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Choosing the right forklift is a tricky decision for any business. The type of mast can sometimes be overlooked, leading to the purchase of equipment that isn't well suited to the required application.
Most forklift masts are of the "straight, upright" variety, although some also have the capacity to swing from side to side. Masts of either type are categorized by the number of stages, which affects both the overall lift heights reachable and the forklift's capacity to "free lift". From the most basic single-stage mast up to a quad (four-stage) high-lift variation, each type has its own distinct advantages and limitations.
Before you buy, read the following carefully to make sure you pick the mast type which best supports your overall productivity.
A single-stage upright mast also called a single mast or simplex mast is the most basic setup available on a forklift and is designed to prioritize load capacity over lifting height. The system consists of two fixed outer rails, each with a movable inner rail. The single-stage mast has one channel within, on which the inner section slides. Each inner rail is driven by its own hydraulic cylinder and, as these rails are raised, a chain drive assembly operates alongside this movement to lift the carriage and forks. The forks typically lift at twice the rate of the rail movement due to the gearing on the chain.
Simple and durable, these masts are best suited for heavy work and rugged conditions which could damage more intricate assemblies. Outdoor operations such as moving construction materials around a site or loading/unloading from trailers will usually employ a simplex mast forklift.
However, the lack of free-lift capacity (usually only 4-6") means the forks can't rise very far before the inner rails extend above the outer, increasing the overall height of the forklift and limiting utility in situations with limited overhead clearance. This is another reason the single-stage mast is best suited to outdoor or larger warehouse applications, where overhead clearance is abundant.
The two-stage mast, also called the duplex mast or full free lift mast looks very similar to simplex masts to the casual observer.
Like the simplex version, a duplex mast has one pair of outer fixed rails and another sliding inner pair. The key difference is a centrally mounted free-lift cylinder, which drives the forks to the full height of the rails (4-5' depending on model) before the movement of the inner rails is directly engaged to provide extra lift height (averaging around 14' total).
Not only does this modified assembly increase the overall lifting height of the forklift, but the ability to lift the load a significant distance without moving the mast also reduces the overall height of the forklift in relation to the elevation of the forks. This means you can lift loads closer to a ceiling without the top of the inner rails getting in the way. The two-stage lift truck is a popular choice for cross or double-stacking jobs in warehouses.
A two-stage forklift mast is also a popular option because the duplex upright mast retains similar operator visibility to the simplex mast, whereas a more complex vertical assembly can be limiting in this regard.
The three-stage upright, also called triplex mast, is often considered the most versatile forklift mast type overall. The three-stage mast contains three sets of rails, with two inner sets which can move up and down the mast channels and are driven by their own lift cylinders.
With the added benefit of a central full free lift mechanism, triple-stage mast types provide a significant increase to lift height for material handling applications where loads are taken from, or placed in, significantly elevated positions.
As well as being able to reach lift heights of over 15', 3 stage masts often also allow for the horizontal extension of the forks. This added degree of freedom makes triple-stage an excellent solution for reach trucks or any jobs where the forklift might not be able to drive as close to the picking or depositing position as desired.
The downside of the three-stage mast is that maximum lift capacity is significantly reduced as the lift heights approach maximum fork height, and even more so when the load backrest is extended away from the carriage.
The four-stage upright mast, also called quad mast, acts in a very similar manner to the three-stage version. The difference is having four sets of rails, with an extra chain drive assembly to lift the inner mast rails even further once a 3-stage extension has been reached.
The quad mast is specialized for maximum lift height and there are indeed applications where a mast must extend higher than even the triplex versions can reach. Maximum fork height for a four-stage mast can be well in excess of 20' but it's important to remember the effects of elevation on load capacity. Material handling close to the overall capacity of the forklift will still be subject to limited lifting height to ensure safe operation.
The most common use for a four-stage mast is in warehouses with high-rise shelving systems, where products/materials are arranged so that lighter items are kept on the upper levels while bulky, heavy items are stored at and transported from a lowered height.
The majority of lift trucks use one of the "straight" forklift mast types discussed above. In all of these, the forklift mast is part of a fixed assembly on the front of the vehicle.
With any straight type of mast, the whole forklift has to be maneuvered into position so the load is lined up to the forks without significant horizontal or angular offset at the forklift mast itself.
This is usually not an issue but can become problematic if you're trying to optimize storage capacity in a limited area. Wide aisles suitable for the turning circle of most forklifts are going to eat into your overall space considerably.
Swing-mast, also known as "articulated" forklifts have a significant advantage where room to maneuver is limited.
The entire forklift mast assembly can be rotated 90° from the direction the forklift is facing.
This reduces the need for turning the lift truck itself in narrow aisles, allowing an efficient balance between storage optimization and mechanical material handling or product picking.
Swing masts are even available in two-stage, three-stage, or quad variations, so why don't we use swing mast forklifts all the time? There are two reasons, of which the most pertinent is cost. A swing assembly adds significantly to the overall forklift price compared to straight forklift mast types, so the benefits to your company need to be significant to make these worthwhile. There is also some reduction in lifting capacity due to the strain on the articulation mechanism, so most swing masts aren't particularly suitable for heavy jobs.
The very first thing you need to check for any operation is whether the equipment can safely handle the loads you will be handling. There's no point whatsoever having all the freedom of movement of an articulated three-stage mast if you can hardly ever use it due to the weight of your most commonly moved items. Unless you either need to achieve significant lift heights or have limited overhead clearance, there's little need to look beyond a sturdy, simple, single-stage mast.
Assuming your material handling needs are light, and lift capacity is not a limiting factor, look at how the different types of forklift masts will work in the spaces in which you tend to operate. The Full free lift capabilities of multiple-stage masts let you make the most of areas with limited headroom, while the increased maximum fork height will help optimize usage of your whole volume in a high-ceilinged storage area. Narrow aisles? Consider swinging forklift masts.
If versatility really is key, a swinging triplex mast gives you a very impressive amount of freedom.
Weighed up against versatility (and, to a certain extent, even loading capacity), you need to consider whether the extra functionality of a complex type of mast will actually save you money over time. Not only are these more expensive to buy, but also require more costly maintenance. The purchase price and ongoing cost of any system need to be considered carefully against the bottom-line benefit.
See our parts of a forklift page for a complete guide to each part.