Posted by Harold Kestenholz - Hydronic Network on January 05, 2000 at 09:32:53:
In Reply to: Air in Hot Water Heating System posted by C Dolansky on January 05, 2000 at 03:07:14:
The concept of purging is to force the air from one end of a series of pipes out the other.
First, make sure the pressure in the system is high enough to force air out of the system. Estimate the height of the highest radiation in the system above the boiler. Multiply that height by 1/2. Add four pounds. Usually 12 psig takes care of a two-story house. Be sure that the pressure in the system is at least high enough to force air from the highest radiation or when you purge air, it will come back inn again.
Mark the original position of the balancing (butterfly) valves. (They are there to always force water from the least-resistance pipe to the greater-resistance pipe length. This is checked by turning the butterfly valve of the pipe length that has less than a 20F drop in temperature from one end to the other until the other length has a 20F drop), so there is even heat.)
Turn the balancing valve so it closes the pipe (usually this is a notch that is placed crosswise the pipe using a screwdriver.) Make sure the pressure reducing valve is open to the system (the feed water valve near the boiler from the cold water line.) Open the boiler drain (purge valve) to let water out until the water runs clear of bubbles. Close the purge valve and reset the balancing valve to the original position. Do this in every loop.
There is more important information in the free lessons at http://www.hydronic.net