Mixing valves for multi temp zones

[Willman]

Anyone have any pics of mixing valves for multi temp zones ?
I am slowly converting my late 1800's farmhouse to radiant heat. Lowering my load requirements. not quite as exotic as installing a new gasser but will be beneficial when I do. One zone is ultra fin which likes 145* water. Two new zones which will be infloor under ceramic tile. Water temp should be 100ish* or so. And the remaining BB which is full temp. Just wondering if systems use multple mix valves or is there another way.
Also I do understand circs should pull water thru mixing valve instead of push. I would like to know why this is so.
Thanks.
Will

 

[Sting]

You pull reduced or spent energy bearing liquid from the bypass leg because its under higher pressure than hi energy liquid - lower pressure liquid, in the primary loop.

This allows you to run a cooler heating loop than primary.

 

[Sting]

or ...

http://www.houseneeds.com/shop/HeatingProducts/boilers/baxi/boilerprimaryloop.asp

 

[Willman]

Thanks Sting, the pic is just what I was looking for. The schematic helps too. Still don't quite understand pulling water thru versus pushing. Is it damaging to valve or circ or is it just more efficient ?

Will

 

[Sting]

Hi William

I have gotten my AXX kicked several times last season for suggesting that the pump needed to be in the location as the link posted. It was the way I was shown to do it by a dead plumber and it works because the pump is drawing from two balanced sources.

If the pump were on the return side - some would say its still on the supply and system pressure negates all the drama - but it doesn't and the pump now pushes into two unbalanced loops. If the pump were before the crossover - well why would it pump thru the loop = it simply would pump the path of least resistance - the bypass.

So its a pumping thing. Once you set the bypass ball valve into the correct position, to add a set amount of spent energy liquid back into the loop - via the pump drawing on both the return of the loop and the supply of the loop, you get the temperature reduction you want as a percentage of primary loop temp. now- remove the handle from the bypass valve to prevent further adjustment, and from now on, control the primary loop temperature or the boiler temperature or both by ODR and you will have a comfortable and economized wet system.

 

[Willman]

Thanks Sting, It is becoming clear to me now, I am a DOldF you know.
Will