Ed King's Air Brake Article, April 04 Trains

[Anonymous]

A rather egregious mistake slipped into Ed's article in the April 04 issue on air brakes -- our mistake, not his. The incorrect information is that leakage in a brake pipe leads to a brake release. That's so obviously wrong I can't believe I didn't see it. The correct information is this:

"Leakage, if allowed to be more than the allowable limit (5 lb/min) can greatly increase the time required to charge a train; with long trains it can take a lot longer to charge. Then, after you make a brake application, leakage affects the time required to get a train to release (some of the air you want to get back to the rear to make the brakes release has been lost to the atmosphere).

With the AB valves as we covered in the story, they're designed to put some of the air from the emergency reservoirs into the brake pipe to assist in releasing brakes farther back in the train, but that air must also be replaced. Leakage
makes that a more difficult task. Without engine brake valves with pressure maintaining, when the brake valve handle is placed in lap after making an
application, leakage will cause the application to increase; remember, in lap, no air is being put into the train line. If this happens, the brakes will eventually apply hard enough to cause a stop. Two things mitigate this condition - the pressure maintaining feature, which will hold the brake pipe pressure at the level of the application against reasonable leakage (most were effective for more than the legal leakage), and retainers. Retainers held the brakes on a train while the first application was made and then released so the brake pipe could be recharged.

An example in practice: I was running a long train one very cold night with a locomotive in the lead without pressure maintaining. All that was necessary was to lap the brake valve; leakage would make a brake application for me."

-- Ed King

[Anonymous]

Everyone makes a boo boo now and then. [:)]

Thanks for letting us know the correction. [;)]

[zardoz]

Mark / Ed--
I seem to remember when I left the CNW that a new type of triple valve was being developed called an "ABDX" or something like that.

The concern was that this valve had such a sensitive quick-release feature that during the process of "self-maintaining" trainline pressure (small amounts of air sent into the trainline to maintain desired pressure), the valves would cause similar valves to do an unwanted release causing a cascade effect thereby inadvertantly releasing most or all of the train brakes.

Did the ABDX ever come into use, and have there been any known problems with it?

[Anonymous]

I used to work an industrial job where I usually had an EMD SW 1 with no pressure maintaining. Every night we would shove a large cut [25/35] of cars down hill to our work. With the SW 1, I also would just lap the brake and the leakage would do the job; by the time we reached the signal, I was shoving with the brakes applied. Once in a while, we'd get a newer engine, like an SW 9, and sure enough, I'd forget to cut out the press. main. until we were well down the hill. I'd be all messed up with the "improved' gear.

[jeaton]

Mark,

Well that's two mistakes. Actually, kind of rushing through the article in my press for time in the semi part of my retirement, I got that as a "release" of air from the reservoir to the brake cylinder, rather than a release of the brakes. I guess I just ignored the run-away part.

Face it, this is complex. How is a train stopped? Airbrakes! The engineer lets air out of the brake line which causes air to be released into a brake cylinder which puts pressure on the brake pads. Huh??? Well its a long story.

Ed King did a great job of telling the story, and I'd recommend it for anyone with a real interest in the subject.

Jay