Talk:Railway air brake
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[edit] 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.
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- 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.
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- 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)
[edit] Terminology
Not to be overly pedantic about it, but "trainline" is a single word—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)
[edit] 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—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"—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—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)
