Equipment – March 2004

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General Motors’ Allison Transmission is introducing its new Allison DOC (Diagnostic Optimized Connection) For PC Version 4.0, a full-feature diagnostic software application supporting control systems for Allison transmissions.

Mack Trucks recently received a $1.2 million contract through Southwest Research Institute to develop diesel hybrid electric technology that will ultimately be used in military and commercial vehicles. The majority of the work is to be performed at Mack Powertrain in Hagerstown, Md.

Webb Wheel Products is recalling all Platinum Series Brake Drums with cast date codes 017-01 to 273-02 (Julian style date) for premature friction-surface cracking.

Sirius Satellite Radio and Penske Truck Leasing announced a multi-year agreement to offer Sirius satellite radios in specific lease, commercial and consumer rental vehicles.

According to the CK Marketing and Communication’s Q1 2004 Fleet Sentiment questionnaire, 68 percent of responding fleets plan to purchase power units in the next six months; 60 percent also plan to buy trailer equipment during the same period.

ChevronTexaco Global Lubricants announced that motorsports legend Mario Andretti will conduct an autograph and photo session at the CTGL booth at the Technology & Maintenance Council’s Annual Meeting on Tuesday, March 16.

Ample oil usually is a good thing, but not when it comes to air dryers – vital components that help ensure your brakes get clean, dry air. An air dryer’s internal workings would last forever except that oil from the compressor eventually works its way into the dryer and keeps the desiccant beads from grabbing water the way they should. So the desiccant bed and oil separator (if so equipped) have a limited life – normally about one to three years.

Because the desiccant bed and oil separator have much shorter lives than the rest of the air dryer, the components are assembled into the dryer together as a replaceable cartridge. The single most important aspect of dryer maintenance is replacing that cartridge at the right time. As with almost everything in trucking, the duty cycle of the truck greatly affects cartridge life. Brake air system maintenance also plays a big role because leaks mean the compressor handles more air, and that means more water for the dryer to take out.

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More routine air dryer maintenance consists of draining the wet tank and primary and secondary storage tanks periodically. This, says Larry Donaldson of the Bendix Tech Team, serves as a check of dryer function and should be done at least every 25,000 miles, 400 hours or three months, whichever comes first. Jon Canale, senior project engineer, Meritor WABCO, says it’s smart to do this as often as once a week.

If the dryer is the right one for the application, and the air system is in reasonable condition, a lot of moisture in the tank – normally mixed with some oil – means it’s time to replace the cartridge. “It’s normal to see a tan colored goo in the air stream that some describe as ‘mayonnaise,’ Canale notes. “Some is normal, but you should not have much if the dryer is working properly. You’ll just see a little mix in the initial blast of air. In ideal applications, there won’t be any.”

Canale also advises that fleet managers don’t need to empty air tanks when they drain them. “Just pull the cord and hold it open for a few seconds, so you can see what comes out.” Completely draining the tanks interferes with dryer performance, putting some water downstream until things stabilize.

If oil is accumulating around the purge valve and just below where the exhaust port is, you should at least examine the cartridge, Canale says. Heavy evidence of oil there can be a sign of an incorrect installation of the dryer on the vehicle, such as a line between the compressor and dryer that’s too short. It definitely means the cartridge isn’t working the way it should if there is also oil in the air tanks and bottom of the dryer. That means the cartridge is saturated with oil, and it’s passing right through.

Leslie Kern, heavy duty product manager at Chicago Rawhide, says CR air dryers should have the cartridge replaced every three years in linehaul service, two years in urban delivery, and every year in refuse and off-highway applications. CR sells its cartridges as part of service kits that also include the turbo cutoff valve and purge valve and recommends that operators replace all three at once.

Replacing the cartridge
Replacing the cartridge is normally straightforward, but the actual procedure varies widely with the construction of the dryer. Regardless, the first step is to drain all air from the system, so it will be safe to begin disassembling parts that normally hold pressure. On the Bendix AD-9 air dryer, eight bolts – two of which fasten the unit in place – must be removed so the outer shell can be lifted off the base. The cartridge is then unscrewed with a strap wrench, replaced along with its two O-rings, and the unit reassembled. On the Bendix AD-IP, removing a through-bolt from underneath the dryer base allows the cartridge (which slightly resembles a spin-on oil filter) to be simply lifted off.

On the Meritor WABCO System Saver 1200 and the CR Turbo-2000 and Turbo-3000 air dryers, the cartridge is almost exactly like a spin-on oil filter and is removed similarly.

On all units, wipe out any accumulated oil and moisture. A few units have an integral sump to help collect them. Also, see service literature for any further details.

Canale adds a word of caution: Many aftermarket designs are cheaper than the $30 to $40 price of OE parts, but some makers substitute plastic for the metal. Canale says this material isn’t strong enough to withstand normal operating temperatures and can fail, allowing beads to clog the system.

Dealing with winter
Many dryers have a heater for the purge area to prevent expelled moisture from freezing and blocking it. But a problem with the heater won’t show up until it’s cold outside. Then, if it fails, it’s “tough to stay out of trouble,” says Randy Nichols, air dryer engineer for the Bendix AD-9. Nichols says heaters most often fail because of “lack of voltage due to a broken wire, a corroded connection or blown fuse. Put a voltmeter on the plug going into the heater. It’s a simple test that can be done in any weather and covers most failures.”

Bendix’s Larry Donaldson says if it’s cold outside, first turn off the truck for a while to cool the dryer to below 40 degrees F. Then, unplug the connection to the heater and run an ohmmeter between the connector pins. With a standard 12-volt system, resistance should be 1.5 to 3 ohms. If the unit happens to operate at 24 volts, resistance should be 6 to 9 ohms. Otherwise, replace the heater.

If in doubt, consult the manual for your particular brand and model of dryer for exact resistance values.

Bendix vehicle systems senior staff engineer Chuck Eberling adds a last bit of cold-weather advice: Right after shutting off the engine, “take a minute to cycle the brake pedal to vent the system to below its cut-in pressure.” That will ensure that the purge valve is closed and can’t freeze in the open position, preventing recharge of air brake system pressure.

In sum, once you have the right dryer, and you know it’s installed properly, regular tank draining and periodic cartridge replacement and heater checks will keep the dryer working right and your brake system protected from moisture.
– John Baxter

In February, we asked why air gets hot when it’s compressed. At press time for this month’s issue, no one had come up with the correct answer, which follows:

The temperature of air molecules is determined by their kinetic energy, or speed. When the temperature of a quantity of air is constant, the average speed of the molecules remains constant.

Air molecules bouncing around inside, say, an engine cylinder (engine off) travel at the same speed before and after each impact with cylinder walls, head, valves, piston and each other. In other words, initial speed equals rebound speed.

As the piston begins its compression stroke, molecules moving in a downward direction strike the upward moving piston, and rebound with increased speed – like a ping-pong ball striking a paddle moving in the opposite direction. The energy received by those molecules is quickly distributed, through intermolecular collisions, to the rest of the molecules in the cylinder. The average kinetic energy of the molecules, hence heat, is momentarily increased.

Hey, it’s a new month, and there’s a new puzzler. Be the first to e-mail [email protected] with the correct answer, and you’ll receive a CCJ Air Brake Book, a chrome pen engraved with the CCJ logo, and a mention in next month’s Equipment department. And, if you have a puzzler you’d like to share, send it in. If we use it, you’re a winner, too.

This month’s Puzzler:
Here’s another bit of failure-analysis: What could possibly have happened to this piston, which was removed from a relatively high-mileage engine?