The air brake system part of the discussion on the UP 844 thread got thinking that this may be a good place to ask a question that I've had for some time. In later years, NKP used the Bluebird PAs as lead units in freight service. According to several sources, they made some modifications to the air brake schedule. These modifications allowed the 24-RL equipped PAs to lead the 6 equipped Geeps and RS units. Just what did they change or add?

My best guess is that they added a relay valve to the brake cylinder pipe on the PAs, and that the output from that relay valve went to a third hose, connected to the independent apply and release pipe on the trailing 6 units. This would mimic applications, releases and bailoff. Does this make sense? Is there anyone that really knows? Agreed, this is a bit of fairly useless trivia, with no practical value today, but I've often wondered just exactly what they did.

Did any of the NKP PA's ever receive N&W lettering or paint, or were they retired prior to any such changes?

Traded in to Alco before the merger, in 1961. NKP got some RS-36s (blt Feb 1962) in return.

Howard P.

What flavor of 6 did the geeps have? I'm by no means an air brake expert, but will offer this: Looking through the Soo Line locomotive diagrams, all of their original road units (F3's, F7's and FA's) were equipped with 24RL from the get go, while the road switchers of various makes were all equipped with some variant of 6: 6DS, 6SL, 6BL. None of these units had MU capability as delivered.

In 1954 the Soo's motive power policy changed, and they began to buy GP9's equipped with MU. However, these units were not equipped with 24RL, but rather a variant of 6, 6BLC, They must have felt that 6 was a better choice for switching service... can anyone comment?

People who worked with them at the time said they would train with the 24RL equipped road units. I have been told that the 6BLC equipped units had FIVE MU hoses on each end plate... the standard four used with 24RL and a fifth that was a direct connection to the unit's brake cylinders which was to be used to operate with locomotives not equipped with relay valves. The fact that the GP9's, equipped with 6BLC brakes routinely operated with the 24RL equipped units seems to indicate that they also had relay valves.

So, in answer to your question, it would appear that the NKP had relay valves on the geeps, either as built, or added later. Conversely, the PA's could have been modified with a direct connection to their brake cylinders so the could lead consists not equipped with relay valves, but the first course seems more likely.