Non-Contact Backstop Device .

NF are Tianiu non-contact backstops for high-speed shafts. In forward rotation above a threshold speed (350–450 rpm depending on size) the shaped sprags are lifted off the raceway by centrifugal force, so the backstop runs without contact and wear; when the drive stops and tries to run back, the sprags engage. 11 sizes NF10–NF250: rated torque 1,000–25,000 N·m, bore 40–160 mm (E7, shaft h6, key to GB/T 1095-1979), maximum speed 1,500 rpm (up to NF125) and 1,000 rpm (NF160–NF250), weight 27–256 kg. The reaction torque is taken by the housing arm.