Getting the Garbage Out
What’s the best way to get garbage out of a transfer trailer? Live floors, horizontal hydraulicejectors, and tippers each have advocates.
Michael Riggs, product manager for J&J Truck Bodies & Trailers in Somerset, PA, has seen demand for live-floor trailers decrease by 40% over the past two years.
Dan Taylor, a sales executive for Western Trailers Inc. in Boise, ID, says his firm builds 200 transfer trailers a year. “Seventy-five percent are tipper trailers, and 25% have live floors,” he reports. “Five years ago it was 50-50.”
Both Riggs and Taylor believe the market for hydraulic-ejector trailers, commonly called pushouts, is more limited.
The choice of an ejection method can be exceedingly complex. An extensive list of variables, some seemingly contradictory, confronts anyone just starting a transfer-trailer operation.
This complexity magnifies logarithmically for any large municipal solid-waste hauling firm having multiple contracts, wastestream volumes, and disposal arrangements. The greater the diversity of such a firm’s accounts, the more it needs a separate ejection-technology analysis for each aspect of its operations.
A tipper is a mobile platform positioned at the working face of a landfill. It has a diesel engine powering a hydraulic pump, which operates two hydraulic cylinders that raise and lower a hinged deck.
A driver backs a trailer onto the tipper deck until it hits the backstop. He sets the brakes, gets out of the truck, disconnects the air and electrical lines, unlocks the kingpin to the fifth wheel, opens the rear doors, then moves the truck forward about a foot so the kingpin is just outside the fifth wheel’s jaws. The tractor supports the front of the trailer until the deck rises and makes contact with the trailer’s raised landing gear. Then the deck supports the trailer and the truck pulls forward onto the approach ramp. The deck and trailer tilt to a high angle (generally above 60°), causing the trailer’s contents to spill from its open rear doors.
After the deck returns to a horizontal position, the driver connects the fifth wheel, attaches the air and electrical lines, closes the rear doors, and pulls the trailer off the platform.
“The cycle time is three minutes—a minute and 40 seconds to go up, a minute and 20 seconds to come down,” says Jeff Van Raden, an engineer with tipper manufacturer Columbia Corp.’s parent company, Columbia Industries LLC in Hillsboro, OR. The average truck-to-truck unloading time is five or six minutes, but Van Raden says an experienced landfill team engaged solely in tipping can unload up to 120 truckloads (one every four minutes) in an eight-hour day.
Some tippers are self-propelled, but most have a fifth wheel that attaches to a motorized dolly for towing as the working face of a landfill moves.
While a tipper is in operation, outriggers stabilize it in the landfill’s soft, spongy soil, while safety hoops and a tie-down hook secure the trailers on its deck, explains Daniel Darcey, a sales engineer for tipper manufacturer Phelps Industries Inc. in Little Rock, AR.
Jiggling or Shoving
A live floor consists of 21 parallel slats, roughly 3.5 inches wide, that run the length of a trailer in three staggered sets of seven. In operation, each set moves forward independently in a one-two-three sequential order. The first set of slats travels 8.5 to 9 inches toward the front of the trailer, then the second set moves forward, then the third. Because only a third of the slats moves forward at a time, these forward movements don’t displace the load, which rests on the stationary two-thirds of the slats. When all of the slats reach the front, they all move in tandem toward the rear, and this synchronized rearward motion shifts the load toward the rear doors.
The slats in most live floors are aluminum, but steel slats for abrasive loads are available. Bearings of high-molecular-weight urethane plastic reduce friction between the slats and a metal sub-deck below the bearings. A hydraulic system under the floor drives the slats.
Live-floor technology is a duopoly. All trailer manufacturers buy their live floors from Hallco Manufacturing Co. in Tillamook, or Keith Manufacturing Co. in Madras, OR. Each sells a kit consisting of the floor mechanism and an integrated hydraulic system packaged in a frame that fits in the bottom of the trailer. Each firm has patented discrete aspects of its design. Hallco’s hydraulic system includes more hoses than Keith’s, which relies to a greater extent on hard metal plumbing. Dan Jackson, senior sales executive at Keith, notes that Keith has registered the Walking Floor name to describe its products.
Unloading a live-floor trailer takes seven and a half to nine minutes, depending on the density and weight of the load, as well as such design characteristics as stroke speed and hydraulics, says Don W. Wilton, vice president of sales and marketing for Hallco. Jackson says Keith sells a “running-floor” refinement that can reduce unloading time to about three minutes.
In a pushout trailer, a trunnion at the front of the trailer anchors a multistage hydraulic cylinder arm with a pusher blade attached to the end at an angle of 70 degrees. Extending the arm moves the blade toward the rear of the trailer, pushing the load out the rear doors.
Some pushout trailers have their own auxiliary engine and hydraulic power supply, while others rely solely on the tractor’s systems.
An ejection-technology decision precedes a large capital investment and a long-term commitment, so converting to another ejection technology before the end of the existing equipment’s useful life probably won’t be feasible. Choosing the wrong technology for a given application could dilute operating efficiency and profitability for years, but even if the appropriate technology is chosen initially, significant changes in a hauler’s operations before the equipment is ready to retire may force an earlier re-evaluation.
“A tipper costs $200,000 to $300,000, and its maintenance and operating costs run about $20,000 a year, says Darcey. “Diesel fuel is the main operating expense item.” Van Raden estimates tipper operating costs at about $5 an hour.
A tipper trailer is “a cheap sheet-and-post trailer,” says Wilton. “You don’t have to put anything mechanical in it. It’s just a blank generic trailer with no hydraulics and a wooden floor. You open it and tip it, like a Kleenex box you shake until all the tissues fall out. Trailer guys like it because they don’t have to outfit their trailers. They let the mills and dump areas incur the expense.”
Phil Bortz, vice president of sales and marketing for MAC Trailer Manufacturing Inc., in Alliance, OH, puts the cost of a tipper trailer at $40,000 to $45,000, and that of a live-floor trailer at $50,000 to $60,000.
Pushout trailers range in cost from $60,000 to $110,000, Riggs says. Their higher cost is due in part to the complexity of the hydraulic-ejection mechanism, and also to the need for a thicker skin on the trailer body to withstand the high sidewall pressures when the blade starts to compress and push out the load. Jackson says the side posts that lend strength to a trailer’s walls must be about 4 inches deep on a pushout trailer, versus 2 inches or less on a live-floor or tipper trailer, and the skin on a pushout trailer must be twice as thick (a quarter-inch versus an eighth of an inch).
With respect to maintenance costs, Riggs estimates that a live-floor trailer requires eight times more maintenance than a tipper trailer with a standard floor. Pushout trailers typically require less maintenance than live-floor trailers—but Wilton notes that if the telescopic cylinder on a hydraulic ejector fails, replacing it could cost $8,000 to $9,000.
Wear-and-tear issues set live-floor trailers apart from the others, Jackson says. All trailers wear most at the rear, where the garbage exits the trailer. Repairs to tipper and pushout trailers involve replacement of wood planks or metal sheeting on the floor at the rear.
On a live floor, Dan Jackson, senior sales executive with Keith, says, “you unbolt the slats and reverse them, almost doubling the wear-out time of a Walking Floor plank versus a tipper floor or a pushout with a static floor.”
The cost of discharging a load is another consideration. Tipper trailers must pay tipping fees unless the transfer-trailer operator also owns the tipper and landfill. Live-floor and pushout trailers don’t require a tipper’s assistance to unload, but may pay dumping fees, which could be the same as or less than tipper fees.
Payload and More
“More important than the cost of a trailer is how much payload you can haul in it,” insists Van Raden. Live-floor and hydraulic-ejection technologies add weight to a trailer and sacrifice load space.
Riggs says a typical tipper trailer weighs 12,000–13,000 pounds, a live-floor trailer weighs 15,500–18,000 pounds, and a pushout trailer could weigh as much as 23,000 pounds. Weight becomes a consideration as a rig’s gross loaded weight approaches the legal limit for the jurisdiction in which it operates.
A tipper trailer can carry 115–125 cubic yards of payload, a live-floor trailer 85–90 cubic yards, and a pushout trailer just 75–85 cubic yards.
MAC Trailer Manufacturing provides a tipper-trailer refinement: smooth-side wall-panel construction using hollow-core extruded aluminum panels. “It affords an additional 6 cubic yards of payload over the traditional sheet-and-post tipper trailer,” Bortz says. “The sidewalls are thinner, so you gain more interior capacity. People are looking for ways to reduce the weight of the trailer, so more people are going to aluminum for municipal solid waste, though steel is still used in the scrap marketplace and for more aggressive and abrasive materials such as construction debris.”
Western Trailers offers a different refinement: the drop-center trailer, or “possum belly.” On a standard flat-floor trailer 42 inches wide, 102 inches long, and 13.5 feet high, dropping the floor by 18 inches increases payload space 22%, from 113 to 138 cubic yards. “When you top-load a drop-center trailer in a transfer station, it requires less compaction,” Taylor says. “You don’t have to tamp the load as much; you just push it in, so there’s less damage and less maintenance to the trailer. Also, the trailer handles better when you get that load low.” Drop-center trailers have been hauling wood chips since the late 1960s. Western Trailers built the first such trailers for refuse in the early 1990s, and Taylor says 95% of the tipper trailers his firm builds today have drop centers.
From Van Raden’s perspective, the key question to ask when selecting transfer vehicles for MSW is that of how much it costs to move one pound for the distance of one mile. He cites a study for a vehicle with an 80,000-pound gross weight that includes expenses for fuel, tires, insurance, maintenance, licensing, operating permits, a driver, a supervisor, a dispatcher, an office for the dispatcher, a shop, and parking for vehicles.
“Take that cost, then ask how many miles you’re traveling a day and multiply by the number of rigs to get what it’s costing per year to run these miles,” he says. The study, conducted in 1990, estimated the cost at $1.15 per pound per mile. Today it would be significantly higher.
Distance and Time
In general, the higher a hauling operation’s volume and the longer its haul, the more appeal tipper trailers have—assuming they are going to a landfill equipped with at least one tipper.
Photo: Columbia Tipper
|Cycle time for this tipper—up, dump, and down again—is about three minutes.|
“If you have a high volume with a lot of trailers, the tipper makes more money sense than anything else,” Darcey says. “The break point is around 300 to 500 tons per day, and it’s specific to each hauler based on distance, fuel cost, and the amount of volume he’s handling.”
“If the haul is over 40 miles, many people look toward tipper trailers,” Bortz says. “For shorter runs and for versatility, haulers lean more toward the live-floor system.”
A negative aspect of tipping is its total reliance on tippers. “If 20 trailers arrive at a tipper at the same time, they can’t all go on at once,” Jackson notes. “While one is unloading, the others are waiting. With Walking Floor technology, they can back in side by side and all unload at the same time. If the distance of your haul is long enough, the wait time at the tipping platform becomes immaterial; but for a short haul, waiting in line may cost you one or two loads per day. A Walking Floor trailer doesn’t require any other unloading device that would tie up your fleet.”
Jackson points out that live-floor trailers can unload on a tipper. “When you pull in and there’s no line, if the landfill charges the same whether you use the tipper or not, you just let them tip. You don’t have to use your hydraulics and Walking Floor. If there’s a line, you use the Walking Floor. You see that done most often in the forest industry. It’s less common in municipal solid waste, but it does occur.”
Photo: ESI Waste
|Bales are unloaded at a rail yard in Kentucky.|
Other Pros and Cons
People who don’t like tippers also complain about having to disconnect and then reconnect the tractor and trailer; the difficulty of backing onto the tipping platform in inclement weather and muddy terrain; stability of the tipper when it’s working on an uneven, uncompacted surface; the potential for high winds or wind sheer to overturn a tipper and the trailer it’s unloading; and the possibility that the tipper’s hydraulic cylinder could get stuck in an extended position with a trailer aboard, requiring complex and costly repairs. “If you destroy a tipper, then your whole fleet is shut down,” cautions Wilton.
Tipper proponents say some of these concerns are irrelevant and others are highly unlikely. They cite safety benefits for operators and drivers in tipper operation. “You’re on an island. That’s where you do all your work,” Van Raden says. “No ’dozers or compactors are operating around you, and a tipper is well-lit at night.”
Pushout trailers have what Wilton calls “pinch points,” where someone could fall in and land behind a moving blade. “The telescopic cylinder is unforgiving,” he says. “It will crush everything that’s in the trailer.”
Wilton says a live-floor trailer is the safest technology of all. “You can stand on it while it’s moving,” he explains. “It won’t pinch or bite you; it just slides under your feet.”
In cold climates, loads have been known to freeze inside a transfer trailer. Tipper operators may solve the problem by rocking a trailer back and forth to dislodge its load. For a live-floor or pushout trailer, solutions include unloading by hand, surrounding the trailer with a canvas or vinyl skirt and lighting a propane heater underneath to warm the floor and walls, or bringing the trailer inside a heated building to thaw. Still another option, pumping hot truck exhaust through a trailer’s tubular frame, has been abandoned because chemicals in the exhaust will corrode the frame.
Jackson says freezing is a non-issue for people who know how to operate a live floor. “
You position it with all three sets of slats in tandem when you turn the floor off,” he instructs. “When you turn it back on, you finish the cycle, moving all of the slats to the rear to break the load loose from the walls. Then you break the load loose from the floor one-third at a time. After one cycle, the load is no longer frozen to the walls or the floor.”
Pushout trailers, Riggs says, are appropriate for three kinds of specialty applications: mobile transfer stations for small municipalities, hauling sludge, and hauling debris.
“A small municipality can collect solid waste in a pushout trailer with an auxiliary engine on the front and a roof with a 90-inch hydraulic opening in front, a side-swing door, and a rear tailgate rounded to withstand pressure. Residents bring garbage to the trailer and drop it into the roof opening if the trailer is in a pit, or into a small packer that ejects into the side of the trailer.
“The quantities coming in daily aren’t enough to fill the trailer. Each day the engine compresses the load, then pulls the blade to the front again, and people dump more stuff in. Once or twice a week it travels to the landfill and unloads.” In the evenings, transfer-station personnel can close the side door and roof to contain odors. Riggs says such a trailer must be fully enclosed and leak-resistant.
“A pushout trailer is good at containing leakage,” he notes, “so it’s a leak-proof way to haul sludge, which has a high water content, and it has excellent side and floor cleanout with wet materials. Typically this is an open-top application with a vinyl cover.”
Riggs recommends pushout trailers for hauling hurricane debris and construction and demolition waste because it’s the safest way to remove such debris from a trailer. “People are dropping stuff that you don’t want to drop into a live-floor trailer,” he says. “A pushout trailer can haul more cubic yards than a dump trailer, and keeping the trailer on the ground to unload is safer. Tree stumps and other hurricane debris want to hang up in a tipper trailer. So does big, bulky construction waste, such as boards, rebar, and piping."
Author's Bio: George Leposky is a science and technology writer based in Miami, FL.