NJ Series Contact Sprag Backstop
NJ series contact sprag‑type holdback is dedicated anti‑reverse safety device for low‑speed shaft applications such as belt conveyors and bucket elevators.
During forward rotation, inner parts make light contact. Once reverse rotation happens, sprags wedge tightly under spring force to lock the shaft and prevent reverse running. Compact structure, easy installation with low requirement for mounting precision.
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Main Features
1. Scope and Application
NJ‑series backstop is a contact‑type anti‑reverse device for low‑speed shafts. Compared with conventional backstops (roller backstops, ratchet‑wheel backstops and band‑brake backstops), under the same transmitted anti‑reverse torque, it offers advantages of light weight, compact structure, reliable torque transmission, easy disengagement, convenient installation and low requirement for mounting precision.Its overall mechanical performance outperforms other ordinary anti‑reverse devices. It is the preferred safety protection unit for lifting and conveying equipment, generally applied to belt conveyors, bucket elevators, scraper conveyors and other equipment requiring anti‑reverse protection.
2. Working Principle |
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| NJ‑series backstop consists of several sprags arranged in a certain pattern between the inner and outer rings. When the inner ring rotates forward, the sprags make light contact with inner and outer rings.
When the inner ring rotates reversely, the special‑shaped sprags wedge the inner and outer rings tightly under spring force, so as to bear the anti‑reverse torque. (See right figure) |
3. MOdel and Marking
3.1 Meaning of Model Code
3.2 Marking Examples
NJ200‑S‑180 represents a contact‑type backstop with rated torque 38000 N·m. Viewed from the shaft end, the inner‑ring rotates clockwise, and the mounting bore diameter d is 180 mm.