Forgive what is probably a lengthy post, but I wanted to give as much detail as I can. I've done a bit of research, and even purchased the book "Lost Art of Steam" (which is kinda why I know about this forum), but am still working thru it.
The house is ~1915, a typical Four Square, nothing outstanding. As best as I can tell, the boiler for the single-pipe heating system was replaced in 2006 (or so the service stickers indicate). A year later, in 2007, my father passed away, and I "inherited" the house.
One of the things I do is routinely drain the boiler, mostly to get rid of the junk that builds up in the lines. Sometimes that takes care of the hammering, but it's been getting progressively worse. Some of the hammering is obvious, but there's also a lot of pinging, like a quarter is rolling around in the pipes, but I assume is the same phenomenon.
I've identified and fixed a few problems so far: replacing a non-working relief valve, and repacking the valve stem on another radiator (was hissing out of the valve).
I've attached two pictures of the boiler unit, one from front and another from the rear. I've put some text notes on them, let me know if I am correct or not:
The rear view, boiler-1.jpg:
there are two drain valves whose purpose I am unsure of. I've taken to draining those every now and again. They do get muddy.
I assume the short vertical pipe is the riser, going to the horizontal pipe which is the header. I guess the pipe going from the header back down towards the drain is the Hartford loop. There are two vertical pipes coming off the header, what I marked as "mains"; each going off to various locations on that side of the house.
The front view, boiler-2.jpg:
The drain below the sight glass is the main drain when I do yearly draining. You can't see, but the sight glass is at mid-point. There is another drain to the left of that which I also empty, when I can remember.
The pressuretrol was originally set at 0.5 and 2.0 PSI. I've lowered this to a notch or two under 2.0, not exactly 1.5.
In reading Dan's book, the magic number to keep in mind is 24" between the header and the middle of the sight glass. If I did my measuring correctly, it looks like this one is at 19". I don't know if that is the source of my banging. I read a little about the "false water line", but that's arcane to me, and not sure if that would address my issue.
Thanks for reading.