Descripción general The Marley external Disc Anti-Reversing Device (ARD) backstop is a custom designed, welded stainless steel assembly that is bolted directly to a Marley Geareducer® with input shaft diameters from 1.125" up to 2.625". Specifically designed for all right-angle Geareducer models the Disc ARD prevents reverse rotation of the fan, Geareducer and motor and can be field installed.


This anti-reversing device prevents standby fans from reverse rotation when duty fans are operating. It also helps eliminate damaging and costly fan “reverse windmilling.”

Under reverse rotation, the eccentric mass of the Disc ARD pawls extend away from the rotating disc and engages the stop bracket catch point, preventing the mechanical equipment from operating in reverse direction.

  • Designed for all right-angle Geareducers

  • Welded stainless steel assembly

  • Can be field installed

  • Prevents reverse rotation