Levelok® Cage Holding System

Improved Productivity. Enhanced Safety.

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.

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How It Works

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.

See How It Works!

Benefits

Learn how the Levelok® Cage System can benefit your mine.

Safe Transfer of men
and material

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

FAQ

Frequently asked questions about the Levelok® Cage Holding System

Why should I consider using the Levelok Cage System?

  • It permits safer loading and unloading of both men and material.
  • Damage to equipment is prevented.
  • Time and labour are saved as the onsetter / cage tender is able to lock the conveyance in position in a short time after it comes to rest.
  • Installation is simple and no structural modifications are normally required to either the bridle, cage or shaft.
  • Either electrical or air supply is required to power the unit.
  • One system on a conveyance can be used to clamp the conveyance at any level.
  • The system can be used with multi-deck cages.
  • Clamp units can be supplied for any desired load, providing there is sufficient guide contact area.
  • The clamp system can simply be interlocked with the shaft bell and winder safety system.
  • No extra labour is required to operate the system at each station.
  • Inspection and maintenance are minimal and the recommended spares holding is reasonable.

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?

With the 9 tonne system, the time from the plug in of the air supply to fully clamped is approximately 6 to 7 seconds, but with a larger capacity unit the time will increase slightly.

Initially the clamp arms move into contact with the guide at low pressure and pressure is then built up by the action of a reciprocating pump until a stalled condition is obtained at the set pressure. The decompression period is adjustable by means of the metering pin and it has been found that a period of 4 seconds provides good results and does not give an excessive amount of rope oscillation when the clamps release.

The 4 seconds refers to a rope stretch of 600mm or more when material is being handled but where greater stretch is experienced and when men are being carried, the period may need to be lengthened.

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?

Normally within 14 weeks for a mild steel Levelok cage system.

Who Uses Levelok® Cage Holding System?

The first cage holding system was installed on a cage at Matchless Mine in Windhoek in 1970.

Canada

  • Xstrata Nickel Craig Mine & Nickel Rim Mine
  • Xstrata Copper Kidd Creek Mine
  • Hudson Bay Mining & Smelting 777 Mine
  • GoldcorpRed Lake Mine
  • Nickel Rim South Mine Ontario, Canada
  • Vale Totten Mine

USA

  • Underground Vaults & Storage Hutchinson Facility
  • Hecla Mining Lucky Friday Mine

South Africa

  • AngloGold Ashanti Moab Khotsong,
    Great Noligwa Mine,
    Tau Lekoa Mine ,
    Mponeng Mine,
    Kopanang Mine
  • Anglo Coal Zibulu Colliery
  • Goldfields East Driefontein No 5 shaft, South Deep Mine
  • Rio Tinto OPalabora Copper Mine
  • Harmony Gold Target Mine, Tshepong Mine, Phakisa Mine
  • Impala Platinum No 11C Shaft
  • Anglo American Corporation Black Mountain Mine.

Mongolia

  • Rio Tinto Oyu Tolgoi #1 and #2

Australia

  • Tower Colliery
  • Cordeaux Colliery

BROCHURES

Further reading about the Levelok® Cage Holding System.

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