Air and drain traps automatically discharge condensate that has flowed into the trap body, but since air is a non-condensible gas, if the air inside the trap body cannot be replaced, condensate cannot flow into the trap, making it impossible to discharge.

This is known as air binding, and can be prevented by installing a pressure balancing line, enabling the air inside the trap to be replaced with condensate.

The pressure balancing line should be set linking the top part of the trap to an area in the system above any possible condensate accumulation, such as a receiver tank or air main line.