I have been interested in this concept for a long time. The need is obvious for operating in territory with steep grades and extremely cold weather. ECP brakes could address that need, but I am of the opinion that North American practice will never adopt them. The cost of conversion is deemed to be too great, and conventional pneumatic brakes work okay most of the time. Nevertheless, there is always the possibility of an ECP mandate if the need is highlighted by a major catastrophe.
The concept for automatic parking brakes for freight trains was highlighted by the Lac Megantic runaway, and more recently by the runaway at Field B.C.
This topic has come up before on this forum, but there have always been objections to the feasibility of automatic parking brakes. The discussion always veers into highway trucking practice of truck brakes being failsafe by applying by spring force when air pressure for the “straight air” brakes is lost. Always introduced is a fatal flaw scenario of trains suddenly losing their air and the parking brakes locking up at speed, kind of like putting your car in “park” at 60 mph.
But with a little more thinking, the way to avoid that issue and come up with the proper execution is clear. That is to set the parking brake by making either emergency application or a maximum service application. This application is then locked in by a mechanical means in the same way that when you close a door, the
Euclid that’s exactly how ours work. If your airline pressure drops below 60 psi we get a warning light in the cab along with a 120 dB buzzer that is to remind you that hey there is a problem with the brakes buddy and pull over. If you ignore those and let your air pressure drop to 40 psi then the emergency aka parking brakes apply automatically and slowly bring you to a stop. It’s about the same pressure being applied as a normal service stop. It’s fast enough to get you stopped but you still have control to steer. Then once you are stopped it remains applied until you have regained pressure to override the springs not in the brake chamber but the valves themselves. So unless the valves see over 80 psi in the lines after a brake failure event on our system they won’t even release the air to the chamber to release the brakes. This is on a 120 psi system. Now we do have runaway trucks sadly but those happen when drivers forget that you can climb a mountain as fast as you want as many times as you want. However you better remember slow and steady downhill wins every time.
Probably the same way brakes are released today - the control valve senses a rising pressure in the brake pipe. It would just need to have a way to un-set whatever mechanical mechanism if holding the shoes against the wheels.
This is interesting in that, unlike ECP brakes, it seems a brake system like this could be made to be interoperable with the existing brake systems on cars. Brakes still apply and release based on the signal provided by the brake pipe. Whatever complexities get added to “set the parking brake” would be traded off against not having to have a manual brake wheel and the associated linkage.
Just how are you going to switch cars off air? Especially hump yards, industrial locations that have no air to charge brake lines, my local siding that uses some type of mechanical vehicle to move cars, etc?
He’s gonna have fun paying AAR/TTC (MxV Rail) in Pueblo to validate his concept and pick him apart in Pueblo! (while he’s waiting behind the epb brake testing)
I have been looking for explanations of exactly how this new parking brake works. It is described in the TSB report of the Field, BC runaway.
That report is here: #R19C0015.pdf
You have to copy/past this pdf file into your browser to open it.
They mention this automatic parking brake in the report because it would have prevented the wreck. These are key details of the wreck:
As I understand: The method of emergency application recovery was a choice between setting retainers-or-setting handbrakes. Either method was deemed to be capable of achieving the recovery. Setting retainers was chosen because it would require far less time and labor than setting (and subsequently releasing) handbrakes.
However the choice of setting retainers was fatally flawed because the cylinder and reservoir pressure retention ability was negated by leakage of the cylinder packing due to the packing having lost its resiliency primarily due to relatively low ambient temperature. In other words, the retainer function could not retain cylinder pressure from a space that was otherwise leaking past the piston from the pressure side of the cylinder, and venting away to the atmospheric side.
Cursory reading of the TSB report to me indicates that the locomotives involved were not equipped with a pressure maintaining feature to hold the trainline air pressure steady. Secondly when the train stopped and 'a job briefing was held with the Trainmaster - the TM’s remedy was not sufficient for the crew to maintain control of the train - the apply retainers and ‘hope’ the trainline air pressure can be regained before it is necessary to make another brake applicaion is a guaranateed recipe for failure. There is no mention of Dynamic Brakes being used by either the original crew or the relief crew. The original crew, once the train was stopped in emergency DID NOT APPLY HAND BRAKES to any cars in the train.
I am not a Engineer, with that being said, I have worked with numerous engineers that are involved in handling trains on the worst main line grades on the former B&O’s mountainous territories with grades in the same neighborhood as those that were involved in the runaway derailment in the TSB report. The knowledge I have gleaned from those engineers collective experiences lead me to believe what CP was doing in the instance was in reality 'worst pr
The current air brake system allows for switching cars with the brake cylinder air bled off and air pressure still in the air reservoir. The air pressure remaining in the reservoir could keep the automatic parking brake released for switching.
You should not forget that cars may sit for days, weeks, or even more than a month especially at locations that store cars waiting for the need of that special product. Think speciality plastic pellets. These are often shipper or receiver owned cars.
Blue Streak1 we can recharge from totally empty a SIT car in our yard for movement in our yard if we do need to move it in less than 2 minutes with just the air compressor mounted on the engine on an OTR truck. Even a standard air compressor could provide enough air to release the brakes if needed then put a check valve and manual shut off to allow the car to be moved. When it is moved pull the air off and reset the brakes.
We have a trailer that was rear ended by a teenager in 08. The impact killed him and pushed the car in front of him under the trailer. Of part of the case was settled in 2010 but his family is still fighting in court the amount they’re supposed to pay. So that trailer is still sitting out in the back of our yard once a year to keep it legal incase we need to move it for the case we go to it hook up drag it into the shop grease it inspect it replace tires if needed document everything done to the freaking screw and why and put it back.
In my opinion, an ‘automatic parking brake’ that doesn’t hold at least as long, or as well, as a good manual securement is functionally worthless, and dangerously unsafe.
It should also not compromise positive application, or positive release, of the individual manual brake at the wheel or lever, which is not an easy thing to assure.
There should also be an unambiguous, easily seen from well outside the ‘fouling zone’ between or at the ends of cars, that shows the automatic function has engaged. If I were doing it, the mechanism would also ‘squawk’ some kind of transponder, like an individualized ELT, that would identify each car that is locked or released.
The possible functionality of an Automatic Parking Brake (APB) was described in 2019 by Wabtec/GE here, on page 26 (page 24 as it appears by page folio):
To quote: “This device will not replace the conventional handbrake, but could serve as a secondary securement device. It would automatically engage to retain braking force by mechanically preventing the brake cylinder hollow rod from retracting in the event the brake cylinder pressure leaks off. The device engages when brake pressure drops below a certain point. Otherwise, the device remains disengaged, allowing normal operation of the brake cylinder.”
That is my understanding. Here is how I would explain it:
Automatic parking brakes developed by Wabtec and New York Air Brake cannot inadvertently release due to leakage of air.
Here is how they work:
An emergency application of air brakes loads mechanical pressure to force the brake shoes against the wheels. Then a mechanical locking mechanism locks that air brake application force. Then if the air brake application air is released by any means, the mechanical lock will continue to maintain that stored brake force indefinitely unless the brake pipe of the air brake system is recharged. When the brake pipe is recharged, the mechanical lock will release.
So the locking action of the mechanical lock is not dependent of air pressure to keep it in a locked position. It only depends on air pressure to release it.
pick him apart in Pueblo! (while he’s waiting behind the epb brake testing)