BioCycle April 2007, Vol. 48, No. 4, p. 20
From moving sawdust to moving biosolids, live bottom trailers offer flexibility in handling a wide variety of organic materials.
Craig Coker

EFFICIENT materials handling is one of the most important influences on costs – and profitability – in the organics recycling and composting industries. Whether moving feedstocks from generators to a composting facility or moving products to end users, hauling by tractor trailer is the most widely used method to optimize that aspect of materials handling. Live bottom trailers offer a unique combination of efficient materials transport and efficient materials handling, with an added advantage of being suitable for access where overhead clearances are limited.
This fourth article in BioCycle’s What’s New series looks at live bottom trailers, both belt floor and live floor. Trailer makes, models and features don’t change that frequently (relative to other types of equipment used in composting), and many share similar features and characteristics.
There are four main types of trailers used in the composting industry to move both wastes and products. Dump trailers are widely used and are available in either end dump or side dump configurations. Conventional box trailers are used for moving palletized product that can be off loaded with a skid steer loader, but if used for hauling bulk materials, some sort of unloading system like a hydraulic dumper is needed. Hopper-bottom trailers are available, but rarely used; these are better suited to denser, drier materials and require an underground pit to discharge into. Live bottom trailers are characterized by the method of material movement out of the trailer; they are either conveyor belt or slatted, live floor trailers. Box trailers equipped with an interior hydraulic ram (“push out” trailers) are often used to move solid waste.
Live bottom trailers featuring conveyor belt systems are either continuous or segmented belts with either direct-drive or chain-drive systems. Live bottom trailers featuring slatted, live floors are sometimes referred to as “walking floor” trailers (although “walking floor” is a patented trade name, it is often used to describe these types of trailers). The obvious advantage of a live bottom trailer is that the contents discharge out of the back of the trailer without having to lift the trailer into the air (either by a trailer-mounted hydraulic telescoping pole or by a separate whole trailer dumper), which allows the trailer to access areas for materials unloading where overhead constraints would make an end dump trailer unusable (i.e. delivering ground woody bulking agent inside a composting facility building), or where ground level conditions might cause an end dump trailer to tip over.
Conveyor belt live bottom trailers have a conveyor belt in the floor of the trailer that moves the trailer’s contents to the rear and out a discharge door. Like most live bottom trailers, they are loaded from the top. Conveyor widths vary from 25′ to 63′, although most manufacturers limit conveyor width to 48′. Both continuous belt and segmented belt options are available. “The Trinity Eagle Bridge chain and flap belt floor assembly is basically a conveyor consisting of overlapping flaps made of tough, flexible pieces of conveyor belt attached at the leading edge to steel pintle chains,” says John Christofferson, Sales Manager for Trinity Trailer Manufacturing (Boise, Idaho). “Usually there are two chains separated by steel or aluminum cross bars. This chain assembly is stretched over sprockets in the front and rear of the trailer. The chain assembly rides on a floor of plastic attached to the trailer floor. This product rides on the flaps/chain assembly. A hydraulic motor assisted by an electric motor, PTO, or gas engine unload system supplies the power to move and unload the product.”
The side walls of the trailer taper in to meet the edges of the belt, where a tight seal is possible when hauling wetter materials. The trailer walls can be coated with high or ultra high molecular weight polyethylene (HMW or UHMW PE) that greatly reduces the friction between the load and the trailer walls and facilitates rapid product unloading. Conveyors are driven by hydraulic motors linked to the truck’s power take off (PTO) system. These drive motors have high gear ratios (30:1) to maximize torque (greater than 8,000 foot-lbs). Trailer bodies are predominantly aluminum or stainless steel.
Live floor trailers use a full width series of interlocking, sliding slats (parallel to the long axis of the trailer) powered by either a PTO-driven hydraulic pump or by an electric hydraulic power unit. These hydraulic power units move subframe cross drives (these drives are perpendicular to the long axis of the trailer) which are bolted to the floor slats in an “every third slat” configuration. In other words, the hydraulics move different slat groups towards the front of the trailer (a slat group is every third slat moving as a unit, or group) sequentially (the load doesn’t move while each slat group is moved forward). Then all the slat groups move to the rear of the trailer simultaneously, moving the entire load 10′ toward the discharge door and out of the trailer, then the process repeats itself. The slats themselves are aluminum and come in different thicknesses, depending on the application (for example a live floor hauling MSW might be 1/4′ thick slats while one hauling haylage might be 1/8′ thick). One advantage of this type of live bottom trailer over a belt-type trailer is that this system can also be used to unload palletized bagged products.
MATERIALS HANDLING ISSUES
Main issues associated with the materials handling aspects of a live bottom trailer are: ability to handle materials of differing moisture contents, bulk densities, and cohesiveness; sealing against water leakage from wetter materials; load bridging (or tunneling) tendencies; unloading speed; and chemical and abrasive corrosion resistance.
Different materials – Either type of trailer can move the types of materials found in the composting industry. Belt floor trailers are somewhat better than live floor trailers for moving wetter materials. Continuous belt systems are somewhat easier to keep clean between different loads than segmented belt systems. “We offer a spring loaded scraper bar on our continuous belt trailers so you can get a very good clean out of product,” says Dean Badinger, Product Sales Manager for Trail King (Fargo, North Dakota). Christofferson notes that heavier, more dense products are hauled in shorter length and lower height trailers (9’7″) with up to four axles. Lighter bulkier products are hauled in longer or higher (14′ where legal) trailers.
Water leakage seals – Both types can be equipped with rubber watertight seals on the rear discharge door, but the very operational nature of live bottom trailers can make it difficult to guarantee water tightness in the floor systems. Live floor trailers (equipped with either Keith or Hallco Walking Floors) can be outfitted with a full pan under the floor to contain water and moisture. Trail King offers the “Five Star” Live Bottom Agricultural trailer with a continuous belt system; the belt is lipped and flashing between the belt and the side sloped walls minimizes water infiltration into the internal workings of the floor below the belt. Christofferson notes that the Trinity Eagle Bridge was designed to haul any feedstock, including wet and sticky feed. The design includes sloped walls, a solid stainless steel body, slick plastic side liner, and conveyor flaps with gripping properties. “Trinity Eagle Bridge is not designed to haul liquids, but if the fluid is suspended in a feedstock or similar product, chances are we can haul it,” he says. “The plastic side liners are molded over the solid steel bodies and welded to the plastic floor liners, enhancing our leak resistant design. Optional drip pans/tanks, front and rear wet seals, and slide up doors are available to assist in retaining moisture.”
Load bridging – Bridging (also called tunneling, ratholing, or channeling) occurs when a bulk solid has, within the constraints of the trailer, gained enough strength to support itself where that strength exceeds the frictional force of the moving floor. Bridging is a greater problem with wetter materials and in narrower (less than 32′ wide) belt floors, but can be minimized by applying HMW or UHMW PE liners on the interior of the trailer walls. Smaller particle sizes can greatly exacerbate the bridging tendency of a high moisture load. Bridging is rarely an issue with live floors as the entire width of the trailer moves. Badinger noted that Trail King offers belt widths up to 63′ in their Hi-Lite Live Bottom trailers and 54′ in their Five Star trailers, which he says are very effective at unloading material like haylage, which has a high bridging potential.
Unloading speeds – Generally speaking, belt floors unload product at a faster rate than live floors. Belt floor trailers can unload in four to five minutes, compared with 10 to 15 minutes for a live floor. A video on the Trinity Trailers website shows a 42 cubic yard load of compost unloaded from a belt floor truck in one minute, 45 seconds. For unloading systems driven by the truck’s PTO hydraulic system, unloading speeds are controlled by the truck engine RPMs. Trail King offers a rear-mounted flow control valve that modifies the belt speed at constant engine RPMs.
Corrosion resistance – As some trailers are available in stainless steel, chemical corrosion is not an issue with them. In the moving parts beneath a live bottom trailer, use of powder coated chains, painted sprockets and active chain oiler systems help resist corrosion and prolong life. Keith Manufacturing Co. (makers of Keith Walking Floor™ Systems) uses chromate coating on aluminum frame parts to minimize corrosion. Trail King offers a spray-on plastic liner (like the bed liners available for pick-up trucks but without the grittiness) that offers both chemical and abrasion resistance. Abrasive corrosion in the trailer body is usually controlled by use of plastic liner panels. These liner panels, like Quicksilver™ Dump Liners, are UHMW PE plastic panels that protect the trailer walls as well as greatly reduce the frictional resistance of the load being moved off truck. “Our carbon steel trailers have an epoxy coating under the plastics liners as a resistant to rust and corrosion,” notes Christofferson. “Our Stainless Steel construction is the most effective way to combat corrosion, allow long trailer life and retain top resale values.”
TRUCKING ISSUES
The main issues to consider from a trucking perspective are: how the trailer deals with uneven terrain; payloads and vehicle gross weights; trailer sizes and clearances; and maintenance costs.
Uneven terrain – Western’s trailers are built with a full steel frame like a center frame flat bed which allows flexibility both up-and-down as well as side-to-side. “We have customers backing 90 degrees into a barn through a mud hole to unload feed into a feed bin,” says Dan Taylor, Sales Manager of Western Trailer. “Our steel frame allows the trailer to negotiate that type of terrain without overturning.” Trail King uses a welded center I-beam in its Hi-Lite trailer and a box system (rail and post frame) on its Five-Star model. “Both of our trailers can withstand a 24′ torsional twist test,” notes Badinger. Trinity Trailers’ lightweight “Eagle Bridge” frame is built of steel, provides up to 36 degrees of longitudinal twist without distortion and is designed for several thousand full oscillations.
Payloads – The actual payload, or load carrying capacity of a trailer is obviously dependent on the bulk density of the material being hauled. Often, the legal weight limit on over the road tractor trailers (80,000 lbs in most states, 105,500 lbs in several western states) constrains the size of the load below the maximum volumetric capacity of the trailer. Taylor points out that Western’s 48-foot long, 8.5-ft. wide, 13.5-ft. high trailers have an empty volume of 120.4 cubic yards in their live floor trailers and 114 cy in their belt floor trailers. Trailer empty weights vary proportional to trailer size. Trail King’s Five-Star series comes in capacities ranging from 38 cy (40 ft. long by 9.5 ft. high by 8 ft wide) to 104 cy (52 ft. long by 12.5 ft. high by 8.5 ft wide).
Sizes and clearances – All trailers are either 96″ or 102″ wide, lengths can vary from 30 feet to 45-feet-plus, and heights are usually 13′ 6′. Some belt floor trailers can have low walls (~4′ high), but wall extensions are available.
Maintenance costs – Maintenance requirements outside the traditional tire and brake needs of any vehicular equipment are to keep moving parts greased or oiled, keep drive chains tight, and, in the case of live floors, turn the floors periodically (“turning” a live floor means swapping the floor slats around front-to-back, as they wear more on the back side near the discharge door). The life of a chain drive system and belt in a belt floor trailer obviously depends on the types of loads carried, notes Badinger, but he estimates most owners would get five to seven years out of a system, then would have to pay $7,000 to $10,000 to replace the chain and belt. “It is also a huge price difference replacing or repairing a solid conveyor belt system vs. our [Trinity Trailers] economical segmented flap system,” notes Christofferson. Over a five-year period, trailer owners can expect to spend $5,000 to $7,000 in routine maintenance (add another $2,500 to $3,000 to “turn” a floor, or $10,000 to $12,000 to replace it completely).
Trailer wall types and materials of construction – Trailer walls are made of aluminum, steel, or stainless steel, although one European manufacturer offers a trailer with walls made of composite fiber-reinforced resins. Walls can be “sheet-and-post” construction (sheets of aluminum riveted to aluminum posts every 16″), or can be smooth side walls that can be painted with company advertising. J&J Truck Bodies (Somerset, PA) makes their smooth sided live bottom trailers with multiple interlocking extrusions. Titan Trailers (Ontario, Canada) offers a “Thinwall” trailer. The Thinwall panel is a hollow core extrusion that achieves high strength with light weight similar to the way that corrugation turns paper into a high strength cardboard. The inner wall is thicker than the outer wall to absorb load impacts and to prevent interior damage from penetrating to the outside. The aluminum web between the walls is integral to the extrusion, with no mechanical joining.
Unloading system drive mechanisms – Belt floor trailers are operated by a chain driven system powered by a hydrostatic drive for maximum speed variability. Chains can be either roller chains or pintle chains. The drives are, in turn, powered by the PTO hydraulic system of the truck. Several manufacturers offer both independent gasoline- and electric-drive motors for floor unloading systems, in addition to PTO drives. Trail King uses a dual direct drive system on their trailers when the floor widths exceed 48″. “We decided to go with a dual drive system so each drive has a smaller gearbox and motor,” notes Badinger. “Otherwise, the drive motors would stick out past the side of the trailer.”
Suspensions – Suspensions are the link between the trailer chassis, the axles and the trailer body, and, as such, have a more important role than simply ride comfort. Also important are the articulation of a suspension (i.e. the amount of “flexing” it can withstand), durability and longevity, and maintenance costs. Many live bottom trailers (e.g. Trail King) come with standard three leaf spring suspensions; others (e.g. Peterson Blower trailers) come with air ride suspensions. Spring suspensions are like those found in passenger cars; a series of metal “leafs” that form a spring to absorb road vibrations to keep the load and vehicle from bouncing around. As they are made of metal, they are not as flexible as air suspensions. Air suspensions use air filled rubber bags (filled by the same air compressor that actuates air brakes on a truck) and provide excellent on-highway ride conditions.
The nature of organic materials recycling and product distribution requires a transport system that maximizes flexibility and efficiencies while keeping maintenance costs reasonable. Both belt floor and live floor trailers are now available in a wide variety of capacities and are suitable for hauling different materials into a composting facility and different end products to market.
Craig Coker is a Principal in the firm of Coker Composting & Consulting in Roanoke, Virginia, who specializes in providing technical support to the composting industry in the areas of planning, permitting, design, construction, operations and compost sales and marketing.
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Blower Trailers
MANY have seen blower trucks spreading compost or mulch blankets or building compost berms or filter socks. This blower truck technology is also available in trailer size configurations. Two manufacturers of blower trailers are Peterson (Eugene, Oregon) and Western Trailers/Express Blower (Boise, Idaho/Eugene, Oregon).
These blower trailers look like conventional box trailers but they have both a live floor system for moving product (either compost or mulch) and a hydrostatic blower. Hydrostatic drives are a very cost-effective way to get fully variable speed drive performance that maintains precise speed under varying loads and allow variable speed control from zero to maximum.
The main difference between the two types of blower trailers is in the moving floor system. Peterson uses a Hallco TopSeal™ live floor, while Western/Express Blower uses a 40″ wide conveyor belt floor system. The Peterson trailers have the blower feed system in the front of the trailer, as opposed to the rear of the trailer with the Western/Express Blower trailers. Both manufacturers offer trailers with 70 cy payload capacity (depending on load bulk density) and Peterson offers a unit with 90 cy capacity.
Side Dump Trailers
MOST dump trailers operate like dump trucks; the movable dump body rises up from front to rear, and the load slides out of the slanted body onto the ground. With a dump trailer, the front of the trailer rises 25-30 feet in the air (fully extended). This can create significant stresses on the trailer chassis if the trailer is parked on uneven terrain, and tip over is often a problem.
Side dump trailers were developed to overcome that potential limitation to end dump trailers. A side dump consists of a trailer equipped with hydraulic rams which tilt the dump body onto its side, spilling the material to either the right or left side of the trailer. These types of dumping trailers can be used to stockpile the material or they can be unloaded while the truck is moving, creating windrows. Unloading times are on the order of 10 to 12 seconds. Key advantages of the side dump is that it allows rapid unloading and can tolerate somewhat more uneven terrain. Side dumps are not immune to tip over; if dumping is halted prematurely, the weight imbalance might pull the trailer over on the dumping side (depending on the nature of the load). It is recommended that once the dumping procedure is started it should be completed.
SmithCo (Le Mars, Iowa) is one of the larger manufacturers of side dump trailers in the U.S. Their side dumping technology is available on a wide variety of truck chassis, ranging from small dump trucks (7.4 cy capacity) to 47-1/2 foot long side dump trailers with a capacity of 40 cy. Their SHV line of trailers is specifically designed for lower density, higher moisture payloads like sludges. The SHV series has a tare weight of 14,000 lbs. and a waterfull capacity of 40 cy. Because there is no end tailgate on a side dump trailer, they are watertight (unlike a live bottom trailer) and can carry very wet materials.
Because the tub walls of a side dump are structural, SmithCo uses AR400 steel to make the tubs. Protection from corrosion is available with either an optional spray in polyurethane paint or a spray in UMHW liner. Stainless steel is not an option for corrosion protection. “We tried stainless steel many years ago,” explains Rick Lawrence, Sales Manager of SmithCo. “Stainless is a mild steel. The live bottom trailers can use it as a liner, but because the tub of a side dump trailer is structural, it’s too mild a steel for use in side dumps.”
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Live Bottom Trailer Directory
E.D. Etnyre & Co.
1333 S. Daysville Rd.
Oregon, IL 61061
(800) 995-2116
www.etnyre.com
Hallco Manufacturing Co.
(slatted floors only)
P.O. Box 505
Tillamook, OR 97141
(800) 542-5526
www.hallcomfg.com
J&J Truck Bodies & Trailers
10558 Somerset Pike
Somerset, PA 15501
(800) 262-6578
www.jjbodies.com
Keith Manufacturing Co.
(slatted floors only)
401 NW Adler St.
Madras, OR 97741
(800) 547-6161
www.keithwalkingfloor.com
MAC Trailer Mfg.
14599 Commerce St.
Alliance, OH 44601
(800) 795-8454
www.MACTrailer.com
Raglan Industries, Inc.
5151 Simcoe St. North
Oshawa, ON
L1H 7K4 Canada
(905) 655-3355
www.raglan.ca
SmithCo Side-Dump Trailers
P.O. Box 932
Le Mars, IA 51031
(800) 779-8099
www.sidedump.com
Titan Trailers, Inc.
1129 Highway No. 3
Delhi, ON
N4B 2W6 Canada
(519) 688-4826
www.titantrailers.com
Trail King
300 East Norway
Mitchell, SD 57301
(800) 843-3324
www.trailking.com
Trinity Trailer Mfg. Inc.
8200 S. Eisenman Rd.
Boise, ID 83716
(800) 235-6577
www.trinitytrailer.com
Trout River Industries
RR#3
Coleman, PEI
C0B 1H0 Canada
(888) 995-1200
www.troutriverindustries.ca
Western Trailers
6701 Business Way
Boise ID 83716
(208) 344-9928
www.westerntrailer.com