Remote release

?Using remote release hooks, the crane sets the load down, a rigger presses a couple of buttons on a remote control and the hook opens, releasing the load and freeing the crane hook for another pick. They have technical safeguards that prevent the hook from opening when the load is in the air. The devices range from unpowered and completely manual devices to sophisticated electronic systems. The appropriate choice depends on the application.

The simplest of all is Caldwell's manually operated Rig-Release. It uses a spring to keep the main hook closed while loaded, but allows the hook to be released when the load is set down.

Users hang one end of the rigging on the automatic main hook. The other end of the rigging hangs on a small auxiliary hook. When the unit is unloaded, or loaded only with a sling, a user pulls a cord attached to a lever that pushes the hook to the side, and out through a slot cut in the steel case. When the hook opens, it releases one end of the rigging, while the other end remains attached to the hook. The system can be used with rigging arranged in basket and choker hitches.

The two-piece unit has a hook assembly that hangs on springs inside a heavy sheet steel case. When the unit is carrying a load, a user cannot open the hook, even if he pulls the cord. When the unit picks up a heavy load, springs inside the unit stretch, and the hook assembly slides down inside the case, beneath the slot. The inside wall of the case blocks the hook from opening. Once the load is set down on the ground, the springs coil up again, the hook assembly moves up, and the hook can be opened. An alternative model has a lanyard that pulls up instead of down. All the lanyards are fitted with a breakaway chain that tears apart in case it gets caught on a site obstruction. It comes in capacities of 1, 2.5, 5, 10 and 15 US tons (907kg-13.6t). It also offers 20 & 30 US ton units for basket hitches only.

Intelligent Equipment International's unpowered version of its EZ-Release remote release hook works in a similar way. It is intended for underwater lifting or lowering applications. As the load is set down, tension on a locking clasp drops, and the device automatically releases the load. It can lift a maximum load of 2 US tons (1.8t). All the models have been tested at 400% load.

The EZ-Release's rigging arrangement is different to Caldwell's. It comes with a length of chain permanently attached at one end. Users thread the chain around the load, or around load rigging, and then fasten the other end to a locking clasp on the EZ-Release. Then they perform the lifting or lowering operation.

Both the Rig-Release and the EZ-Release have powered versions that are activated with a radio remote control. When loaded, the systems are protected from opening in the same way that the manual versions are. To reduce the chance that the hook might open accidentally when unloaded, both systems require a double keypress sequence to open the hook. First, users press the 'arm' button, then they press the 'release' button to open the hook. The remote-controlled EZ-Release comes in lifting capacities of 1.8t or 2.86t. A standard version of the remote-controlled Rig-Release comes in lifting capacities of 2.5 or 5 US tons (2.25t or 4.5t), or an extended-capacity version of 10 US tons (9t) for basket hitch rigging.

Both the EZ-Release and Rig-Release only open the hook remotely; they still require riggers to attach the load to the crane in the first place. A new remote hook system, launching in February 2009, aims to not only release the load, but attach it to the crane as well.

The Elebia remote-release hook has a permanent magnet attached to the base of the unit that attracts slings with steel content, such as chains, wire rope, rings, or the magnetised sections in the two straps of its proprietary bulk bags. Then users press a button on remote control to lower a hook that had been previously rotated up on one side of the unit. The hook swings down underneath the straps and the tip of the hook latches in place.

As the crane takes the load, the straps are pulled away from the magnet and on to the hook. Once the load is set down, users can use a radio remote control to activate the battery-operated electric motor that rotates the hook. A sensor detects resistance to rotation, for example, in case a hand gets caught, and cuts the power supply.

The Elebia has been developed by Spanish firm Vivendi over the past two years. Designer Oscar Fillol says he came up with the concept when working in the company's bulk concrete aggregate processing business. The unit will cost EUR2,400 and lift 5t. Its remote control could also be configured to transmit on a free channel of the crane's remote control.