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]

no comments ?

[Mayner]

A bit techy for modellers, probably best to try and chat to someone who has driven or maintained 071s or 141s.

[rebelred]

I drove vacuum trains so will try & answer some of your queries. The 2 handles are the Loco Brake (red) which only applies brakes to the Loco & the train brake (Black) which applies brakes throughout the train including Loco. The 'auto release' doesn't serve any purpose & is the most forward position of the Loco Brake & is in 201's also. In regards to the train brake you have 3 marked positions - release (5 bar of pressure), full service (3.5 bar) & Emergency (0 bar) which empties the cylinders of air. In between release & full service you can put the brake in to various positions which apply different amounts of 'grip' or brake. If you move the train brake a small bit down from release towards full service, that is what we called the 'lip' which is a slight rub of the brakes. The same thing applies for air brakes but the difference being air brakes come on & off faster so there is a bit more skill needed to drive a vacuum train.

 

There was a 'Blended Brake' fitted to the 201's when they were built but is permanently disabled which maybe similar to your 'Bailoff' function but I'm not 100% sure. Also the Amp/Power metre was fitted to the 071's but is disabled permanently also. Hope this helps, it's much easier explaining this to someone with the controls in front of you!!

[Junctionmad]

I drove vacuum trains so will try & answer some of your queries. The 2 handles are the Loco Brake (red) which only applies brakes to the Loco & the train brake (Black) which applies brakes throughout the train including Loco. The 'auto release' doesn't serve any purpose & is the most forward position of the Loco Brake & is in 201's also. In regards to the train brake you have 3 marked positions - release (5 bar of pressure), full service (3.5 bar) & Emergency (0 bar) which empties the cylinders of air. In between release & full service you can put the brake in to various positions which apply different amounts of 'grip' or brake. If you move the train brake a small bit down from release towards full service, that is what we called the 'lip' which is a slight rub of the brakes. The same thing applies for air brakes but the difference being air brakes come on & off faster so there is a bit more skill needed to drive a vacuum train.

 

There was a 'Blended Brake' fitted to the 201's when they were built but is permanently disabled which maybe similar to your 'Bailoff' function but I'm not 100% sure. Also the Amp/Power metre was fitted to the 071's but is disabled permanently also. Hope this helps, it's much easier explaining this to someone with the controls in front of you!!

 

 

Thanks

 

my understanding is that as the vacuum brake is applied it merely controls the rate of brake application rathe then then pressure of brake application , maybe I'm wrong here. Ie if you leave the lever partially on , the brakes will continue to build pressure on the wheels , is this the case ?

 

 

dave

[Railer]

If you leave the leaver partially on iy will continually apply that set amount of pressure until either released or increased further it won't continue to build.

[Noel]

Thanks Railer, this is very interesting. Did the brake pads on locos apply physical friction pressure to the wheel surfaces or to separate axle brake discs? Did this configuration change with later models such as the 071 or 201s?

[irishthump]

There was a 'Blended Brake' fitted to the 201's when they were built but is permanently disabled which maybe similar to your 'Bailoff' function but I'm not 100% sure. Also the Amp/Power metre was fitted to the 071's but is disabled permanently also. Hope this helps, it's much easier explaining this to someone with the controls in front of you!!

 

Was the 'Blended Brake' a form of dynamic braking?

Dynamic brakes would be standard on US locos, but they would be of little on Irish rails.....

[rebelred]

Thanks Railer, this is very interesting. Did the brake pads on locos apply physical friction pressure to the wheel surfaces or to separate axle brake discs? Did this configuration change with later models such as the 071 or 201s?

 

That's correct Noel, Loco brakes are blocks that apply to the rim of the wheels. Mark 3's, 4's & all DMUS are Disk brakes

[rebelred]

Was the 'Blended Brake' a form of dynamic braking?

Dynamic brakes would be standard on US locos, but they would be of little on Irish rails.....

 

Yes, I think it was designed for really long freight trains which we don't have here hence why it is permanently disabled/isolated.

[Junctionmad]

If you leave the leaver partially on iy will continually apply that set amount of pressure until either released or increased further it won't continue to build.

 

I think people are mixing up air and vacumn brakes , even Rebelred is, because vacumn bakes operate at low negative pressures around -.7 ( point 7) bar or , and not at +5 bar which is the air brake . Vacumn is by definition maxed out at -1 bar

 

 

How did it do that , that's not the classic operation of a train vacumn. brake , typically all that happened is you admit air to the train pipe. If you keep admitting air the vacumn keeps getting destroyed , my understanding is leaving the valve lever open ,brake pressure would build. Closing the valve but not engaging the vacumn exhauster ( ie release ) would cause the brakes to remain on , at the current vacumn level. hmmmm , ???

 

Say you needed 10 " of vacumn , you would open the brake valve until the train pipe vacumn gauge showed that vacumn , the. Shut the valve, if the exhauster was not engaged , the vacumn would remain at that ( less leakages ) , is this not the way it works on the GMs vacumn train brake

 

Note that you are correct in your description of the independent air brake. It's a graduated system , because it's not required to be fail safe. ( ie the same as loco steam brakes etc ) I was specifically referring to train vacumn brakes

 

Note that vacumn is measured in negative bar , millimetres or inches of mercury etc , so , typical train vacumn is low around - 20 inches of Hg , -.7 bar. Full vacumn -1 bar

 

Blended brakes , are a form of interaction of dynamic braking and air brakes and would have been disabled on Irish EMD locos.

 

Bailing off , or bail off , was a /is technique to release the loco brakes while keeping the train brakes on. Historically loco brakes , whether steam, air or vacumn were " servoed " to the train brake, with a small delay to mitigate bunching , bail off control overrode that by allowing the loco brake to be released ( some or all ) while keeping the train brake on. It was available in many steam locomotives by releasing steam pressure in the loco brakes. , but I'm not aware of the extent of that control on Irish EMD vacumn braked systems

 

 

Ps presumably one of the gauges on Irish EMDs on the console was a vacumn gauge which wouldn't have been fitted to US EMDs

Edited October 14, 2016 by Junctionmad

[Broithe]

Indeed, you can suck all you like and never get more than one bar, but you can blow away and get as much as the mechanism and pipes will stand.

 

Big cylinders is the only way to get bigger loads with a vacuum system, pressure systems give you a lot more choice about how things are arranged.

[Junctionmad]

Indeed, you can suck all you like and never get more than one bar, but you can blow away and get as much as the mechanism and pipes will stand.

 

Big cylinders is the only way to get bigger loads with a vacuum system, pressure systems give you a lot more choice about how things are arranged.

 

Indeed and I think here, many people are mixing air with vacumn and getting confused

 

Vacumn systems got introduced in uk and Ireland , because firstly , the issue of very long trains wasn't as prevalent , the vacumn was simpler all round and suited steam based exhausting via ejector which has no moving parts. In addition at the time, the air brake could not be partially released and this was seen as an issue for the typically faster UK railways.

 

As speeds built however the brake force needed also increased and vacumn ran out of puff

 

Still my question , I don't beleive vacumn brakes force application were proportional to the position of the lever

[Broithe]

This big plus with vacuum systems, correctly arranged, is that you can make them fail-safe.

 

You can do this with pressure systems, too, but you lose some of the extra advantages of pressure if you do that.

[rebelred]

I think people are mixing up air and vacumn brakes , even Rebelred is,

 

My job is to drive the train, not to explain quantum physics!!!! (Just kidding!) It was a very technical question with quite a few queries which I tried to explain as best I could in layman's language. Basically Vacuum braking relies on a suction of air or 'Vacuum' to release the blocks from the wheels, any leak or break in the hoses will cause the brakes to apply again which was a fail safe system, however the vacuum brake was slow to apply & slow to come off. Air brakes are a lot faster to apply & release as it is air being 'forced' rather than suction being used to apply brakes. As opposed to the technical aspect of it, you explained it quite well (I think!) Anyway, here's a photo of the brake lever layout on a 201 Loco, Same set up for all locos...

Edited October 14, 2016 by rebelred

[Blaine]

I find the easiest way to make trains stop is to turn the power knob to zero or to press the red stop button

[Junctionmad]

I think people are mixing up air and vacumn brakes , even Rebelred is,

 

My job is to drive the train, not to explain quantum physics!!!! (Just kidding!) It was a very technical question with quite a few queries which I tried to explain as best I could in layman's language. Basically Vacuum braking relies on a suction of air or 'Vacuum' to release the blocks from the wheels, any leak or break in the hoses will cause the brakes to apply again which was a fail safe system, however the vacuum brake was slow to apply & slow to come off. Air brakes are a lot faster to apply & release as it is air being 'forced' rather than suction being used to apply brakes. As opposed to the technical aspect of it, you explained it quite well (I think!) Anyway, here's a photo of the brake lever layout on a 201 Loco, Same set up for all locos...

[ATTACH=CONFIG]25507[/ATTACH]

 

 

Thanks for the pic , What I trying to ascertain , is that the train brake on a vacuum equipped diesel was or was not proportional , as conventional steam vacuum setups did not have promotional braking, proportional braking is where the force of the applied brake is directly related to the position of the brake lever. with the Independent ( loco) brake , this WAS a proportional system , primarily because it was not fail safe. On a vacuum system , the position of the train brake lever adjusted the rate on the admittance of atmospheric pressure air into the train pipe. hence it was proportional to the rate of air being admitted , but not the application of brake force, but Railer suggested it was proportional and I cant see how that was arranged technically

 

 

My reasoning for this , is I an programming a new version of MERG dcc throttle and I want to see if I can make the brake lever idea work in DCC

dave

[Glenderg]

My reasoning for this , is I an programming a new version of MERG dcc throttle and I want to see if I can make the brake lever idea work in DCC

dave

 

Why didn't you say that at the start..of...this..thread...?

[Mike 84C]

I have also driven vacuum and air over here in GB. Juctionmad if you are asking, I apply the brake and leave the handle at one position what will happen? with either system you will stop. The vacuum will continue to increasingly leak on and apply the brake harder on the train. The things to remember with vacuum are, the brakes on the front of the train apply first but release first so the rear will still be braking when the front is released. So a gentle initial application then quite heavy to get the train under control and then a gentle, apply release technique to slow to a stop. The plan is always to stop on a rising brake e.g. heading towards release and a 15" application at maybe just rolling to come to a stand. Hold the train on the air/steam brake and blow the train brakes to release ready to go.

On BR 21" of vac was the norm and brakes really start to bite at 15" of vac. Slowness of release is mainly due to the vac; cylinder relies mainly on its own weight to fall and release but they are bloody heavy! and all the levers, fulcrums and rods used in the system. Of course all this depends on the quality of the braking on the carriage set you are pulling, no two will be the same so lots of variables for your driver to suss! When I was on BR steam I fired regularly to a driver who on stopping passenger trains had two brake positions when running into a station; full application and release with the large ejector wide open. Very rapid stops! I would have the blower on,a white hot fire and the injector going filling the boiler. The departure would be just as rapid. Western 6100 tanks could really take a lot of abuse! Hope that lot helps your questions and sorry for the wave of nostalgia.

[Garfield]

It's possible for a given level of vacuum pressure to be maintained if the rate of air exiting through the ejectors is equal to the amount of air coming in through the brake valve. A vac brake operates almost like a graduated self-lapping brake...

[Mike 84C]

Garfield, that is true but for that you need a perfect world! Experience tells me that the driver will be making small adjustments of the brake valve. The ejector is normally set to maintain 21"of vac; using a minimum amount of steam. Ejectors are very good at what they do but will consume a lot of water if not properly adjusted by the driver. Please don't ask how much per hour! I have forgotten.

[Garfield]

Garfield, that is true but for that you need a perfect world! Experience tells me that the driver will be making small adjustments of the brake valve. The ejector is normally set to maintain 21"of vac; using a minimum amount of steam. Ejectors are very good at what they do but will consume a lot of water if not properly adjusted by the driver. Please don't ask how much per hour! I have forgotten.

 

Hi Mike, I was thinking more of vac brakes on diesels...

[Mike 84C]

I should have said the exhauster runs at a constant speed even when braking and to speed up the exhauster the brake handle has to be returned to the release/running position and then pressed down thus speeding up the exhauster. The loco brakes are applied by air via a proportional valve when using the vacuum brake. I can only offer advice on locos I had experience of Sulzer type 2&4 and English Electric type 1&4. But see no reason why a 141 should be any different in the way the foundation brake system works. be interesting to find out! So many ways to get the final result!

[Junctionmad]

Hi Mike, I was thinking more of vac brakes on diesels...

 

Ejectors aren't used on diesels , rotary exhausters were. I dont believe any vacumn brake was proportions, mike84c account confirms that. As long as the valve is open the vacumn brake will continue to increase brake force at a rate determined by the setting of the brake valve/lever .

 

To hold a given brake force the brake lever would be returned to running . This confirms my memory. Of the drivers of 141 ,who would work the train brake on and off , because otherwise leaving the brake lever partially on would result in increasing brake force and a hard stop.

 

On steam locos the large injector was needed for brake release.

 

On diesels typically the exhauster was either electrically or mechanically drive. Which is why I always understood the notch up on stopping of the EMD, this was presumably to exhaust the vacumn and begin the brake release process.

[Junctionmad]

Why didn't you say that at the start..of...this..thread...?

 

Didn't want to side track debate in to dcc throttles. I wanted first to understand the way a vacumn train brake was used in real life before seeing if it could be transferred across to dcc

[Glenderg]

Didn't want to side track debate in to dcc throttles. I wanted first to understand the way a vacumn train brake was used in real life before seeing if it could be transferred across to dcc

 

Could have prefaced this highly technical thread with that. We all have crackpot ideas, this one might have got more traction if you approached it with some transparency.

 

Pun fully intended.

[rebelred]

So we are all agreed then - pull lever = brakes applying

[Junctionmad]

Could have prefaced this highly technical thread with that. We all have crackpot ideas, this one might have got more traction if you approached it with some transparency.

 

Pun fully intended.

 

I think you miss the point. Firstly I've been attempting to understand the way vacumn braking works. I've also posted similar questions on rmweb , where there are no issues with the debate and an exchange of experiejces followed , with contributions from steam and diesel drivers.

 

However the Irish situation is rather unique in that it's American designed engines which would have been exclusively air brakes , but were fitted with vacumn and I was interested in how they operated. I've been working in MERG with a raspberry pi interface and also interested in moding an open source dcc throttle to make in more consistent with Irish EMD brake operation see http://model-railroad-hobbyist.com/node/25866?page=13

 

The reason I didn't bring this up is few people would wish to discuss the intricises of the software behind the brake function on dcc. It fact even fewer understand it.

 

Equally , I like to understand how the real thing works. Even here you can see there are confusions about how vacumn train brakes work.

[Junctionmad]

So we are all agreed then - pull lever = brakes applying

 

Indeed , butbwere it that simple

[Junctionmad]

I should have said the exhauster runs at a constant speed even when braking and to speed up the exhauster the brake handle has to be returned to the release/running position and then pressed down thus speeding up the exhauster. The loco brakes are applied by air via a proportional valve when using the vacuum brake. I can only offer advice on locos I had experience of Sulzer type 2&4 and English Electric type 1&4. But see no reason why a 141 should be any different in the way the foundation brake system works. be interesting to find out! So many ways to get the final result!

 

That's interesting , your experience with early BR locos is invaluable and it explains the purpose of the spring detect in advance of release Or labelled auto release , even though it's being commented to me that this position did nothing on Irish EMDs locos.

 

I'd like to thank all those that contributed their knowledge , memories or experiences. If anything else springs to mind , please feel free to add it to this thread

Edited October 15, 2016 by Junctionmad

[richrua]

One would imagine that this would be the best (or only) place for asking highly technical questions about Irish EMD locos.. It is wrong to mock those who do . They might stop asking and then all the discussion ends

[Junctionmad]

This big plus with vacuum systems, correctly arranged, is that you can make them fail-safe.

 

You can do this with pressure systems, too, but you lose some of the extra advantages of pressure if you do that.

 

How so, the transistion from simple vacumn brake to automatic vacumn brake mirrors the transistion from simple air brake to automatic air brake. The air system was always arguably a better system , which is why it's practically universal now.

 

I don't understand your contention that you loose certain aspects by making air fail safe. In fact the drawbacks ( limited availability of reservoir ) are present in both systems. The vacumn system was adopted in the uk arguably because it was cheaper to implement , suited steam , and with small trains common in the uk , the disadvantages were not as acute over air

Edited October 15, 2016 by Junctionmad

[Junctionmad]

It's possible for a given level of vacuum pressure to be maintained if the rate of air exiting through the ejectors is equal to the amount of air coming in through the brake valve. A vac brake operates almost like a graduated self-lapping brake...

 

Did it though , early diesel air , of the cie 141 era did not have self lapping air brakes ( correction some did ) . I've yet to see any mention of self lapping vacumn brakes. Did they exist ?

Edited October 15, 2016 by Junctionmad

[Garfield]

Did it though , early diesel air , of the cie 141 era did not have self lapping air brakes ( correction some did ) . I've yet to see any mention of self lapping vacumn brakes. Did they exist ?

 

As I said... as long as an ejector OR a rotary exhauster can expel air at the same rate it's entering through the valve. It's not a specialised system.

[Junctionmad]

As I said... as long as an ejector OR a rotary exhauster can expel air at the same rate it's entering through the valve. It's not a specialised system.

 

So did the Irish EMDs have the ability for the driver to control the specific exhauster rate so that he could balance that against the brake lever position. This seems to be different to mark4c description of BR vacumn diesels operation . Interesting , there must have been electrically controlled balancing , in the US self lapping air brakes arrived in the late 50s with the 26L air brake valve , quite a complicated beast and not transferable to vacumn. Where did the controls on the Irish EMDs exist that controlled exhauster rate ? . It's interesting that they were different to early BR diesels

Edited October 16, 2016 by Junctionmad

[Junctionmad]

As I said... as long as an ejector OR a rotary exhauster can expel air at the same rate it's entering through the valve. It's not a specialised system.

 

Oh I understand that , but to make this work requires automation, ie quite a complex vacumn automation system that balances exhaustion rates with the desired inrush rates , and that this only occurs after the appropriate vacumn braking level is established .

 

Something like this was achieved in the 50s with the introduction of the 26L self lapping air brake valve, it was quite complex. I have yet to see any equivalent mechanism for vacumn brakes, most likely because vacumn automating would require bulky control systems ( as they are low pressure ) and also the long delays in establishing steady brake pipe vacumn would make the system hard to implement automatically

 

Even today , in the US, the 26l valve and its self lapping successors are mainly used n high speed passagner applications , and many freight locomotives are still using manual lap valves

Edited October 16, 2016 by Junctionmad