Available in round and rectangular sizes, EWC Controls' model SBD bypass dampers make bypass set-up simpler than ever. No measuring instruments are required. No weights to adjust. No springs to crank. The SBD is ACCA Manual Zr compliant. As an added benefit of the unique blade design and the smart, self-balancing feature of the SBD, there is no need to install and setup a separate bypass balancing hand damper.