I have a 1950's house with original water-based whole-house baseboard hydronic heating system. Maybe the re-circ pump is newer, but the rest of it looks original. It still works really well too, apart from the water trickle noises (which are fairly loud when there's no other noise in an otherwise quiet house).
I know I am getting air in the system and I assume it must be from air in the supply water. If I bleed my system by connecting a hose and draining until air noises/bubbles stop, the system is then good again for 3-5 days and then the water trickle noises start to come back. I can then repeat this cycle once a week.
I have what I initially thought was a flow control valve, but now (after seeing some pics on-line) believe it to be a Air Relief/Scoop valve. Can someone confirm if this is the case (please see photos in zip attachment - couldnt get jpgs to upload). As you can see, its been painter over long ago (not me!) and am wondering if this has ceased and is now longer functioning.
It seems like it would be an easy replacement, so if someone can point me in the direction of a suitable replacement I'd really appreciate it (the pipe is 1 1/2" dia).