Steam boiler venting (single pipe)

Sparkybruno

Have been trying to eliminate water hammer in one second story room of the house. Checked the usual suspects, radiator pitch, radiator vents, pressuretrol settings.... Water hammer seems to behappening at the middle/end of the cycle. In the morning I get some short cycling but then during the rest of the day it seems fine. Since the basement is finished , I cant locate the mains vent. Dont want to go breaking holes everywhere to try and find it. 1) where should I expect to see the mains vent? 2) I have access to about 10-15 feet of mains pipe in either direction of the boiler, should I try and add venting in the areas I have access to? Will this work or should I really try and find the mains vent?

Thanks

Hitzkup

Pitch

Try checking the pitch of the runout leading to the problamatic  radiator, an easy fix that could work is a smaller radiator vent.