperature you drive the oxygen out of the water. As it leave the boiler and goes through the air separator which causes agitation you will have better air elimination.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I have never heard that you want an air scoop in the hottest part...

    I am not a professional, but it is not my idea. In John Siegenthaler's book, Chapter 13, he says, in part, "The preferred location for an air purger is near the outlet side of the heat source about 12 pipe diameters upstream of the inlet port of the circulator. This allows the water entering the purger to be as hot as possible while also being at a relatively low pressure. ..." The microbubble air separators do not seem to need this much separation.
  • lchmb
    lchmb Member Posts: 2,997

    Although the standard is to put it on the supply pipe leaving the boiler, the return side will function also. To answer the original question, I dont see any issue with having the pump on the supply as well as the zone valves. Your control system will shut the circulator off at the end of a call for heat and then the zone valve will close, so it shouldnt cause any banging...
  • billtwocase
    billtwocase Member Posts: 2,385
    I see no problem

    With that set up. The end switch should break contact before the zone valve fully closes
This discussion has been closed.