Understanding Air Systems Can Prevent Headaches
Storrow Drive eats buses. Right off Boston’s expressway, it looks SO tempting to coach drivers goofy enough to believe in rational road construction.
And so it was no surprise when the driver of a GM 4905 was seduced into ignoring warning signs and ventured forth. Locals were not surprised when a low overpass snared the “Buffalo”.
The real surprise came when the local constabulary decided to help. They looked at traffic trapped behind the bus, and decided that, since there was ALMOST enough clearance, a gigundous tow truck should pull the bus forward, the rest of the way under the bridge… and so the disaster commenced.
Each time the tow truck made a little progress the bus squatted a bit, until the leveling valves sensed it was time to spring into action, and raise the suspension. This process repeated itself until the roof was crushed inward the length of the bus. When that jewel spat out the other side of the bridge it more closely resembled a sway back nag than a Buffalo.
The point here is not about overhead clearance, but rather the fact that if the driver had a rudimentary understanding of how the coach’s air suspension worked… there would have been less crushed metal. Disconnecting the leveling valves would have saved a ton of pain.
Modern air systems are far more reliable than in ye olden days. Properly maintained, there isn’t a lot for drivers to do, if all goes well. No need to drain air tanks daily, fill alcohol bottles, or thaw tanks and hoses.
It’s when things don’t go well that a drivers’ understanding of how things work can avert disaster.
Without going into specifics (because you’d find out how little I know), it might be worthwhile to include the basics of the air system and suspension in driver training.
Contemporary braking systems have all sorts of check valves and redundancy to make sure that, no matter what, the coach has SOME brakes.
The down side is that, if a driver doesn’t have a basic understanding of what’s happening down there, they may THINK they have a whole system, when they’ve only got half… hence those flailing gauges and flashing lights. If you only have half a system, and something happens to that half, you have potential for bodacious mischief.
There are several different types of air actuated parking brakes on buses. One type requires a stomp on the brake pedal to release, while the other is delighted to get rolling as soon as the yellow button is pressed. When the coach is parked on a hill… you get it.
Current bus models all come to a shuddering halt as the emergency brake automatically sets when air pressure drops below minimums. While this better than charging through traffic like a bull in a china shop, it can be embarrassing in the middle of an interstate. Drivers should understand how that all works, and should know if their coach has an override.
Every bus manufacturer now installs an “air drier” to keep moisture out of the system. These jewels regularly (and spastically) purge themselves of accumulated water, and drivers should understand that it’s a normal process.
If their passengers have irritated them, drivers can gain a bit of satisfaction by parking the idling coach’s drier over a puddle in hopes it will relieve itself in a timely fashion, while the unloading folks are passing. If they like their group, they may get better tips if they avoid that puddle. Either scenario only works if they know where the drier is located.
It’s not necessary that drivers be expert on the air system, but periodic training in its basics can prevent, or mitigate, all sorts of problems.
There is a safety component too. Some simple understanding of how this stuff works can prevent all sorts of mayhem.
Years ago my friend Mark was trying to repair some obscure part under the front of a Scenicruiser. There was no pit available, and because he was a bit too plump to wriggle under the coach, he grabbed a bottle jack, maneuvered it under a sheet metal compartment, and lifted the front end.
Just about the time he got his head underneath to begin work, a naive leveling valve decided that “the body is a bit too high; I’ll dump some air out of the suspension”. At that point, the weight of the entire front end was on the bottle jack, and it punched through the sheet metal, allowing the body to rest on… Mark’s head.
Years after his skull returned to its original shape, his nickname was still… Cowpie.
