Vacuum brake operation on GM 141

[Junctionmad]

I was reviewing some stuff on vacuum and air brakes

 

I was trying to relate the standard US control stand to the brake controls on the 141 GM

 

The black brake lever was the train brake and the red on e, was the independent brake ( i.e. train brake )

 

The black one had the typical release position ( vacuum being generated and the vac pipe being emptied ) , Then it had a full service , which was typically the full application of the brakes , Normally vacuum brakes had a " run " position , i.e. no vacuum being generated and the driver typically moves the lever from "run" to full service to modulate the train brakes

 

 

I notice that on the independent brake ( which I presume is air operated ) there is an additional position in front of " Release " which is on a spring detent, This is described as " Release Auto "

 

IN most US controls stands the air brake has 5-6 positions on detents, including release, running , lap, full service and emergency

 

Looking at various videos , and from memory the 141 drivers, brought the brake lever to the mid position and then back to release and modulated the brakes that way, full service only being applied at the very end . Was it that the brake positions just weren't marked on the irish GMs ?

 

in the US, there is the concept of " bailingof, or Bailofff" i.e. applying the train brakes whilst leaving off the loco breaks to avoid snatch and jerk. Since the normal way train brakes work is the the train brake lever also activates the engine brakes , did Irish GM engines not have Bailiff control?

 

 

The other aside is that on most GM engines there is a amp/power meter , yet I dont think this was every fitted to Irish locos

 

for a treatise on how it worked on steam https://books.google.ie/books?id=1w8TAwAAQBAJ&dq=steam+locomotive&hl=en&sa=X&redir_esc=y&output=reader&pg=GBS.PA163 you can knock yourself out on technical detail !!!!!

 

Dave

Edited October 7, 2016 by Junctionmad

[Junctionmad]

Thanks everyone. Based on feedback across a few fora and this one , I think I can conclude that vacumn brake valves certainly up till their effective demise , where never self lapping. You couldn't leave the lever in any " on " position without brake force continuously building and had to be essentially modulated by applying the train brake back and forth between "on " and " off"/ lap with occasional partial " releases " if you needed to briefly restore vacuum and reduce brake force ( interesting partial releases were not possible with many types of air brake to this day )

 

On steam locos with seperate ejector control and where the brake valve allowed it, it was possible to partially balance an " on" position with a level of exhaustion. So that a consistent brake force could be better maintained down a long gradient , but this was not universally possible nor common usage as far as I can see. On diesels manual control over the exhauster was less evident and hence such balancing act wasn't possible

 

fascinating subject , if anyone has further knowledge or experienced please post them here.

 

I've enough now to see if the same process can be replicated in dcc but initial inspection seems to suggest that DCc protocols only support a subset and are more attuned to air brake then vacuum ( for example simulating partial release isn't possible )

Edited October 16, 2016 by Junctionmad

[rebelred]

[Glenderg]

 

You're not alone Red.

[Garfield]

You're not alone Red.

 

+2

 

Thanks everyone. Based on feedback across a few fora and this one , I think I can conclude that vacumn brake valves certainly up till their effective demise , where never self lapping...

 

http://www.google.com.na/patents/US2781235

 

Also see the EQ vacuum brake system used by BR, as well as the self-lapping vacuum brake system developed by Knorr.

Edited October 16, 2016 by Garfield

[Warbonnet]

I'd like to express my sincere gratitude for this topic existing too. I've been suffering from a terrible bout of insomnia recently but this topic has cured it. Happy days!

[Junctionmad]

I'd like to express my sincere gratitude for this topic existing too. I've been suffering from a terrible bout of insomnia recently but this topic has cured it. Happy days!

 

You now know more about the workings of the vacumn brake then you'll ever need to know !!!

 

Technical topics make a welcome change from time to time !!!

[Warbonnet]

Or ever wanted to know, to be honest! As Blaine said, turn the big knob to off and trains stops.

 

Interesting, engaging topics about railway modelling would make a nicer change as there seems to be a dearth of that recently. But that's just my 2 cents.

[Junctionmad]

+2

 

 

 

http://www.google.com.na/patents/US2781235

 

Also see the EQ vacuum brake system used by BR, as well as the self-lapping vacuum brake system developed by Knorr.

 

 

Thanks for those pointers, The EQ brake was I think from reading its application in railUK, somewhat different to self lapping brakes and was more of a " choke " system . the KNorr patent I was aware of but did it actually see light of day ?

Edited October 17, 2016 by Junctionmad

[Junctionmad]

Or ever wanted to know, to be honest! As Blaine said, turn the big knob to off and trains stops.

Actually it doesn't in DCC .

 

Interesting, engaging topics about railway modelling would make a nicer change as there seems to be a dearth of that recently. But that's just my 2 cents.

as opposed to ones about recoilless rifles !!!! ( which I actually liked by the way)

 

The solution is not to read posts that dont interest you. There are other posting ranging from trawlers and submarines to lots of other stuff that are there for the reading if you desire

 

Id like to thank Rebelled,Railer,IrishThump,Brothie,Mike84C,Garfieldghost and richua for their meaningful contributions .

 

I think garfieldghost feels I have come to the wrong conclusion, but in the absence of direct testimony ( and I have direct testimony of manual lap operation in other forums ) I have to try and reach some conclusion. I will follow up with some drivers I know as to what was specifically implemented on Irish EMDs.

Edited October 17, 2016 by Junctionmad

[Warbonnet]

Actually it doesn't in DCC .

 

 

as opposed to ones about recoilless rifles !!!! ( which I actually liked by the way)

 

The solution is not to read posts that dont interest you. There are other posting ranging from trawlers and submarines to lots of other stuff that are there for the reading if you desire

 

Id like to thank Rebelled,Railer,IrishThump,Brothie,Mike84C,Garfieldghost and richua for their meaningful contributions .

 

I think garfieldghost feels I have come to the wrong conclusion, but in the absence of direct testimony ( and I have direct testimony of manual lap operation in other forums ) I have to try and reach some conclusion. I will follow up with some drivers I know as to what was specifically implemented on Irish EMDs.

 

Depends on the the trottle you're using, like some of the Lenz ones. I also think you're misinterpreting a comment or two in jest (like the one about the power knob) as a serious statement. I can assure you it was an attempt to inject a little humour into proceedings, nothing more. The forum has had such a tone for a bit of craic along the way for many years, which was part of my original comment too.

 

As for my second comment, you seem to be getting defensive. To be perfectly honest it was a call much wider than this topic. As I said, there seems to be a dearth of content from the railway modelling side itself and there seems to be more niche topics popping up. That's all fine and dandy, and there is a place for it all (including this topic) but it would be nice to see some content of railway modelling interest flowing again and a bit of humour along the way.

 

And before anyone shouts at me "lead the way!" IRM is where my modelling space lies these days, trying to get those wagons out there as well as the day job

[irishthump]

Actually it doesn't in DCC .

 

 

Juist out of interest, exactly what type of effects are you trying to reproduce with your throttle?

[Junctionmad]

Juist out of interest, exactly what type of effects are you trying to reproduce with your throttle?

 

Im am member of MERG ( merg.co.uk) and I am in a group that is working on alternative DCC throttles to go with our DCC command station , we've just finished a smartphone based interface , that allows IOS and Android phones be used as a DCC throttle . My interests in this group lie in creating a miniature Irish GM EMD cab based around this throttle idea ( which is open source hardware and software )

 

 

As you can see its based on a 70-80s style EMD control stand. But would make a very close approximation , turned on its side of an Irish EMD GM throttle .

 

However , The brake function on DCC is a very curious beast ( and I delve into detail here ) and in reality bears little resemblance to any reality , air or vacuum brake . and therefore I was trying to understand in detail the operation of the train brake lever on the 141s, to see how well it could be mapped across to this throttle and to DCC. ( in reality the mapping is very poor ) . Its effectively impossible to simulate Vac brake operation in any proper way on DCC ( for example partial release is impossible to simulate ) , even with some of the most sophisticated decoders like ZIMO. Ive engaged in correspondence on several forums, and its interesting to hear the different views.

 

 

Im currently working on the new throttle software ( which I modifying from PIC assembler , ugh, to "C") to see how close I can get , like lots off things , hobby projects get pushed aside when paying works comes along, so progress in slow.

 

 

The idea would be to make the red lever cowl of the 141 and turn the throttle longways , with a second strap hole on the other aside and wear the throttle more like a RC aircraft control

dave

Edited October 17, 2016 by Junctionmad

[richrua]

Ooooo that's a good looking controller! Very kinaesthetic!

[Junctionmad]

Ooooo that's a good looking controller! Very kinaesthetic!

 

isn't it just , the lads in iowa scale engineering are to be congratulated ( as I did on their blog) for doing a very good job, with standard off the shelf electronic components ( getting the right rotary encoders is a hell of a job) . you could imagine it with a red 141 "hemisphere cowl", and the flying small emblem and it would be very "cool" . I Have the controller control board for the MERG units built up and the next job is to replace the MERG throttle wheel etc with these switches etc . ( the LCD will be driven from the existing MERG board . then a bit of glue software !!!!!!!

 

 

dave

[Mike 84C]

That is very very wow! soooo cool looking controller. Could be so much more intuitive to use than almost anything I have seen.

[Junctionmad]

I must apologise to Garfieldghost and others here. I just finished reading some very interesting WABO tech documents and reading some old forums on vacuum systems fitted to export US locomotives

 

It would seem and I can't confirm it. That the standard method that US locos used was air priority . the driver operated the train brake , which was air operated on the loco and behind the scenes the pneumatic automation combined with valves ensured that the vacumn was slaved to the air brake.

 

The driver merely treated the train brake as if it was air , and the control system reduced the vacumn in proportion to the loco air pressure

 

In that respect both the air and vacumn were " effectively " self lapping , ie the handle could be left in any position from barely on to full service and the system automation maintained a constant vacumn by relay valves connected to the exhauster. All this was transparent to the operator. Since both the air operated loco brake and the vacumn train brake were capable of progressive or partial release , the lever coould be moved back and forth in the service " area " and the system adjusted both the loco air brake and vacumn behind the scenes as appropriate. This pneumatic automation operation , in effect created a self -lapping vacumn brake. ( actual self lapping vacumn was quite rare as I said before )

 

The primary reason for this is US locos were typically built with train capable air compressors and an assumption that eventually operators would dump vacumn and switch to air, in fact the arrangement mentioned above allowed for a very simple switch over with no additional work by the driver

 

It also meant for multiple unit working , both the loco air and vacumn connections had to made between locos , I presume that was the case with the CIE EMDs.

 

It's turns out the whole system was more complex then I thought. In fact there may not have been a vac gauge in the cab ( was there ? )

 

Note that still isn't EQ brakes which were quite differebt

 

Now making an equivalent Dcc brake is virtually impossible, because variable application of brake force isn't possible , there is just one service level brake deceleration ( in Zimo this is cv 349 ) so the best that can be simulated is the effect of moving the train brake lever to one fixed position, holding the brake on ( lap ) and then full release . Which would mean the Dcc throttle , brake lever would have two positions , on ( and lap ) , off with release

 

But mike84c , the Dcc throttle is really cool isn't it. I have the bits coming to build one up but there's a lot of bits to make it all work. The faceplate is too big for my little cnc mf50 proxxon mill so that will have to made elsewhere ( Iowa scale engineering have only produced prototypes to date )

 

Ps. I also worked out what Release Auto was meant to be on the 141 brake console legends , it means that the loco brakes are released while the train brakes remain on !! , its spring loaded position and now the video on the DCDR cab ride in a 141 finally makes sense. Woohoo

 

Dave

Edited October 17, 2016 by Junctionmad