Talk:Railway air brake

More facts to be worked in
Here are some other random facts and/or edits I was planning on working in, but I ran out of steam (no pun intended).
 * On the Alaska Railroad, trains operating entirely with passenger equipment operates with the train line at 110 psi. Other trains (i.e. most freights) operate at 90 psi. BNSF operates at 105 psi and 90 psi, respectively, and Amtrak has their own regulations. Working some of these numbers in might be a good contribution.
 * Speaking of which, these settings are set by the regulating valve. Need to discuss this, too.


 * Perhaps more detail about individual brake system components--like the triple valve, which is made up of three portions (the pipe bracket, the service portion, and the emergency portion), and the exhaust port, which at least in the U.S. is a "retaining valve," which can be used to affect the way the brakes release.
 * To someone not familiar with the system, I wonder if it's all too confusing. I think we need to reorganize and/or rewrite it so that a lay person can understand the mechanism behind how it works--in other words, that a REDUCTION in brake pipe pressure creates a TRANSFER of air FROM the (U.S.: service portion of the dual-compartment) reservoir TO the brake cylinder, and an INCREASE of brake pipe pressure causes the air to EXHAUST FROM the brake cylinder and also to RECHARGE the reservoir. Upon second observation (the need for which is why I'm NOT trying to edit the article right now), the bulleted list near the beginning of the overview section is an excellent start, but I still think it may not be clear to normal folks exactly the way the air flows through the system. (If someone could come up with an animation, that would be absolutely killer!)
 * When the brake cylinder releases, the air is exhausted both because it is under pressure but also because there is a spring in the brake cylinder (without the spring, the brake shoes would still rub against the wheels).
 * Various service reductions cause various amounts of air to transfer to the brake cylinder. For example, a minimum service application, which (in the U.S.) reduces the brake pipe pressure by ~5 psi, transfers a small amount of air to the brake cylinder, while a full-service reduction (~20 psi) equalizes the pressures between the service portion of the dual-compartment reservoir and the brake cylinder. An emergency application results in an equalization of both the service and emergency portions with the brake cylinder, making the total air pressure in the brake cylinder around 73 psi, I think--I have the chart out in my car.
 * Related to this, the dual compartment reservoir's service and emergency portions (at least in the U.S.--I wish I knew more about how we compare to other countries!) have 2500 cm^3 and 3500 cm^3 of capacity, respectively. The brake cylinders hold 1000 cm^3 of air. Because the reservoirs hold the same pressure as the train line (i.e. 90 psi in an American freight), these ratios determine how much pressure will end up in the brake cylinder. This might be good fodder for a table.

I know I'm barely making sense here, but I figured I'd spew all this info out before I forget it all. If anyone can take the above info and run with it, feel free--otherwise I will hopefully not forget to come back and try to straighten this all out. Check out this link, which is linked to at the bottom of the article, and see if you can pry any ideas from there (without performing a copyvio, of course). A quick glance at that page seems to indicate that it's well-written. Also see the companion page discussing specifically North American brake systems.

cluth 05:26, 8 September 2006 (UTC), (who really shouldn't be typing right now)


 * Q: If the standard air pressure varies amongst railroads, would Electronically controlled pneumatic brakes help overcome such differences?   Tabletop (talk) 04:05, 22 November 2010 (UTC)


 * I'm an ordinary (non-technical) person who (I think) grasps the basic concepts pretty well. I was first exposed to the topic in an article published in Trains Magazine back in the '60's or '70's.  I would like to see a bit more information on the triple valve.  I have a difficult time imagining just how this part works (and a cutaway drawing in the magazine article did not help much).  In addition, cluth's entry, above, introduces a new question for me.  Is the "retaining valve" in U.S. operations a separate valve?  Or is it a function of the triple valve when that valve is set in a certain way?  My impression is that a train's crew will set the "retaining valves" on the train's cars when the train is about to begin, for instance, a long downhill run requiring control of speed and the conditions are such that normal operation of the train brakes will not offer sufficient (safe) control.  NorthCoastReader (talk) 02:40, 12 February 2012 (UTC)

Terminology
Not to be overly pedantic about it, but "trainline" is a single word&mdash;not "train line." However, what is being referred to in the article as a "train line" is in reality the "brake pipe," which is two words. :-) Generally speaking (in North America) the term "trainline" usually refers to electrical interconnections.  I've heard the usage "trainline air" to refer to locomotive main reservoir pressure being conveyed to cars (e.g., for dual pipe brake systems, pneumatic door operators, etc.), but never for the brake pipe itself.  We should try to keep the terminology in line with customary railroad practice.

BDD 19:23, 7 March 2007 (UTC)


 * @BDD - as one who works in the business (incidentally, also kind of a pendant, too—I guess if we weren't we wouldn't be on Wp, much less commenting on a talk page!) I'd love to see a crisp distinction between BP & the electrical signals you mention (those in the MU cable.) Unfortunately, I don't find things as crisp as you say. For example, the term train[ ]line emergency is used for a break in the brake pipe, whether due to a conductor valve or a train separation.
 * That said, I think it would be best for the article to refer to the BP as such consistently.
 * Tuna Fish 5 (talk) 23:36, 2 January 2021 (UTC)

Just to add some words, I have here a brake supply drawing from a Erie built GE 85 Ton shunter: the air line are named as "Brake Pipe", "Main Pipe" and "Main Reservoir Pipe". --Hosdo (talk) 15:51, 16 October 2012 (UTC)


 * @Hosdo -
 * Brake Pipe is the line that feeds the whole train. (The train[ ]line, if you will!)
 * MR Pipe is the line that shares main reservoir air among locos in a consist. Is is done so air compressors on trail locos can help charge the BP, plus other reasons.
 * Main Pipe is a term I've never heard. Perhaps it's specific to shunters?  (a specialized variation on MR pipe, maybe?)
 * Other pipes on North Americal 4-pipe road locos (connecting locos in a consist) would be the 20 pipe and the 16 pipe (Independent Application & Release Pipe (IAR.))  3-pipe locos (outside NA, normally,) would use a single BCE (brake cylinder equivalence) pipe in place of these 2 between locos.
 * Tuna Fish 5 (talk) 23:36, 2 January 2021 (UTC)

International Clarifications
In the UK, "train line" is commonly understood to mean a railway route (e.g. between two cities: "the train line from London to Bristol"). If "break pipe" is an equally suitable terms to train line then perhaps it should be used instead (I'm not a specialist in this area).

Again in the UK, the "trainline" is often the name of the electrical feed used in locomotive multiple working. It means that a driver's desk has been switched on and results in power being applied to the electrical machines - exhausters, compressors etc.

Again, I'm not a train engineer but I do travel regularly by train in the UK. I've never been aware of an engineer connecting pneumatic pipes between trains as two trains are combined into one (or vice versa). Do UK trains use a pneumatic line, or do they tend to have electronically controlled brakes? This article is written to imply that all train brakes are pneumatically controlled (which may well be the case).Thelem 02:52, 10 March 2007 (UTC)


 * What you are probably seeing is one of the newer automatic couplers - the various pneumatic and electrical connections are all contained within the coupling and are connected as part of the coupling process. All trains, as far as I am aware, have continuous pneumatic brake connections - even if they are applied electrically. This provides a fail safe in case of a problem with the electrical system.--Thepurpleblob 11:59, 31 July 2007 (UTC)

Here in the USA, we occasionally use the word "line" to refer to a railroad, although seldom with the word train. In North America, any railroader, upon hearing the word "trainline," will immediately think about electrical interconnections that run the length of the train. The same term has the same meaning in electrically propelled subway or elevated trains as used in urban transit systems.

Cables that link the trainlines of one car to another (or one locomotive to another) are often called "jumpers," such as the 27-pin MU cables that join locomotive control systems together. Similar jumpers are used to convey hotel (head end) electrical power back to passenger cars, link automatic door control systems together, and so forth. In other words, most railroaders, at least here in the "New World," will immediately think electrical when trainline is mentioned.

I can't recall ever having heard the brake pipe being called anything but a brake pipe, as it has a very specific role in the overall control of the train. If another pipe passes locomotive main reservoir air pressure back to the cars it is called "trainline air" and is understood to be air at relatively constant pressure (the brake pipe pressure, of course, varies according to how the engineer manipulates the automatic brake). By the way, air connections between locomotives are generally called MU hoses&mdash;their function relates to locomotive control and not general train control.

Regarding what type of braking system may be used, it depends on your definition of "train." If you include subway or elevated trains used in metropolitan rapid transit systems (what we Yanks often refer to as the "el" or "L"&mdash;the former a New York City term, the latter a Chicago term) into the "train" definition, then no, not all trains use pneumatic braking. For example, the L trains in Chicago use a combination of dynamic (rheostatic) and electromechanical braking and, in fact, the dynamic system is the primary means of reducing speed. There's also an auxiliary track brake that may be used in an emergency if the rails are slippery.

As a practical matter, pneumatic braking styled after Westinghouse's invention is nearly universal on locomotive-hauled trains due to the weight involved and the relative simplicity of the system&mdash;especially important if there are a lot of cars. I'm not familiar with the technical details of how UK electric trains are braked, but I suspect that, again due to weight, as well as speed, it is most likely an electro-pneumatic system.

As for coupling up air hoses, the trains on which you normally travel are designed so that all interconnections are built into the coupling mechanism, obviating the need for anyone to get down between cars and connect hoses. This arrangement is very common with electrically powered transit vehicles and is nearly universal on North American rapid transit and light rail (tram or street car) applications.

BDD 05:35, 16 March 2007 (UTC)

Within the global railway industry, the term 'trainline' (one word) is internationally accepted and understood. It refers to a connection (pneumatic or electrical) that is carried between vehicles in a train. It does not refer to a 'rail line' (a line of railway) as has been suggested here. The use of the word 'train' where the writer actually means 'rail' or 'railway' is like a father telling a young child "Look at the big train" when they are pointing to a locomotive. It's OK for the kids but it's Thomas The Tank Engine stuff... it's naff and it has no place in in this section of Wikipedia. 203.153.205.105 (talk) 10:38, 12 August 2013 (UTC)

Call Casey Jones?
Something on the history/development of railway brakes would be of interest... TREKphiler  hit me ♠  18:43, 4 August 2008 (UTC)

Electro or Electronic?
This is a bit out of date:

Electro-pneumatic brakes are currently in testing in North America and South Africa in captive service ore and coal trains.

Should be Electronically controlled pneumatic brakes, which by 2012 are going into service. Tabletop (talk) 22:56, 9 August 2012 (UTC)

See Longest trains

Tabletop (talk) 11:16, 1 November 2008 (UTC)

Electro-Pneumatic brakes
I noticed the recent addition of the Westinghouse HSC electro-pneumatic braking system to the article, but the edits missed a few key advantages of this system. Due to the fact that the "straight-air pipe" is charged and discharged by solenoid valves on each and every car of a train with HSC braking (air supplied by aux reservoirs on the cars, charged from the trainline), it can react much quicker than the standard airbrake system (charged and discharged only at the controlling locomotive, and slightly delayed by the valving). The EP system also allows a much more graduated release than is available via the trainline (with 24RL or D-22L locomotive brakes, you are typically limited to only 2 or 3 graduated releases per application).

A minor point that could be added to this section would be a mention of the D-22L brake system, which was the original HSC locomotive brake schedule. D-22L used the service and emergency valve portions of the D-22 passenger car brake schedule, with additional portions (including a unique brake stand and independent brake valve, visually resembling, but not interchangeable with, 24RL equipment) to allow for independent brake and other locomotive braking functions. To my knowledge, only 1 operable locomotive still exists with D-22L, CB&Q EMD E5A 9911A, at the Illinois Railway Museum. Wuhwuzdat (talk) 17:18, 16 May 2009 (UTC)

Article is written in the US dialect of English
Please discuss any rationale for changing to another Dialect here. Wuh Wuz  Dat  22:10, 23 November 2010 (UTC)
 * The inventor, George Westinghouse, was American so I think American English is appropriate. Biscuittin (talk) 11:41, 13 July 2013 (UTC)

Triple valve diagram
An annotated cross-section of a modern (but straight air) triple valve would be helpful. Even better would be an animated diagram! Casey (talk) 02:21, 5 July 2011 (UTC)


 * I've seen a simple (static) cross-section diagram of a triple valve in a magazine article and it did not help me much. I would agree that a (hopefully) simple animation would be a great help.  NorthCoastReader (talk) 02:46, 12 February 2012 (UTC)

Merge Railway air brake and Air brake (road vehicle)?
It would seem that air brakes for trucks and trains are based on the same principles, have similar advantages, similar history (they spread to trucks after Westinghouse proved them in trains) and have somewhat similar circuits (barring such additions as antilock systems on trucks) so we could save a good deal of duplication by merging them into a common article. Thoughts? -- Chetvorno TALK 21:42, 9 August 2012 (UTC)
 * KEEP - Apart from cross-references, keep separate.    Tabletop (talk) 22:37, 9 August 2012 (UTC)
 * What about brakes on planes?


 * Air brakes on airplanes is a complete different technology. -- T HE F OUNDERS I NTENT  PRAISE 15:35, 10 August 2012 (UTC)

Westinghouse is not the universal brake system
There's a lack of contents on this article: mainly the problem is that only the Westinghouse brake system used in the US is explained. Here in Europe Knorr Bremse was the pioneer of brake equipment and already in the early 50s was developing a new generation of Control Valves different from the "Triple Valve" to reach the inexhaustible condition.

Already in 1959 the "KE.1a" brake control unit was able to apply gradual brake release by proportional control of the brake to the cylinders and also preventing the auxiliary reservoir to run empty by using a secondary equalizing reservoir used as "pressure imprint": in this way only if the auxiliary reservoir is back to the nominal pressure the brakes could be completly released.

Of course in modern times european passenger coaches used the main reservoir pipe to supply air to the auxiliary reservoir from the locomotives allowing faster filling time and brake release related also to the use of "R" brake capability with the support of electric survelliance preventing skid it high speed.

Not to be forget that in UK in the early years the Hardy vacuum brake was in use and it is still a standard in many English-made narrow gauge systems as also by the Austrian 760mm rail system.

Also to be noticed, Swiss railways was equipped with Oerlikon brake system, should be the first company to develope the Self regulating brake control valve; I don't know if also French railways had a different type of brake.

Minor brake system could be recognized within Europe, such as Dako, Bozic, former Hildebrand Knorr and Kunze Knorr, Breda (only in Italy as a result of protectionism), Westinghouse Hannover and Westinghouse Torino. Fur sure Russia had it's own brake type certainly developing same results as American and European developers. — Preceding unsigned comment added by Hosdo (talk • contribs) 15:44, 16 October 2012 (UTC)

Beg to disagree, somewhat. Continental European air braking originated with an American expatriate, Jesse Carpenter, who lived in Russia and developed an air brake arrangement for the Prussian State Railways. This occurred after the 'invention' by George Westinghouse so Carpenter would have been aware of the technology. Carpenter had recruited a young technician from the Prussian State Railways whose name was Georg Knorr. Knorr later became the owner of Carpenter's company and renamed it Knorr Brake (Bremse, in German). The K-B company went on to develop the quintessentially European equipments (the previous contributor has named some of them)... but the original concept should be acknowledged as having post-dated the work Westinghouse (and certain others) had already done. The 'graduated release' functionality of European equipment was always possible because European freight trains were short where American freight trains were getting longer all the time. The inapplicability of the Westinghouse triple valve to graduated release (the European practice) was always acknowledged by Westinghouse. So really, all air braking derives in some way from the Westinghouse developments 203.153.205.105 (talk) 10:53, 12 August 2013 (UTC) — Preceding unsigned comment added by 203.153.203.243 (talk)

Lac-Mégantic a limitation of the Westinghouse?
Was the Lac-Mégantic runaway train disaster related to the inability of the Westinghouse system to recharge when there is no pressure from the locomotive? The locomotive was shut off due to fire, and hours later the train rolled downhill. 108.160.30.206 (talk) 02:20, 9 July 2013 (UTC)


 * The simple answer is NO, but your question is oddly worded. The more complicated answer will have to wait for the report from the TSB.--Daffydavid (talk) 03:08, 13 July 2013 (UTC)
 * It would appear that, in fact, the Lac-Mégantic incident does reveal a limitation of the Westinghouse system. (I.e. shutting off compressor and a slow leak disables the fail-safe functionality of the system). See the discussion on Lac-Mégantic rail disaster & cited TSB findings. I think a note on this page is appropriate. I don't really understand westinghouse brakes well enough to do it myself. When reading about it, one item I also noticed is that "Brake Pipe" is not well defined or explained on this page, I had to read it several times to understand (I think) how it works. -User:Lommer | talk 17:50, 16 January 2015 (UTC)

Clarification needed
I thought I knew how air brakes work but, after discussions at Talk:Lac-Mégantic derailment, I'm beginning to doubt it. I thought the working range of the train pipe was from 0 psi (brakes on) to 70 psi (brakes off). It now seems that the range is 65 psi (brakes on) to 90 psi (?) (brakes off). Is this correct? If so, it would allow some re-charging of the train reservoirs even when brakes are on. Biscuittin (talk) 02:33, 13 July 2013 (UTC)

One does not need to go all the way to 65 psi to get an application, the further you reduce the brake pipe the more force generated on the brakes, just like your car brakes can be on a little or a lot. Westinghouse only guaranteed an emergency application if there was a minimum of 38(have to confirm this figure since it's late and I'm doing this from memory and I'm tired) psi in the train line. I will try to dig out some reference material and update this article when I can. 0 to 70 psi may be in Europe but I am unfamiliar with this. Besides it's my understanding that most valves in Europe are not by Westinghouse and this article is pretty much only about that valve so operation may be different. --Daffydavid (talk) 03:17, 13 July 2013 (UTC)


 * I have added a section on working pressures. Please check that I have got it right. Biscuittin (talk) 09:30, 14 July 2013 (UTC)

The following is for "conventional" North American Freight Air Brakes, not EP. Brakepipe pressure can range from 0 psi - 110 psi. China can be 500 kpa (73 psi) or 600 kpa (87 psi). Typically North American freight is 90 psi (except where it isn't!) The way the system works is ELV (Emergency Limiting Valve) is set to say 90 psi. Your ER pressure (Equalizing Reservoir) is then automatically 90 psi. Your BP (Brakepipe) is uaually a pound less at 89 psi. A MIN reduction (Minimum reduction) is reducing ER to 83 psi. BP will follow to within 1 psi of ER. You should get a BC (Brake Cylinder) application of between 7 psi - 13 psi (depends on the railroad). A Full Service application or Lap is a reduction of ER to about 63 psi, with BP within a pound of ER. BC increases to about 63 psi also. Emergency application is when BP is immediately reduced to 0 psi, with ER following more slowly to 0 psi. BC will increase to 73 - 78 psi. There is up to a 1 minute wait before you can recover the Emergency. 15 yrs testing this stuff! — Preceding unsigned comment added by LocomotiveTechEditor (talk • contribs) 14:21, 3 October 2014 (UTC)
 * Your explanation is clear as a mud and flawed in a couple places. Regardless, if you think you can improve the article, then do so. This is not a forum.--Daffydavid (talk) 20:50, 3 October 2014 (UTC)

Train Disaster Movies and Braking Systems
Train Disaster Movies often pretend that braking systems "need to be pressurized", when the modern common standards would in fact brake the train when pressure is released (the reverse of the common plots!). There should be a minor heading regarding this. — Preceding unsigned comment added by 220.245.43.24 (talk) 04:09, 9 September 2015 (UTC)

Assessment comment
Substituted at 01:11, 12 June 2016 (UTC)

Service brake is incorrectly redirecting to this page
There are many types of brake used for service braking, such as regenerative brakes and eddy current brakes, so this redirect is incorrect. A new page should be created for service brake. Should the redirect be immediately removed? Botatao (talk) 15:14, 30 August 2017 (UTC)


 * Many redirects are synonymous with the title of the article that is the target of the redirect. For example Aeroplane redirects to our article Airplane. However, not all redirects are synonymous - many redirect to the closest article we have on the subject. This serves to take readers who are interested in a particular topic to a somewhat similar article, even though that article does not comprehensively deal with the topic in which they are interested. It also shows those readers that we don't actually have an article that provides exactly the information they are looking for, and hopefully one of those readers will recognize the need and start a new article.
 * You obviously have some knowledge about service brakes. Can we encourage you to cancel the redirect and replace it with a stub article on the subject? Dolphin  ( t ) 12:45, 1 September 2017 (UTC)

Am I being daft...?
Wouldn't this system be made truly fail safe ... by the addition of a simple spring? So a little pressure has to be retained in the cylinder to keep the brakes released, and if that's vented, the spring pushes the cylinder into the operating position? Anything that requires a positive action in order to work (as this system appears to) is not fully fail-safe and can still be knocked out by anything that prevents that positive action happening. What you need is a passive backstop, such as the aforementioned spring which needs at least some minor positive pressure to defeat and keep the brakes off...? Surely such a modification must have been made sometime in the last 100+ years?? 80.189.129.200 (talk) 17:11, 19 March 2018 (UTC)


 * If the design was changed as you propose then it would require the handbrake to release the brake not apply it. This would make switching without air incredibly slow as each handbrake would have to be applied(or released depending on how you view the action) to allow the car to freely roll. In short, it creates just as many problems as it solves. Not to mention the fact that each car would require this modification and would be incompatible with non-modified cars. That's only the beginning of the problems. In short, this isn't feasible. BTW, transport brakes operate under a system similar to your proposed solution. --Daffydavid (talk) 07:41, 23 March 2018 (UTC)
 * You're not daft. In fact it already exists. At least since the 1980s, modern UK EMUs (eg, Networkers) have had an Automatic Parking Brake. There is an additional cylinder located behind the main brake cylinders on some vehicles (often the driving motors) containing a spring and piston which are held back by the pressure in the Brake Reservoir supplying air for that cylinder. The reservoir pressure should always be at least 7 bar, so if it drops significantly the spring will push the piston forwards, acting on the linkage of the usual disc brake mechanism. When fully deployed this gives the equivalent force of a Brake Step One application, which is only a holding brake setting, but is enough to stop a train from beginning to roll on a gradient. This was introduced to do away with the need for manual parking brakes - you may be familiar with old Southern stock such as the British Rail Class 415 EPB which had a massive handle looking like a ship's steering wheel on the non-driver's side to manually apply a brake. Well the auto parking brake does the equivalent nowadays. Dr Sludge (talk) 09:39, 23 October 2018 (UTC)

"Comparitively simple brake linkage" diagram seems erroneous and/or incomplete
To whit: the "push linkage" between each wheel brake lever looks like it should be higher up on the 14" levers, and particularly *above* some (missing) fixed pivot point on the frame, otherwise when the brake is applied on one wheel, it will be pulled away from the other (and the linkage will not operate in the "push" mode). Similarly, the longer "pull linkage" that connects to the lever directly connected to the cylinder should do so lower down, and *below* a (similarly missing) pivot, in order to actually act as a pull not a push, and so properly activate the brakes on its end of the carriage or truck. The picture is probably 10+ years old now (given edit dates and the software used), and was apparently copied from something drawn up in 1969... it's probably overdue a bit of retrospective proof reading. 80.189.129.200 (talk) 17:19, 19 March 2018 (UTC)
 * I agree that the action would require pivoting around points that are not marked as fixed. However, the general positioning of the linkages and absence of other anchor points seems in keeping with other references. See for example http://techinfo.wabtec.com/DataFiles/Leaflets/TP-2008.pdf where on page 5 is a comparable diagram and on page 17 are the directions of motion for it in action. I can't find any diagrams that have other pivots noted. DMacks (talk) 17:50, 19 March 2018 (UTC)


 * Refs seem to distinguish between a "live lever" and a "dead lever", with the latter being the anchored one (see for example ISBN 9781435712218). The discussion at ISBN 9781430317470 page 689 seems consistent with the "live" one floating. DMacks (talk) 18:11, 19 March 2018 (UTC)


 * LOL at picture is probably 10 years old - truck brake rigging hasn't changed in 110 years if not more, so you can be sure it's been well "proofed".


 * Anyway since it seems to be confusing, here's how it works. Looking at the left truck, assume the brakes are released, and the brake shoes are hanging free of the wheel.  Now as the brakes are applied, the blue rod at the top will pull toward the brake cylinder.  This will cause the 14/7 arm to pivot around the green rod until the left brake shoe contacts the left wheel.  At that point, as the blue rod continues pulling toward the brake cylinder the 14/7 arm will pivot around the left brake shoe, pushing the green rod to the right and forcing the right brake shoe against the right wheel.  With all the slack taken up pressure will now start to be applied to the wheels by both brake shoes.


 * Note that the 10/5 arm actually anchors to the truck frame, not the carbody (as drawn). The 14/7 arm can't anchor to anything since it needs to be free to move as the truck rotates in curves.  Altho you can't see it in a 2D picture, the 14/7 arm is actually angled diagonally across the truck (right to left) so that the two ends move in opposite directions when the truck rotates, cancelling out the motion of the top end (connected to the pull rod) of the arm.  It's an amazingly simple and effective design.  — Preceding unsigned comment added by 2601:589:380:130B:0:0:0:A2F9 (talk) 23:21, 22 October 2018 (UTC)

Translation request
From the first paragraph in "Limitations" - and that the car reservoir pressure will rise only to the point of thermodynamic equilibrium

What does this mean in everyday-speak? Thanks.Pieter1963 (talk) 21:03, 31 January 2021 (UTC)

Different brakes on same axle
Why do some axles have a disc brake one side and a tread break on the other? eg Toronto GO/Metrolinx cars. ThanksPieter1963 (talk) 21:16, 31 January 2021 (UTC)


 * I'm not sure, but it may have disc on each axle, just on one side. Tread brake can be used for parking brake (like on České dráhy coaches) or for supporting main brake. Cody3223 (talk) 23:34, 11 August 2023 (UTC)

This must be wrong
"Pressure changes during a service reduction propagate at the local speed of sound, ...". Please correct this. I am not certain how to describe pressure changes in a pipe initially charged with compressed air, and later opened at one end, but I am confident that it depends on the rate of escape of gas; propagation of incremental pressure changes will only approach the speed of sound when the rate of escape is zero. Andrewg4oep (talk)

References at www.sdrm.org
I've changed a couple references by changing "www.sdrm.org" to "www.sdrm.info", as the latter appears to have a copy of the old sdrm.org/psrm.org website. Is this acceptable, should other parameters in these citations be adjusted, or should these just point to the copy at the wayback machine (if there is one) instead? (At least Diesel locomotive appears to have a reference at sdrm.org in the same situation, BTW: / (although in that case there is an archive URL there already). njsg (talk) 10:11, 12 February 2023 (UTC)

Modern Systems, activation delay
The local speed of sound is not the limiting factor in compressed-air systems. That applies only to incompressible fluids. In a train's compressed-air brake system, the limiting factor is the ability of enough air to overcome pipe friction (usually only a 1-eench pipe, plus at least two 45° and one 90° (the gladhand) elbows for each car) and the limiting flow coefficient (Cv) of the exhaust port.

Is "several seconds" correct? It seems like it must take a LOT more time for air to escape through a mile of one-eench pipe and 300 pipe elbows. Drcampbell (talk) 21:18, 11 March 2023 (UTC)
 * Exhausting a small amount of air through the driver's brake valve reduces the pipe pressure sufficiently enough to open the triple valve adjacent to each brake cylinder, thus exhausting that cylinder directly to atmosphere without the air having to flow the length of the pipe. -- Red rose64 &#x1f339; (talk) 23:37, 11 March 2023 (UTC)
 * Well, i don't know how it work on US railroads, but for standard long european freight train (~700m) full braking (reduction from 5 bar to 3.5 bar) takes really several seconds. I think that 10-20 seconds for full brake is normal, I doubt that more than that would be acceptable. I don't have any source because it is hard to find any document that mention train driver's main valve pressure dropping speed, however I'm certainly sure that some of the UIC leaflet or EN norm describes how main train valve should be built or what is expected from it. Sadly, those are paid technical standards and I cannot access them. Cody3223 (talk) 23:20, 11 August 2023 (UTC)