Elvas Tower: Vacuum Brakes - Elvas Tower

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Vacuum Brakes Rate Topic: -----

#1 User is offline   steamer_ctn 

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Posted 16 January 2018 - 06:29 PM

As part of continuing work on the small steam ejector, numerous enhancements have been made to the steam vacuum brake code. These have been released in #4032.

Some changes include:
i) Change HUD to display vacuum piped vehicles correctly (currently appear as air piped wagons)
ii) Introduction of new controller - to simulate controller fitted to BR steam locomotives
iii) Revision of code to now correctly respond to pipe charging values - currently uses air brake code, and logic appeared to be reversed for vacuum operation
iv) Allowance for vacuum brakes to operate without an equalising reservoir, as most vacuum brake systems did not have equalising reservoir
v) Calculation of brake system volumes, and adjusting timing parameters depending upon variation of brake system volume, and thus braking performance

More detailed information on the changes, and the relevant parameters will follow at some stage in the future.

In the meantime the following executive summary is provided.

ENG Parameters -
In addition to "normal engine" parameters, the following have been added:
ORTSBrakePipeChargingRate - Sets rate at which brakepipe charges (ie. Brake releases ), this should be calculated based upon a trains with a brake system volume of 200ft^3, so that timing parameter variation can be correctly calculated
ORTSBrakeServiceTimeFactor - Sets rate at which brakepipe discharges under normal operation (ie. Brake applies )
ORTSBrakeEmergencyTimeFactor - Sets rate at which brakepipe discharges under emergency operation (ie. Brake applies )
ORTSBrakePipeTimeFactor - Impacts rate of vacuum propagation time along train
BrakesTrainBrakeType - Determines whether equalising reservoir is used or not, setting requires - "vacuum_single_pipe_eq". Off by default.

Note: Brake will not experience leakage if no value is assigned for TrainPipeLeakRate in the ENG file.

WAG Parameters -
In addition to "normal wagon" parameters, the following have been added:
ORTSDirectAdmissionValve - Car has direct admission valves fitted - set 0=false, 1=true
ORTSNumberBrakeCylinders - Number of brake cylinders fitted to wagon - set as integer value
ORTSBrakeCylinderSize - Size of brake cylinders fitted to wagon
ORTSAuxilaryResCapacity - Volume of vacuum reservoir

All of the above have standard default values, so they only need to be varied if performance variations are required.

To achieve the most realistic braking performance, it is important that the correct controller configurations are used. The relevant controller parameters, as found on common prototype control valves, have been defined in the code, and need to be selected by the user as appropriate.

The following two are suggested as a possible starting point.

BR Standard Vacuum brake Controller - 2 position - ON and OFF, variable between these two points

Brake_Train ( 0 1 0.1 0.4
            	NumNotches( 1
         		Notch(0	1 TrainBrakesControllerVacuumContinuousServiceStart ))) )


Dreadnought Ejector - 3 position - RELEASE, RUNNING (A lap position where vacuum remains at the same value, depending upon the TrainPipeLeakage), APPLICATION

Brake_Train ( 0 1 0.3 0.4
            	NumNotches( 3
         		Notch(0	0 TrainBrakesControllerReleaseStart )
         		Notch(0.3  0 TrainBrakesControllerRunningStart )
         		Notch(0.6  0 TrainBrakesControllerApplyStart ))) 


Normally these were operated on non-EQ brake systems.


#2 User is offline   Hannes44 

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Posted 20 January 2018 - 02:30 PM

Thank you! this is the first time vacuum brakes are useable and quite realistic at that.

#3 User is offline   darwins 

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Posted 20 January 2018 - 10:03 PM

Hi Hannes

I believe Austria had vacuum braked trains in the past. If you are able to find any technical information on how vacuum brakes were set up on Austrian Railways I would be interested to see it.

Just found this odd article about a vacuum braked loco in Australia, made in Austria. It mentions vacuum brakes also being used in Sweden. http://www.tracksand.../supplement.pdf

#4 User is offline   Hannes44 

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Posted 21 January 2018 - 01:54 AM

Hi!

The inventor of one type of vacuum brakes, Hardy had founded a company for railway equipment in Vienna. So vacuum brakes were in use in Austria until the 1930s on mainlines.

We still have vacuum brakes in use on the older rolling stock used on 760mm narrow gauge railways. Although there are quite a lot of these railways to be found in Austria, information is scarce especially re brake system. The only fact I found is, the difference between atmospheric pressure and system pressure is 52cm Hg (seems to be standard). Data about pipes and brakecylinders etc. one can only get from blueprints and those are not easy to get.

Btw the article is quite interesting.

#5 User is offline   darwins 

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Posted 22 January 2018 - 11:55 PM

I am pleased to say that vacuum brakes can now be considered functional in Open Rails. :sign_thanks:

Three pages on the Coals to Newcastle website give more information for those interested:

Vacuum Brake Information
Vacuum brake parameters
Vacuum brake controllers

Please be aware that there may still be some further changes made.

#6 User is offline   midneguy 

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Posted 10 February 2018 - 10:19 PM

This is all very interesting, and I'm glad to see work being performed on other aspects of the sim and braking systems. As it turns out, my current project is the first for me that requires vacuum brakes to be modeled, but after reading through the original post and this thread it appears there's another version of vacuum brakes that needs to be considered. For instance, the Mason Bogie model I'm working on now used Eames vacuum brakes and this type of system had two operating levers or "controllers" if thinking in sim terms. One valve admitted steam into the ejector to generate the vacuum to apply the brakes, with the ultimate level of vacuum generated and/or the rate of vacuum application being varied by how far this steam valve was opened. When the steam valve was closed, a check valve in the ejector then maintained vacuum in the brake pipe (subject to leaks in the system of course). To release the vacuum, a second lever was used to vent the brake pipe to the atmosphere.

Since I am modeling a 3D cab for this project, I have created a prototypical Eames vacuum ejector which has the two operating levers present - one to control the steam and generate the vacuum, and the second lever to vent the brake pipe to atmosphere and release the brakes. As I understand it, there is only one controller available which does not allow for the proper use of the two levers / valves in this type of system. So, would it be possible to add two new controllers for this type of system? I'm thinking these would be called something like "Brake_Train_Vac_Apply" and "Brake_Train_Vac_Release", or something similar that would make sense.

Here's a couple sources that can be referenced for how the Eames vacuum brake system worked:

http://www.catskilla...ra/chapt22.Html

https://books.google...20gauge&f=false

https://books.google...20gauge&f=false

#7 User is offline   copperpen 

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Posted 11 February 2018 - 01:39 AM

The old GWR in the UK had a similar system with one lever to break the vacuum and another to restore it. They also used a mechanical pump to maintain the vacuum. The vacuum model we have right now is based on the Dreadnought type which had all functions on one lever. Far as I know, other versions are to follow at some point.

#8 User is offline   darwins 

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Posted 11 February 2018 - 01:49 AM

Thanks for that. Sadly it is more than a couple of levers different to the automatic vacuum brake in Open Rails. The Eames brake is not an automatic brake - there is no fail safe - the vacuum is used to apply the brakes rather than to release them.

In Open Rails at present there are two kinds of automatic brake:
Automatic Vacuum Brake and
(Westinghouse) Automatic Air Brake (including twin pipe and EP variations).

In a more modern context dynamic braking or rheostatic braking could be considered as 'non-automatic' brakes, but they are always used together with an automatic train brake.

In the early days before the introduction of automatic brakes, several non-automatic brakes were tried including (straight) air brakes, (Eames) vacuum brakes and mechanical brakes such as Webb's chain brake. These would need to be set up in a different way.

However in later years, direct (non-automatic) brakes were (and still are) used on locomotives.
It would be good in time to see these fully functional in Open Rails, but this would require a major change to allow 'mixed brake types' in the same eng file - as well as allowing 'direct action' brakes.

Steam brakes - were widely used on steam locos - mostly vacuum braked.
Straight air brakes - were used on steam locos and are still used on diesel and electric locos, both vacuum braked and air braked.

#9 User is offline   darwins 

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Posted 11 February 2018 - 01:56 AM

Quote

The old GWR in the UK had a similar system with one lever to break the vacuum and another to restore it. They also used a mechanical pump to maintain the vacuum. The vacuum model we have right now is based on the Dreadnought type which had all functions on one lever. Far as I know, other versions are to follow at some point.


Basically there were two variations of ejectors.

If the ejector was inside the cab - such as Dreadnought, SJ, VB, RM - commonly used by the LNER and SR then the large ejector was operated by the brake lever having a RELEASE position.

If ejector was mounted outside on the side of the firebox or boiler there was normally a separate control for the large ejector. This was normal for GWR, MR, LMS and BR standard locos.

I have suggested that a separate control be added for the large ejector ON/OFF. This could use Ctrl J as a toggle (or if you want to have on and off separately it could use Ctrl J and Shift Ctrl J).

It would be nice to see this added to the vacuum brake model. I suspect we will need to put it on a Trello card on the road map to be added during a future cycle of development.

#10 User is offline   keystoneaholic 

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Posted 11 February 2018 - 02:06 AM

And whilst we are talking about GWR vacuum brakes, don't forget that they used a higher vacuum pressure than other UK railways. When a GWR loco came off the train and was replaced by another loco the brakes on each vehicle had to be manually released.

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