Maintenance IN SYNCH

An important safety feature on friction hoists is the re-synchronizing mechanism. On completion of the hoisting cycle for one conveyance, it is automatically spotted at a predetermined position in the headframe, and the hoist auxiliaries, which include the hoist controller and hoist regulating devices, are checked for synchronism. If any discrepancy exists, the auxiliaries are automatically calibrated to register the true position of the conveyance. This checking arrangement ensures that there is no accumulation of rope creep or slip which would result in the auxiliaries registering the position of the conveyance in the full speed zone when, in fact, it is approaching the limits of travel. In addition, three more devices have been found very useful: * a motion switch connected to a deflection sheave or rope riding pulley, which trips the hoist if the drum moves faster than creep speed and if there is no movement of the rope (a jammed conveyance); * a tread wear switch which opens in the event of tread wear caused by rope slippage; and * a balance rope loop switch which opens if any of the loops rise. *