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Machine Design

Pneumatic module lets bus kneel

Buses and RVs often feature a kneeling option that lowers the vehicle and eases the task of climbing on and off.

Parker's Kneeling Module controls pneumatic actuators that lower buses, motor coaches, and RVs for easy access.

But this typically forces the manufacturer to assemble an array of pneumatic valves, connectors, and other components into a customized system.

Cleveland-based Parker Hannifin (, has developed a Kneeling Module that integrates the pneumatic components, simplifying installation and maintenance while providing a range of kneeling capabilities on large passenger vehicles.

The new module consists of a durable, lightweight manifold with a machined-aluminum anodized body. It houses four pneumatic poppet valves that inflate and exhaust air bags mounted on the vehicle axles. Depending on system requirements, at the flick of a switch the unit routes compressed air to provide split-level kneeling, left or right tilting, complete kneeling, or a "high-boy" position that elevates the bus or motor coach for over-the-road travel.

Standard 22-mm grommet-style P2F Series mobile solenoids actuate the valves. The combination of a solid housing, poppet valves, and heavy-duty solenoids results in a durable unit that stands up well to dirt, water, and salt that the vehicles commonly see, says Paxton Augustine, a product manager with Parker's Pneumatic Div.

Exhaust protectors — flapper-type devices on the manifold — permit unrestricted airflow out but keep contaminants from entering the valve, adding to system reliability, says Augustine.

The system also features Viton seals designed for temperatures from -40 to 122°F. The Kneeling Module operates at pressures from 60 to 150 psi, and coil voltages are available in 12 or 24-Vdc versions.

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