E-PSA-CP: Single-blade bypass damper, installed on one side of the supply duct. This damper's function is to connect the air supply of the air conditioner with the return when the pressure in the supply duct rises excessively. In this way, the pressure inside the duct will remain at acceptable levels even when only one interior zone is in demand.

E-PSA-CPE. Pressure compensator with external counterweight. It should be used in installations where the return is ducted and the bypass duct is rectangular.