Contemporary dock seals come in two basic type. We will call these “butt seals” and “side seals,” although standard names for these types do not yet exist in the industry. Figure 2 shows both types. Each type has advantages and disadvantages in particular applications. There are variations within these two types. With butt seals, the rear of the truck or trailer butts against thick pads on the outside of the wall opening, squeezing the pads between the vehicle and the wall. By far the most common seal of this type is made of a spongy rubber material, covered with a wear-resistant surface.
Less commonly, a butt seal may consist of an inflatable bladder. The bladder is inflated with a small high-pressure fan. This type is more adaptable, but more expensive. Figures 3 and 4 show this type. Some docks seals may use an accordion seal made of rubberized fabric. This type is unusual. The other major type, side seals, slide along the sides
and roof of the vehicle. These consist of a more flexible rubberized material. The top seal may consist of a heavy
curtain of adjustable height that drapes over the top of the truck. Dock seals should be sheltered from precipitation.
Otherwise, they will collect water, rot the wooden structure, leak into the wall, and suffer freeze damage. If the building does not provide adequate shelter, as in Figure 1, you can buy appropriate hoods from dock seal manufacturers, or from other sources. The hood may be separate from the dock seal, or it may be an integral part of some dock seal assemblies.
The seal along the floor of the vehicle is a special problem. The floor height varies from one vehicle to another, and the height varies as the vehicle is loaded and unloaded. If the floor height remains close enough to the dock height, a simple butt seal may suffice. This can be used in combination with butt seals or side seals for the sides and top of the vehicle.
An adjustable ramp, called a “dock leveler,” is commonly installed in the floor of the loading dock. Figure 5 shows a typical unit. The dock leveler adjusts to changes in the height of the vehicle floor. Unfortunately, the space underneath the dock leveler is a large path for infiltration. Dock levelers may be equipped with side guards, as shown in Figure 5. The side guards are intended as a safety feature, and to keep things from falling into the dock leveler pit. They may substantially reduce infiltration, especially from wind. One of these days, dock leveler manufacturers will realize that these guards can easily be augmented to make them effective infiltration seals. If you get dock levelers, make sure they have this feature.
Dock levelers are made of steel, so condensation and ice tend to form on the ramp when the outside air is cold. This is dangerous. To avoid this problem, you can order insulation as an option on the dock leveler. Get this feature. It also saves a small amount of heat loss. An older method of minimizing infiltration at truck docks is to attach a short tunnel to the outside of the building. It is effective primarily against wind, rather than convective heat loss. The tunnel must fit the vehicle body closely to be effective. This requires that all vehicles have the same dimensions, and it is more difficult to back the vehicle into position properly. The availability of effective dock seals has made this method obsolete.