The Bibbigard Series 300 Torque Limiting Controlled Release Backstop is of a similar construction to the Series 300 PCR, but incorporates a torque limiting facility. Designed for use on single motor drive or multi-motor drive conveyors where two or more Backstops would be employed, it prevents the torque resulting from a staked (hold-fast) condition being transmitted to, and thus overloading, the gearbox.
A series of M24 socket head cap screws (2), each with a stack of Belleville washers (4) under the head, pass through the clamp ring (1) and are threaded into the adaptor plate (6). These are tightened to provide the braking torque. On the same PCD a series of M24 hexagonal head ‘tension release’ screws (3) are threaded through the clamp ring (1) so that their domed ends can bear against the adaptor plate (6). Tightening the tension release screws (3) results in the clamp ring (1) being drawn back to further compress the Belleville washers (4) against the underside of the heads of the socket head cap screws (2), and so releases the pressure on the brake lining. The speed at which the controlled release operates is dependent on the degree to which the tension release screws are tightened. Under normal circumstances the braking torque is preset and the torque adjustment screws (2) locked with security seals.		Operation 1. The brake is applied at the preset torque while the conveyor is operating normally. 2. In the event of a staked (hold-fast) condition arising in the conveyor belt, switch off the conveyor drive and establish the reason in accordance with the appropriate Code of Practice. Do not attempt to clear the obstruction at this time. 3. Remove cover (5) from the Backstop Unit to gain access to the tension release screws (3). 4. Gradually tighten the tension release screws (3) a maximum of a quarter turn at a time in diametrically opposite order to release the brake. This permits the locked Backstop and drive shaft to rotate slowly, dissipating the stored energy in the belt, and allowing the conveyor to be let down under control.	5. The obstruction may now be safely cleared. 6. Before re-starting the conveyor, loosen the tension release screws (3) completely to allow the brake torque to be re-established. 7. Re-fit the cover (5) and re-start the drive. Important On conveyors fitted with more than one Backstop, operations 3 and 4 must be repeated on each Backstop before operations 6 and 7 are carried out on any of them. Failure to do this will result in the belt retaining some stored energy.