How important are air valves to the efficiency of the steam system?

JUGHNE

That article implies that main venting is needed at the end of each main. If you remove that cross over pipe the return line will become the new end of your single steam main.
That is where you would want all the main vents. You could add a Gorton #2 and relocate your existing vent there also.

Also I had a "brainstorm" for removing the cross over pipe.
First you unscrew the drop which is newer black pipe and should not be an issue to un-pipe.
You could "whack" the tee that has the drop to your boiler return. This is holding a 10 lb sledge on the back of the tee and whack the front of the tee with a 2 lb hammer.
This will crack the fitting (only works with cast iron) and you can peel the pieces off the pipes.
Then for the main you screw on a cap.
The return gets a reducing 90 pointing down and you repipe the newer pipe to that point while adding a tee in the drop to give you the venting tree attachment as described above.
The red 90 and cap will be close and you may have to push the return to the left as you screw on the fittings.
FWIW
I am considered old and lazy, but I look for solutions with the least amount of work.

tomsloancamp

@motoguy128 I did notice the 2 large radiators I vented with the Gorton #4’s have been venting at the same time the main vents are. Fortunately, all the radiators are heating fairly quickly (it’s still not  cold
out so it remains to be seen) and the cycle lasts 10-15 minutes before it reaches the desired temperature. 

tomsloancamp

@JUGHNE I’m curious about the article Dan wrote about coal-fired boiler and piping. His suggestion in the article was “ That's the way the old-timers frequently did it when they converted an old coal job to oil. They couldn't repipe the mains, so the did the next best thing. They vented the heck out of them." I’m guessing unless I vent at the end of the main I will continue have issues with uneven heating. Here’s what I don’t understand though... was it not as important to vent the main steam system of a coal fired boiler? It seems like the vent should be at the end of the main. However if you have a loop for a main, the steam isn’t going to go in one direction. Now it will go in both directions. Wouldn’t that make the middle of the loop the end? 

Jamie Hall

Two good questions there, @tomsloancamp ! With regard to the venting question. A coal fired boiler didn't need as much venting as an oil or gas fired one, for a rather simple reason: you can't bring a coal fire up to full song quickly (you can't stop it quickly, either, except by raking it out on the floor!) and so steam came up rather slowly, and there simply was no point in trying to vent faster. Oil and gas fired boilers, on the other hand, are very nearly at full output from the moment they light, and steam comes up very quickly -- so if they aren't more heavily vented, they build pressure, which is undesirable.

Once people mastered traps or orifices, and started building very low pressure two pipe vapour systems, they often found that no vent as such was needed at all -- simply an open pipe at the ends of the dry returns, where they join before dropping to the boiler. Vents on these systems are related to the devices used to control pressure differentials -- a topic all in itself (these systems do not have vents on the mains at all, by the way -- a common but serious error on the part of later knuckleheads).

With regard to the looping main. In principle, you are correct. The problem is that steam may not define "middle" the way one might expect, so that what usually happens is that the vent may be in the geometric middle, but steam from one direction will get there before steam from the other direction. This closes the vent, and leaves air trapped in the slow main. Further -- and perversely -- which direction is fast and which is slow will change from time to time for various reasons, so one can't just move the vent to accomodate.

tomsloancamp

Btw what is the best material choice for fittings? Galvanized? Black iron? 

Jamie Hall

Match the pipe. Probably black iron either cast or malleable.