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Kerns. "It was determined that the new conveyor would fit in a hallway running under the silos, but we knew that once installed, it would completely fill the available space." As a result, cleanup of any fugitive material accumulat‐ ing under or around the conveyor would be extremely difficult and potentially dangerous without stopping the adjacent pan conveyor and shutting down production. That realization led to the search for a highly reliable conveying system with the proven ability to operate for extended periods with very little maintenance, one that could prevent the escape of fugitive material and also protect the load from rain that would introduce un‐ wanted moisture to the product. Selecting an Air-Supported System After reviewing a variety of designs and proposals, the company specified a Martin Engineering Air‐Supported Conveyor, a simple and economical system that resolves many of the issues encountered with conventional belt conveyors. With no moving parts that require mainte‐ nance on the load‐carrying side, the system could be in‐ stalled in the close quarters of the hallway under the clinker silo. "Air-supported conveyors eliminate the carrying-side idlers used on conventional conveyors, and instead use a film of air rising from a troughed pan to lift the belt," explained Greg Bierie, global project manager for Mar‐ tin Engineering. "By removing a source of friction that requires periodic maintenance, air‐supported designs offer significant advantages – including energy, environ‐ mental and safety benefits – yet the cost is competitive with traditional belt conveyors," he said. The Martin Engineering system does not require a com‐ pressor, powering up to 600 ft. (183 m) of conveyor supported by a single low‐power centrifugal fan. Ex‐ tremely low friction inherent to the design can reduce overall drive power requirements by as much as 30 per‐ cent on a horizontal conveyor. The use of air‐supported conveyors also eliminates the need for idler adjustment to correct belt tracking issues. The advantages include extended belt life and reduced maintenance costs, as well as improved safety by limit‐ ing employee exposure to moving components. Simple Concept for a Smooth Ride The concept of the air‐supported design is fairly simple, with the load zone and carrying sections contained in a plenum that's pressurized by the centrifugal fan. The carrying surface of the plenum is typically shaped to the parabolic curve profile of a conventional belt conveyor, with a 35‐degree trough. Holes in the top of the plenum create an air film between the plenum and belt, which www.rockproducts.com The air-supported conveyor design features a load zone and carrying sections contained in a plenum that's pressurized by a 15 hp (11.2 kW) centrifugal fan. As the material enters the discharge tower, it passes over a belt scale and into a retractable dustless discharge chute, which extends down into the railcar opening. ROCKproducts • OCTOBER 2011 19