• Air Brake Questions

  • General discussion about locomotives, rolling stock, and equipment
General discussion about locomotives, rolling stock, and equipment

Moderator: John_Perkowski

  by Engineer Spike
I have a few questions which I have never been able to get a straight answer to from mechanical people at work.

My first question is about the #6 brake system, with 2 pipe MU. How did that system send the pressure to actuate to a trailing system? How does this work with a 26 system? I have seen various MU2A valves. Some have the positions "trail 6 or 26", "trail 24" or "lead". If the 26 is leading, how is it set up to know whether or not to send the bail signal via the actuation line?

Isn't there one version of the #6 which uses 3 lines? I have seen some bastardized conversions. The ex CB&Q SD9s had #6 brakes, but the independent had been replaced with a SA26 independent brake valve, and a MU2A valve.

What is the difference between 26L, and 26LUM? I see the LUM on many CP SD40s. The used ones, like the ex MP and KCS units have straight 26L.
  by kevin.brackney
You know way more about it than I ever will. A No. 6 is practically relegated to museums by now. When I was a student engineer, we had one unit that had one, and a couple of others with 24RL brake valves. I have operated some older Army locomotives with No. 6 brakes too. Never had to MU any.
  by locomotive112
The 6ET system had a two pipe systyem, one pipe for the trainline, and one for the locomotive braking or "independant" brakes whos line stopped at the last locomtive in the power lashup.

The train brake (or automatic brake) pipe uses over-pressure to realease and feed, and lowered pressure to apply, the brakes.

On the independant brake pipe, its allopposite; the pressure goes up to apply and down (to zero psi) to release.

To Apply the indenpndant brakes (on the 6ET system) pressure was sent by the "#6 distriting valve" to the independant brake pipe untill the pipe pressure was where the engineer set his S6 valve's handle.

To Release the independant on the 6ET system, the #6 distribing valve releases the pressure from the independant brake pipe as the engineer places the handle for his S6 brake valve back to its release position.

There are some 3-line 6ET systems, they are home made. The D&S has one of these. The third line is really just a straight air line, that acts sort of like the independant brake line. It recieves pressure from the air reservoirs through the engineers 3rd valve (that can be just about any kind of valve you want to use) and pressurizes or releases its trainline to apply, hold, or release its pressure. The 3rd line is piped right into the release holes on the triple vales and it can prevent them from being able to release their air from the brake cylender. So, if you send air via this 3rd pipe, into the tripple valves they either stay pressurized and cannot release, or if they have no pressure, the pressure would go through the tripple valves and pressurize the brake cylinder, thus applying the brakes. This is done wihout effecting the automatic or train brake orits line (much, I think) . That 3rd pipe brake system is referrred to as a "Pressure retaining or Pressure maintating system". It allows the retainer vales to be removed, and makes recharging the reservoirs while the brakes are applied and in motion possible, since the brakes stay applied as long as you want them to (the air has no place to escape to). The #6 Distribuing valve controls the trainline side of the car brake air, and the 3rd line controles the exhaust side of the car brakes air, so you control the entrance and exit of the air toand fromthe car brakes, total air control,and it only costs you the instalation of the 3rd pipe line onthe locos, a second train air line for the rollingstock, (and all its glad hands and cut out valves , if they are used) for every car in the train.

Here is a sort of step by step, or comment by commment explanation about the differences and advances of each system, (but the 3rd pipe might not be mentioed here); http://www.rypn.org/forums/viewtopic.php?f=1&t=6567

I know, the Spelling is bad. My PC will not let me cut and paste (to spell check) so I'll repair this when my PC cooperates later.
  by EDM5970
I can't say that I agree with the info presented in the long paragraph above. This is not a true description of a 6ET system that has been modified for 3 pipe. It sounds more like the Orinocco system used at Erie Mining and DMIR, which was a straight air system added to the automatic air.

There have been some 6 systems converted to having three lines, (MR, apply and release and actuate/bailoff). The 6 independent is replaced with a 24 or 26 independent. Or, the locomotive gets 26-NL or 26-FNL, which has a 26 brakestand controlling a 6 distributing valve.
  by Engineer Spike
Thanks for the replies. The BN exQ SD9s had 6. Their independant had been replaced with a 26. This way they could mu with the ex GN SD9s with 24RL.
  by locomotive112
EDM5970 wrote:I can't say that I agree with the info presented in the long paragraph above. This is not a true description of a 6ET system that has been modified for 3 pipe.
What would be an "agreeable" or "true" 3-line 6ET system? What is not agreeable or true about the D&S's 3 pipe 6ET system?

Using the 6ET loco & Tender schedule and the KC & KD car brakes, how else could a 3-pipe system function?
  by EDM5970
Are we talking about locomotive brakes in MU, or train brakes here? I think this factor is causing some confusion here.

First, I am not familiar with the D&S 3 pipe system, apparently home made. I am taking a guess that D&S is Durango and Silverton, supported by locomotive112's mention of the narrow gauge forum in his signature? The system as described functions like the Orinoco system, which has the normal brake pipe connection between cars and an additional 'straight air' pipe. Just what are the three pipes on the D&S system called?

In locomotive MU practice, there are some good basic descriptions in a paper. "MU Brake Arrangement of Outbound Locomotive Consist", presented by the St. Louis Air Brake Club and published in 1974. In this paper, they refer to the 24-RL and 26-L as 2 pipe systems; actuating pipe (independent bailoff), and independent application and release pipe. (The brake pipe and main reservoir equalizing pipe, are not included in the 'pipe count', nor are sanding hoses).

While this paper does not directly address the 6 system as used on diesels in MU as a 1 pipe system, the single pipe (added to MR and BP, of course) is called the brake cylinder equalizing pipe. This pipe also is used on MU equipped 14-EL systems, although 14-EL is not mentioned in the paper.

The St. Louis paper answered a lot of questions for me; I found it on eBay several years ago. And nowhere is the mention of '3 pipe' made; that term must have come from this D&S system
  by locomotive112
"Are we talking about locomotive brakes in MU, or train brakes here"

We should have been talking about MU, but the topic was unclear and I was on trainlines, sorry.
I now understand 3 pipe MU brake system terminology and I see that this topic was specifically about MU pipes, not train lines.
Maybe the title should have MU in it as in "Air Brake MU questions", then it would be clear and this could stay on topic with that in the title.

Sorry for the "side track", but please continue, as I'd like to talk MU pipes and setups with your gauys as well.