[Genma Saotome]

copperpen, on 09 July 2015 - 01:00 PM, said:

The three positions are EX = out to atmosphere. LP = low pressure and HP = high pressure. Far as I can tell, OR is using retainers in the correct way.

Back to the slow release of the final few PSI. I am becoming more convinced that it is a bug in the brake code that is hard to locate, which is why we have the Initialise Brakes key press.

Perhaps the way around that is to recognize that the first couple of PSI in the brake cylinder go to taking up the slack in the gear and moving the shoes into position... not really applying any braking power. Might it be more practical than finding and fixing that bug to simply drop the braking effect to zero when the PSI hits 2? Many fewer hairs pulled out that way..

[Genma Saotome]

One more data point:

Quote

Dave,
The release time on a car (not a train) is quite rapid. With the ABD valve, it takes an increase of 1.5 pounds of brake pipe pressure to start the release process. At that time, air is transferred (through the control valve) from Axillary air reservoir into the trainline (brake pipe) to accelerate the process. Then you are just waiting for the brake rigging to let go of the wheel. That includes the air in the brake cylinder bleeding off. I was never told just how fast that was but I would guess (experience by standing beside a car, never timing it,) about 3- 5 seconds and that could very a little depending on the condition of the brake rigging

[copperpen]

I have been fiddling about with the numbers in the brake control data and have reached a point where I can recharge the system ( 3 Aces and 40 cars ) in about 6 minutes minutes. The brake cylinders however, apart from the first 7 units which are showing 0 in the few seconds, are showing from 1 to 8 psi after the system has recharged. It takes a further 2 to minutes to fully empty the brake cylinders along the train.

I am wondering how this from BrakeSystem.cs - public float BrakePipeVolumeM3 = 1.4e-2f; // volume of a single brake line
is equal to this taken from the manual ------------ wagon(brakepipevolume - Volume of car's brake pipe in cubic feet (default .5).

I also note that the statement goes further to say

This is dependent on the train length calculated from the ENG to the last car in the train. This
aggregate factor is used to approximate the effects of train length on other factors.

Is one of these factors the time it takes the Brake Cylinder to empty?. If so I feel that the wrong approach has been taken for this as the brake cylinder is activated through the triple valve using air pressure differential to empty the cylinder. Although this will ripple along the length of the consist as brake pipe pressure changes the last car cylinder should be empty long before the brake pipe is at full pressure. At present the brake pipe pressure is at max before the brake cylinder is empty, and a reapplication of the brakes gives different brake cylinder pressures along the train even when all cars are using the same data.

[Csantucci]

So is there consensus on these points, related to an air brake system with no partial release?
1) in real world, once the brake cylinder venting has started because the brake pipe pressure has reached a certain threshold, it brings BC to 0 in a more or less fixed (and not big) time
2) this does not occur in OR, where very often the discharging of the BC slows down at a certain point, and then requires very long times to reach full discharge.

[steamer_ctn]

The operation of the brakes is a reasonably complex field in its own right, when thinking about railway operations. I have spent a bit of time trying to understand it, enough for me to set up braking for some of my projects. I have reproduced some of the data that I have managed to find and extract from various sources on this brake page. Using it has hopefully allowed me to configure brake systems on cars as realistically as possible. Whilst it is written for NSWGR operation most of the principles will be similar to other systems. The main differences will be the system operating pressures.

I believe that, before we can confidently determine whether the braking code in OR has a bug(s) in it or not, we need to complete the following two activities:

i) Configure a train with realistic prototypical information in the ENG and WAG files
ii) determine some realistic expectations that we can then test the code and the rolling stock created in i) above against.

In regard to the first point above, even default trains in MSTS appear to be very poorly configured as far as brake operations are concerned, for example take the consist "gp38.con", which is two GP38 with 35 mixed freight cars attached. To demonstrate my point, run this consist in OR and open the Brake Information HUD.

A couple of points to note from the HUD:
i) The locomotives have 70 psi pressures in their brake cylinders, whereas the cars have 50 psi (ie different values of BrakeCylinderPressureForMaxBrakeBrakeForce( 70 ) )
ii) Wagons 5 & 6 don't show up correctly, so perhaps there is a problem in their respective WAG file.

Then looking at the respective ENG and WAG files for the stock in the consist.
i) As suggested in the post earlier, the locomotive Main Reservoir volume seems low and the Compressor charging rate needs checking.
ii) In addition, the locomotives and wagons seem to have auxiliary brake reservoirs of around 7 - 10 cu ft. Typically I believe that the auxiliary reservoir on a wagon should be in the order of 1 - 2 cu ft. See here for an example specification.

So, when compared with the locomotive main reservoir volume of 8 cu ft, I think that the train air supply in the main reservoir will be very quickly exhausted, if it is trying to fill 35 x 7 cu ft reservoirs. The other factor that is not necessarily clear, is the size of the brake cylinder, and how much air is being used to apply it and release it, as this will be the actual air used by the system in each application/release cycle.

Typically for the brake system in this consist, a drop of 1 psi in the brake pipe will increase the pressure in the brake cylinder by 2.5 psi, and similarly in reverse, a 1psi increase in the brake pipe will decrease the pressure in the brake cylinder by 2.5psi.

Thus the system operates between the following limits:
i) Full brake release (BP = 90psi, BC = 0 psi)
ii) Full brake application (BP = 70psi, BC = 50 psi)

Typically the brake operation is influenced by various pressures, and volumes within the system. Thus it is possible that incorrectly specified reservoirs may be using too much air, and exceeding the ability of the main reservoir and compressor to supply the air in a timely fashion. For example, if the BP air pressure has dropped to 80 psi (which means that the BC = 25psi), and the main air reservoir volume has been exhausted, then the brakes will need to be recharged by the compressor. This may may take a reasonable period of time depending upon the compressor specifications. In this event, you will see the main reservoir pressure slowly increasing, and in turn the BP, and as a result the BC slowly decreasing.

Remembering that excessively rapid brake operations will eventually discharge the air in the system, and result in "faulty" operation of the brakes. Over the years a number of trains have runaway when descending steep gradients as a result of poor driving, and exhausted air supplies.

So the question now becomes, is it the OR code or the poor specification in the MSTS ENG and WAG files, or train operation that is causing some of the issues being seen? As suggested the only way to determine this is to have a test configuration with the correct values in it, and then test the OR code against it.

To assist in identifying these sorts of issues, I would like to see the main reservoir and wagon reservoirs included in the Brake HUD.

[edwardk]

I came across a post under train sim which is about 3 years old. This could be what you are discussing here. http://www.trainsim.com/vbts/showthread.php?312204-How-to-get-brakes-to-apply-release-fast

Edward K.

[copperpen]

Let us be clear on one point here. The train brake line itself and the res are working fine for me. It is the brake cylinder empty time that is wrong. For the three engines and first four cars in the consist, release to empty is very fast. At the EOT the PSI is still 15PSI. From car 8 to car 43 EOT the time to reach 0psi is in the order of 6 minutes.

I am using this in the freight cars

MaxReleaseRate( 600 )
MaxApplicationRate( 50 )
MaxAuxilaryChargingRate( 600 )
EmergencyResCapacity( 40 )
EmergencyResChargingRate( 70 )
EmergencyBrakeResMaxPressure( 90 )
TripleValveRatio( 2.5 )

BrakeCylinderPressureForMaxBrakeBrakeForce( 50 )

and this in the locomotives

TripleValveRatio( 2.5 )
MaxReleaseRate( 600 )
MaxApplicationRate( 10 )
MaxAuxilaryChargingRate( 600 )
EmergencyResCapacity( 100 )
EmergencyResChargingRate( 600 )
EmergencyBrakeResMaxPressure( 90 )
BrakeCylinderPressureForMaxBrakeBrakeForce( 70 )

AirBrakesMainResVolume( 170 )

[Lindsayts]

Now just in case this may help, I have just tried one of my own pass consists, with normal barke parameters. The consist is 10 car pass hauled by two loco's, one of 2400bhp the second 2200bhp. Trailing load is 10 cars total weight 600tons. The consist is setup for Air_Twin_Pipe and both "Triple_Valve" and Graduated_release_Triple_valve" were tried, both brake systems performed OK. On application and release there was a slight propergation delay down the train, but it was nothing unusual. An interesting point is "Graduated Release" in OR's options menu apparently had no effect, both stamdard and Graduated release triple valves working as expected.

I have put a lot of effort and testing into these WAG files to get the trains brake performance to reflect the real world as seen by local documented brake tests.

Now I have had single pipe consists that did show serious delays in brake release, but it certainly not showing up in a twin pipe setup.

Note: OR v1.0 is being used.

Lindsay

[steamer_ctn]

I have created a test consist of default rolling stock, using the GP38 and a Hopper wagon, and done some initial tweaking to the ENG and WAG files.

With this consist, I can release the brake in around 1 min along the full train.

The brake pipe pressure should only be operated within the limits of 68 - 90 psi to achieve full application and release of the brake cylinder.

Try it with and without graduated release selected in the options menu.

How does this compare with other experiences?

In the attached zip file there are three files:-
gp38_brake_test.con - to go in consist folder
gp38_brake_test.eng - to go into gp38 folder
us2hoppercar_brake_test.wag - to go into the us2hopper folder

For those who are interested in a simple good explanation of brake operation try this document.

There is some additional refinement that could be done.

Attached File(s)

•  Brake Test.zip (6.93K)
  Number of downloads: 207

[copperpen]

Aha Peter,
A quick comparison between between yours and mine reveals I am using too big a figure in EmergencyResCapacity. A change to your very much smaller figure does the job without changing anything else. I suppose that Kuju in their infinite wisdom decided that the emergency res and the auxiliary res are the same item. This actually makes MaxAuxilaryChargingRate redundant which is something I had not realised until now. At least, if I comment that line in my test wag it makes zero difference to the figures on the brake info page. I am getting the fast recharge that I want and the fast brake cylinder drop to zero.