Westinghouse Air Brake Model 26L

[R. Steele]

Looking over brake parameters in engine files I find plenty of variance in MaxBrakeForce. However, when I go to data sheets for the locomotive (usually The Diesel Shop is first stop, then digging out manufacturers data sheets in some cases)
I find many units use the same model Westinghouse 26L.

So the question is: why the variance? Isn't this type of air brake - factory fresh - rated for a specific maximum braking force?
Or do the designers and manufacturers tinker with it for the requirements needed for the unit being built?

What other factors am I not aware of that would influence this variance...or is it just the quirks of individual content creators?

[tbundy1982]

I would imagine the variance in MaxBrakeForce is merely an interpretation of what the MaxBrakeForce should be. I think the most recent locomotives that I've uploaded to the file library have a MaxBrakeForce set between 60-70% of the Mass. I have no idea if this is correct; I probably read it somewhere on a forum and determined that it felt right. I also take note of how many brake shoes and brake cylinders are present. From anecdotes of engineers, it appears that a GP38-2 with 8 brake cylinders will stop much quicker than a unit with 4 brake cylinders and 4 shocks. That makes sense. Also, older locomotives had cast iron brake shoes, which have their own braking characteristics (brakes harder at lower speed, brakes less when hot....).

I would think a correctly operating 26L brake stand with the 26C controller would be fairly uniform between locomotives equipped, and in my experience it has been, but I haven't operated hundreds of different units to know for sure. I do know that the earlier brake stands like 6L and 24RL can have a life of their own. You have to feel them to operate them well.

One thing about MSTS brakes that I've had difficulty understanding: Why do .eng files with 24RL brakes have a 0-100% Apply section? I don't have any recollection of being able to have any subtle control of psi reduction rate in real life. It's not just on or off either, as it is a valve opening. I think most engineers get a hand on the handle and push it until they hear the flow of air as it comes out of the brake valve. Eyes are on the Equalizing Reservoir gauge. On my personal .eng file edits, I always use the full on/off method so my focus can remain on the brake pressure gauge. A brake application should be done quickly and efficiently as there is always something else to focus on just around the corner.

Also, a brake pipe reduction rate has a finite limit, as releasing the pressure too quickly will initiate an emergency application. I think it was something like 60 ft per second but I don't really know for sure.

EDIT: Just to clarify, MaxBrakeForce is based on the Mass of the locomotive and has nothing to do with the brake controller in the cab.

Also, I wouldn't fully trust The Diesel Shop for any specific info. I've found more demonstrable untrue info than true in some cases. I think the 26L brakes came out in '59 or '60, and almost every locomotive built afterward has had some variation of these "easy brakes".

Tyler

[muskokaandtahoe]

My guess is nobody knew the facts and just went with what seemed about right. Subsequent edits tweeked what was there to reflect a different opinion about what was right, leaving all of us with a dogs breakfast of values.

We probably should be using all the same values for each .eng file that uses a particular model air brake. This is the great benefit of include files -- two files for the 24RL (one with and one without dynamics) used by n number of .eng files.

I've got a \common.fleet folder with subdirectories of \US, \UK, etc., etc., and in my \common.fleet\US folder I do have

• Westinghouse_24RL_Brakestand_W_Dynamics.inc
• Westinghouse_24RL_Brakestand.inc

That lets me write an Include() statement in my .eng files that looks like this:

• Include ( "..\\Common.Fleet\\US\\Westinghouse_24RL_Brakestan d_w_Dynamics.inc" )

At this point in time it does not matter to me if the values contained therein are not quite right. The point is when I learn / am told of something better all I need to do is change the two .inc files and the whole fleet is automatically updated.



FWIW, I also have these files in \common.fleet\US

• Single_Pipe_AB_Brakes.inc
• Single_Pipe_KC_Brakes.inc
• Std_Type_D_Coupler_Generic_Draft_Gear.inc
• Std_Type_E_Coupler_Generic_Draft_Gear.inc
• Std_Steam_Locomotive_Bar_&_Coupler.inc
• Std_Tender_Couplers_Generic.inc

Just to name a few others I find particularly useful.

[muskokaandtahoe]

I would imagine the variance in MaxBrakeForce is merely an interpretation of what the MaxBrakeForce should be. I think the most recent locomotives that I've uploaded to the file library have a MaxBrakeForce set between 60-70% of the Mass. I have no idea if this is correct; I probably read it somewhere on a forum and determined that it felt right.
Tyler

Prior to some date in the range of 1960-1990 the figure of 60-70% the value of max is good for MaxBrakeForce -- on freight cars. This is based on figuring out what application of brakeforce would cause an empty car to have wheel skid. Loaded cars could use a higher brakeforce but then freight cars are not always loaded.

That raises the question of what to do with passenger cars, where the difference between empty and loaded is not all that great as well as diesel locomotives where we're talking about the weight of the fuel, and steam locomotives where there it is always a loaded weight.

In those cases, clearly, a higher value can be set for MaxBrakeForce() -- but how much higher is not something I know, so I just guess.

I've been told that changes in brakeshoe composition can make a difference and of course modern braking technology too, but that step sinto eras I don't follow so I've no suggestions on that.

[tbundy1982]

Good insight, Dave. I think the composite brake shoes in these modern times are known to have a more even range of braking capability. They can withstand more heat build-up at higher speeds and don't drag and grind at lower speeds. I bet the braking curve built into the simulators is more like the composite shoes than the cast iron versions. It sounded to me like the latter's curve was more pronounced.

For those few out there who may not understand all of the model numbers and lingo, think of the Westinghouse (WABCO) 26L brake stand as the kind that you find in the default GP38 and Dash9. It is a 'self-lapping' brake. You move the brake handle counter-clockwise to any position and the brake pressure will automatically reduce and hold at that pressure until you move the handle further into application or release.
Previous models like the 6 and 24 brake stands required the engineer to place the handle in full service position and manually determine when to close the valve back to the lap position. Moving the valve to Full Service and leaving it there should drain all the air from the brake pipe without triggering an emergency application.

Tyler