Lift Capacity, Safe Work Load, Operating Load, Tipping Loads – What Do They Mean?
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The most relevant specifications to compare different brands of mini loaders and skid steers is the Safe Working Load (SWL) or Operating Load of the articulated loader, mini telescopic or skid steer and to make sure these calculations have been done using the AS, ISO or SAE. It is of paramount importance to check that the SWL measurements have been performed using one of the above codes, as some manufacturers may state tipping load at the hitch, which is not the centre of gravity of the bucket or pallet forks, so the actual capacity will be a lot lower. Further details are explained below.
If a mini telescopic loader is being compared to a front end loader, then the tipping height must also be taken into account. Often mini telescopic loaders do not have a useful working height when retracted and must be telescoped out before they can load a truck or a trailer. Sometimes they don’t even have any clearance from the wheels when retracted. In the case of a telescopic loader the useful working height’s tipping load must be taken into account as the tipping load decreases significantly when the mast is telescoped out from the loader. The way to compare tipping loads of a front end load to a telescopic loader is to extend the telescopic mast so the pivot point is the same as the front end loader and then compare the tipping loads.
Specifications such as hydraulic lift capacity have no relevance as to what a loader driver can actually lift. The hydraulic lift capacity merely states what the loader, if chained to the ground so it couldn’t tip over, could lift.
The accepted method for determining a loaders capacity is to measure the loaders tipping load. The figure gained determines the Safe Working Load (SWL), also commonly called the Operating Load. There is a recent trend to call the recommended capacity Operating Load as it shows the driver they must still operate the load in a responsible manner, as this load in particular situations is enough to create instability in loader.
The tipping load of a front end loader, mini loader, wheel loader, or skid steer is measured with the mast fully extended laterally. A loader mast creates an arc in the air when lifted from the lowest point to the highest point. The tipping load of the front end loader is highest when it is lowest to the ground as the tool frame is closest to the front axle. As the mast moves upwards to the horizontal position, the tool frame is in the most distant position from the front axle, giving the lowest tipping capacity of the front end loader. This is because the centre of gravity of the load is further away from the machine. A similar principle applies to people – try picking up 10kg close to your chest and then extend your arm out to full extension – it is a lot more difficult to lift and it creates a tipping movement in the direction of the load. As the mast moves in an arc further upwards, to its highest point, the centre of gravity of the load on the tool frame actually comes closer to the machine, so the tipping load increases again.
Tipping load is measured using a weigh cell
The tipping load for a front end loader with a set of forks is calculated with the pallet forks in a horizontal position and the weigh cell positioned at the centre of gravity of the load on the forks. It is important when comparing loaders to check where the manufacturer states their centre of gravity is on the forks, as the closer to the machine will give a higher tipping load.
One must note that the tipping load is a STATIC MEASUREMENT taken on a hard even surface, so this figure shouldn’t be taken as the weight a loader can actually lift in the field. Uneven terrain, boggy ground, slopes, braking, momentum from travelling and raising/lowering the mast must all be taken into account and so guidelines for SWL have been set up.
The above description of measuring the tipping load when the vehicle is straight is true for rigid bodied loaders such as skidsteers and backhoes. This is because in a rigid bodied loader the effective distance of the counterweight relative to the tool frame cannot change. However in an articulated loader, the front chassis turns independently to the rear chassis and on full articulation the counterweight is closer to the tool frame, changing the tipping load.
When tipping loads measurements are being taken for SWL calculations wtih articulated loaders, they are measured in two positions - one when the articulated loader is straight and the other tipping load when the loader is fully articulated.
After tipping load measurements have been performed these are used to calculate the SWL or Operating Load’s. For rigid bodied loaders, 50% of the tipping load straight is used as the SWL. For articulated loaders, 50% of the fully articulated tipping load is used as the SWL. 50% of the tipping load is used to take into account the variables mentioned above – such as uneven terrain and momentum from travelling.
The golden rule for operating any loader, in particular articulated loaders, is to load with the vehicle straight. Articulated steering is to be used for maneuvering and the bucket or weight is best kept low for this. A lot of reserve safety is built into articulated loaders as 50% of the tipping load when ARTICULATED is used for the SWL, and an operator should never have his bucket in that position. However in a rigid bodied loader, 50% of the tipping load is used, so less reserve is really built in.
Many operators of articulated front end loaders are amazed how much they can lift, as this is because the tipping load when the vehicle is straight is so high, however the operator should always be careful to load within the vehicles SWL for safety. The Australian Standards also state that less weight/material should be put in the bucket of any loader if the operator is working in rough terrain as the terrain will affect the tipping load greatly.
In summary, tipping loads are calculated to determine the SWL or operating loads that are recommended for each model front end loader and skidsteer. Loader operators should be aware of the SWL and drive the loader within its limits to guarantee their own safety and safety of personnel in the vicinity.