INTENTIONAL BLOWOUT

Jim Park

What’s worse than bitter-cold weather? Well, it might just be the up-and-down conditions of late winter, with their wide variations in temperatures: instead of the earlier one-time shut-down, you get a freeze-and-thaw, freeze-and-thaw cycle that can make you –and your equipment — miserable several times in a month instead of just once.

Air-brake components are especially susceptible to the cold, because any moisture they contain will then freeze. And air-system contaminants like oil will thicken and cause malfunctions that never appear during warmer seasons. The result can be sticky or non-operative brakes.

But this assumes you’ve done nothing to blow away those cares and woes by giving the air-brake system a good clean-out — or by equipping your truck or tractor with a good air dryer, which will wring-out moisture and filter-out contaminants in the first place.

Servicing the air dryer is among the steps suggested by supplier reps and fleet maintenance managers who belong to The Maintenance Council (TMC) of the American Trucking Associations. Their Recommended Practice 617 lists nine steps for removing contaminants from the air brake systems of tractors, plus another 10 steps for trailers and converter dollies.

Some basic procedures are common to both vehicle types:

* Disconnect and/or disassemble air lines, vales, and other components;

* Blow out these components with clean air from the shop compressor, usually in the opposite direction to the system’s normal air flow (i.e., backwards); and

* Inspect all parts and replace them if necessary. For this, it’s important that the mechanic follow instructions and guidelines from each component’s manufacturer.

Not specified, but implied, is this procedure: if oil or other contaminants are found, find the source and fix the problem. Oil usually comes from the air compressor (it may need repairs), and has therefore gotten past the filter on the air dryer. Dirt could mean the truck’s air cleaner element needs to be changed.

Particles of rubber come from somewhere in the system, and must be traced to their source(s). Excessive moisture comes from a non-working dryer (which you’ll check-out and service) or — worse — the absence of a dryer in the system at all.

The TMC recommended practice says to proceed in this order:

1. Clean the line between the truck’s compressor and the air dryer.

2. Service and clean the dryer, including replacing its desiccant and filter.

3. Clean out the wet tank. To do it right, the shop compressor’s regulating valve should be set at 5 to 8 psi, and the air run through the tank and out its petcock for a half hour (your mechanic will be able to proceed to other jobs while this is under way).

4. Clean out the governor regulator line, or any other line supplied by the wet tank.

5. Clean the one-way check valves protecting the two service tanks.

6. Blow out the lines between the service and wet tanks.

7. Disconnect the supply line between the service reservoir and the foot valve, and blow it out. If no oil is found in this line, you’re done cleaning and can skip on to Step 9. If oil is found in this line, however, blow out all other lines from the service reservoir, and add this next step:

8. If oil was found in the service line, inspect the bottom of the foot valve by removing the lower housing. If there’s oil inside, all other valves (foot, dash, tractor protection, replay and two-way checks) must be disassembled, and cleaned or replaced.

9. With everything back together, do a system check for proper operation.

Similar operations must be performed on a trailer or dolly air-brake system, as follows:

1. Check the service and supply gladhands, cleaning-out the strainer screens (if used) inside.

2. Open petcocks on all reservoirs and drain them. Mark the lines so they’re reconnected correctly later.

3. Disconnect service and supply lines, and blow them out.

4. Clean the reservoir tanks, blowing them out for the same half-hour period as with the tractor’s wet tank.

5. Check the exhaust portion of all valves for oil and sludge. If these contaminants are found, dismantle the valves and clean them, or replace them.

6. Check the service and parking (emergency) lines for contaminants. If found, disconnect them and blow them out.

7. Check all interconnected reservoir lines for contaminants. Blow them out if necessary.

8. Check all other accessories (air bags, leveling valves, etc.) for contaminants. Clean and/or replace if necessary.

9. Check the service brake chambers and pintle clamp chambers for contamination. Clean and repair or replace if needed.

10. Reassemble the system, and do an operation check.

In replacing valves and air lines, TMC has long emphasized that it’s vital that any new parts be of the exact same specifications as the item being replaced. Each replacement valve, for example, should be the same make and model as the old one, so that the crack pressure (the point at which the valve opens) stays the same.

Each now air line should be of the same diameter (for example, a 3/8-inch outside diameter), and fittings should be of the same type (connectors, unions, elbows, and tees) as the old, so the same volume of air is carried.

If you ignore this concern, the performance of the air brake system will change. This will probably throw off your brake balance on all the axles, and perhaps even between brakes on the same axle. It may also adversely affect brake timing between the tractor and the trailer.

And all this could mean it might be a cold day in Hell (which, as you probably know, is a town in Michigan) before your brakes work properly again.

Jim Park

Jim Park was a CDL driver and owner-operator from 1978 until 1998, when he began his second career as a trucking journalist. During that career transition, he hosted an overnight radio show on a Hamilton, Ontario radio station and later went on to anchor the trucking news in SiriusXM's Road Dog Trucking channel. Jim is a regular contributor to Today's Trucking and Trucknews.com, and produces Focus On and On the Spot test drive videos.

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