The overhead cranes term “true vertical lift” is pretty clear. It describes the motion of a hoist lifting a load straight up, avoiding any lateral movement.
Vertical lifting equipment accomplishes this action through double reeving. In this configuration, two ropes come off the drum – one of each end, with grooving for each rope cut opposite hand. As overhead cranes lift the load, the ropes wind onto the grooved drum from the ends toward the center. As a result, the hook and load stay lined up with the drum’s centerline, achieving a true vertical lift – or center lift.
True vertical lift cranes typically handle higher capacity loads – 25 to 30 tons or more – as the two ropes split the weight. Cranes with True Vertical lift or “Center Lift” are also best suited for applications where there’s little-to-no tolerance for side-to-side movement of the hook, such as in aerospace and other precision assembly operations.
On the other hand, single reeving, the most commonly used and simplest reeving option, is reserved for lighter loads – 25 tons or less. For all but precision lifting applications, single-reeved hoists are up to the task.
With a single-reeve setup, the crane’s wire rope winds around the drum in a single layer across the length of the drum, and the hook follows along, horizontally, as it rises.
Konecranes offers a third alternative, called True Lift™. Not to be confused with true vertical lift, this single-reeved system comes relatively close to delivering a true vertical lift without the increased cost of a double-reeved system.
True Lift works by way of incorporating “fat drum” technology. The drum of a True Lift hoist has a larger diameter and much shorter length than conventional, single-reeved hoist drums. This limits the horizontal movement of the hook, because the rope has less distance to wind horizontally across a fatter and shorter drum.
While the horizontal hook movement of a conventional single-reeved hoist with a 10-inch diameter drum may result in 10- to 12-inch horizontal hook movement, a True Lift hoist with a 20-inch diameter drum could cut the horizontal movement to just a few inches.
It’s not dead center like true vertical lift, but it greatly minimizes the horizontal movement.
In addition to costing less than a conventional double-reeved hoist, a True Lift hoist, by virtue of its compact size, greatly improves end approaches. The hoist hook can travel closer to the end of the bridge span and thus covers more floor area than other brand single-reeved or double-reeved hoists.
For more information about Konecranes hoist options and vertical lifting equipment, contact a Konecranes representative.