Strange hydronic fitting identification needed

[Eric Hinkle]

On my hydronic baseboard heating system I have 3 zones and a single circulator pump. Each zone's return line has one of these (see pic). Does anyone know what it is? I'm thinking some kind of stop/check but dont know.
Thanks,
Eric

 

[hj]

It is a balancing cock. The "slotted "thing" is a ball valve and the plug is for a thermostat so you can adjust the various zones for proper operation.

 

[Sponsor]

 

[Sylvan]

On my system Cira 1921. The balancing valves are on the return and are more like a gas cock (plug valves) live and learn

 

[Eric Hinkle]

Thanks! A follow up question...one of my zone valves (1st floor) is stuck open and I cannot purge the air from the second floor zone (path of least resistance I believe). Could I use this to isolate the faulty zone's return?