When choosing a forklift, you need to ensure it has sufficient load capacity for the job, both for your own peace of mind and to comply with OSHA regulations. However, the rated maximum capacity isn't the whole story, so how are you expected to work out the real figures?
Several factors contribute to the true safe load capacity of your forklift when lifting a specific type of burden. I've laid these out below, so you can choose the right forklift for your operation without any slip-ups in this key aspect of forklift safety.
Forklift Load Capacity Explained
When we talk about the load capacity or lifting capacity of a forklift, we are referring to the amount of weight the mast and hydraulics can lift using the forks (or other attachments). This is obviously a key measure in choosing a forklift for most material handling jobs, as the truck needs sufficient capacity to safely carry the loads for which it is intended. Too much weight or improper placement can cause damage to the lifting assembly and/or the forklift overbalancing.
Difference Between Rated Capacity and Payload (Net) Capacity
The rated capacities of forklifts are a measure of the absolute maximum weight the forklift can lift safely. These are usually stated as a weight, and a length. This length is the recommended distance from the rear of the forks to the center of mass of the load. So, a forklift's raced capacity might be given as 6000 lbs @ 24 inches load center of mass.
However, several other factors affect the true safe capacity of the forklift under real-world operating conditions.
The size, shape, and weight distribution of the load have a significant effect, as well as changes in the center of mass caused by using certain forklift attachments.
Therefore we have to consider the Net payload capacity, which can be thought of as the forklift's true capacity under a specific set of circumstances. This is calculated using a set of data points including the rated capacity of the forklift, the vertical height from the face of the forks and horizontal distance from the vertical face of the backrest of the payload's center of mass, the weight and forward displacement of any attachments being used, and the intended maximum lift height.
This allows operators to estimate a safe load capacity with oversized loads and/or an unusual attachment. The appropriate OSHA training includes practice with the relevant formulae so any certified forklift operator should be well versed with performing payload capacity calculations.
Forklift Data Plate
A forklift's data plate takes the form of a metal sheet attached to the chassis by the forklift manufacturer and printed with key information regarding the forklift model and operating parameters.
The content of data plates will include the service weight and load capacity (at specific load center distances) of the forklift, as well as other useful details such as the correct tire sizes and pressures, battery voltage and weight, the amount of back-tilt available at the mast etc.
It's important for forklift operators to check data plates carefully before ascertaining whether a particular load can be carried without impacting the safety and stability of the forklift. They essentially constitute an important piece of safety signage and OSHA regulations forbid the removal or obscuring of a forklift's data plate.
How Much Capacity Do I Need For My Circumstances?
The required forklift capacity varies wildly between different material handling applications.
Warehousing operations handling relatively light pallets of goods will not need their forklifts to lift a maximum load of anywhere near as much weight as those involved in large construction projects especially.
The first thing to consider then is the load weight. You should be able to work out the average weight you need to lift easily based on the products, materials, or components you generally work with.
A good general rule of thumb is to then choose a forklift with a maximum capacity of at least double the load you are expecting it to lift.
This builds in some allowance for if the center of the load is high enough or far enough forward to give a net capacity significantly lower than the forklift's rated capacity. So, if you are moving palleted loads of up to 2500 lbs, a 5000 lb capacity forklift should be sufficient.
Of course, you could go with the approach of "bigger is better", but there are two issues with that. Firstly, the cost of forklifts with high capacities can be prohibitive. Second, these machines tend to be large and bulky and may not be physically suitable for your premises. There's no point purchasing a lift truck with a capacity of 50000 pounds if you can't drive it down the aisles in your warehouse.
So, aside from the capacity, you need to ask yourself a few other questions before choosing a forklift truck e.g. How narrow are the spaces it will be operated in? How high do I need my forks to raise from the ground? Will my forklift primarily be used indoors or outdoors?
How Do Attachments Affect Capacity?
Forklift operators sometimes have to perform material handling tasks for which a standard set of ITA forks are not suitable. For this reason, there are a near-infinite number of attachments available for forklifts. From bale or carton clamps to carpet poles, cement hoppers, crane jibs, and rotating forks, there's an attachment for all occasions.
However, if using any non-standard attachment, there is likely to be an impact on the forklift's capacity. The forklift operator needs to consider this in order to estimate the safe load capacity for the job at hand. Three factors relating to the attachment itself affect the net load capacity.
Firstly, the weight of the attachment itself. Some of these pieces of apparatus are quite heavy, and fitting an attachment weighing 1500 lbs means the forklift is essentially already carrying an equivalent load before you go to pick anything up with it.
Second, the shape of the attachment needs to be considered. If the attachment is longer than the standard forks, the load center of gravity will be positioned further away from the carriage, giving the weight of the load greater leverage to unbalance the forklift.
Finally, the movement of the forklift load whilst being moved. Some attachments either increase the forklift's effective lift height or allow for forward extension. Both of these will affect the maximum capacity load which can be safely transported due to changes in the maximum displacement of the load center.