Loading and emergency brakes
It must be possible to lock the rolls to permit loading and unloading of the vehicle. These consist of either disc brakes fitted to the roll shafts or brake pads applied to the inside surface of one or both rollers. In normal operation these brakes have to be of sufficient power to resist the torques associated with driving the vehicle on and off the rig. Pneumatic or hydraulically powered, they are controlled either by the operational controls (vehicle loading) or by the safety instrumentation (EM stop) and are designed to be normally ‘on’ and require active switching to be off (machine operational).
It is not considered good practice to rely solely on these brakes to bring the rig to rest in the case of an emergency. They should only be used to supplement the braking effort of the main drive system. In addition there must be a well-thought out ‘lock-out’ system to ensure that all personnel are outside restricted areas before start-up, particularly important in large facilities where the operator may not be able to see all areas.