Dumb question>Main vents belong where?

fsk

In my neighbors house I saw the other day that he has two main vents in his one pipe steam system,installed on the wet returns.
Is it something normal?
Also on his system I dont see any main vents on his steam mains ...

I would as always greatly appreciate an insight,on when the vents shall be installed on the wet returns.And is the installation on the return more advantageous than installing them on the steam main.

Thank you very much.

gerry gill

on the wet return

makes no sence..they can go on the drip from the main to the wet return tho..if you were air inside the pipe, could you make your way to the air vent without going under water to do it?

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