South African hydraulics company Horne Hydraulics is contributing to mining safety by supplying Levelok conveyance chairing and emergency braking systems to several mines in Southern Africa.
Levelok is known as the world’s largest cage system, and has been developed over the last 30 years. The system is being used in mines in Southern Africa, North America and Australia.
The Levelok system consists of a power pack and clamps, which hold a cage or skip steady during the transfer of loads while the clamp is still applied. The clamps then release their grip at a controlled rate to allow the rope stretch to be taken up smoothly.
While the system’s safety record is impeccable, its opera- tion is quite simple. When the cage is in position, the station air supply quick coupler is connected to the connection on the cage.
The power pack, also known as the air or oil intensifier, boosts the hydraulic pressure up to the required pressure, whereafter the pump stalls and clamp force is maintained indefinitely. This operation usually takes about ten seconds for the pump to boost the pressure to full clamping force.
When loading or unloading of the cage is complete, the station air supply is removed, resulting in a rapid loss of air pressure in the power pack. This starts the decompression cycle, which takes about ten seconds.
As the oil pressure drops, the clamps release their grip at a controlled rate and the cage slides smoothly to its new posi- tion in the shaft. The clamp arms will then fully retract, thus allowing the cage to be moved.
Advantages of the Levelok cage system includes the safe transfer of men and materials during loading or unloading of the cage, increased rope life on skip systems owing to no shock loading, and no spillage as the skip is held in one position during loading.
Another benefit of the Levelok system is the fact that it can be adapted to operate as an emergency brake.
Emergency braking under slack rope conditions can easily be added into a standard cage holding system, which is achieved by incorporating an accumulator into the system.
The accumulator is charged to working pressure when the system is used for the first time. Should the conditions for an emergency situation be met, oil would then automatically be released from the accumulator, thus activating the Levelok clamps, which then grip onto the shaft guides in a controlled manner. The deceleration rate is adjusted according to the individual customer’s requirements.
Skip Holding System
Further, the cage also consists of a skip holding system, which is designed to hold a skip in the shaft during the loading of ore. This eliminates spillage and the transfer of shock loads to the rope, and increases rope life.
The skip system is installed at the level in the shaft where the loading occurs. The skip is fitted with clamping bars, onto which the clamps grip, thus holding the skip in position. The system is programmable logic controlled and is, therefore, fully automated.
Besides supplying Levelok systems, Horne Hydraulics is also the supplier for Oleo hydraulic buffers and Technogrid energy absorption devices.