[darwins]

The introduction of the new triple valve features should allow more accurate modelling of a range of triple valves and distributors.

Due to the complexity of this I have started a new thread to try and collect information that will allow us to try to build a picture of the main types of valve.
It should be possible to put together a summary or include file (or script) that covers the important features of each type of valve.
Some of the parameters may require trial and error to get the numbers right - but this can not really been done until after the propagation model has been updated.

Developments in North America:

https://i.imgur.com/jXrbPcI.jpg

Separate valves were developed for passenger and freight operation.

Retaining valves and emergency reservoirs were introduced to overcome the problem of brakes becoming exhausted.

Some of the additional features that might be required:

for the PM triple valve then the higher emergency pressure decays to service pressure over 45 seconds;

for some of the freight triple valves the emergency application rate seems to be much faster than the service application would this perhaps need the addition of ORTSMaxEmergencyApplicationRate in addition to MaxApplicationRate?


Developments in Europe:

https://i.imgur.com/6W296F0.jpg

The G-P changeover valve allows slower application and release rates for long "goods" trains.

To prevent brakes becoming exhausted UIC rules require MaxAuxiliaryChargingRate > 85% of MaxReleaseRate.

Two stage braking was introduced for express trains and remains a UIC requirement of "Rapid" braking mode for vehicles with cast iron brake shoes.

Two stage braking (based either on deceleration rate or on speed) is not yet available in OpenRails.


Developments in Australia and New Zealand:

https://i.imgur.com/hHZ6KiT.jpg

Accelerated release is achieved in the W triple valve by using an "accelerated release reservoir". I have not yet tried to see if quick release can be modelled in OR without an emergency reservoir in the system.


I do not have information about historical developments in USSR/Russia or China, although it should be possible to add some present day information.

[darwins]

Trying to work my way through all the possibilities. Perhaps we should start with the modern type of triple valve on US freight wagons. What would be a standard set of values for the AB or ABD or ABDX triple valve? Would there be any differences between these valves in OpenRails?

Based on the train brake pipe being at 90psi my first guess might have been something like:

Comment ( AB type freight triple valve )

TripleValveRatio                            	( 2.5 )
EmergencyResVolumeMultiplier                	( 1.4 )
MaxReleaseRate                              	( 10psi/s )
MaxApplicationRate                          	( 3.0psi/s )
MaxAuxilaryChargingRate                     	( 1.8psi/s )
MaxEmergencyChargingRate                    	( 0.9psi/s )
ORTSEmergencyDumpValveRate                  	( 80psi/s )
ORTSMaxServiceCylinderPressure              	( 64psi )
BrakeCylinderPressureForMaxBrakeBrakeForce  	( 77psi )
ORTSQuickServiceApplicationRate             	( 16psi/s )
ORTSQuickServiceLimit                       	( 15psi )
ORTSQuickServiceVentRate                    	( 2.5psi/s )
ORTSAcceleratedApplicationFactor            	( 0.5 )
ORTSAcceleratedApplicationMaxVentRate       	( 1psi/s )
ORTSUniformChargingThreshold                	( 3.0psi )
ORTSUniformChargingRatio                    	( 2 )
ORTSEmergencyResQuickRelease                	( 1 )

Looking at an include file for an OR wagon then some different values are given:

TripleValveRatio( 2.5 )
EmergencyResVolumeMultiplier ( 1.50 )
MaxReleaseRate( 2.50psi/s )
MaxApplicationRate( 10.00psi/s )
MaxAuxilaryChargingRate( 11psi/s )
ORTSEmergencyValveActuationRate ( 18psi/s )
ORTSMaxServiceCylinderPressure ( 50psi )
BrakeCylinderPressureForMaxBrakeBrakeForce ( 70psi )
EmergencyBrakeResMaxPressure ( 90psi )

What would a complete correct description look like?
Are the auxiliary and emergency charging rates as high as suggested? (If these are high surely air will have to completely refill both reservoirs before brakes are released!)

Hopefully we can start to get some guidance on how to use the new parameters and agree some standard sets of values.

[pschlik]

Folks have had a habit over the years of dramatically overestimating the res charging rates. With just a bit of investigation it's not hard to determine that it should take minutes to get the auxiliary and emergency reservoirs up to pressure, setting the aux and emergency charging rate to ~ 0.5 psi/s (with uniform charging ratio of 2, set the charging rate token to ~ 1 psi/s) is way more realistic than 11 psi/s.

Other things I'd recommend is to NOT use ORTSMaxServiceCylinderPressure, there is no dedicated device to limit brake cylinder pressure on US control valves, as this allows different brake pipe pressures to be used. Hook up any regular freight car to 110 psi brake pipe and it will be able to produce 79 psi brake cylinder pressure. In that regard, BrakeCylinderPressureForMaxBrakeBrakeForce might be better set to something higher like 100 psi to allow use of the same code at higher brake pipe pressure (94 psi would result from an emergency application at 110 psi brake pipe pressure, and that's as high as it'll normally go), but you'd have to keep that pressure in mind when setting the brake force values.
You also have your list of tokens for an AB valve-AB control valves don't have accelerated application at all. ABDW, ABDX, and DB-60 all do have that, and I've found an accelerated application factor of 0.75 matched test results well for the ABDW valves, and 1.5 matched ABDX testing. Never found any testing for the DB-60 control valve so I guessed that's probably a bit quicker than ABDX and went for a factor of 1.75. AB valves also should not use ORTSEmergencyResQuickRelease, that came about with ABD valves and later.
I also find that folks tend to greatly overstate application and release rates. Various bits of research and testing I've seen show that the application rate on these newer valve types is like 5 psi/s and release is even more drawn out in the range of 1-2 psi/s. Maybe in the past valve designs were willing to throw air around in less than a second but that is exactly how you break a 100 car train in two.


If you want to see what I've figured out, I have some physics mods out on the TrainSimCommunity website and with a bit of patience the parameters I used can be found in there. SP Shasta Route Physics Overhaul - Train Sim Community Everything brake related is in TRAINS\TRAINSET\Common_psc\Air_Brakes\Control_valves, but it's all modular so it's not exactly easy to read.

[Weter]

Hi, Darwin.
Nice thread.

Indeed, Phillip: with some brake valves, driver can adjust working BP pressure, setting it higher for freight/mountains, or lower for passenger/plains.

[darwins]

Quote

Other things I'd recommend is to NOT use ORTSMaxServiceCylinderPressure

That sort of makes sense (at least for USA where different pressures may be used for yard freight, main line freight and passenger as well as by different companies!)

In that case the question is what to set as BrakeCylinderPressureForMaxBrakeBrakeForce ( )
Should this be 70psi, 64psi, 77psi, 83psi, 90psi? All are possible with different systems.

If not specified will the Triple Valve Ratio and the presence of an emergency reservoir (of the correct size) determine the correct pressures for both service application and emergency application?

[pschlik]

darwins, on 07 November 2023 - 01:20 PM, said:

That sort of makes sense (at least for USA where different pressures may be used for yard freight, main line freight and passenger as well as by different companies!)

In that case the question is what to set as BrakeCylinderPressureForMaxBrakeBrakeForce ( )
Should this be 70psi, 64psi, 77psi, 83psi, 90psi? All are possible with different systems.

If not specified will the Triple Valve Ratio and the presence of an emergency reservoir (of the correct size) determine the correct pressures for both service application and emergency application?

I have been personally using a max brake cylinder pressure of 100 psi just because that's a nice number to work with and it covers pretty much all cases that are likely to show up. The only way to get above 100 psi would be with unrealistically high brake pipe pressure. Just need to remember that the value of MaxBrakeForce/ORTSMaxBrakeShoeForce occurs at BrakeCylinderPressureForMaxBrakeBrakeForce, so brake force would have to be multiplied by 1.3 to convert from 77 psi to 100 psi.

And as long as both TripleValveRatio and EmergencyResVolumeMultiplier are set correctly (2.5 and 1.4 respectively) the expected pressures will be developed without the need to artificially limit anything. Even with the max brake cylinder pressure set to 100 psi, full service will only produce 64 psi and emergency 77 psi when initially charged to 90 psi.

[darwins]

@ Phillip

I have downloaded the settings from your route. Thanks for that. I hope to be able to work out a number of standard triple valves from there. Certainly your application, release and charging rates look much more like what I would expect in a real system.

One problem remains though, the K-type triple valve, this does have a higher emergency brake cylinder pressure, but does not have an emergency reservoir. Are we going to need another way to model this? Perhaps EmergencyDumpValveBrakeCylinderPressureRatio ( 1.20 ) or something?

Similarly for passenger service, TrainDude has suggested adding a High speed reducing valve for the PM type triple valve. I am not sure where we go for the K type triple valve, will it work just to treat the supplementary reservoir as an emergency reservoir or do you think a different approach will be needed?


@ Weter

It would be really good if you can help with information. My problem sometimes is having too much information, but not being able to work out the specific things needed for Open Rails! There are I think five different sets of standards in use:

UIC / Europe

AAR / North America

Australia + New Zealand

Russia + CIS

China

Which of these can you help with? I will bounce some ideas on this thread soon.

[pschlik]

Fancy features of older valve types will require another code change, probably nothing too complicated. I think I need something smaller to do anyway.

[darwins]

The higher emergency pressure, without the use of an emergency reservoir was not only part of the Westinghouse K type valve, but also a part of some older European valves, such as the Knorr K1 and the Kunze-Knorr Kkp valve. (Same idea of the emergency dump valve moving a quantity of air from the train pipe into the brake cylinder.)

Putting together the information from your package, it seems like most US freight valves are now fully described.

https://i.imgur.com/IB9zmvH.jpg

With regard to US passenger valves, two matters arising would be how to model the supplementary reservoir and the addition of the High Speed Reducing valve already mentioned for the PM valve.

https://i.imgur.com/E64thFp.jpg

For a complete model of other European valves the additional feature needed would be two stage braking. As mentioned above the change from higher pressure to lower pressure was dependent either on the speed of the train or on the deceleration rate.

Present day European standards in general have faster application and release times than USA. This is probably because trains are generally much shorter. Auxiliary charging rates are also higher, which is necessary with no emergency reservoir to prevent the brakes being exhaustable.

[darwins]

Looking at some numbers, then those used for US triple valves are mostly similar to the UIC standards for distributors, except that UIC timings have faster application times in Passenger mode and faster Auxiliary charging times.

https://i.imgur.com/6bltaZ2.jpg

There have been some changes in the UIC specifications over time:

https://i.imgur.com/n8I6iIM.jpg

From 1953 onwards the option to use retaining valves on freight trains has been made redundant by the requirement for faster auxiliary charging rates.

Older triple valves used in USA may have had faster Auxiliary Charging rates than later valves that included an emergency reservoir as well. The table below was published in 1935 and gives charging times for some older valves.

https://i.imgur.com/q030L8w.jpg

H, K and L presumably apply the H, K and L type brake systems. Does F correspond to a standard plain triple valve and G to a quick action triple valve? What systems do M, P and R correspond to?