Clanging Pipe One End of Main

Paul C.

I have a one pipe system with I believe are dry returns as they run parallel to the mains before dropping below the water line. There are two radiators at the far end of the main which refuse to accept steam unless a #6 or #C air valve is installed. Then this one radiator will hiss, spit, gurgle and hammer, but will heat. Boiler water level also drops several inches while firing. Water is clean with a pH of 8. Replaced all vents. The returns pitch toward the boiler, but the mains pitch away from the boiler toward the returns. Any ideas why these two rads. are not heating?
Thanks in advance.

bigugh_4

JUST-a- GUESS

Are the pipes insulated ? Seems the rest of the building is makeing more condensate that can be returned to the boiler. Has the other rooms been changed in any fashion that would increase their need for head, (cooling off steam more than design) Or is it just so cold where your are that the system is overstressed? bigugh

scrook_2

main vent?

What do you have for a main vent on that main & where? Is it working? If the main vent's missing or broken than the radiator vent would have to do its work for it. I trust the main's insulated, the radiator's pitched toward its inlet and its valve is fully open.

Paul C.

Mains are insulated, however, there never were any main vents nor any tappings to install one. I'm thinking of pulling the rad. and checking the valve. What pitch should I be looking for on the mains?