A dock lift is a scissor lift style materials handling product designed to load and off load trucks from the truck bed to the grade level. Dock lifts can be manufactured to suit a recessed concrete pit or installed on a pre-poured concrete slab.
This link illustrates a standard recessed pit style dock lift; View PDF
This link illustrates a standard surface/slab installed dock lift; View PDF
As standard a hinged 60” wide x 18” long one piece bridge plate is located on the truck end of the dock lift platform. The hinged bridge plate has a chain attached to one side of the bridge plate, the opposite end of the chain is connected to guard rail that is installed on the dock lift platform.
The bridge plate is stored pulled back into the slightly back from center vertical position when not in use. Standing on the dock lift the dock attendant raises the dock lift deck until the platform is at the same height as the truck bed and then manually lowers the hinged bridge plate downward creating a transition plate between the dock lift platform and the truck bed.
Depending upon the width of the dock lift and the distance from the dock lift to the truck there is a significant size range of hinged dock lift bridge plates available. In addition dock lifts can be equipped with hinged bridge plate assemblies on any of the platform sides and end to best accommodate the traffic flow.
Standard bridge plates are available in a one piece full width construction or the most common style ordered is a 2 piece, split width design. A 2 piece, split width bridge plate design offers 2 advantages. Due to the reduced weight the individual sections of bridge plate are physically easier to raise and lower by the dock attendant with a truck in position and the 2 piece design allows for some lateral, left to right compensation for a slightly off level truck bed.
Standard hinged bridge plates are manufactured from steel and vary in length from 18” to 42” long and vary in widths from 48” to 96” wide, one piece or two pieces. Depending upon the size and the physical mass of the hinged bridge plates they can also be equipped with a hinged lift assist spring to reduce the operating forces to position the hinged bridge plate.
As the hinged bridge plate lowers from the somewhat vertical position an expansion spring connected within the lowering chain starts to stretch. With the bridge plate in the fully lowered position and the expansion spring stretched it makes it very easy for the operator to pull up and return the bridge plate to the vertical position when the loading is completed.
If the circumstances warrant specialty light weight bridge plates manufactured from aluminum are also available. Due to the decreased weight the aluminum bridge plates significantly reduce the amount of manual labor required to raise and lower the bridge plates onto the truck bed. The increased cost for aluminum bridge plates is significant.
In an application where a large hinged bridge plate assembly or ergonomic requirements call for little to no physical effort to position a bridge plate fully hydraulic hinged bridge plate arrangements are available. The fully hydraulic bridge plate works strictly from constant pressure hand held push button controls assuring the operator is under full control of the hinged bridge assembly at all times. There are different configurations of hydraulic bridge plates available.
Page 6 and page 7 of this link show examples of one piece, 2 piece and hydraulic operated hinged bridge plates. View PDF