The recessed dockleveler is the most common type and has the greater operating range above and below dock. It also has the greater load range and longer life expectancy. It is available in ramp lengths of 1.8 m to 3.6 m.
Recessed docklevelers are available in powered, push-button operation or spring- loaded mechanical operation. Powered push-button models are easier to operate.
Powered push-button docklevelers are activated by either an air or hydraulic system. The low pressure air operated system (Fig. 30) has a very simple design: an air bag connected to a fan lifts the ramp. The weight of the ramp then extends the lip onto the truck bed. The design is very reliable and requires only minimal maintenance.
Push-button hydraulic docklevelers (Fig. 31) are powered by a hydraulic system that raises the ramp. They are very reliable but require more maintenance than air powered designs because of their more complicated components, fluid circuits and electrical circuits.
Mechanical, spring loaded docklevelers (Fig. 32) are upwardly biased with a spring and linkage system and are held down by a releasable ratchet device. To raise the ramp, a dock worker pulls a release chain connected to the ratchet mechanism. The worker then walks out on the ramp to force it down onto the truck bed. Once on the truck bed, the ratchet mechanism re-engages to prevent the ramp from rising again. Mechanical docklevelers require regular maintenance and adjustments for reliable operation.
Depending on ramp length, recessed docklevelers can serve trailers as much as 45 cm above and below the dock. A common range is 30 cm above and 25 cm below dock height. They are available in capacities up to 40 tons.