Without a Balancing Line
In applications where the volume of liquid being drained is large enough to fill the complete diameter of the pipe, the potential for air binding exists. This is occurs because Float type drain traps are normally closed, with the weight of the float keeping the valve in the closed position. Liquid must first enter the body of the trap to lift the float and open the valve. When the liquid tries to flow down the pipe, the air pressure inside the trap will continue to build and stop the flow of liquid causing the trap to air bind. A balancing line will equalize the pressure allowing the liquid to freely enter the trap and lift the float, allowing proper discharge to take place.