18.1 Mechanical and Vacuum Lifting Devices

Match the retaining method to the load

A mechanical lifting device retains a load through a designed geometry, engagement or gripping mechanism. Examples include C-hooks for coils, pallet lifters and purpose-built grabs. A vacuum lifter retains a suitable surface through a pressure difference across its pads. Both are below-the-hook devices, but they solve different load-handling problems and have different failure modes.

A coil lifter needs the specified coil dimensions, weight, orientation and CG range. A pallet lifter needs a stable, retained load on an appropriate pallet; fork capacity alone does not secure loose packages. A scissor grab needs the approved dimensions, contact conditions and operating sequence. Do not assume every mechanical device relies on friction, or that every grab remains locked after hoist tension is removed.

A vacuum lifter may be useful when attaching slings would damage a finished surface or when glass or sheet material lacks conventional lifting points. It must be intended for overhead lifting of that material. Hand-held vacuum cups and a below-the-hook lifting frame have different applications; hand cups do not become an approved crane lifter by attaching several to a sling.

Mechanical selection and operation

Verify the device's rated load, self-weight, dimensional range, load orientation, suspension connection and opening/closing mechanism. Determine how the load is captured and what could release it. A C-hook supporting a coil from its bore has a defined load position and counterbalance; extending its nose or using it on a different shape can shift the load outside the approved geometry.

Before lift-off, engage the mechanism fully according to the instructions. Keep hands clear of moving jaws and locking parts. Inspect for cracks, bent members, missing pins, damaged contact surfaces or an unreliable lock. A device that sometimes catches is defective even if it looks structurally intact.

During travel, avoid shock, collision and unapproved rotation. Observe engagement from a protected position. To release, first land and support the load, then operate the mechanism as directed. Never trigger release while someone is beneath a retained load or use a worker's hands to prevent the grab opening.

Vacuum selection variables

Vacuum capacity depends on more than the plate or glass weight. The proposed pad arrangement must suit dimensions, stiffness, curvature and surface condition. The lifter must also be rated for the planned horizontal, vertical or tilted orientation. Supporting a sheet horizontally and resisting sliding on a vertical sheet impose different demands.

Use the manufacturer's selection worksheet and operating manual. Do not assign a universal vacuum value, pad spacing or emergency holding time. Some systems have independent circuits, reserve tanks and alarms; the actual arrangement determines the tests and response. A reserve tank does not guarantee retention on a leaking or unsuitable surface.

Inspection and readiness

Inspect pads, sealing lips, frame, hoses, fittings, filters, gauges, valves, alarms, battery or power supply and motion locks. Complete the specified vacuum and leakage tests. Establish that indications are readable by the person responsible for monitoring them and that the release control cannot be activated accidentally.

Check the charge or power condition before beginning. A powered pump may maintain a marginal seal until power is lost; that does not prove the load will remain attached during an outage. Plan a nearby safe landing area and a response to low vacuum, alarm or failed power. Keep personnel clear throughout the lift because retention can deteriorate quickly.

Selection example

A 900-lb polished panel is within a lifter's stated 1,200-lb capacity for vertical handling. The proposed pads lie partly over joints, and the panel's finish is damp. The numerical comparison alone is insufficient. Confirm the approved pad layout, soundness and surface conditions; clean and dry only by the permitted method, and complete the required tests. If these conditions cannot be met, select a different approved lifting method.

For the crane load inventory, include the lifter's self-weight. If the approved device weighs 350 lb, the panel and device contribute 1,250 lb before the separately applicable hook, rigging and load-line items. A device rating and a crane chart answer different capacity questions.

Lifting and release sequence

Position the pads on approved contact areas without dragging them across sharp features. Activate attachment, verify adequate vacuum and indications, and make the planned low trial lift. Check load balance and stability without reaching under the panel. Monitor vacuum continuously as required by the instructions while maintaining the exclusion area.

For an alarm, stop and follow the prescribed controlled landing response; do not continue to a distant destination on an assumed reserve time. Before intentional release, confirm that the panel is supported against tipping or sliding and that its weight has transferred to the destination. Release pads only through the designed control sequence. Store pads and the frame so sealing surfaces, hoses and controls remain protected.

Sources: CCO reference manual, ASME B30.20 extracts, WPG lifter selection, WPG operating resources.