Levelok®’s Cage Holding System has been providing safe and rapid transfer of workers, material and ore with mine conveyances used in vertical shafts since the 1980s. The Levelok® Cage Holding System consists of a power pack and clamps which hold a cage steady during the transfer of men and/or material. The clamps release their grip at a controlled rate to allow the rope stretch to be taken up smoothly.
An electric power pack is also available.
When the cage is in position, the station air supply quick coupler is connected to the Levelok connection on the cage. The power pack (air/oil intensifier) boosts the hydraulic pressure up to the required pressure. The pump stalls and clamp force is maintained indefinitely. This operation usually takes about 10 seconds for the pump to boost the pressure to full clamping force.
When loading or unloading of the cage is completed, 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 position in the shaft. The clamp arms will then fully retract, thus allowing the cage to be moved.
Safe Transfer of men
Time saving, as re-decking of the cage will not be necessary during loading of men and material
Quick and easy to use; single person operation
The system can be complemented with an EFA System
Can be used equally well on steel, rope, rail and wood guides
No Shaft obstruction
Why should I consider using the Levelok Cage System?
What load can the clamps support?
Clamps can be designed to suit any load conditions and the limiting factors are the strength of the guide and the shoe area. To date clamps have been designed for loads of up to 80 tonnes using four clamps. Please note that the clamps do not have to support the cage mass but only the load being transferred to or from the cage.
What force is applied to the guides?
The clamping force on each guide is approximately 4 times the total mass to be supported divided by the number of guides. Thus if two clamps support a 10 tonne load, the clamp force on each guide would be 20 tonnes. The guide also has to be capable of supporting a vertical load equal to half the holding capacity of the clamps.
What factor of safety is used on the clamps?
All the clamp units are designed with a minimum safety factor of 5 on ultimate tensile strength. On clamping force, a safety factor of 2 is used.
How heavy are the clamps and powerpack?
The mass of the two 4.5 ton clamps required for a 9 tonne system is 185kg per clamp and the powerpack weighs about 20 kg. Thus the total weight of the 9 tonne levelok system would be about 390kg which excludes the necessary pipes and fittings.
What material are the clamp shoes made of?
The material used is mild steel and the shoes are milled from a single piece of mild steel. This material has been found to be quite satisfactory under wet and dry conditions. In special cases we do use high grip friction materials which greatly increases the load bearing capacity of the clamps.
What clearance is there between the shoe and the guide?
The normal design clearance is 16mm so that there is virtually no possibility of the shoe making contact with the guide while the cage is in motion.
Can the clamps clamp while the cage is in motion?
No, the clamps are spring loaded to the open position and they can only be operated when an air or electrical supply is connected to the cage.
How long does it take for the clamps to operate?
How are the clamps fitted to the cage?
The clamps are normally fitted on top of the cage in place of the bridle roll brackets and the latter are bolted on top of the clamps.
Fitting clamps to the bottom of the cage is not recommended. If a load is added to the cage, the bridle channels are put into compression, a condition for which they are not usually designed.
In attaching the clamps to the bridle, adaptor plates may be required if holes do not match up, but in any event, all holding down bolts should be able to support the maximum clamp load with the required factor of safety. When fitting bridle roll brackets above the clamps, care must be taken to ensure that there is sufficient clearance between the wheels and the clamp arms, as on some installations, brackets have had to be modified.
Where should the powerpack and accumulator be mounted?
The powerpack should be located as close as possible to the clamp units and it can often be conveniently mounted on top of the cage or on the side of the main bridle cross member. A suitable cover should be provided to protect the powerpack and accumulator against spillage.
What air or electrical supply is required to operate the system?
On each level where the levelok system is to be operated, a filtered, dry and lubricated supply of air is required at 50 c.f.m. with a minimum pressure of 5 bar.The power pack is selected to suit the available electrical supply in the shaft.
What happens if the driver pulls away when the clamps are still clamped?
An interlock system is essential to prevent the driver from trying to raise or lower the conveyance while the clamps are in operation. The design of the interlock system can vary from mine to mine, due to individual preferences, but the interlock system is normally arranged to isolate the hoist brakes until pressure has been released from the clamp system. A slack and tight rope monitoring device with communication capability up the rope can be used to send a clamp release signal to the driver from the clamp limit switches.
We therefore have no standard interlocking system but we do put forward suggestions and recommendations.
The Levelok Interlocking Brochure
What happens if a hose fails?
Air pressure is locked in the system by a check valve on the hose as well as a solenoid operated valve on the powerpack. The check valve in the hose will keep the air locked if the hose fails. Should the hydraulic hose/pipe between the powerpack and the clamp be severed, a clamp lock valve installed on the back of the clamp will retain 75% of the clamp pressure.All clamps are designed to hold twice their rated load, therefor loosing 25% of clamping pressure will not release the cage.
What is delivery time on the complete Levelok Cage System?
The first cage holding system was installed on a cage at Matchless Mine in Windhoek in 1970.