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).
Originally Posted by stevekstevek
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.
Originally Posted by stevekstevek
Short answers...No, Yes, and depends upon the feed valve setting for the brake pipe. :D
Originally Posted by stevekstevek
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:
(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
Initial Brake Service Equalization Brake Pipe Reduction
Pipe Pressure Pressure to Obtain Equalization
90 psi 64 psi 26 psi
105 psi 75 psi 30 psi
110 psi 78 psi 32 psi
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).
Originally Posted by stevekstevek
Hope this helps...