Suitable for long bodies, cable systems position the tarp on a series of bows. A cable below the top rail slides the tarp and bows back and forth along the top of the body.
Automatic arm systems let drivers cover the load without getting out of the vehicle. These systems use spring-loaded pivots to pull the tarp over the load. Photos: Pulltarps
By: Glenn Ray
Covering up a load has multiple environmental and safety benefits: It satisfies federal, state, and local laws designed to keep hazardous material from falling onto highways; improves fuel mileage by reducing wind resistance; and prevents debris from hitting the windshields of other vehicles.
Because no single tarp works best for all potential applications, knowing how tarping systems work will help you specify the most versatile solution for your operation.THREE TYPES OF DEPLOYMENT
Pull tarps have few moving parts and don't require operators to climb on the vehicle. Because they're deployed over the load from the ground, they're not recommended for covering light, powdery materials or construction debris such as broken concrete, wood studs, and rebar.
These tarps can be made from a variety of specialty fabrics and ordered with side flaps to keep loads dry or to hold heat in for asphalt applications. Suitable for dump trucks and short trailers, they've available in manual or automatic arm configurations.
Customers can specify a manual system in which the operator pulls a rope attached to the arm set from the back of the vehicle or releases a locking mechanism from a hand crank and controls deployment by slipping a clutch.
As the term implies, automatic systems retract and extend the tarp using an electric, air, or hydraulic motor. They work well for covering almost any type of material and are more suitable than manual systems for longer applications.
Cable bow systems consist of a tarp covering on a series of bows that slide back and forth along the top of the body. The bows are attached to a single or dual cable, just below the top rail, that drives the system. They use two cables, one on each side of the body. This design isn't as reliable as the newer single-cable type, in which the cable runs continuously down one side to avoid misalignment and jamming of the bows.
Electrically or manually driven, cable systems are appropriate for longer trailers, belly dumps, and dump trucks where there is space at the front to retract the system out of harm's way when loading.
Tarps for cable systems are made of mesh fabric or waterproof vinyl. Most are confirmed to cover the top opening, but they can be made to cover the entire top rail and continue over the side of the trailer. A mesh tarp covering the top opening is satisfactory for hauling sand, soil, and aggregate that doesn't have to be kept dry. A vinyl tarp with full coverage over the side is best for fine materials or holding heat in asphalt.
Side-to-side or roll tarps are used when sealing the load is the primary concerin, but limit loading to one side of the vehicle. These systems consist of a vinyl tarp attached the entire length of one side of the body. The tarp is rolled on a pipe that runs the length of the body.
Although most of these systems are manual, electric versions are available. On longer applications, such as trailers, bows or hoops must be added to the trailer opening to support the fabric when the tarp is deploted. THREE FABRIC CHOICES
Choosing the right fabric for the application is as important as choosing the right tarping system. For most tarping applications there are three types of fabrics: woven, mesh, and vinyl.
Woven fabrics include materials from canvas to the same synthetic fabric used in automobile air bags. These are good, general-purpose materials and can be found in specialty types for special uses.
Mesh fabrics are applicable where waterproofing is not required and the material being hauled is coarser than the mesh openings. The most popular mesh fabric is a heavy-duty vinyl-coated polyester weave that resists ripping. For severe service application, such as waste hauling, thick open-weave polypropylene mesh is used. Its large openings make it unsuitable for sand and soil.
Vinyl types are generally a polyester woven base fabric (scrim) coated with polyvinyl chloride (PVC). The thickness of these waterproof fabrics is measured in weight per square yard. The most common weight, 18 ounces, is good for most applications where waterproofing or heat resistance is required.
Vinyl fabrics made for covering asphalt have an additional coating of urethane to increase heat resistance and reduce the tendency of asphalt to stick to the tarp.MEASURING FOR SUCCESS
Bodies and trailer configurations vary greatly, but most truck dealers and body manufacturers can supply any system you specify.
If outfitting an existing vehicle, measure the dimensions of the body, particularly the inside and outside width, overall length, and cab shield configurations. The body width at the system mounting location and the rear hinge configuration are also factors. Having the dimensions ready will ensure that you get an accurate quote when shopping and save you time when ordering.
— Glenn Ray is director of marketing and product development for Pulltarps Manufacturing, El Cajon, Calif.