Dock equipment basics

Seals and shelters, dock doors, vehicle restraints and leveler combine productivity with improved ergonomics and safety.

By Corinne Kator, Associate Editor -- Modern Materials Handling, 12/1/2006

Reliable loading dock equipment is vital to the smooth flow of materials in and out of a warehouse or manufacturing facility. Here, Modern offers basic descriptions of the most common types of dock equipment—from the seals, shelters and doors that protect and secure a loading dock to the vehicle restraints and dock levelers that ease the transition from dock to trailer.

Seals and shelters

Dock seals and shelters are fabric structures built on a wood or metal frame that surround the top and sides of a dock door opening.

"Both products are used to close the gap between the truck and the building," says Alice Permigiani, marketing director for Flexon (412-749-0400). They prevent outside weather from getting into the building and can help prevent theft, she says. "And they provide safety at the dock. Rain pouring in and making the dock floor slippery can be really unsafe."

Dock seals are more prevalent than dock shelters, says Permigiani, with most companies choosing a shelter only when a seal won't do the job.

A typical dock seal is made of foam mounted to a wooden back board and covered with fabric. When a trailer backs into the dock, the seal compresses against the back of the trailer, creating a tight seal.

A dock shelter consists of a wood or steel frame with heavy fabric curtains along the top and sides. A dock shelter is wider than a dock seal, and a trailer backs through shelter curtains, creating a seal along the outside and top of the trailer.

Dock seals are less expensive than dock shelters and create a tighter seal, says Tra Tramonte, director of sales for Kelley (800-558-6960). But, he says, dock seals don't last as long, they accommodate a smaller variety of trailer sizes, and they don't come in widths greater than 10 feet.

While dock shelters cost more, says Tramonte, they last longer because they don't have to withstand as much abrasion as dock seals do. Shelters are also more versatile. Because they don't have to fit snugly against the back of a trailer, says Permigiani, shelters are better for steeply sloped driveways, and they're a good choice when accommodating a variety of trailer sizes.

Dock seals and shelters are available in a variety of fabrics. Higher grade fabrics add to the durability and the cost. A dock seal costs roughly $500 to $1,000, depending on the quality of its materials. A dock shelter costs roughly $800 to $1,800.

"You can buy a dock seal that lasts two years, four years or six-plus years," says Tramonte, "depending on what you're willing to spend."

Dock Shelter - A trailer backs through the curtains of a dock shelter, creating a seal along the outside and top of the trailer.

Dock doors

Like any exterior door, a loading dock door secures a building and provides a barrier from the elements. Most dock doors are sectional overhead units similar to residential garage doors.

Dock doors need to be rugged, says John Davis, sales manager for Overhead Door Co. of Boston (781-871-3850), so they are often made of steel. Ceilings are usually high enough in loading docks, he says, that dock doors can go straight up the wall as they're opened rather than bending overhead as garage doors do.

There are a few options when it comes to doors. One is insulated doors. Davis says heavy insulation is a necessity for his customers in the Northeast.

Another option is powered doors. Because they are raised gently and evenly with every opening, powered doors often last longer than manually operated doors, says Davis. A typical 10 x 10 foot insulated door is heavy, says Walt Swietlik, customer relations manager for Rite-Hite (800-456-0600), so powered doors are often a good ergonomic choice.

Flexible doors that better withstand the impact of a lift truck are growing in popularity, says Swietlik, as are breakaway doors designed to pop out of their tracks when a lift truck hits them.

A typical dock door costs around $1,000. Impactable doors range from $1,500 to $3,000. Adding power to a door, says Swietlik, adds another $1,000 to the price.

Vehicle restraints

Vehicle restraints latch onto trailers, securing them to the loading dock. Restraints are more reliable than simple rubber wheel chocks for preventing trailers from driving or rolling away from the dock prematurely.

The most common type of vehicle restraint latches onto the trailer's rear impact guard (RIG), also known as an ICC bar. For specialized trailers without RIGs, hydraulically activated wheel restraints are available that capture the rear wheels of the trailer.

Vehicle Restraints - Vehicle restraints latch onto a trailer's rear impact guard, securing the trailer to the loading dock.

Many vehicle restraint systems include a set of communication lights. Red and green lights indicate to the driver and the dock operator when a trailer is secure. Dock seals and shelters often block the view between the dock and the trailer, so the lights are a critical component of a safe vehicle restraint system, says Mike Pilgrim of Systems Inc. (262-255-1510), which makes Poweramp, DLM and W.B. McGuire dock equipment.

Since their debut in 1980, vehicle restraints of many different designs have appeared. However, all restraints work on the same basic principle: When a restraint is triggered, an arm—or often a hook—extends to secure the RIG.

Restraints can be triggered manually or automatically. They can be integrated into a dock leveling system or installed independently. They can be mounted on the ground below the dock door, mounted on the outside wall of the building or recessed into the wall.

Active restraints, according to Pilgrim, seek out the RIG and pull it snugly toward the dock. Less sophisticated passive restraints, he says, allow a few inches of running room. With so many options, these restraints vary widely in price from about $1,000 to $7,000.

Dock levelers

Dock levelers provide a stable bridge between the building and a truck trailer. "They essentially level the building to the truck, which explains how they got their name," says John Carroll, director of sales for Serco (800-933-4834).

There are a variety of levelers to choose from, including dock boards and plates, and choices depend on such factors as frequency of use, size of load and the disparity between dock and trailer heights.

Dock boards and plates

Aluminum and steel dock plates and boards, the most basic types of levelers, must be set in place each time a trailer arrives at the dock. Dock plates accommodate only human traffic, says Matt Pirkle of Handle-It (800-236-1080), while heavier dock boards have side curbs that allow them to accommodate lift trucks.

Dock Leveler - Pit-mounted dock levelers provide a stable bridge between the building and the trailer and are best suited for frequent use and heavy loads.

Aluminum dock boards have lower capacities, can usually be moved by hand, and cost just a few hundred dollars. Steel dock boards are stronger, require lift trucks to set them into place, and range in price from $300 to $1,500. Handle-It offers steel dock boards with capacities up to 20,000 pounds that can accommodate up to 13 inches in height difference.

Edge-of-dock levelers

Moving the dock plate before and after every load can be time-consuming, so companies with higher volumes can opt for an edge-of-dock leveler. These levelers are essentially a hinged lip installed on the edge of the dock. The lip is raised as a trailer backs into the dock and then lowered onto the trailer bed. The lip can be raised manually with a lever or hydraulically at the push of a button.

Edge-of-dock levelers have a limited operating range—often only 5 inches above or below the dock height—which can result in steep inclines if trailers are substantially higher or lower than the docks. For this reason, says Carroll, edge-of-dock levelers are most common among freight companies with dedicated truck fleets and other companies with very predictable trailer heights.

A typical edge-of-dock leveler has a capacity of 25,000 pounds and costs less than $1,000.

Pit-mounted dock levelers

For frequent use and heavy loads, there are pit-mounted dock levelers. They consist of a steel deck mounted on an activation mechanism that raises and lowers the front edge of the leveler.

The activation mechanism sits in a pit about 2 feet deep, allowing the deck to sit flush with the dock floor. Manual levelers are activated with a spring mechanism and a pull chain, while automatic levelers are activated by air or hydraulics.

Like edge-of-dock levelers, pit-mounted models have a hinged lip along the front edge that extends into the trailer bed. But a pit-mounted leveler has much greater operating range, typically about 12 inches above and below the dock. That's because it can use the length of its deck in addition to the length of its lip to ease the slope of the incline between dock and trailer.

When choosing a pit-mounted dock leveler, consider price, activation method, length, width and capacity, say the experts.

"Capacity is one of the trickiest things," says Swietlik of Rite-Hite. "If a leveler has a capacity of 20,000 pounds, that doesn't necessarily mean you can take 20,000 pounds across it."

Each manufacturer calculates capacity a bit differently, says Swietlik, taking into account the size and weight of a typical load, the equipment used to move the load, frequency of use and the expectation for the life of the equipment. In other words, determining the correct capacity requires input from both the supplier and future user.

As for activation methods, says Carroll, mechanical levelers are the least expensive (about $2,500), but they require more maintenance than powered levelers, so the overall cost of ownership may be higher. And the capacity of a mechanical leveler tops out at 50,000 pounds.

Hydraulic levelers start at about $3,500 and range in capacity from 20,000 to 100,000 pounds. Automatic levelers, whether hydraulic and air-powered, are easier and faster to use, says Carroll, so they minimize downtime while improving ergonomics.

Trends in dock levelers

"Mechanical (pit-mounted) levelers have been the workhorse of the industry, but the industry is trending away from them," says Carroll.

Air-powered pit levelers are replacing mechanical ones, he says, because they're only slightly more expensive while being much easier to use and maintain.

In some applications, pit-mounted levelers themselves are beginning to be replaced by vertical-storing levelers, he says. Vertical-storing levelers are roughly the same size as pit-mounted levelers, but stand up on the dock floor when not in use, so they don't require a pit. This option is attractive for refrigerated warehouses, says Carroll, because pits can allow cold air to escape from refrigerated docks.

Another trend, says Swietlik, is toward pit-mounted levelers with safety lips that prevent lift trucks from driving off the edge of an open dock.

Dock equipment: Who makes what

Talkback

We would love your feedback!

Post a comment

» View All Talkback Threads

Related Content

• Topics
• Author

Preventing dangers at docks

07/31/2002

Making Safety a priority at the dock

06/30/2000

Better dock safety and ergonomics

05/31/2006

Product Focus on Dock equipment

06/30/2009

New Products

05/31/2001

Also by this author

• Corporate Social Responsibility: Industrial and social symbiosis

• Top 20 lift truck suppliers 

• No more heavy lifting

• Web-based tool will facilitate product recalls

• Manhattan demos hi-tech command center

»MORE

Sponsored Links

• Resource Center
• Browse Categories
• Browse Companies

Featured Company

• Motorola

  

  Motorola is a global leader in providing integrated communications solutions and embedded electronic solutions. These include: Software-enhanced wireless telephone, two-way radio and messaging products and systems, as well as networking and... more

---

Most Recent Resources

• Propelling Productivity Through the Rising Demands of Material...
• Flexible Factories Need Flexible AGVs
• Special Report: 5 Strategies for Gaining Management Approval of WMS
• New Report: Nine Telltale Signs You Should Replace Your Current WMS
• The Visible Supply Chain: Ensuring End-to-End Optimization