A dock leveler forms a ramp to bridge the distance between the dock and truck. It must be able to compensate for the up-and-down movement of the trailer during loading and unloading. A dock leveler must support extremely heavy loads, service a wide range of truck heights, and compensate for tilted trucks. A dock leveler includes a ramp and a lip. The ramp is hinged at along its rear edge, and the lip is hinged at the front of the ramp. To use a dock leveler, raise the ramp. The lip will swing out. With the lip extended, lower the ramp until the lip rests on the truck.
The two common types of dock levelers are recessed and edge-of-dock. A recessed dock leveler is installed in a pit formed in the loading platform and is generally a minimum of 6 ft long (Figure 40). An edge-of-dock dock leveler is normally installed on the face curb of the loading platform (Figure 41).
Recessed Dock Levelers
The recessed, or pit-style (Figure 42), dock leveler is the most common type of dock leveler because it has a greater operating range, load range, and life expectancy. Dock levelers are most often installed into pits that are formed into the concrete ahead of time. The pits are sized to meet the exact requirements of the dock levelers being used.
The standard range a recessed dock leveler can serve is 12 in. above and 12 in. below dock height. Special configurations of dock levelers can serve as much as 18 in. above and below, depending on ramp length and pit depth.
Recessed dock levelers are available with a spring-loaded mechanical activation system or powered with a push-button activation system. Powered, push-button models are easier to operate and are activated by either an air or hydraulic system. Although the initial cost of a mechanical dock leveler is less than a powered dock leveler, the long-term operating cost for a powered dock leveler can be lower.
Mechanical Dock Levelers
Mechanical dock levelers are suitable for most applications. Mechanical dock levelers do not require expensive electrical provisions and hookups. They will operate even during power failures.
A mechanical, spring-loaded dock leveler (Figure 43) is upwardly biased with a spring and linkage system. It is held down by a releasable holdown device. To raise the ramp, pull the release chain connected to the holdown mechanism. Then, walk 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.
A mechanical dock leveler requires routine maintenance, lubrication and adjustments for reliable operation.
Mechanical Free Fall
Mechanical safety legs prevent the ramp from falling more than 4 in. below dock level. The legs must be manually retracted to permit servicing a trailer below this level. Although safety legs do improve safety, safety can be better addressed by using hydraulic dock levelers with hydraulic free fall protection.
Full-Range Toe Guards
Full-range toe guards close off the sides of the dock leveler when the ramp is in the fully raised position. Full-range toe guards eliminate pinch points at the sides of the ramp during lowering. Full-range toe guards are standard on hydraulic and air powered dock levelers, while mechanical dock levelers include toe guards that cover the working range of the dock leveler with full-range toe guards as optional equipment.
Powered Dock Levelers
Powered units are initially more expensive, but they offer many benefits.
Powered dock levelers are easy to operate and do not require the operator to bend and pull a release chain to operate. Activation takes place through constant pressure push button controls.
Powered dock levelers are also safer than mechanical dock levelers due to the flexibility of the power source. Powered units also facilitate interlock to other loading equipment.
A push-button hydraulic dock leveler (Figure 44) is powered by a hydraulic system that raises the ramp. This design is very reliable but requires more maintenance than an air-powered design.
Air-powered dock levelers (Figure 45) incorporate the use of a low-pressure, high-volume air system to raise and lower the platform. A single push button activates the air power system to raise the leveler and extend the lip. This simple very reliable design requires only minimal maintenance.
Auto Return is a safety feature on hydraulic units that automatically returns the dock leveler to its stored position when the truck leaves. This feature is important because powered dock levelers are downward biased. The energizing of the hydraulic system causes hydraulic dock levelers to move upward.
NOTE: An air bag dock leveler moves up as the bags are inflated by the electric air pump.
The dock leveler is moved downward by its weight and the force of gravity. A powered dock leveler in its raised position lowers unless it is supported by pressure, the truck bed or another device such as a maintenance stand. If a dock leveler does not have Auto Return, when the truck drives away, the dock leveler’s ramp and lip settle on the dock leveler’s bottom support stops. This causes a hazardous slope toward the door in the floor. If a dock leveler does have Auto Return, the dock leveler automatically returns to the stored position.
The emergency ramp stop is a safety feature that allows the operator to immediately stop the ramp at any time by pressing a button on the control panel.
Hydraulic fallsafe protection prevents the dock leveler from lowering to avoid the loading vehicle rolling off the dock. A velocity fuse on the base of the hydraulic cylinder locks the cylinder and limits the ramp in place when a loading vehicle is on the ramp and the truck pulls away.
Powered dock levelers can be interlocked to other pieces of loading dock equipment such as truck restraints and overhead doors. Interlocking the loading dock equipment increases safety. When interlocked to a vehicle restraint, the dock leveler can operate only if the trailer is restrained. If the trailer cannot be restrained, an override switch allows independent operation.
Full-Range Toe Guards
Full-range toe guards close off the sides of dock levelers when the ramp is in the fully raised position. Full-range toe guards eliminate pinch points at the sides of the ramp during lowering.
The Edge-of-Dock (EOD) levelers (Figure 46) is a low-cost alternative with a short ramp. An EOD is mounted to the face of the dock and secured to a curb channel embedded in the concrete. They are available in standard load capacities of up to 35,000 lb.
Due to its short ramp, the EOD is restricted to a narrow service range of 2 in. above or below the dock. It is suitable only for applications where there is little variation in bed height and where pallet truck under-clearance is sufficient (Figure 47).
NOTE: Using manual hand pallet carts with even a 2 in. difference in height between the dock and trailer can be difficult. If using an EOD with a hand cart, make sure the dock and trailer are at the same height.
EODs are commonly 72 in. and 66 in. wide. Width selection is primarily based on the loading method. The 72 in. wide EODs offer the most flexibility, but the 66 in. wide EOD is the most popular choice.
Two types of EOD activation systems are available: mechanical and hydraulic.
To activate a mechanical EOD, the operator pulls the lip and ramp into the raised position. Then, the lip is lowered down onto the truck bed. Once the truck pulls away, the EOD retracts into the stored position.
To activate a hydraulic EOD, the operator presses the button to raise the lip. Once the EOD is fully extended, the operator releases the button and the dock leveler lowers to rest on the trailer bed. Once the truck pulls away, the EOD retracts into the stored position.
Specify The Correct Dock Leveler
Because a recessed dock leveler has a wider range of operation, it is the best choice to accommodate a wide range of bed heights. Only choose the EOD dock leveler if the facility operates within the EODs narrow range of applications.
Dock levelers have long lives and contribute significantly to facility efficiency. It is important to provide accurate specifications for the dock levelers, including;
- Lip projection
- Load capacity
- Activation system
- Environmental capability
The length of the dock leveler is an important determinant of the dock leveler slope. This slope must be less than the maximum grade capability of the loading equipment. The length of the dock leveler is based on the maximum height difference between the loading platform and the truck beds.
Dock levelers are available in lengths from 5 to 12 ft. The most popular length is 8 ft., which is suitable for most applications.
The normal maximum grade operation for a manual pallet truck is 7%. For an electric pallet truck, normal maximum grade is 10%. For an internal combustion forklift, normal maximum grade is 15%. Consult the equipment manufacturer for maximum grade recommendations.
NOTE: These normal maximum recommendations may vary depending on equipment specifications for design changes.
The lengths shown in Table 7 are the minimum dock leveler lengths required to keep the dock leveler ramp slope within the capability of the loading equipment.
For height differences or loading equipment not shown in the figures, the minimum dock leveler length is the height difference divided by the equipment’s maximum grade capability.
Forklifts and pallet trucks must have sufficient ground clearance to move freely and safely over a dock leveler (see Figure 49 and Figure 50). It is especially important to check ground clearances of pallet jacks on EOD dock levelers (Figure 46). Pallet jack clearance is less of a concern on recessed levelers. If there are concerns about clearances, consult with the loading equipment supplier.
Dock levelers are available in standard widths of 6 ft, 6-1/2 ft and 7 ft. The most common width is 6 ft, which suits most applications. However, 6-1/2 ft and 7 ft wide dock levelers are becoming more popular for wider trailers and side-by-side pallet arrangements (see Figure 51, Figure 52 and Figure 53).
7 ft wide dock levelers provide the best access for below-dock loading and end-loading side-by-side pallets. The end of the dock leveler lip should taper from 7 ft to 6.5 ft wide in order to service narrow trailers. However, it is not always necessary to taper the lip due to the standard trailer width increasing to 96 in. Maintaining the full width allows for the greatest maneuvering space and eliminates the drop-off area created by the taper.
The dock leveler lip must extend at least 4 in. into the truck per ANSI MH30.1 (Figure 54). A standard lip is 16 in., which projects 12 in. in front of the dock bumpers. Longer lips may be needed to accommodate the special rear step and rear door configurations on some trailers. The step of a refrigerated trailer may require a lip projection that is 14 in. or longer past the bumpers.
The load capacity of the dock leveler depends on the gross vehicle weight (GVW) of the forklift. For light to normal usage, the minimum required dock leveler load capacity equals the forklift GVW x 2.5. For normal to heavy usage, use a multiplier of 3 to 4.
GVW = Weight of forklift + Weight of maximum load
Load Capacity = GVW x 2.5
Example: 12,000 lb forklift gross weight + 6,000 lb gross load = 18,000 lb x 2.5 = 45,000 lb load capacity
If the exact capacity is not available, use the next higher capacity. Using a higher-than-required load capacity will extend the life of the dock leveler.
The following conditions affect load capacity:
- Each dock position serves eight trucks or more each day
- Forklifts do not drive straight onto the dock leveler
- Forklifts with three wheels are used
- Forklift speeds exceed 4 mph
- Forklifts are equipped with front end attachments or fork side shifters
Push button activation is the most ergonomic and safest type of dock leveler activation system. Manual or spring counterbalance activation should be used only when electrical power is not available. Push button-operated dock levelers may be less expensive over the long term as they require less service.
On inside/outside docks at temperature-controlled facilities, use perimeter weather seals to help prevent outside air from entering the building.
At refrigerated facilities, the underside of the dock leveler ramp should be insulated. Condensation on the underside of the ramp causes corrosion and structural problems. Expanded foam insulation helps prevent the warmer outside air from condensing on the underside of the ramp. Insulation also saves energy by minimizing the loss of refrigerated air.
Consider adding optional features to increase the effectiveness of the installation.
Increase Lip Length
Dock levelers are normally supplied with a 16 in. lip plate that will suite the majority of applications. Lip length can be increased to 18 in. to 20 in. projecting out further from the dock face. Increased lip projection is necessary to deal with bumper projections of more than 4 in., substantial dock and truck bed height differences, and setback internal truck beds–typical with refrigerated trucks and trailers.
When loading or unloading a truck with a setback internal truck bed such as trailer with swing doors, the lip must be sized to ensure lip contact with the internal bed. If the lip does not project over the internal setback and therefore rests on the step below the internal truck bed, the material handling equipment will strike the edge of the step up to the bed on every entry, making product transfer both rough and inefficient.
Neoprene strips attach along the sides and/or rear of the deck assembly to better control the climate. The preferred weatherseal to protect against rodent entry is brush seal.
The zinc metalized spray process produces the optimal finish. Each dock leveler component is galvanized before assembly to provide complete protection. Galvanizing is commonly used in facilities that handle corrosive materials or are near harsh environments such as salt water.
Benefits of Hydraulic and Air Bag Dock Levelers Over Mechanical Dock Levelers
Hydraulic dock levelers have lower lifetime ownership costs. Including maintenance, the estimated 10-year ownership costs for a dock leveler are $3200 for a mechanical dock leveler, and $1000 for a hydraulic or air bag dock leveler.
Air bag dock levelers are ergonomically correct, reducing the potential of employee injuries, and easier to use with their push button configuration.
Air bag dock levelers have a “stump-out” safety feature where fall safe legs impede below-dock and dock-level situations. The safety legs come to rest on the floor while the dock leveler is being used.
Hydraulic and air bag dock levelers log fewer hours and therefore have longer working lives. Because mechanical dock levelers are upward biased and the springs and holdown are in the stressed condition, the moving parts wear over time. However, hydraulic and air bag dock levelers are working only when they are being used and while the button is being pressed.
Hydraulic dock levelers increase safety on and around the loading dock. There is improved fall safe protection due to the velocity fuse fall safe over mechanical legs. The fuse will stop within 3 in. of drop.
Hydraulic dock levelers can accommodate higher load capacities. Mechanical and air bag dock levelers can handle a maximum rating of 55,000 lb, while hydraulic dock levelers can be used for load capacities of up to 100,000 lb.
Specifying The Elevating Dock
Hydraulic elevating docks lower forklifts from the loading dock down to the ground. They allow forklifts to enter trucks with very low or high bed heights that are outside the range of dock levelers.
Elevating docks are typically a scissor-lift design. A 6 ft vertical travel is common for a standard dock. Lips on the dock allow movement of the forklift to the dock and to the Truck (Figure 57). Elevating docks also make it possible to load from the ground (Figure 58).
Elevating docks are rated for maximum gross vehicle weight (GVW); 10 tons is the maximum capacity for standard elevating dock.
The most common installed elevating dock has a 6 ft wide, 8 ft long table with a capacity of 4500 lb.
The most common installed elevating dock using a rider forklift has a 6 ft wide, 10 ft long table with a capacity of 5 tons.