vulturenest Wrote:
-------------------------------------------------------
> One more new this!
>
> What's the difference between the brake systems,
> and how can one tell one from the other?
>
> Mike Conder
The A-I was an early version of applying automatic air brakes to the locomotive and tender. The locomotive and tender both had triple valves (plain triples such as an "F" type used on the NG passenger cars before they were converted to K-valves, the RPO's on the C&TS still have F valves). Also there was an auxiliary reservoir under both the locomotive and tender.
The automatic brake valve was an earlier model - usually a "G-6" valve. A separate independent "straight air" valve (think it was an "SWA" valve) to separately control the engine and tender brakes was optional . Not every engine had an SWA. I know the C-class engines had SWA's. The pics I've seen of 463 when it was in California show a G-6 valve but no SWA valve. I have never seen a cab pic of a 470 or larger engine when it had A-1 air, so I can't say if they had straight air valves or not.
To set the engine brakes, you made an automatic air set. To release the engine brakes, you released the automatic air. Making a fine spot with the brakes took some real talent as you could not "feather" the brakes on and off easily like with later systems. On the tender there was a retainer valve for use on long down grades - just like any other car in the train. To release the engine brakes after an automatic set when running down grade, there was a simple bleed off cock in the cab. Some straight air valves had an engine brake release function built into them.
The big disadvantage to A-1 with out the straight air valve was you could not manipulate the engine and tender brakes without increasing or decreasing the brake pipe pressure, and effecting the braking effort through the entire train.
The more modern "6-ET" system uses a distributing valve to control the automatic air brake application on both the engine and tender while allowing full independent operation of the engine and tender brakes regardless of how the train brakes are handled. The engine and tender brakes still apply with the automatic application, but they then can be released, reduced or increased as desired without effecting the automatic brake status.
I should be pointed out that A-1 goes back to the 1890's (?) and 6ET was state of the art by the late teens. Having A-1 installed in the 1920's was pretty "old school".
Through the years, I have surprised to see how many engines kept A-1 brakes to the end. The C&S 641 in Leadville still has A-1, and I have seen other stuffed and mounted engines that still carried A-1 until retirement.
The 470's, 80's and 90's had their A-1 changed to 6ET in mid-late 1940's. At the same time mechanical lubricators were installed to oil the valves and cylinders. All these parts came off older SG engines getting scrapped. The K-27 kept their A-1 brakes. When 464 was put into service as the Durango Switcher in the 1950's it had its air converted to a more modern version of 6ET called "14L" it was intended for use on diesels. It used a different automatic valve, but the same independent. The independent valve mounted to the top and side of the automatic brake valve. It made for a more compact set up. Diesels 15 & 19 have 14-L brakes. When 463 was rebuilt in the 1990's, the A-1 system replaced by 6ET to make it more user friendly to the crews for the same reason A-1 was used in 1923-46 - it was what the crews were used to.
The most famous locomotive with A-1 brakes is Sierra RR #3. Until it got recently rebuilt, it ran with basic A-1 with no straight air valve for then engine brakes. The Sierra guys tell me that switching with the #3 was "interesting".
The big visual difference with the air systems is with A-1 you will find a large auxiliary reservoir and triple valve under the cab somewhere. On the 70's and 90's they were on the right side and on the 80's they were under the left side of the cab. Also there was a large reservoir under the tender. 6ET had none of this. There was small reservoir hidden behind the distributing valve located on the right side under the engineer's seat.
