2 returns for single zone valve?

tryingtobeaplumber

Hi all,
I'm trying to better understand my heating setup. I have 4 zones (taco zone valves) with 4 supply lines but the return for 1 zone has 2 return lines with additional ball valves (circled in green in the picture and I'll call these sub-zones).

What's the main purpose of the ball valves in this case? Is it mostly for purging reasons to isolate the sub-zones or is the idea that you can also regulate the sub-zones a bit since they are controlled by the same primary zone valve? For example, if one of the sub-zones heats too much, you could partially close the ball valve a bit to reduce water flow in that zone?

Thanks for your help.

neilc

I think you nail your situation,

the ball valves allow purging each of the 2 loops on that one zone,
then you could balance flow between the loops, although others will tell you there are better valve assemblies for the balancing.

the other zone valves allow their loops to purge,

EdTheHeaterMan

Do you experience a problem with "SUB ZONE '' Imbalance? I believe your question is an academic exercise as opposed to a question of balancing your particular system. You can reduce flow with a ball valve, however, as @neilc alluded to; that is not the best choice for balancing. A butterfly valve or a gate valve might have been a better choice for that task.

Your ball valves are primarily for purging.

tryingtobeaplumber

Got it. Thanks for the additional info!

hot_rod

The valve can also be used to isolate components for repair, the zone valve below for example.
you can do some balancing with a ball valve, try not to close it more then 50%