[steamer_ctn]

 joe_star, on 08 January 2021 - 03:29 PM, said:

While reading up on vacuum brakes recently, I also realized that running a train at elevation would have the effect of reducing the effectiveness of vacuum brakes.

Can you provide specific details and reference material?

[joe_star]

 steamer_ctn, on 08 January 2021 - 04:48 PM, said:

Can you provide specific details and reference material?

Hello.

A reduction in performance would be expected with rising altitude. The vacuum exhauster/pump or ejector system would work optimally at sea level where it would be able to generate maximum vacuum. Sea level being 29in Hg, and assuming perfect efficiency, achieving 21in Hg or so vacuum (i.e. a reduction in the system down to 8in Hg), I am just using the british system as a reference.

When gaining altitude, around 1in Hg is lost every 1000ft. This is probably negligible up to several thousand ft, but would come into play both on the performance of the exhauster (i.e. how much vacuum it can generate).

I found several references to the effect of altitude on vacuum brakes in trains, listed below:-

https://www.quora.co...ilway-mechanism

The American Railroad Passenger Car, Part 2 By John H. White: pg 548

https://en.wikipedia...s_vacuum_brakes

https://news.ycombin...tem?id=20455302

None of them really go into technical details unfortunately

And more general for vacuum device peformance at altitude, this at least has some numbers.

https://www.schmalz....uum-technology/

Interestingly, the last rail related link does mention "negative marketing" by Westinghouse to discredit the Vacuum brake in the US, precisely for this reason, being that many railways operate there at higher altitudes. I wonder how much is actual fact vs hype.

[steamer_ctn]

 joe_star, on 22 January 2021 - 06:21 PM, said:

I found several references to the effect of altitude on vacuum brakes in trains, listed below:-

Thanks for that. I will have a look at it and see if I can do anything with it.

[steamer_ctn]

 joe_star, on 22 January 2021 - 06:21 PM, said:

A reduction in performance would be expected with rising altitude. The vacuum exhauster/pump or ejector system would work optimally at sea level where it would be able to generate maximum vacuum. Sea level being 29in Hg, and assuming perfect efficiency, achieving 21in Hg or so vacuum (i.e. a reduction in the system down to 8in Hg), I am just using the british system as a reference.

When gaining altitude, around 1in Hg is lost every 1000ft. This is probably negligible up to several thousand ft, but would come into play both on the performance of the exhauster (i.e. how much vacuum it can generate).

In the latest unstable version I have added functionality to model the loss of vacuum efficiency with increasing altitude.

For most instances it may not make a great deal of difference.

You can test this by using the ejector to release the brakes on a vacuum braked consist on these routes:

i) CTN Test - sea level

ii) Settle & Carlisle - approx 320m

iii) Marias Pass - approx 1500m

Thanks for the suggestion and detailed information.

[joe_star]

Perfect! I'll put it to test soon.

[joe_star]

 steamer_ctn, on 24 January 2021 - 09:57 PM, said:

In the latest unstable version I have added functionality to model the loss of vacuum efficiency with increasing altitude.

For most instances it may not make a great deal of difference.

You can test this by using the ejector to release the brakes on a vacuum braked consist on these routes:

i) CTN Test - sea level

ii) Settle & Carlisle - approx 320m

iii) Marias Pass - approx 1500m

Thanks for the suggestion and detailed information.

Hi,

I tested the elevation effects on Vacuum Braking, they seem to be functioning as expected, appreciate the effort in adding it.

@ 2500ft (Khyber Pass - highest point) : 2 inHg reduction in pressure, 43.9klbf braking force on the lead loco

https://i.ibb.co/GQXhP73/Open-Rails-2021-02-22-10-48-13.png

@ 11400ft (Peru, switchbacks outside Cusco enroute to Machu Picchu) : 6 inHg reduction in pressure, 31.3klbf braking force on same lead loco

https://i.ibb.co/qgPwzBZ/Open-Rails-2021-02-22-10-12-48.png

[steamer_ctn]

 joe_star, on 22 February 2021 - 01:56 PM, said:

I tested the elevation effects on Vacuum Braking, they seem to be functioning as expected, appreciate the effort in adding it.

Thanks for the feedback.