[railguy]

On the topic of mechanical vs. electric air compressors, I believe that the GE locomotives have used electric air compressors for many years. If so, then the .eng file from SLI has the incorrect parameter. Prior to the ET44 series, there is a characteristic audible "whoop" when the compressor electric motor starts. From what I've read elsewhere, the compressor starting routine has changed on the ET44 (and maybe on retrofits, too), so the characteristic starting "whoop" is no longer present in the compressor startup sound. I believe that EMD held on to mechanical air compressors longer, but their newer locos have electric compressors. I recently heard a Union Pacific mechanical person talking on the radio to an engineer about a malfunctioning newer EMD locomotive, telling him that throttling up the prime mover to increase compressor output would do no good because the compressor was electrical. In any case, code showing a mechanical compressor is always "active"--if "active" means running--is incorrect. Mechanical diesel locomotive compressors are clutch activated when they need to run. Also, because they are mechanically tied to the output shaft of the prime mover, their RPM speed and air output will vary with prime mover RPM.

So, this goes back to one of my original comments. On MU'ed locomotives, all compressors should contribute to charging the train line. Moreover, on mechanical air compressors on diesel locomotives, throttle position should affect compressed air production from the compressor.

[Weter]

Quote

audible "whoop"

Direct-powered asynchronous machine.
So, they might use variable-frequency drive for soft starting...

[steamer_ctn]

Csantucci, on 25 September 2021 - 04:43 AM, said:

OK, waiting for others' intervention, I digged into the case and found out what causes the problem: at the beginning of September a change has been inserted in the official code, which causes that locomotives with mechanical compressor don't show the compressor state. This is true only for locomotives different from the player locomotive: the player locomotive always shows the compressor state. Accordingly to the added code comments mechanical compressors for diesel locomotives are always active.
In the test I did, the SLI ES44AC have a mechanical compressor accordingly to the .eng file, and so the state of the compressor is not shown (except for the player locomotive).

Moreover IMHO if mechanical compressors in diesels are always on, they should be shown in state ON in the HUD, rather than being not shown at all.

Thanks for identifying this issue.

I have added a patch to the latest unstable patch so that the current status of the compressor is restored to the HuD.

Can you please confirm that it appears to be ok now, and I will move it to the rc1.4.

Thanks

[Laci1959]

Csantucci, on 25 September 2021 - 04:43 AM, said:

OK, waiting for others' intervention, I digged into the case and found out what causes the problem: at the beginning of September a change has been inserted in the official code, which causes that locomotives with mechanical compressor don't show the compressor state. This is true only for locomotives different from the player locomotive: the player locomotive always shows the compressor state. Accordingly to the added code comments mechanical compressors for diesel locomotives are always active.
In the test I did, the SLI ES44AC have a mechanical compressor accordingly to the .eng file, and so the state of the compressor is not shown (except for the player locomotive).

Moreover IMHO if mechanical compressors in diesels are always on, they should be shown in state ON in the HUD, rather than being not shown at all.

Hello

Designing an energy-free control car can cause the problem. This thread deals with:
My link
It may not be koze to it, but the timing is pretty much the same.

Regards Laci 1959

[Csantucci]

Hi Peter,
your fix is OK for me, thank you.

[James Ross]

steamer_ctn, on 25 September 2021 - 09:13 PM, said:

I have added a patch to the latest unstable patch so that the current status of the compressor is restored to the HuD.

Can you please confirm that it appears to be ok now, and I will move it to the rc1.4.

It looks like you've started this from "master" branch. That means you'll have to rebase, cherry pick, or re-do your change to have it included in 1.4, because you must start the branch from "release/1.4" if you want to include it in the 1.4 release.

Please know that the starting branch does not affect the Code Bot, so starting from "release/1.4" will still allow it to be included in the Unstable Version, and the Testing Version once merged, as usual.

[steamer_ctn]

James Ross, on 26 September 2021 - 01:20 AM, said:

It looks like you've started this from "master" branch. That means you'll have to rebase, cherry pick, or re-do your change to have it included in 1.4, because you must start the branch from "release/1.4" if you want to include it in the 1.4 release.

Hopefully now done as PR#502.

[ErickC]

railguy, on 25 September 2021 - 05:30 AM, said:

On the topic of mechanical vs. electric air compressors, I believe that the GE locomotives have used electric air compressors for many years. If so, then the .eng file from SLI has the incorrect parameter. Prior to the ET44 series, there is a characteristic audible "whoop" when the compressor electric motor starts. From what I've read elsewhere, the compressor starting routine has changed on the ET44 (and maybe on retrofits, too), so the characteristic starting "whoop" is no longer present in the compressor startup sound. I believe that EMD held on to mechanical air compressors longer, but their newer locos have electric compressors. I recently heard a Union Pacific mechanical person talking on the radio to an engineer about a malfunctioning newer EMD locomotive, telling him that throttling up the prime mover to increase compressor output would do no good because the compressor was electrical. In any case, code showing a mechanical compressor is always "active"--if "active" means running--is incorrect. Mechanical diesel locomotive compressors are clutch activated when they need to run. Also, because they are mechanically tied to the output shaft of the prime mover, their RPM speed and air output will vary with prime mover RPM.

So, this goes back to one of my original comments. On MU'ed locomotives, all compressors should contribute to charging the train line. Moreover, on mechanical air compressors on diesel locomotives, throttle position should affect compressed air production from the compressor.

On EMD units with mechanical compressors, the compressor is always "running" in that the parts are always rotating, but the cylinders aren't always pumping (see the F40PH service manual for details). The old system worked fine to emulate this. Now we're in a world where the compressor always sounds like it's pumping, whether it ought to or not.

[railguy]

ErickC, on 26 September 2021 - 02:08 PM, said:

On EMD units with mechanical compressors, the compressor is always "running" in that the parts are always rotating, but the cylinders aren't always pumping (see the F40PH service manual for details). The old system worked fine to emulate this. Now we're in a world where the compressor always sounds like it's pumping, whether it ought to or not.

Erick,

Thanks for the clarification. The challenge here is this--the compressor may be rotating, but it is not pumping air unless air is required to replenish the main reservoir:

"The unloader pistons cut out compressing action
by blocking open the intake valves in the high Fig.
and low pressure cylinders . When air pressure is
removed, the unloader releases the intake valves
and the compressor resumes pumping."

This creates a challenge in the sim, because the sound triggers for the compressor are tied to the compressor being in a "running" state (the sound one hears is the compressor actually pumping air). So, for the sound triggers to work as designed (a relic of MSTS), the compressor must be in a state of "not running" for the compressor sound file to not play continuously.

Further down in the next paragraph in the manual, it confirms what I have also said is a deficiency in the old MSTS (and OR) handling of air and air compressors--that ALL compressors in a physically MU'ed locomotive set will contribute air to fill the main reservoirs until ALL are filled. Distributed power (DP) locomotives are not physically MU'ed to the lead locomotive set, but are generally cut into the air system of the whole train, so their compressors would respond to changed in air pressure in the train line. DP sets can (through digital radio commands from the lead locomotive) either respond identically to the lead locomotive set (how they currently run in OR), or the engineer can choose to run the DP set(s) independently from the lead locomotive set by, in railroad terminology, "building the fence." Building the fence is quite common on DP-equipped trains when running on undulating grades--an even more common occurrence with today's very long trains, where the lead loco set, mid-train DP set, and rear DP set may physically be more than a mile apart from one another. With either an end-of-train device (EOT or "FRED"), or DP sets, the engineer may also "dump the air" from the EOT or DP sets in addition to the lead loco set to speed up brake application--similar to a Conductor opening the air valve in a caboose.

It would also be interesting to know, if Erick or others have manufacturer information, what EMD/Progress and GE/Wabtec locomotives have electric motor or direct mechanical compressors.

[ErickC]

railguy, on 26 September 2021 - 02:52 PM, said:

Erick,

Thanks for the clarification. The challenge here is this--the compressor may be rotating, but it is not pumping air unless air is required to replenish the main reservoir

Yep, that's the point I made in the other thread. What determines the sound a mechanical compressor makes is whether or not it's pumping, which means that the old system was more accurate in terms of overall effect (so long as the compressor sound was modulated with engine RPM). In addition to multiple locomotives supplying air, mechanical compressors should also supply more air when the engine is running at a higher RPM.