sizing main air vents

Steamhead (in transit)

two Gorton #1 vents on the shorter one, and one Gorton #2 on the longer one. The #2 is the fastest steam main vent made today.

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=367&Step=30">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>

ChasMan

One main is 2 inch pipe and runs 24 feet before it reaches the last radiator on its run then it reduces to 1 1/4 inches for a 21 foot dry return.

The other main is 2 inch pipe and runs 40 feet before it reaches the last radiator on its run then it reduces to 1 1/4 inches for a 36 foot dry return.

Each main/dry return run has only one vent which is at the end of the dry return before it drips to the wet return. I can't make out the size of the current vents but they are raised 6 inches above the returns on 3/4 " nipples.

What would be the correct size vent for each supply/return loop?

Ideally should the vents be at the end of the main supply before it reduces to the dry return?

Thanks