The Philadelphia Zoo recently installed a 20-foot long gravity conveyor with spinning rollers, but the system will never see a box or pallet.

Instead, the zoo installed it as the perimeter to its exhibit of Galapagos tortoises. The 500-pound, 200-year-old creatures refuse to walk on the spinning steel bars, so the conveyor acts as the perfect barrier. The arrangement allows children and turtles to view each other eye-to-eye instead of peering through bars or over a fence.

Even though it will never move loads, the conveyor is not just decorative, says Paul Nangle III, president of Leeds Conveyor Manufacturing Co. which supplied the equipment. The steel is 316 stainless coated with black PVC to ease sun glare for zoo visitors.

Nangle had to ensure the coating wasn't poisonous in case the turtles tried to nibble their way to freedom. Also, the bearings are sealed so they'll endure exposure to the elements. And finally, he had to specify an extra broad, three-foot wide conveyor, to contain the turtles' long necks.

"It's one of the only conveyors in the world that doesn't carry anything," Nangle says.