A power plant had several large fans in their system. Unfortunately, the idle fans pin-wheeled in the reverse direction due to ambient airflow, even when the dampers were closed. When the idle fans were started, a significant chock load resulted in rolled keyways and broken shafts.


The operating and installation procedures were reviewed. Options were discussed including several spring set brake designs. One of the challenging problems was identifying the actual reversing torque—which is much less than normal motor torque. The question was: how much less?

Ultimately, the simplest and best answer was an over-running clutch. This device free wheels (over-runs) in one direction and locks up in the opposite direction. It is automatic and instantaneous, eliminating controls. The load is never allowed to reverse.

Our customer was able to mount the backstop on an extended shaft with a reaction arm hanging down between two stops. The large torque capacity in a small envelope guaranteed we had adequate torque. If you have something reversing that shouldn’t-give us a call!