Pumps and Quiet

WHILE IT CAN'T DO ANYTHING about the brisk city breezes, National Waste Services, a Chicago-based division of Allied Waste Industries, is helping Windy City residents sleep a little more soundly by reducing diesel engine noise associated with refuse truck operations. The company recently tested a new hydraulic pump system that may soon be emulated in other Allied divisions across the country because of its success in increasing the peace and quiet.

According to National Waste, it wanted to eliminate excess diesel engine noise typically associated with the truck's hydraulic functions (engine rev-up), while simultaneously reducing the original sweep/pack cycle time to improve productivity. To achieve these goals, the company installed a new Denison Hydraulics pump system from Parker Hydraulics and upgraded the control valves on a Leach Packmaster 2RII. The pump setup, an operate-at-standard-idle-speed (OASIS) system, consists of a double-vane pump, unloader valves, an inlet recirculation block and electronic control module. This system provides enough flow to allow the operator to work the hydraulic functions while the engine remains at idle.

The problem with noise associated with refuse trucks is that the hydraulic cylinders used to grab, lift, pack and eject trash are typically powered by a single-section, fixed-displacement pump that produces flow proportional to engine speed. To supply enough power to operate the hydraulics, the engine speed usually must be increased, thereby creating more noise.

One solution is to use a larger pump to reduce engine speed and maintain or increase the hydraulic flow at idle. However, larger pumps are not only more expensive, but the higher pump flow also can increase hydraulic system heat, leading to premature fluid breakdown and component failure. When the engine speed increases during acceleration and over-the-road operations, the increased heat generated by excess flow through the hydraulic system must be compensated for.

On the other hand, the Allied test system employs a double-vane pump that reduced the original cycle time by 8 to 10 seconds, while keeping the engine speed steady at 650 revolutions per minute (rpm). At higher engine speeds, one section of the double-vane pump unloads its flow directly back to the pump's inlet, reducing the total flow to the system. Less flow means less generated heat. The vane pump technology also provided more efficiency at lower turning speeds than the standard gear pump, reducing leakage and system heat. During normal truck functions, however, the increased flow to the truck's hydraulic control circuit still generated more heat than the original system. So to reduce the heat input, truck engineers replaced the original equipment control valves with larger, higher-flow versions. Bigger valves restrict flow less, and thus, generate less heat.

Bob Bulthuis, fleet maintenance supervisor for National Waste, says he is pleased with the test's initial results and anticipates long-term maintenance benefits. “Operating the engine at idle should not only improve fuel economy and reduce noise, I expect it also will reduce normal engine wear and tear because the rev-up features are no longer needed,” he says.

Yet drivers and customers receive the most benefits. Ken Doot, a test truck operator, says he has received compliments from customers because of the quiet operation. “It's great because I don't disturb the surrounding homes and businesses when I am on the street or in an alley picking up,” he says. “The quieter operation is a lot easier on my hearing, too.”

Further testing of the system in other regions of the country is currently underway with a number of refuse truck fleets and several refuse body suppliers.