Tonnage Ratinds and weather Reductions for locomotives

[NW Mailing List]

Picking up on a comment below, cold air is denser (heavier). Airplanes have much better climb performance in cold air than they do in hot air (what’s good for the airplane is bad for the train). Airplanes can be weight restricted on very hot days in order to have adequate climb performance. Air is thinner (lighter) at higher altitudes as well as when it’s hot and when it’s humid (water vapor is less dense than air) so a pilot really needs to check airplane performance for those dreaded triple-H departures - hot, high, and humid.

-- 
Larry Stone
lstone19 at stonejongleux.com





> On Dec 17, 2018, at 10:01 AM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:
> 
> It is true cold weather can have very adverse effects on trainline air pressure.
> In the 70's & 80's a normal eastbound coal train out of Williamson was 120 cars.  On one particular January day the temperature was around 0 degrees.   Due to the temperature sufficient air pressure (60 lbs.) could not be obtained on the rear of the train. Our train had been reduced to 80 cars and after sometime the required air pressure was obtained and after a lengthy brake test we departed Williamson.  During this trip the air pressure dropped to 56 lbs. Fortunately  we did not have trouble with sticking brakes.  As we entered Elkhorn Tunnel the air pressure was till around 55 lbs. on the rear.  As we passed thru Elkhorn the air pressure rose to 60 lbs. After exiting Elkhorn tunnel  speed of the train increased to 25mph and air pressure on the rear dropped to 55lbs. Staying at this pressure all the way into Bluefield Yard. 
> I can only assume the reason for the air pressure to rise while moving thru Elkhorn tunnel was the temperature inside the tunnel and due to the length of the tunnel, the heat from the exhaust of the locomotives caused the air in trainline to warm and  expand and to not be so heavy.  
> Also in cold weather it was not uncommon for ice to form in the air hose and trainline (I assume from condensation) restricting the air flow.  Rubbing Alcohol would be poured into the air hose and as the air moved thru the trainline the ice would melt allowing sufficient air pressure to be obtained on the train.
> 
> -Jeff Hensley.
> 
>                     From: NW Mailing List 
> Sent: Saturday, December 15, 2018 8:36 PM
> To: nw-mailing-list at nwhs.org 
> Subject: Tonnage Ratings and Weather Reductions for Locomotives
> 
> By time-table instructions train tonnage in the steam era was reduced as ambient temperatures fell. Reductions were as much as 25% at temperatures below 0 degrees F (Rating G).
> 
>  
> 
> Were there multiple reasons for this reduction? Was the primary reason the increased rolling resistance of cars with friction bearings? Were other factors involved?
> 
>  
> 
> Thanks,  John Garner,  Newport VA
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