Old boiler, banging noise

wonka1981

Hello this is my first post.  First house with a boiler but have been reading up on this site. It has been helpful but I am still having issues. I have a 50's era American standard boiler with cast iron baseray baseboards. System still works and heats well, but i have been having issues with trapped air and banging noises when the main upstairs zone kicks in. The other two zones a r e fine. Things I have done so far is:
-Replace bleeder valves on all baseboards that have them.
-Had a plumber friend add an air separator on each zone (return side before the circulators)  he also added hose connections and valves for purging the system and replaced the old failed expansion tank.
As you will see in the photos, I now have a hybrid of old and new. He did what he could based on the existing piping setup from previous owners. 

I continue to have a banging sound on a few of the baseboards even with the air separators and bleeding the valves. I can still hear water flow which leads me to believe there is still air getting in somehow?

I am beginning to think that it may be expansion/contraction?

Sorry for the long post,  any help from someone that knows to they are talking about would be great. 
Thanks in advance

JUGHNE

What pressure is the system sitting cold/cool at?

wonka1981

Cold it is at around 12-13.  When running it jumps to close to 20.

clammy

Where’s the banging noise coming from and what’s the temperature the boilers aquastat is set for ? What is the boiler running at when Any or all the zones are calling . Are your sure your pumps are running and the boiler is just maintaining temperature . Have you used a decent contact thermister type thermometer is see the supply temp ,you could be over shooting your aquastat setting and that may cause one extra expansion noises . If the banging noises are directly from the boiler I de check the temps ,the aqua stat settings and listen is the boiler if that’s where the noises are coming from and your not over limit you may just have a build up of lime and calcium on the inside of the boiler . This is from having hard water and possible a lot of make up water .
Peace and good luck clammy

mattmia2

The arrangement of the pumps and air separators aren't ideal. one of them should at least be in the outlet of the boiler of you can't get the pump and an air separator on the outlet. The hot water will give up air a lot more readily than the cold water.

What are all the water stains from? Does it hold pressure if you turn off the water feed?

wonka1981

Clammy, thanks.  Banging is coming from the first baseboard in line after the boiler. I turned the thermostat on the boiler down to about 160, but I do not knkw true Temps coming out of boiler. Sound definitely not coming from the boiler, but pipes/baseboards. 

Mattmia2, thanks as well. I am now understanding that the air separators being on the return before the pumps is not the best scenario. Pumps have been in that location long before me.  The guy I had recommended putting the air separators where they are now. Can I move one or more air separators to the supply side without moving the pump locations?  I do not want to put much more money and time into this age boiler.
Not sure what the water stains are from. At this time, nothing is leaking water anywhere on the system. And yes holds pressure even when the water supply is off. 

wonka1981

Any boiler pros on here in the Denver area?