If you intend to use a hydraulic gantry to lift a heavy load, the most obvious thing to note is the weight of the load. You will then be able to determine if your gantry has the capacity to get the job done.
Seems easy enough? Well, there’s more to it than you might think.
If your gantry has the right capacity and can be configured to accommodate the length and breadth of the load, you’re on the right track – but there’s still another important factor to consider: the center of gravity of the load (CoG).
If the CoG is not central to the load, and if the load is close to the gantry’s capacity limit this becomes increasingly more important. It can be the difference between success and failure.
Gantry Capacities Explained
When we look at the SL400 Hydraulic Gantry, this has a maximum total capacity of 400 tons, which is shared across the 4 units. Therefore, we know that each individual unit has a maximum capacity of 100 tons. Note that with a telescopic gantry, this is the capacity at the first (lowest) stage, it will be much less at the fully extended third stage.
The maximum capacity figure applies when the CoG of the load stays central to the footprint of the gantry. The images below illustrate the point. In Fig 4 a single leg is bearing most of the load which will cause overload.
Center of Gravity of a Load: Hydraulic Gantry Examples
load with even center of gravity with gantry
Fig 1: The load suspended by a gantry with the load spread evenly across the four leg units.
offset center of gravity load with gantry
Fig 2: Here we see a load positioned centrally within the gantry’s footprint, but when the center of gravity of a load is offset this means two of the legs are bearing extra load.
side shift gantry center of gravity
Fig 3: This shows a load with a centralized CoG. Caution is needed because side shift units are being used and the result is that two legs are to bearing extra load
gantry overload center of gravity
Fig 4: OVERLOAD! One leg is bearing most of the load
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Using Side Shift Units with a Hydraulic Gantry
As we can see above, side-shifting has the potential to overload a gantry leg, even if the total load is within the gantry’s capacity. This is especially true as the length of the beams increase – the longer the beams or length of the object, the larger this unwanted effect is.
Center of Gravity of a Load: Key Takeaways
• Always make sure you know all details of the load, instead of just the total weight.
• When the load is offset, and/or you are using side shift units, a larger capacity gantry may be needed.
• Be aware that an off-center CoG and/or side-shifting can result in overload.
• Remember to take the weight of the header beams and rigging into account in your calculations.
• If in doubt about the application, or the correct gantry size, please contact your Enerpac Heavy Lifting Technology Specialist.
