"An improperly functioning door is a critical safety issue on a bus," says Gregory Beck, the director of engineering at bus manufacturer Krystal Koach. So when plummeting temperatures made some bus doors freeze and fail, he put on his detective's hat and began solving the case.
"There were a variety of problems, including water accumulation downstream of the compressor," explains Beck. "When the water froze in air lines, pneumatic components failed." In addition to closed doors failing to open, open doors sometimes failed to close completely. Therefore, the seal normally formed between the door and the doorjamb sometimes remained slightly open, allowing cold air into the bus during operation.
Beck tried overcoming the problems with filters. He also tried desiccant dryers. His solution came with the use of PMD miniature air dryers from MTI Puregas (Anaheim, CA).
The small, 8-inch high by 3Ĺ-inch wide dryers use pressure swing adsorption (PSA) to remove water vapor from ordinary compressed air. A four-way valve directs wet air into one of two desiccant chambers where most water is removed. The dry air then passes through the outlet shuttle valve.
An orifice in the outlet shuttle valve redirects air back through the off-line desiccant chamber, purging it of any remaining moisture. Purged air then exits the four-way valve.
PMD air dryers deliver dry air to better than -100F dew points, with -40F standard.
Operating pressures in Krystal Koach buses are up to 125 psi, well within the 50 - 150 psi range of PMD dryers.
For more information about air dryers from MTI Puregas: Enter 537