Why does the engineer on a locomotive press down the brake lever on the locomotive brake?
,HF1001
Pressing down on the handle cuts the trainline brakes out on the locomotive, to allow the engineer to control the locomotive independant brakes. You generally see this if a train goes into emergency, the engineer will press down on the handle so the locomotive wheels do not get flat-spotted.
This is called “bailing” off the locomotive brakes . Engineers are required to do this each time an automatic reduction is made on the brake pipe to prevent brake cylinder pressure on the locomotive from developing .
In emergency braking, do all the wheels on the train lock up and develop flat spots>
Engineers will generally “bail off” any time there is an application of the automatice brake. It keeps the brakes released on the locomotives, and is one way to control the slack action in the train.
It’s also important when in dynamic braking, to keep the locomotive wheels turning.
Nick
Although this is a common visual device in movies and television, it doesn’t actually happen. Sliding wheels provide less braking than wheels that are still turning but being restrained by the brake shoes.
I’ve ridden several trains where emergency braking was applied, the train slowed and stopped rather quickly but there was no wheel sliding.
If there are a lot of empty cars, the wheels could slide in emergency.
Engine wheels can and do lock up from braking. Seems to be more common with clasp type brakes, as there are 2 brakeshoes grabbing each wheel. Add a little moisture, and sliding is very possible.
most modern bathtub gons for coal have device that detects carload and will reduce braking force for empty cars…
In refference to the wheels sliding, you dont have to be much of an expert to realize this (not saying the person who asked is stupid, afterall, I believed it myself before) Steel wheels sliding on steel track, you can imagine, wouldent do good. It would be like ice sliding down a slide, it slides for ever. But imagine if you were to add enough pressure on the wheels to almost the point of sliding, the train would be forced to stop, since theres no way out of it, there is strain on the train, lol, rhyme, which would cause braking quicker. I know my explanation is hard to understand, but its pretty much like this: F=VM/SP [:D]
Bathtub gons have them, also covered hoppers, rapid discharge coal cars, so that time is not spent after a unit train loads or unloads the carman has to set the retaining valves(is that what the retaining valve lever does?).
It’s a load/empty switch, quite different from retainers.
You don’t “bail off” when using dynamic brakes.
You don’t? please , explain why not ?
I’m a locomotive electrician for U.P. and this is how our locomtives operate… As soon as you go into dynamic brake setup, any automatic brake application will be bailed off the locomotive by energizing the dbi mag valve. The engineer never has to bail it off manually. If an engineer applies the independent brake while the locomotive is in dynamics one of two things can happen depending on the type of locomotive. On EMD units, the extended range feature will be disabled. On GE units, dynamic power will be reduced to minimum effort. This is for dc type locomotives. I’m not sure how AC locomotives deal with it.
An engineer is NEVER relieved from the responsibility to manually actuate the bail feature , this includes locomotives equipped with DBI’s. Failure to do so is an operational failure. (at least on the railroads I worked for).
If your locomotive is operating the DBI in brake setup you should double check the system , it should only operate as soon as the handle is moved OUT of setup into braking.
I don’t bail the air if I’m going into DB on the new units, but I do on our older units, because they say we don’t have too. I got gigged when on the simulator for doing just that, so I quit doing it.
As far as the sliding wheels, that can, and does, almost always happen when the car is being switched somewhere, as opposed to going into emergency out n the road. Either someone will drag it out of a spot without bleeding the brakes, or an old-school railroader got up there and put his foot in the hand brake!
I’m a locomotive engineer for the UP and the train handling/air brake rules require you to bail off any automatic air brake application, even in dynamics. We are not to rely on the dynamic brake interlock valve to keep the independent released during an automatic application when in dynamic braking.
Jeff
i have never had to bail off my engin brakes while use ONLY dynmaic breaking to help maintain or reduse speed… the only time i have ever bailed anything off while in dynamic is if i set an automatic application for more breaking force… then yes… i have bailed off…but with just dynamic… never had done it…and have yet to see any brake cylinder PSI show up on my air gagues with just dynamic…
csx engineer
infact…even thow this totaly aginst the rules… (on some stepper but not long grades) i have on some occations put 10 PSI independant brake and put sand down while in dynamic to help shave another MPH or 2 off the speed to help hold it back if the dynamic is weak or im in the 8th notch of it… …it dose work…but they frown on it…and you dont want to go above 15psi or the dynamic brake interlock will kick in…and you lose all your dynamic untill untill you drop below the 15pis range agin… this was shown to me by an old head some years ago and have only ever used it a few times but it dose work to help keep your speed in check…totaly frowned appon…but sometimes you have to do what you have to do out there…
csx engineer
Keep these things in mind fellas;
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What clash didn’t tell you is that on UP units, if for some reason you knock the dynamic off while the automatic is still applied, the independent brake pressure builds back up to the level it should be when the automatic was put on to begin with!
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ALWAYS bail off in D/B if there is a BN unit in your consist. That is especially true for those Green & White units. They don’t have a DBI!