Lock-out systems prevent specific crane functions when the crane indicator goes into alarm. A Lock-out system generally refers to a kit that includes some combination of valves or switches that are added to an existing or new crane indicator with the intention of preventing certain crane movements in the event of a warning alarm. Lock-out systems can be added to a crane load moment indicator (LMI), rated capacity indicator (RCI), crane load indicator, or anti-two-block (ATB) warning system.
The type of lock-out valves used will depend on the type of crane. For example, a rough terrain telescopic boom crane will likely use hydraulic valves in the lock-out kit since this type of crane is normally controlled by a hydraulic circuit. With a large lattice boom crawler crane, it is more likely to be controlled by air valves or a PLC logic board.
An example of a lock-out system to work with an ATB alarm on a hydraulic crane would include a valve to stop the hoist up, boom down, and boom out. These 3 hydraulic valves would be connected to a central relay controlled by the ATB system display. When the alarm is activated, it cuts power to the relay and, in turn to the 3 valves. Once the power is cut to the valves, it shuts off the hydraulic flow for the function you want to close when in alarm. The crane operator should still be able to use the crane and get out of the conditions that would put the Crane into ATB but not make any moves that would put it further into two-block. For example, once in ATB alarm, the lock-out system will let the operator hoist down but not up and telescope in but not out.
Lock-out systems are normally custom designed and installed by an experienced technician, but they are a great addition to any crane indicator system. They will make your system safer, and in some circumstances, they are required.