You are correct. But that scenario still fits our rulebook's definition of bottling air (leaving equipment without a angle cock open) so it was necessary to make a specific exception for this scenario.

Interesting. So I have to assume one of two immediate possibilities and I don't have a COR book here to look it up in. Either there's a problem with my Canadian/English translator (happened plenty of times with Canadian crews before ;-) ), or perhaps since I retired there's been introduced some brake programming that allows a remote unit to maintain a previously set BP pressure while the head end is removed - purely as a maintenance/monitoring function? Seems like it from the way your DP post reads. Am I correct? Please explain if other - I don't keep up with the modern stuff much any more. Because if you're just setting up a DP unit as a leader you're really just making a train with power in the middle and yadda, yadda, yadda... And if that is the case, then I would agree that it would be another instance of permitted bottling of the air, since the brakes are applied and maintained, but not by a leading/controlling locomotive.

Just as a technical clarification I find I need..

First, I think we established that illegal 'bottling' is leaving a cut of cars with both ends of the air line closed off, blocked from rolling only by a service application of the air brakes, without setting handbrakes for a securement, and that the chief reason for this being illegal (and inadvisable) is related to the accelerated release 'feature' being present and potentially releasing the set without advance warning.

A bit Talmudically, what then is the situation when a DPU locomotive that has its engine shut down is coupled into a 'bottled' cut, it behaving like any locomotive being transported dead-in-train or isolated as far as brake operation is concerned, no? And how does that change when the locomotive is set to 'wake up' upon perceived fall in cylinder application pressure (or the functional equivalent in the valve setup) and set the emergency while there is still adequate service-set pressure to hold the cut while the emergency is further pressurizing the cylinders?

I'd think that if you had a cut secured only by service application (with bottled pressure on the trainline) you would not gain anything in service-set 'integrity' by subsequently pumping up the trainline to a higher pressure from an 'awakened' attached locomotive. Wouldn't that have the same effect as pumping up the air in this situation generally does -- set up a release and recharge? (Of course, according to what was said, at the first 1mph of detected movement the locomotive will vent to emergency, but that's a separate programmed valve function...)

I read into it, from sd70's post, that the DP unit has a 'standing maintenance' program that will use the loco's main reservoir to maintain the brake pipe at whatever pressure the cut was parked with, and will, if it can't for some reason maintain that pressure from the reservoir, either start the engine to recharge the main reservoir or alert someone via automated message that there's a problem. I'm hoping sd70dude can enlighten us. Seems like a very useful function in the age of DP, if you can trust the technology, but I won't go into that here.

Is this not exactly the scenario of the Lac Megantic oil train run away?

No, in a number of technical respects.

At Lac Megantic the automatic brakes were never set; the train was left 'hanging' on a combination of the independent brake (straight air, acting only on locomotive axles) and a prescribed number of handbrakes ... which turned out to be grossly inadequate even by company rules.

The straight air is dependent, directly, on the train-pipe pressure (which was being maintained by the locomotive(s) that were running, so all would have been well, except:

Harding (more or less on direct orders from the folks in Farnham) left only one engine running, the demonstrably very sick lead unit. (If the air compressor on this unit had been left running, or some key valves on it left 'as built', all still would have been well)

Unit catches fire, firemen respond and shut down unit -- no more air pumping (and at this point, had the following item not been 'in play', the consist would be as close to technically 'bottled' as it would get, with trainline pressure high between closed angle cocks, but note at this point there is a key difference (you'll get the same sort of result, but through two very different mechanisms). At Megantic, a slow "enough" leak of trainline pressure would eventually cause the cylinder pressure to sag down to where it wouldn't hold the train; in illegal 'bottling' anything causing enough of a pressure excursion would trigger the 'accelerated release' to kick an automatic-brake service application off, presumably 'very quickly', to where it wouldn't hold the train. Note that the idea was NOT to make an automatic-brake application in this case, as I recall so that a walking brake-release test wouldn't be needed for a single-man crew in the morning, so the 'bottled' argument we've been discussing wouldn't have been applicable.

The final domino at Megantic was that the idiot FRED at the back of the train was cheerfully spinning its little turbine, keeping that important little red light blinking at the back. Note that by design this turbine is sized and controlled so it does not reduce trainline pressure enough to cause either a set or emergency application through quick pressure reduction or a sonic pulse through the trainline... don't want those UDEs, don'tcha know) and of course the idiot firemen had no idea this was happening at the other end. In their defense they did ask 'railroad people' but it was the wrong questions to the wrong railroad people; had it not been the Fourth of July holiday it's likely someone would have been informed of this little shenanigan promptly, responded with the appropriate screaming, and all would have been well long before...

... that little turbine spun, and spun, and spun, and the independent slowly sagged off to where the train started to move, and the 2% grade and sharp curve did the rest.

(Even at that, had the crude oil been properly degassed, it's likely the explosion horror would have been less. You will notice that there have been very, very few 'fireball videos taken in the Blast Zone' since this became, quietly, SOP for crude with lotsa light fractions. But that's not part of the brake discussion.)

That's pretty much what it does, and as long as the Autostart system is working properly the DP unit should restart whenever its main reservoir drops too low.

Our procedure for this is as follows:

1. Apply and test handbrakes if required at that location.

2. Make a automatic brake reduction of at least 15 PSI and wait for the exhaust to cease.

3. Using the computer screen in the lead unit, place the DP unit in "Set Out" status.

4. Close both angle cocks, uncouple from the trailing portion of the train, and proceed with your work.

CN started doing this about two years ago, before that we had to place the DP unit in "Brake Valve Out" as well as "Set Out" status, and leave the train vented or in emergency. I understand from discussions on other forums that Union Pacific does this now as well, but I am not sure about the other railroads.

It was indeed made possible with a software upgrade, but not all the locomotives have received it. Notably, the few former BC Rail locomotives (the GE Dash-9's) that have DP are not set up to do this, and we are not to try it with foreign locomotives either.

This is a very useful function, and saves a huge amount of time in winter. You just have to be careful not to accidentally have the lead locomotive go into emergency, or the DP unit will go into emergency too. For that reason I turn the DP radio breaker off while the conductor is cutting in the air, or while we are doing a shop track brake test on locomotives (required after modifying the locomotive consist, testing the emergency brake is one step). All turning that breaker off does is make both units think they are in comm loss, and as long as you recover the lead unit before turning the breaker on again the DP unit will never receive an emergency signal.

I have seen the DP unit initiate an emergency brake application on several occasions when it detects what it perceives to be an unintentional release. Not being back there at the time I can't say for sure whether or not it was right. But I do know that movement over 1 mph triggers it to go into emergency, if the DP unit happens to be where you uncoupled it will often go into emergency when you couple onto it again, normally with a large number of cars in our case.

SD70dude - Thanks for the info. Now I'm curious if this is a Canadian thing, or if it's common down here too. I'd guess the latter given the increased use of DP and monster trains all over. And now, back to our regularly scheduled program....

Back in the days of QARR, we bottled the air during our run around. We made about a 20lb reduction and the conductor set one handbrake. Run around, and couple up. UC and D-22 valves, 90psi train line.

Right or wrong, it worked for us. Train was attended by conductor and at least one trainman.
Steel cars, HEP heat and air, kitchen and bar onboard with live band on the dinner train, and steam loco.
Other steel cars, snack and soda cart, and steam loco for excursion train.

Bottling of the air has caused countless accidents over the years. It only takes one car with a moderate leak, to start the release of brakes on all the cars. With heavy cars on a grade this can happen quickly. If a accident does happen you are going to get the book thrown at you and possible jail time. I understand you are trying to save some time but it doesn't take long to pump up the air on short freight or passenger trains (probably less than 5 minutes). The risk is hardly worth the laziness.

One important point:
The Queen Anne's RR operated on what was probably one of the FLATTEST stretches of track any regular excursion ever operated on (anything out of the Gold Coast RR in Miami would be another contender). You might not be able to find enough of a grade to get a runaway going if you stretched that track all the way across the Delmarva Peninsula. My Google Earth estimates the difference in elevation from the Intracoastal Waterway Bridge to the junction as being about 35 feet in 13 miles.....

If you're wanting to cut down on the time it takes to get your train line pumped back up when "swapping ends", but aren't allowed to bottle the air.. here's a little trick you can use to shorten the time required.

When you drop the air on a train, the brake valve connects both sides of each car's air reservoir to the brake cylinder. Emergency and Service. Maximum stopping power.

When you couple your engine back up to cars and cut in the air, you're refilling both sides of each reservoir. That's a lot of cfm to get them charged back up... and it takes time to do that.

The thing to do is to tell your brakeman to hold his horses and give you a minute to draw down the train line to around 40 pounds before cutting you away from the cars.

Getting the train line down to 40psi prevents the emergency side of the brake valve from sensing the sudden drop in brake pipe pressure and initiating an emergency application and dumping it's side of the reservoir into the brake cylinder.

Therefore, the emergency side of the reservoir is still full and doesn't need recharged when you couple back in to the train. All you're recharging is the "service" side of the reservoir.

The brake cylinders on each car are still pressurized with a full service application, so this is not anything "illegal". All on the up and up.

This is the thing thoughtful engineers do during frigid weather, so that the valve spools inside the brake valves on the cars don't freeze/stick and cause problems with "stuck vent valves" ..... making it nearly impossible to recharge a brake pipe after recoupling.

I think this thread has migrated from its original intent. Long story short, Strasburg has it figured out.