When a dock leveler is activated the deck assembly raises and the hinged lip extends. The deck assembly with the extended lip then lowers until the lip assembly makes contact with the truck bed. The dock leveler is now in the working position and the truck can be loaded or unloaded.
When the lift truck drives across the dock leveler platform onto the truck bed the weight of the lift truck pushes the truck suspension down, when the lift truck drives back off the truck bed the trucks suspension pushes the truck bed up. This regular up and down movement of the truck bed during loading is referred to as dock leveler float. Hydraulic and air powered dock levelers are downward biased, the up and down truck movement during loading has little effect on the operation of the dock leveler. Link to hydraulic dock leveler brochure https://www.pentalift.com/wp-content/uploads/2021/04/Hydraulic-Dock-Leveler-Brochure.pdf Link to pneumatic dock leveler brochure https://www.pentalift.com/wp-content/uploads/2021/04/Air-Dock-Brochure.pdf
Mechanical dock levelers are upward biased and are equipped with a hold down mechanism. One purspose of the hold down mechanism is keeping the dock leveler down when in the stored/closed position.
With a truck in position the dock attendant pulls the dock leveler’s release chain, the deck assembly raises and the hinged lip extends and locks. The dock attendant “walks” the deck assembly down until the lip makes contact with the truck bed. The hold down mechanism holds the dock leveler deck assembly and extended lip tight to the truck bed during loading. Link to mechanical dock leveler brochure https://www.pentalift.com/wp-content/uploads/2021/04/Mechanical-Dock-Brochure.pdf
The hold down assembly is designed to accommodate dock leveler float, the most common design uses a spring within the hold down mechanism. When the lift truck drives back off the truck bed the trucks suspension pushes the locked dock leveler lip assembly upward. The hold down assembly spring accommodates for these upward forces while maintaining positive lip contact with the truck bed. While the hydraulic and air powered levelers naturally “float” with the back of the truck bed. The mechanical dock leveler hold down is continually working to hold the dock leveler in position at the float occurs. The hold down does this reliably but it is a wearable component that requires regular maintenance.
The amount of float varies depending on numerous factors including but not limited to trailer / truck design, load including the weight of the fork lift and the load it is carrying. The majority of trucks serviced at the loading dock area are equipped with an air ride suspension. To minimize the amount of upward and downward dock leveler float the truck operator should always release the air from the air ride suspension before the dock leveler is cycled into the working position.  Failure to remove the air results in substantially higher float travel. This is not desirable.
For additional information on any Pentalift product please contact the Pentalift Sales Department.