BDAPeople used to say that long trains would always take longer to charge or recharge in cold climates because cold air was "thinner" and the train leaked more.
And it certainly got hotter than ambient when it was pumped up, some of which heat would be carried preferentially to any 'leaks', at least forward in the train, during pumping up.
I was taught the usual problem was shrinkage and some hardening in the seals between the gladhands in cold weather. There was an article in Trains many years ago about a solid consist loaded with beets that had this issue in vicious cold weather: they pumped for two hours and got not a whit of trainline pressure. Still makes me shiver a bit thinking about it.
Something I'd like to add about air flow and stretched vs bunched freighters .
People used to say that long trains would always take longer to charge or recharge in cold climates because cold air was "thinner" and the train leaked more .
I remember thinking no , cold air would be denser than warm air so how can this be . Eventually the maintainers said that there are bolted flange joints in train pipes under wagons . Apparently these sometimes don't seal as well when they are cold . This made more sense that the original theory .
A previous employers ore trains I ran were around 9017 feet long and keeping the train pipe charged with head end power only was interesting in winter . These trains used NYAB EP60 equipment and it will only allow the EOT BP pressure to drop so much before it pulls you up .
Interestingly I worked one of these trains out of a mine one winter morning and the EOT BP pressure varied depending on which way the line curvature went left or right . As the sun came up and the temperature increased the problem went away .
BEAUSABRE One thing to note - many mountainous lines preferred F units after trying E units in the hills (GN, NP, ATSF come to mind) because they liked the idea of all locomotive weight being on the driving wheels. So the E unit became a flat land railroad's unit (CB&Q jointty owned by GN & NP continued to buy E's. SP&S, the other GN/NP serf was almost all Alco, not sure about whether the grades down the Columbia River Gorge would have led to E's or F's). As mentioned, as long as D/B was an extra-cost option, these lines figured they didn't need it and could save some money by not ordering it. Of the two biggest E8 owners, PRR stayed out of the D/B club because they figured whether they had E's or F's leading, they'd still need helpers over Horse Shoe and didn;t need it east of Altoona or west of Pittsburgh (I don't think the Buffalo Line (Keating Summit) ever saw E's on a regular basis). NYC? They were the Water Level Route, man...The same logic as the PRR might have applied to the B&O over Sand Patch, but why C&O didn't apply it to its 31 E8's, I must admit is beyond me
One thing to note - many mountainous lines preferred F units after trying E units in the hills (GN, NP, ATSF come to mind) because they liked the idea of all locomotive weight being on the driving wheels. So the E unit became a flat land railroad's unit (CB&Q jointty owned by GN & NP continued to buy E's. SP&S, the other GN/NP serf was almost all Alco, not sure about whether the grades down the Columbia River Gorge would have led to E's or F's). As mentioned, as long as D/B was an extra-cost option, these lines figured they didn't need it and could save some money by not ordering it. Of the two biggest E8 owners, PRR stayed out of the D/B club because they figured whether they had E's or F's leading, they'd still need helpers over Horse Shoe and didn;t need it east of Altoona or west of Pittsburgh (I don't think the Buffalo Line (Keating Summit) ever saw E's on a regular basis). NYC? They were the Water Level Route, man...The same logic as the PRR might have applied to the B&O over Sand Patch, but why C&O didn't apply it to its 31 E8's, I must admit is beyond me
I'm tempted to say tonnage might've been a reason why. The C&O probably didn't have passenger trains heavy enough to consider installing DB on their E8's. Either that or they figured it would be easier to keep replacing any worn-out brake shoes since passenger traffic made up a much smaller portion of their revenue compared to the two other WDC-CHI routes. I'm not too well versed in the mechanics of locomotives or all of their benefits and handling in operation (I'm slightly unsure on what Power Braking is and how that differs from Dynamic), but C&O probably wouldn't want the extra equipment for a market they knew firsthand was quickly out.
Thanks, BigJim. I had read Al Krug's account many years ago, but was glad to brush the cobwebs out of my old brain and re-read it.
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"A stranger's just a friend you ain't met yet." --- Dave Gardner
Paul of Covington It also concerns me that there would be less pressure available in the emergency reservoirs if you do have to use the emergency application.
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Thank you, Dude.
Yes, the brakes can still apply in emergency if the train is releasing. I suspect the railways and regulators decided that the benefits of quicker releases and recharging during service braking outweighed the drawbacks of slightly reduced emergency braking effort during the rare occasions when the crew might initiate emergency braking while the train is still recharging.
I would say a service release takes less than 30 seconds to travel the length of most trains in warm weather, but I'm not sure if the exact speed has ever been measured. It would take a lot longer without this feature.
An unexpected increase in flow or rise in tail end pressure while the brakes are set are signs of an unintentional release. But I've also had one where the first sign was the train starting to accelerate abruptly and unexpectedly.
The trains that I've experienced this phenomenon on have all been unit rock or coal trains on a couple of our steeply graded branchlines. The rock cars in particular leak air like sieves as the customer likes thawing them with flamethrowers during winter, which destroys the seals and gaskets all over the air brake system. It seems like bunching the train up compresses some of the joints and causes the leaks to slam shut. This is what I based my previous post on.
Greetings from Alberta
-an Articulate Malcontent
SD70DudeAlso, when a car releases it pours air from its emergency reservoir back into the brake pipe to speed up recharging and propagate the release faster, in the situation I've described this means that one car releasing can start a chain reaction that leads to the whole train unintentionally releasing.
When I first read about this some years ago, I was amazed that anyone would design a feature like this. If this chain reaction starts, can you still dump air and have all cars apply brakes? It also concerns me that there would be less pressure available in the emergency reservoirs if you do have to use the emergency application.
Also, how soon would you have an indication that this might be happening? Can you tell by monitoring the pressure and flow meters that it's happening before the train speed noticeably increases? It occurred to me after that last question that the sequential releases might be just seconds apart (or less than a second), so I guess that's my next question: how quickly does the release propagate?
It's interesting to me about flow going down when bunched. In my experiences, flow usually goes up when bunched.
If it's an excessive change, that's usually an indication of what we call a "slip joint." Glad hands that aren't seated properly or have very bad gaskets.
Jeff
Thanks, Dude. So many details to consider!
The air brake system always has leaks, which the automatic brake valve compensates for by continuously adding more air into the brake pipe. The control stand has an airflow meter to measure this, calibrated in cubic feet per minute (CFM). When releasing the brakes or charging the train after first coupling on to it you can also use the flow meter and the EOT's tail end pressure gauge to tell how charged the train is. You have achieved fully charged status when the flow and tail end pressure stabilize, and on many trains you will always have some flow.
On conventional trains our air brake rules require a freight train to have a tail end pressure of at least 75 PSI and a flow below 60 CFM before departing. The rules are different and more complex if you have one or more DP remotes or Aircars.
Leakage tends to be a bit higher when the train is stretched out, when you bunch the train up the flow meter's reading will deacrease and the tail end pressure may even increase a bit. The pressure maintaining feature of the automatic brake valve keeps compensating for leakage even with the brakes set, so when you bunch the train up with the brakes set and the leakage suddenly decreases you can get a local increase in brake pipe pressure before the brake valve reduces how much air it is adding to the brake pipe, and cars will release even from only a 1 PSI increase in brake pipe pressure this can cause the train to start releasing even though the automatic brake valve handle is not in the release position.
Also, when a car releases it pours air from its emergency reservoir back into the brake pipe to speed up recharging and propagate the release faster, in the situation I've described this means that one car releasing can start a chain reaction that leads to the whole train unintentionally releasing.
Taking a bit more air as you bunch the train up makes the pressure maintaining feature stop adding air until the brake pipe pressure has reduced to what the valve is now set at.
BaltACD Looking through a 1960's era B&O Cumberland Division Timetable and in conjunction with various Retainer requirements the Special Instruction also specifies that the 'Short Cycle Method of Braking' will be used. Personally, I have never heard of the 'Short Cycle Method of Braking'. How is it done? The Special Instruction applies to Freight and NOT Passenger trains.
Looking through a 1960's era B&O Cumberland Division Timetable and in conjunction with various Retainer requirements the Special Instruction also specifies that the 'Short Cycle Method of Braking' will be used.
Personally, I have never heard of the 'Short Cycle Method of Braking'. How is it done? The Special Instruction applies to Freight and NOT Passenger trains.
Retainers are usually required on steeper grades when the controlling locomotive does not have a working pressure maintaining automatic brake valve which would compensate for brake pipe leakage. As the brake pipe pressure is reduced more and more due to the leakage the brakes apply harder and harder, eventually resulting in the train coming to a stop.
Short Cycle Braking gets around this problem by releasing the brakes before the train stalls. Without the retainers this would result in a rapid increase in speed and possibly a runaway. However the retainers hold pressure in the brake cylinders long enough for the brake pipe to be recharged and the brakes reapplied.
This cycle is repeated as necessary to reach the bottom of the grade.
SD70Dude and this strategy also allows you to take air a bit earlier in winter to warm the brakes up before the train completely tips over. On trains with significant flow I'll usually try and sneak another pound off while bunching up the train, to counteract the potential for an unintentional release as the flow will most likely be less on a bunched train.
SD70, what do you mean by "significant flow"? Or by "flow"?
Never too old to have a happy childhood!
mvlandsw Even with dynamics it was more sometimes more convienent to use power braking. On the B&O line between Pittsburgh and Wheeling there are eight grades - all but one fairly short. It was a pain to keep bunching up the slack to use the dynamics just to have to stretch it out again to go uphill.
Even with dynamics it was more sometimes more convienent to use power braking. On the B&O line between Pittsburgh and Wheeling there are eight grades - all but one fairly short. It was a pain to keep bunching up the slack to use the dynamics just to have to stretch it out again to go uphill.
This is pretty essential with slow loading power like Dash-8s or Dash-9s. By the time you get out of DB, into throttle and wait for them to load up you've lost quite a bit of speed.
mvlandsw At other locations with longer or steeper down grades such as Sandpatch or Bakerstown I found it better to make a light air brake application while cresting the grade and add dynamics as more of the train comes over the crest. Having the air brakes applied allows the slack to be bunched more smoothly and slows the speed increase if the dynamics don't work as expected. Once the entire train is over the crest the air brakes and dynamics can be adjusted to maintain the desired speed.
At other locations with longer or steeper down grades such as Sandpatch or Bakerstown I found it better to make a light air brake application while cresting the grade and add dynamics as more of the train comes over the crest. Having the air brakes applied allows the slack to be bunched more smoothly and slows the speed increase if the dynamics don't work as expected. Once the entire train is over the crest the air brakes and dynamics can be adjusted to maintain the desired speed.
I agree, and this strategy also allows you to take air a bit earlier in winter to warm the brakes up before the train completely tips over. On trains with significant flow I'll usually try and sneak another pound off while bunching up the train, to counteract the potential for an unintentional release as the flow will most likely be less on a bunched train.
mvlandsw Since freight air brakes cannot be partially released if they are applied too much the only recourse is to use power to keep the train moving or stop and recharge the brakes. In some cases it is possible to make a running release and reapply the air brakes but this is usually prohibited on the steeper grades do to the possibility of runaways. Mark Vinski
Since freight air brakes cannot be partially released if they are applied too much the only recourse is to use power to keep the train moving or stop and recharge the brakes. In some cases it is possible to make a running release and reapply the air brakes but this is usually prohibited on the steeper grades do to the possibility of runaways.
Mark Vinski
Our operating instructions also prohibit running releases below 15 mph if the train is over 6,500' or 20 mph if the train is over 9,000', but do not allow for the quicker reactions of trains with DP remotes or Aircars. CN also prohibits power braking above notch 4, but sometimes you just have to do whatever it takes to get the train over the road.
During my training I was shown how to successfully cycle brake on some pretty steep grades with trains in the 3,000' to 6,000' range, but if I end up taking a bit too much air I've always preferred pulling the train down the hill.
As I recall, E8 customers could instead select an additional boiler water tank where the dynamic braking hatch was located on units so equipped. So perhaps C&O selected that option, feeling it was more important to maximize their water capacity than it was to enhance their braking ability?
B&O E units originally got steam helpers ascending Sand Patch westbound. DB would have been useful for the eastbound down grade run, although I remember a rule prohibiting its use on passenger trains even if it was available. I did use the DB on Amtrak trains.
Since freight air brakes cannot be partially released if they are applied too much the only recourse is to use power to keep the train moving or stop and recharge the brakes. In some cases it is possible to make a running release and reapply the air brakes but this is usually prohibited on the steepr grades due to the possibility of runaways.
beaulieu Railroads also used to allow Power Braking for smooth stops. Now it is forbidden on freight trains at least.
Railroads also used to allow Power Braking for smooth stops. Now it is forbidden on freight trains at least.
Funny that you mention this. I used to live in Petersburg, Illinois on the old C&IM line between Springfield and Pekin. The small fleet of EMD locos that the G&W's Illinois & Midland subsidiary inherited from the C&IM did not have dynamic brakes. Whenever the I&M would run a local down the famous Petersburg Hill, the engineer would make a hefty set with the train brakes and PULL the train downhill at a high notch setting. Watching an SD18 working hard going downhill was very disorienting to say the least!
A review of EMD Product Data and Extra 2200 South issue #43, the E8 and E9 roster, shows that four road ordered dynamic brake equipped E units. The four railroads are Milwaukee, Southern, Southern Pacific and Union Pacific. The fifth railroad had former demonstrator #952 sold to Rock Island #643 shows as dynamic brake equipped in the Product Data. The twin 12-567Bs installed in the demonstrator date to January/February 1949.
Ed in Kentucky
No B&O or C&O E8 locomotives had dynamic braking. Only three railroads purchased E8 or E9 locomotives new with dynamic braking. The Milw Rd purchasedd E9 units for the UP's Streamliner pool operation that had dynamic brakes, but the six E9 units purchased specifically for commuter service lacked dynamic brakes. The UP and SP purchased all their E8 and E9 locomotives with dynamic brakes, plus the previously mentioned EMD demonstrator locomotive sold used to Rock Island also was equipped with dynamic brakes.
Jamos Main reason why caused issues and accidents if not properly used. On a train controlled with standard dynamic braking, the engineer applied the independent brake and shut down the dynamic brakes as the amperage dropped between 250 and 200 amps, which usually occurred at 10 to 13 mph. Failure to make this change from standard dynamic brakes to air brakes could result in the head-end of the train running out ahead of the train as the dynamic brakes faded. The ensuing slack could cause a broken knuckle and a train separation.
Main reason why caused issues and accidents if not properly used.
On a train controlled with standard dynamic braking, the engineer applied the independent brake and shut down the dynamic brakes as the amperage dropped between 250 and 200 amps, which usually occurred at 10 to 13 mph. Failure to make this change from standard dynamic brakes to air brakes could result in the head-end of the train running out ahead of the train as the dynamic brakes faded. The ensuing slack could cause a broken knuckle and a train separation.
Modern extended range DC dynamics start to peter out around 5 or 6 mph.
ACs are a completely different animal, you can bring a train to a complete stop and hold it stopped on a grade with just the DB.
jeffhergert The Rock Island didn't (officially) use dynamic brakes. Their train handling rules forbid engineers from using them when foriegn power happened to be on RI trains. The dynamics on engines they bought used were disconnected and on some that were eventually rebuilt, removed entirely. Jeff
The Rock Island didn't (officially) use dynamic brakes. Their train handling rules forbid engineers from using them when foriegn power happened to be on RI trains. The dynamics on engines they bought used were disconnected and on some that were eventually rebuilt, removed entirely.
Canadian National was very similar. While a lot of our older power was delivered with dynamics they soured on it pretty quickly, and it was disconnected or removed on most if not all units. They continued buying new units without DB until the final order of SD40-2Ws were delivered in 1980 (the HR-616s might have been later, I'm not sure if they had DB or not). The only exceptions were a small number of SD40s and SD40-2Ws that were purchased with both DB and pacesetters, and specifically assigned to coal and ore trains on certain branchlines in western Ontario and Alberta.
I don't think CN ever prohibited engineers from using DB if power with it happened to show up somewhere else.
GO Transit also followed CN practice in this regard, the F59s were their first units with DB.
Apparently when DB was an extra-cost option CN figured that they could buy an additional few units for the same price by not getting it, of course this doesn't account for all the brake shoes and fuel that would be saved down the road......
I could be very mistaken - in a book I have dedicated to the B&O's E units from the Box cab #50 through the 4 E9's that were their final purchase in the middle 1950's which included the EA's, E6's, E7's and E8's in the intervening years - the only diagram that showed any reference to dynamic braking was a diagram of the E9. There was no reference to Dynamic Braking in the prose in the book, so I don't know, factually, if any of the B&O's E units actually had Dynamic Braking.
Descending the grades crossing the Alleghenies where were one would expect Dynamic Braking to benefit train handling as there were serious grades on both the routes to Chicago and St.Louis.
Until the development of effective blended braking, which really inherently depended on developments in practical electronics, many of the principal uses of 'cost-effective' dynamics on E units (and other passenger power) would be severely limited and perhaps even dangerous. About the only 'good' use would be retarding heavy passenger consists down long or severe grades -- there was a dramatic Steinheimer picture accompanying a poem in an early-'70s issue of Trains that shows a good example of a situation that would likely benefit from good dynamic. But the fun involved with jockeying throttle and contemporary EMD dynamic in, say, repeated commuter stops while modulating the train brake is not something I suspect most commuter engineers would enjoy.
Until about the 1970's, dynamic braking was considered an expensive option useful for long and heavy grades and not much else. Many Midwestern roads such as IC, RI, MP and C&NW did not equip their locomotives with dynamic brakes since there was no perceived need for them.
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