pumping away from multiple pumps? ?

archibald tuttle

Old cast iron Valiant with two baseboard loops and two pumps on the return and the expansion tank and water in on the feed side. Wrong by pump away from Point of No Pressure Change (PONPC) standards. Of course it is a small system, in a single story rance blown out with second story bedroom addtion and has been working fine.

i'm just moving a piece of baseboard but i charter the possiblity of setting up better bleeding that isolates the boiler but i'm not at a level of redux or failure that supports moving the pumps or consolidating to one and installing zone valves.

so i've got one question. in order to move the PONPC to intake side of the pump, i would need to manifold across the two return lines. i could do it with something small, even 1/2" to the first and 1/4" to crossing to the second, but in theory that is going to give me a cross riff of some modest character when one pump is running and not the other. my theory is it would be de minimus enough not to worry about and that putting check valves to control against thremosiphon or cross circulation would be unnecessarily complicated. (no flow checks in current pump or system and he already has the second floor basically turned off and is heating by thermosiphon.

suppose other possibilty is to just bring the water in , expansion tank connection behind one of the pumps with no manifold to the second zone return. since the system is working now, that would be a better situation for one zone and not a worse situation for the other . . . and if i did it that way do i choose the higher volume more important 1st floor loop, or the 2nd floor loop that needs slightly more reliable head and operating conditions to circulate but is much smaller volumer . . .

thanks,

brian

DanHolohan

If you manifold, you'll set up two points of no pressure change and you'll get circulation between the two points. Not a good practice. There should be just one PONPC for all the circulators in this case, and there's no easy way to do that without repiping the boiler.