Harold Kestenholz
You seem to be describing purge and balance valves which are used for the purpose of purging air from the system after making repairs.
Note and mark one side of the balancing valve position with a magic marker so you can return the balancing valve to the same position as before. Turn the balancing valve to block the flow of water. The slot or indicator should be across the tube to block the flow of water. Then open the drain to let water and air flow out of the lines. Close them when the lines run clear. Return the balancing valves to their marked previous positions.
The removal of air can be improved through proper piping, location of an air scoop and circulator, and air vents. Visit: http://www.hydronic.net
to look at the design instructions and pipe arrangements to see if anything in your system can be improved.
