Air brake control questions

Discussion in 'Railfanning Discussions' started by stevekstevek, Jan 21, 2010.

  1. stevekstevek

    stevekstevek New Member


    I'm trying to understand (and write a very simple simulator) for train brake systems. I've worked with similar systems in the past (not mainline -- rapid-transit-type systems, which are similar, but not quite the same).

    Anyway, I think that if I model types 6BL, 24RL and 26L, I'll have the gamut of typical systems covered; at least anything you're likely to see in diesels.

    I'm looking for technical data on these systems -- I can find operating manuals, etc for these systems, but I can't easily find some data that I'm looking for, nor some operating facets:

    a) First, making sure I'm correct: the major difference between the 6BL and 24RL systems was that the 24RL systems use an equalizing reservoir and feed valve (i.e. the "maintaining feature", while in the 6BL system the handle basically connects the brake pipe either to main reservoir or atmosphere directly?

    b) For the 24RL system, then, It should be pretty straightforward to measure the rate (in Psi/sec) at which pressure changes in the EQ Reservoir vs each handle position? (i.e. you get something like 2.5Psi/sec reduction in service, and 4.5 Psi/sec charge in appy?) Does anyone know where I could find this information?

    c) In all of these systems, is there something that prevents the engineer from making an over-reduction: i.e. if you have a 90Psi brake pipe, once you make a 25psi reduction, that's full service (for a 2.5x ratio system); if the engineer keeps a 24RL handle in "service", does the brake pipe get reduced lower than 65psi? What does the brake pipe go to in full service on a 26L?

    Generally, I'm guessing there's brake service manuals that would have this kind of information, as it's all stuff you'd want to test if you were servicing the systems; I just can't seem to find service manuals like this online..

    Any tips (or even direct answers to some of my current questions) would be appreciated..
  2. BnOEngrRick

    BnOEngrRick TrainBoard Member

    I'll try and answer some. 24 brake will reduce at a service rate to zero as long as the handle is kept in "service "position. An engineer places the handle in "service" until the desired equalizing pressure is reached, then pulls back to "lap".

    26 brake full service with 90# brake pipe will be down to 63-65#.

    6 brake will still have some regulating feature to maintain brake pipe pressure while in "running" position. Otherwise the engineer would have to keep constantly fiddling with the valve to maintain a specific pressure while released in addition to everything else he/she has to keep track of. 6 and 14 are basically the same as far as I know (some "expert" will prove me wrong even though I said "as far as I know"). 14 has an equalizing reservoir, but no pressure maintaining. The "release" position on 6 and 14 is a direct main reservoir/brake pipe position, "running" releases the brakes at a controlled rate up to the setting of the feed valve.

    I have used but not had much experience on 14 or 24.
  3. Charlie

    Charlie TrainBoard Member

    I'm not even gonna try! I'd have to dig out my mechanical books. I only ever worked with
    type 26. Pressure maintaining airbrakes are mandated on US railroads anyway.
    Straight air brakes you find on streetcars,interurbans and trains in museums not anything used in interchange.

  4. LEW

    LEW TrainBoard Member

    I am not an expert either but the 6,8,14, 24 or any position brake always has an equalizing res. That is the only way you can know how much air you are drawing off.On the NYC the holding position was blocked out and could be used as lap. With the 26 and newer brakes you work by zone, service zone etc, which makes for finer control of the train brakes.On some 6 and 14 brakes they blocked out the full service position as on the 26.On the 24 you had the full release position but was of no benefit for recharging the brakes when the trainline pressure on the gage reached its setting. The feed valve then controlled the flow of air through the valve. For what you are wanting remember the amount of brake is controlled by the engineer. I mean in this example that there is not any air leakage in the train line. I think your lbs. of reduction is close enough for government work and also your recharge rate should work.I don't have the figures handy but with 80,90,110lbs of trainline pressure you have more braking pressure to work with. Hope this helps. LEW
  5. LEW

    LEW TrainBoard Member

    On a brake if 25lb is full service that is full service on any brake reguardles of number.Drawing off more is a waste . The next position is emergency. When you make a reduction of the air with the position brake valves you go to service position and watch the equa.hand come down the amount you want normally 5-7lbs. and then move the handle to the left to the lap position. As you need more more brake pressure you repeat the above.I always liked to draw off at least 10-12 lbs. before releasing the brakes to keep from having stuck brakes.With the 26 brake you would go to min. reduction which would get about 9lb. of air, then for more brake you go to the service zone and watching the equ. hand pull down another 5 lb.and stop with the handle and it would lap at that position. As with the other brakes you always wanted around 12 lbs. before release.LEW
  6. Charlie

    Charlie TrainBoard Member

    type 26 also has a "Handle Off" (HO) position which will give about a 40lb reduction in a service mode. It is also what we would use in coldest winter to draw down all the air when tying down the power. Normally we would use full service (FS) position when tying down the power.

  7. taz

    taz TrainBoard Member

    Welcome to the world of black magic... ;) First off, let me say that I'm no expert on air brakes and I can't tell you things like "rates of flow" (except when it comes to an emergency application...Any reduction on any brake stand of 20 psi or more in 1.2 seconds or less is an "emergency application"...Anything else is a "service reduction" or "service application") or (for the most part) air pressures at a given point (except a "full service reduction" for a 90 lb. brake pipe which is 26 lbs.). What I can tell you is that I've run locomotives with 6BL (and 6SL and 6ET), 24RL, and 26L brake systems (in addition to a few others) so I'm familiar with these brake stands and understand (some of) the differences between them from the standpoint of an engineer and what I need to know (i.e., "what does what" and how to use it). As far as "why" (or "where") certain things are done is a different story...That varies from railroad to railroad based on their individual rules for "Air Brakes and Train Handling" (so I'm no help there in terms of "why" UP or NS or any other railroad, other than the ones that I have worked on, does "what" in a particular circumstance and/or the reasoning behind it).

    BTW - As far as I know, BnOEngrRick is correct in that the 6 and the 14 brakes are "basically" the same. The only "real" difference (as far as I know) between the two brake stands is that the 6 was made by Westinghouse and the 14 was made by New York Air Brake...From an engineer's standpoint, there is no difference. (I was also once told that the 14 was cheaper to purchase and maintain than the 6 due to Westinghouse's patents, etc., on the 6 but I don't have any information that indicates that this is true.)

    There are a couple of major difference between the 6BL (or 6SL or 6ET) and the 24RL. Without any of the automatic (train brakes) handle positions being "blocked" out, the 2 brakes appear to be exactly the same from the point of number of "zones" (notches/valleys and humps/bumps, etc.). From the engineer's standpoint here are the major differences.

    With the 6 series brake valve, the positions (left to right) are "running release" (sometimes called "full release"), "release", "engine holding", "lap", "service", and "emergency". Compare that to the 24 where the positions are "running release", "release", "first service/maintaining", "lap", "service" and "emergency". "Running release" is used to put air into the brake system at a faster rate since that air is drawn directly off of the main reservoir at main reservoir air pressure (generally about 135 to 140 lbs...However, only a 15 lb. difference between the main reservoir air pressure and the feed valve setting is required by the rules)...This can lead to an "Overcharge" of the brake system (which I won't get into) if the engeineer isn't careful on how he/she uses it. "Release" is the "normal" position when running a train and the desire is for all of the brakes to be released (barring retainers being set, etc.). "Engine holding" on the 6 series brake valve is used to keep the independent brakes applied (i.e., I can apply the engine brakes with the independent brake valve and then move the automatic brake valve handle to "engine holding" and release the independent brake...The locomotive brakes will remain applied until I either move the automatic handle to some other position or "bail off" the independent brake). "First service/maintaining" on the 24 is used for 2 different purposes...When used as a "first service", the valve will cause a predetermined reduction of the brake system (generally 6 lbs. but there is another valve called a "rotair valve" that controls this based on it's setting)...When used as a "maintaining" position, the engineer makes a service reduction (example, 15 lbs.) and places the handle in "lap" and waits for the air to finish exhausting from the brake stand and then places the handle in "maintaining" to maintain the brake pipe pressure at the desired pressure (on a 90 lb. brake pipe with a 15 lb. reduction, this would be 75 lbs.)...This position will allow the air to be "maintained" at this reduction regardless of brake system leakage (i.e., air will flow through the brake stand from the main reservoir to the brake pipe to "maintain" the desired pressure). "Lap" severs the connection between the brake valve and the brake pipe and is used to "maintain" a service reduction (barring leakage in the brake system...This is different from the "maintaining" feature on the 24 is that no attempt is made keep the brake system at any desired pressure so what initially may have started as a 5 lb. reduction can "leak" to an 8 lb. reduction or more over time based on the brake system leakage). "Service" removes air from the brake system at a predetermined rate (less than 20 lbs in 1.2 seconds or more). The "Emergency" position (sometime called "The Big Hole" but also called by a lot of other names) will exhaust all of the air in the brake system by venting it directly to the atmosphere (at a rate of 20 lbs or more in 1.2 seconds or less).

    One other major difference is that the 6 series brake valve usually (but not always) have 2 separate control valves (for lack of a better word). One valve is the "feed valve" that regulates the amount of air that is allowed from the main reservoir to the brake stand for "normal" use. The other valve is the "distributing valve" which "connects" the automatic (train brakes) brake valve to the independent (locomotive brakes only) brake valve. On the 24 brake valve, these two valves are combined into one valve (just called the "feed valve").

    Both the 6 series and the 24 (and for that matter, the 26 as well) have an "equalizing reservoir" portion for the brake system. When the engineer "sets the air", he watches the "equalizing reservoir" gauge to determine how much air he's taking (reduction) from the system.

    One "minor" difference is that a locomotive equipped with a 24 (or 26 or newer brake valve like the 30CDW) is that there is usually an "air flow meter" that will tell you how much air is "flowing" (in terms of Cubic Feet/Minute) between the locomotive and the trailing cars. I've never seen an "air flow meter" on a locomotive equipped with a 6 (or 8) series brake...
    It's not as straight forward as it might sound. Since the "service position" is actually a "zone" and not a simple predetermined "on" or "off", it varies based upon (the skill level of the :star:) engineer. I'm sure that if you were to look at the "manual" for the various brake valves (from Westinghouse or New York Air Brake), they probably have some of this information based on a brand new valve...Older valves that may be worn somewhat may differ. As far as an "on-line" source for this information, I've never found one available (and I've looked for it) but some of the newer manuals can be purchased from Westinghouse or New York Air Brake and occasionally some of the older ones show up on E-Bay.
    Short answers...No, Yes, and depends upon the feed valve setting for the brake pipe. :D

    OK...Longer answers. An engineer can use as much air as he/she would like...The question is really one of what is effective and at what point does a further reduction of the brake pipe not physically have any effect (or do anything). The answer to that question depends upon what the "feed valve" is set to. Typically on most freight railroads, the feed valve is set to 90 lbs. which will give you a "full service application" of 26 lbs. The reason for this actually has nothing to do with the brake valve itself but has to do with the pressure in the brake cylinders on the individual cars, the brake pipe itself, the brake valve on the individual cars, and the auxiliary reservoir on the cars and the pressure there within (...a little drift here but with a "full service application" of 26 lbs. to the brake pipe, the pressure inside the brake cylinder on a trailing car is 64 lbs...At that point, the pressure in the brake pipe [90 - 26 = 64] and the pressure in the brake cylinder are equal...Nothing can "flow" at this point and the system is said to be "equalized"...). So, if an engineer makes a "service reduction" of 30 lbs (with a 90 lb. brake pipe), only the first 26 lbs. actually "do" anything...The addition 4 lbs. is wasted (...In railroad jargon, it's called "pissed away"). And...It is possible to "piss away" all of your air even to the point where the "Emergency" position on the brake valve will not work. Personally, I've tested this out (with a locomotive with a 6SL stand and a couple of freight cars while standing still on flat track)...I took the brake pipe down (at a "service reduction" rate) to about 10 lbs. and tried to get the cars to go into emergency by "plugging it"...No joy. I also succeeded in getting the brake pipe to go to 0 (zero) with the same set up (...I haven't tried this with a 24 or 26 brake stand but suspect that it is doable...).

    Passenger cars are different than freight cars. Freight cars will let you take the brake pipe all the way down to 0 (zero) without going into emergency...Passenger cars, on the other hand, generally go into emergency if the brake pipe pressure goes below 50 lbs.

    Full service...Depends upon what the feed valve (brake pipe pressure) is set to as to what a "Full Service" application/reduction is. The following is UP's definition (from the "Air Brake and Train Handling" rule book) of a "Full Service Application" and explains it (...probably better than I could... )

    Full Service Application
    A brake pipe reduction made only to the point at which the auxiliary reservoir and brake cylinder pressures equalize. Any further reduction in the brake pipe pressure, except an emergency application, will not affect the amount of pressure in the brake cylinder. Therefore, air is being wasted from the brake pipe (over reduction).

    The chart below shows the reduction needed for a full-service application for various initial brake pipe pressures. Also listed is the brake cylinder pressure at full service for various initial brake pipe pressures:
    [B]Initial Brake        Service Equalization    Brake Pipe Reduction[/B]
    [B]Pipe Pressure[/B][B]        Pressure                to Obtain Equalization[/B]
         90 psi            64 psi                  26 psi
        105 psi            75 psi                  30 psi
        110 psi            78 psi                  32 psi
    (The original document doesn't have the "Code" tags around the table...Disregard those. I added those in an attempt to get the table to format properly...:at-wits-end:)
    In my experience, you're not going to find the service manuals available "on-line" except as a "for sale" item on sites like E-Bay. Simmons-Boardman Books, Inc. (TransAlert) used to offer a series of books (3 in all) on air brakes called the "ABCs of Air Brakes"...The book on "Locomotive Air Brakes" may have some of the information (at least up to the 24RL information) that you're looking for. Some of the various locomotive manuals have an "Air Brake" section in them which may show some of the piping diagrams as well as the various handle positions and what they're used for...A good place to check "on-line" for older locomotive manuals is at "Fallen Flags and Other Railroad Photos, Operator's Manuals" You're not going to find manuals for SD70s or AC4400s, but there are manuals for older ALCo, EMD, FM, GE, Lima, and even a Krauss Maffei, and it'll cover the basics for the brake stands that you're asking about. Also, there are some really good write ups on how the air brake system works on-line (one by BNSF engineer Al Krug located at "Railway Technical Web Pages, North American Freight Train Brakes" is a really good place to start).

    Hope this helps...
    Last edited by a moderator: Jan 23, 2010
  8. BnOEngrRick

    BnOEngrRick TrainBoard Member

    Along the lines of lack of ability to go into Emergency, CSX rules state that anytime your brake pipe pressure drops to 45 pounds, the engineer should go to Emergency. That is why a "Head of Train Device" will alert and flash at 45 pounds.
  9. LEW

    LEW TrainBoard Member

    Taz, good information. As I said the NYC had the hold blocked out and I often wondered how the actual operation worked.Our only recourse for bad train lines was to brake with the feed valve until the 26 brake came along.Our steam from the H-10,2-8-2 on used the #8 ET.It fell somewhere between the #6 and 24 RL. Again good info. LEW
  10. taz

    taz TrainBoard Member

    LEW, besides "feed valve braking", did you ever use (or work with anyone that used) the "humping" the brake valve method (placing the handle between "lap" and "release", "on the hump", attempting to maintain the reduction)? Personally, I haven't ever tried either of these methods...On the railroad that I work on, both of these methods are "outlawed" (as is "slugging" the independent) but the territory that I work on (and at the speeds that we travel) doesn't require anything more than "simple" applications (or minor dynamic braking).
    I always thought that it was interesting that the 8ET wasn't revised and used in more of the early diesels (although there was an "8EL" brake that was found on some electric locomotives). I wonder if that had more to do with the early hood unit diesels being considered "switchers"...
  11. LEW

    LEW TrainBoard Member

    Tas, I like you have heard of humping but never used it.Yes I think most roads have outlawed the use of the feed or control valve.The plug was never approved here ,but most of the men on this div. used it because the dynamics did not work or were very poor.You had to remember to take them out.The plug I used on the 26 brake had to be taken out when using the independent brake.I never used the penney,it to easy to forget.A few years before I retired,1992, we had a problem with kickers in the trains. It was so bad that I told everyone that we worked with a 2 position brake :running and emerg.. The only way I could overcome this,most of the time, was before setting the brakes ,remember bad dynamics,was to increase the train line pressure 10-15 lbs and wait a few seconds until the increase had traveled about half the train turn it back down to 90lb. and go to min. reduction and whatever to complete the slowdown or stop.With the van trains you used the independent to brake with. You just could not make a reduction of the brakes. This came from the old timers if they had a kicker with the 6 or 8 they would go to full release a couple of seconds and then make their reduction. I think they found the problem was a port was plugged and the size had to be increased a wee bit to take care of the extended time on air brake checks. LEW

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