How long does it take to release the brakes on a 120 car train as an example?
Can the engineer start the train even though all the breaks may not have released?
How long does it take to apply all the brakes on a 120 car train as an example?
Rio Grande Valley, CFI,CFII
The longest trains I run are all of 12 cars (of happy families enjoying a holiday train), so my recharge times are measured in seconds (sometimes more than others).
So I really can't answer your question.
But - if you haven't seen this essay, you need to spend a few minutes reading it. It may not answer your exact question, but you'll have a much better feel for brakes...
http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/north-american-freight.html
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Need more information than just how many cars. Like, what is the outdoor temperature? That may sound silly, but the ambient temperature has a large bering on how fast the brakes can be pumped up. Cold weather can cause an extreme length of time to get the pressure to the proper level... apparently cold air does not pump easily or fast.
BTW: That brings up an answer to your 2nd question. The engineer cannot start the train until the brake pipe pressure is above a certain level, regardless of whether the brakes have actually released or not.
Semper Vaporo
Pkgs.
Semper VaporoNeed more information than just how many cars. Like, what is the outdoor temperature? That may sound silly, but the ambient temperature has a large bering on how fast the brakes can be pumped up. Cold weather can cause an extreme length of time to get the pressure to the proper level... apparently cold air does not pump easily or fast.
Cold air 'pumps' just as good as warm air. What doesn't agree with cold air are all the rubber gaskets between each glad hand in the train line as well as some of the seals in each cars braking valves and pistons. Rubber tends to shrink (just like most things) when the temperatures turn cold. Shrinkage creates leaks and leaks allow air to go to the atmosphere instead of the brake resevoirs necessary to recharge the braking system.
In as much as car sizes run from 30 foot ore jennys to 300 foot intermodal 5 pack cars, stating a train size in cars doesn't mean all that much these days. Train size in the industry is normally stated in feet. 9000 feet, 10000 feet and upto about 15000 feet in 'normal' train lengths.
Never too old to have a happy childhood!
One could argue that cold air actually pumps better than warm air - it's denser. As noted, it's all the temperature sensitive components that cause the problems. Stories abound of long trains that take hours to pump up from zero in sub-freezing temperatures.
JPS1 How long does it take to release the brakes on a 120 car train as an example? Can the engineer start the train even though all the breaks may not have released? How long does it take to apply all the brakes on a 120 car train as an example?
The answers to the first and third questions start with knowing how fast the pressure front to set or release the brakes travels. In the 1970's when I was riding locomotives, no I have never been an engineer, I remember being told that the set wave traveled 13 cars per second. Assuming an average 50 foot brake pipe length that is 650 feet per second. I have this speed in my book collection somewhere, but I think that figure is close enough for this purpose.
Upon detecting the set command, each control valve moves to send air from its auxilary reservoir to its brake cylinder. This takes time, say a second. Then the brake rigging must move to bring the shoes against the wheels. In the conventional brake rod system this probably takes another second. I would figure 15 seconds for all the brakes to be working as hard as they will given the reduction.
The release command should travel at the same speed as the application, and the time taken to release on each car is probably about the same, say 15 seconds for full release.
As to the second question the answer is yes for short trains, but not a good idea for long ones. With enough power you can start a short train as the brakes release. With a long train the issue is slack and how fast the head end is going when the draft forces reach the rear block of cars on which the brakes are still set. This is how trains get pulled apart on starting and is cause for the engineer to recieve 40 lashes due to the damage, delay, and cost to fix what broke. If it is just a knuckle it may not be a big deal. If you break a coupler head off or pull a drawbar it will probably be hours to fix. Very bad!
Mac
Technical question. Do all locos today have cooling for compressed air ? So how warm is the air going into the brake pipe and how much will it cool reducing the pressure in the brake pipe ?
PNWRMNMThe release command should travel at the same speed as the application, and the time taken to release on each car is probably about the same, say 15 seconds for full release.
I don't believe any such thing occurs. The release "command" at the triples is not sonic but pressure-activated, and building appropriate pressure for release at the 'last' triple (furthest from the air-compression sources, or slowest) will likely take much more time than a 'release command' would -- assuming you could reliably create a charge-pressure differential the length of the brakepipe that was the magnitude of the application 'command'.
The technical advantage of ECP is not limited to graduated release; it has the ability to pass a release command nearly instantaneously down the length of even a long train so that the release time becomes valve- and reservoir-determined.
On the 'technical question' -- yes, modern locomotives have post-compression cooling. Look at the temperature rise for compression to 140psi and you will quickly understand why. The air in the reservoir will further try to 'equalize' in temperature with ambient conditions outside the reservoir, and since reservoirs and brake piping are seldom insulated, I doubt this takes much time.
So I'd assume air in the brakepipe starts at or very near ambient temp, and of course its temperature starts to fall the moment it starts expanding and losing pressure. Nominally a given mass of air that was compressed to 140psi (and was then aftercooled) will need the same heat "put back" to reach equilibrium. (This is a major reason why eliminating water from the brake air is significant.)
RMEOn the 'technical question' -- yes, modern locomotives have post-compression cooling. Look at the temperature rise for compression to 140psi and you will quickly understand why. The air in the reservoir will further try to 'equalize' in temperature with ambient conditions outside the reservoir, and since reservoirs and brake piping are seldom insulated, I doubt this takes much time.
The idea of cooling the compressed air far predates current locomotives - look at the piping "folded" under the running boards of many steam locomotives.
That cooling takes place can be found in the inspection instructions for locomotives - one needs to drain the air in the main reservoir. On a humid day, there can be quite a bit of water there. Our locomotives are shut down at the end of the day, so by morning there is usually zero pressure in the main res. I usually open the drain and walk away for a while...
As for the release, as I recall (and it may be in Krug's essay), these days when the "triple valve" senses a release, it dumps a little air from the emergency reservoir into the brakeline, speeding the return to a full release.
tree68 RME On the 'technical question' -- yes, modern locomotives have post-compression cooling. Look at the temperature rise for compression to 140psi and you will quickly understand why. The air in the reservoir will further try to 'equalize' in temperature with ambient conditions outside the reservoir, and since reservoirs and brake piping are seldom insulated, I doubt this takes much time. The idea of cooling the compressed air far predates current locomotives - look at the piping "folded" under the running boards of many steam locomotives. That cooling takes place can be found in the inspection instructions for locomotives - one needs to drain the air in the main reservoir. On a humid day, there can be quite a bit of water there. Our locomotives are shut down at the end of the day, so by morning there is usually zero pressure in the main res. I usually open the drain and walk away for a while... As for the release, as I recall (and it may be in Krug's essay), these days when the "triple valve" senses a release, it dumps a little air from the emergency reservoir into the brakeline, speeding the return to a full release.
RME On the 'technical question' -- yes, modern locomotives have post-compression cooling. Look at the temperature rise for compression to 140psi and you will quickly understand why. The air in the reservoir will further try to 'equalize' in temperature with ambient conditions outside the reservoir, and since reservoirs and brake piping are seldom insulated, I doubt this takes much time.
Modern locomotives have a 'spitter valve'; this valve, attached to the air system operates periodically to 'spit water' out of the air system. On a humid day you will hear it operating about every minute or so.
tree68As for the release, as I recall (and it may be in Krug's essay), these days when the "triple valve" senses a release, it dumps a little air from the emergency reservoir into the brakeline, speeding the return to a full release.
You do recall correctly. Accelerated release is a feature both of ABDX and DB60 brake valves.
A very short discussion of the "history" of accelerated release up to the mid-Sixties can be found in patent 3175869 (which 'added' the accelerated-release equipment in an adapter between an AB valve and its mounting, much as some systems of ECP brake 'add' their equipment for cutover). See 'device 72' for the mechanism they use to produce the 'acceleration' - it would be interesting to consider the specific physics of how sequential activations of these devices would, in fact, create an effective rise transient to activate subsequent valves quickly, net of the action of the chokes. The patent for the ABD valve is 3966269.
Patent 3706480 (circa 1971) contains a description of how the accelerated release is intended to work. In part this notes:
This supplements the rise of brake pipe pressure which has been started by the brake control value and assists in rapid transmission of brake release from one such apparatus to the next such apparatus connected to the same brake pipe in a train. The pressures on either side of the pressure responsive member 40 equalize fairly rapidly by virtue of the choke 42 and the valve closure member 39 is thereby quickly reclosed so that the flow of air from 32 to the brake pipe for accelerated release is only of short duration.
It is quite possible that this could be adjusted to produce a rapid cumulative rise in the brakeline pressure, which is effectively the same as Mac indicated, if we presuppose that a full release cycle is required before reapplication (via reduction in brakepipe pressure).
Some of the implications for 'coexistence' of this system with emergency braking are in patent 3734575.
A chart I have in a 1974 RI Train Handling and Air Brake Instructions shows Time to Initiate Release on Last Car. It shows values for ABD and AB equipment. The table is for release of a 20psi reduction from an intial 80 psi brake pipe pressure (the standard at that time) with minimum brake pipe leakage.
50 cars (2500ft) ABD 4.5 sec AB 6.9 sec
100 cars (5000ft) ABD 8.4 sec AB 13.3 sec
150 cars (7500ft) ABD 13.5 sec AB 31.0 sec
There are other charts showing the effect of higher leakage and/or lesser reductions on time it takes to release the last car. I found a link so you can see the actual charts. Scroll down to page 15 and 16.
http://www.snugglebunny.us/_bigfiles/RI_Air_Brake_rules_1974.pdf
Jeff
Semper VaporoBTW: That brings up an answer to your 2nd question. The engineer cannot start the train until the brake pipe pressure is above a certain level, regardless of whether the brakes have actually released or not.
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While stopped to set off cars, I have seen the the pressure dropping on the EOT while making a brake application and then watch the pressure on the rear start to rise again after the brakeman closed the anglecock before the application had quit exhausting and we had cut away from the train.
BigJim Semper Vaporo BTW: That brings up an answer to your 2nd question. The engineer cannot start the train until the brake pipe pressure is above a certain level, regardless of whether the brakes have actually released or not.
Semper Vaporo BTW: That brings up an answer to your 2nd question. The engineer cannot start the train until the brake pipe pressure is above a certain level, regardless of whether the brakes have actually released or not.
Semper Vaporo BigJim Semper Vaporo BTW: That brings up an answer to your 2nd question. The engineer cannot start the train until the brake pipe pressure is above a certain level, regardless of whether the brakes have actually released or not.
What you witnessed was 'working to the rule'.
From the situation you described, Engineer was PO'd that crew was instructed to pick up cars and even worse after the train had stopped with the understanding (right or wrong) that there was no pickup and the train had been stopped 'neat' with the road crossing. Once the pickup was ordered the crew knew (and everyone in the decision chain SHOULD have known) that road crossing(s) were going to be blocked and blocked for some period of time.
Air Brake Rules (at least on my carrier) state that the EOT needs to be indicating 75 pounds air pressure at the rear of the train before moving. Brakes release with less than 75 pounds in the trainline. One thing not specified in the narrative is if the pickup had been air tested and being held on 'yard air' or not. If the pickup had not been air tested and on yard air within 4 hours of the train making the pickup a Class 1 Brake Test must be performed on the cars picked up - for that to happen, the trainline needs to be pumped to at least 75 pounds, then the brakes are applied and the Conductor walks the pickup to insure all the brakes applied, then the brakes are released and the Conductor walks the pickup to insure all the brakes have released. In most cases this will be done prior to coupling the pickup to the train - but it is not REQUIRED to be done in that order.
For the train to pull after the required air pressure is registered on the EOT and then go into emergency is no the function of a 'kicker'. Kickers happen when air brakes are being applied and a brake valve on a individual car changes trainline pressure at a faster rate than the allowed service rate of change. More likely some person in the vicinity of a blocked road crossing vandalized the train and pulled a cut lever and when the train started to move it became uncoupled.
When it comes to 'pressuring' crews about operations around road crossings (or anyplace else) - the crew holds all the cards. The more you pressure them the more rules they will find that they must comply with and delay the operation further.
Semper VaporoLike, what is the outdoor temperature? That may sound silly, but the ambient temperature has a large bering on how fast the brakes can be pumped up.
This gives me a chance to retell a story I posted a number of years ago.
One winter in the mid-seventies we had a long stretch of -20º F and lower days. Dad was leaving at the end of his dispatching shift on a Sunday when very higher up's were not usually around. He was very surprised to meet one them in the elevator. As it happened, both him and my Dad had been Operators together in the late 1940's, and the other fellow spoke more freely than he might have otherwise.
The man was totally furious. "We can't run trains any bigger than we did with steam!" At this time they had a fairly new fleet of SD40-2's. Air leaks because of contracted joints were doing them in. This guy knew the problem and he couldn't shift the blame to anyone.
It has been thought since, DPU units with their additional air pumps, which always function the same as the lead unit, are more important in winter railroading than the extra power they provide.
In Dad's time DPU's were a mountain railroad thing, now you see them all over North America.
Bruce
So shovel the coal, let this rattler roll.
"A Train is a Place Going Somewhere" CP Rail Public Timetable
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BaltACDWhat you witnessed was 'working to the rule'.
What is the grade on the track in question? If it's on a good downhill (or near one), you damn well want a good charge before moving. Otherwise you'll be digging pretty deep to get an application if the need arises.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.
zugmann BaltACD What you witnessed was 'working to the rule'. What is the grade on the track in question? If it's on a good downhill (or near one), you damn well want a good charge before moving. Otherwise you'll be digging pretty deep to get an application if the need arises.
BaltACD What you witnessed was 'working to the rule'.
I don't know the grade, but it is very slight, and uphill in the direction the train was headed. In watching trains from the other end of the Beverly yards (this event was at the east end), it appears there is a crest about 2+ miles to the west, but I have no idea what the grade down from that crest is, but I can't believe it is of any significance, nor it is long.
Picking up cars that need an intial terminal air test require that the brake pipe pressure at the rear of the train* to be within 15psi of the feed valve setting. For the 90psi pressure most railroads now use, that's 75psi. Besides train line pressure, the air flow must be 60cfm or less before the test can begin. For those engines that can't measure air flow, a leakage test is required and leakage can't be more than 5psi per minute.
If the cars are already air tested, once in the train the rear end still needs to be brought up to at least 75psi and a set and release test is required. The leakage/air flow test isn't required unless the brake test was done with a yard air plant.
Anytime cars are being added to a DP train, between the engine consists, a brake pipe continuity test is required. To run the test, air flow on all consists must be 20cfm (or less) or the brake pipe stabilized for at least 90 seconds. Otherwise the test will usually fail and you have to start over. Even in good weather it seems to take forever to meet either of those requirements.
SV, were you watching at Edgewood Road? For those not familiar with the area, the problem of blocking that crossing has been solved. They built an overpass.
*If the conductor has a hand-held gauge, the road crew could do the brake test and inspection in the yard. Once on the train they would still need the set and release test.
jeffhergert {snip} SV, were you watching at Edgewood Road? For those not familiar with the area, the problem of blocking that crossing has been solved. They built an overpass. Jeff {snip}
{snip}
Yep, Edgewood Rd. That overpass is a frustration for railfanning... could've been a great place, but the pedestrian walkway is on the wrong side of the bridge and traffice can be way too dangerous to stand on the west side to view the yard. And the concrete sides are too tall to see over when driving across in anything other than a tall semi's cab!
Do you know the grade there? Or what the grade is to the west near Farfetched (err... i mean Fairfax)?
0.29% from about the small curve west of the yard to about where the yard office is.
It may be different here in Canada but the requirement to have 75 pounds on the tail end before moving is absolutely not true. You do need 75 (or within 15 pounds if the EQ setting) to do the initial brake test.
Online, if I take a full service application on a fully charged train and bring my tail end down to 62, I can start pulling on the train the second I put the brake handle to release. If I am starting on a hill I need to pull against the release so I don't start rolling back. (You'd need to do this with any brake application where the engine brakes can't hold the train.)
On flat track, I would wait until I got a pressure rise on the tail end. I still don't need 75 before I start to pull.
Here in Canada we have a very scary rule in our book. When enroute, trains only require 60 pounds on the tail end as long as the flow is 60 cfm or less (90 cfm or less with DP as long as one unit does not exceed 60). A train has to pass the initial brake test at the origin terminal - back to the 15 pounds of the EQ setting.
That means, if I have a train with only 60 pounds on the tail end, I have only ONE shot at taking the air and I HAVE to take it to the over reduction or emergency since my tail end is already lower than a full service. How this is allowed and enforced boggles my mind.
This 60 pound thing only ever comes into effect during the winter when air just can't get to the tail end of these huge trains they just don't want to shorten.
Our train handling rules state we have to have a reduction stable for 30 seconds before we can release the brakes. On an 11000 foot train, many times you have to come to a stop before you can release or you will come to a stop before they fully release as you're not allowed to increase throttle until you have a positive release on the tail end. If you do release when you're not supposed to on the longer trains you may come to a stop with your train in more than one peice.
As said before there are so many factors in how long it takes.
Length, temperature, equipment type, number of cars.
Auto racks and intermodal take longer to release. Intermodal I find is the worst. Tanks and hoppers seem to be the best for applying and releasing quickly.
Having a remote in the middle or tail end (or both) drastically increases the speed in which the brakes set up and release. As mentioned earlier with an 11000 foot train I'd lose most if not all my speed waiting for a set up and a release before I can start putting throttle to the train again. With a well positioned remote I essentially have two 5500 foot trains and can apply and release and not lose much more speed than I need to.
I don't agree with temperature not having an effect on the air. Yes, it causes shrinkage and increases leakage but air just doesn't want to move the same. I've had 6000 foot trains at -30 that can't qualify, the car department can't find any leaks to do anything with. As soon as that sun comes up you're good to go.
When it gets below -25C that's when things start to really hit the fan. -40 nearly grinds us to a halt because they just don't want to reduce trains to a reasonable length.
That brings in a whole new issue of the engines getting cold and not working.
10000 feet and no dynamics? Today is going to be a good day ...
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