Mast Dimensions
Determining the type and height of the mast needed depends upon several factors.
The critical dimensions of lift truck masts that you must consider when determining clearances for maneuvering and load handling are:
- Dimension "A" - Overall Height Raised - the overall height of the highest part of the mast when the forks are raised to full height.
- Dimension "B" - Maximum Fork Height - also known as MFH - the maximum height to which the tops of the fork blades can be raised.
- Dimension "C" - Overall Height Lowered (OAHL) - or Collapsed Height of the mast - the height of the mast with the forks fully lowered.
- Dimension "D" - Free Lift Height (FL) - the height to which the forks can be raised before any part of the mast starts to raise.
The overall height of the highest part of the mast when the forks are raised to full height is Overall Height Raised (OAHR):
- If the truck is equipped with a load backrest, this will be the dimension from the ground to the top of the load backrest.
- If the truck is not equipped with a load backrest, this will be the dimension from the ground to the top of the fork carriage or to the top of the vertical back section of the forks. In the case of reach trucks, without a load backrest, the OAHR will be measured to the top of the reach (pantograph) mechanism.
Free Lift Height is the height to which the forks can be raised before any component of the mast begins to raise higher than the collapsed height of the mast. The amount of Free Lift depends upon the design of the mast.
Free Lift is needed when working in areas with restricted overhead clearances or overhead obstructions, in order to allow for the forks to be raised for load handling or stacking.
Most modern triple stage masts have Full Free Lift which means that the fork carriage will raise all the way to the top of the mast before any of the rail sections start to raise.
Two stage masts may or may not have Full Free Lift.
Non-telescopic masts consist of only one stationary rail section in which the fork carriage rides. Non-telescopic masts are full free lift masts.
- If the truck has a "full free lift mast" and is equipped with a load backrest, the Free Lift Height is the height to which the forks are raised when the top of the load backrest is at the same height as the top of the mast.
- If the truck has a "full free lift mast" and is equipped with a standard 48" high load backrest, the Free Lift Height is the OAHL of the mast minus 48".
- If the truck has a "full free lift mast" and is not equipped with a load backrest, the Free Lift Height is the height to which the forks are raised when the top of the vertical back section of the forks is at the same height as the top of the mast.
- If the truck does not have a "full free lift mast", the Free Lift Height will be in the range of "0" to perhaps 18" depending upon the design of the mast.