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brake line pressure just before train departs yard

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brake line pressure just before train departs yard
Posted by gregc on Monday, February 13, 2023 4:38 PM

several questions about brakes usage on cars being assembled into trains in yards.   in general, how is brake pressure established on trains/cars as cars are assembled?

am i correct that car brakes are not applied nor is there a need for brakes while cars are switched either at hump yards or when flat switched?

when are brake lines connected between cars when ready for departure?

when are brake lines pumped up on a train when ready for departure?

are brakes applied on a train before departure?

does a train depart before maximum brake line pressure is established?

greg - Philadelphia & Reading / Reading

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Posted by gmpullman on Monday, February 13, 2023 6:21 PM

It's all right here:

 

https://www.law.cornell.edu/cfr/text/49/232.205

    Then come back if you have more questions.

Good Luck, Ed

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Posted by NVSRR on Monday, February 13, 2023 6:26 PM

I seam to remember a number of 75 psi for brake line.     Yes brakes are applied before the train departs.  it is a test brake application to make sure everything is working.  including the eotd.   Once the train is assembled nd the lines connected they pump them up. as the conductor coming back from connecting them checks as he goes.  he also has from a what is called a car man who helps with assembly and stuff.  

In a hump yard, the yard tracks, more correctly bowl tracks, are bowl shaped to hold the cars without brakes as the trains are assembled.    flat switching doesnt have th bowl but they dont have brakes applied while switching but hand brakes are applied beofre the shift leaves. 

 

That is what I can remember.  

 

SHane

A pessimist sees a dark tunnel

An optimist sees the light at the end of the tunnel

A realist sees a frieght train

An engineer sees three idiots standing on the tracks stairing blankly in space

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Posted by jeffhergert on Monday, February 13, 2023 7:14 PM

Cars are generally switched without using the air brakes.  They will be bled off before switching.  (There are yard where because of grades, some or all of a cut of cars will be switched using the air brakes.)

Once the cars have been switched and (Maybe placed on departure tracks, maybe left on a yard track-depends on the design of the yard.) ready for departure, then someone will walk the track and lace up the air hoses make sure any anglecocks are opened.  Except of course, the last one on the track. 

If carmen are assigned to the yard, they will be the ones who walk the track.  They will also be looking at the cars, fulfilling the safety inspection requirement for initial terminal tests.  At least on the side they walk.  If there aren't carmen, than one of the yard switchmen or, if employed, a yard utility man will do that.

The carmen will also do the air test, where employed.  They can wait for a locomotive to be attached or a yard air plant.  If no carmen, then a switch crew can do the test or the road crew can do the test.

When using a locomotive to do the test, the cars have to be charged to a pressure that is within 15 psi of the feed valve setting (which is the operating pressure when fully charged,) at the rear of the cars.  Most freight trains are operated at 90 psi, so that means the gauge has to register at least 75 psi to do the test. 

A leakage test is also done.  The link provides details of the procedures, etc.

Almost all trains these days are built on two or more tracks because of the growth of the lengths of trains.  Many yards still have track lengths from the late steam/early diesel eras.  So before departure tracks have to be "doubled" up.  Once all the tracks are doubled (or tripled, etc) and the train is complete, a class 3 application and release test is needed.  It's to ensure air continuity throughout the train.  Again, the brake pipe is charged to at least 75 psi at the rear end.  (A hand held gauge or EOT can be used.)  Another leakage test may or may not be required depending on circumstances.  Once that 75 psi is reached, a 20 psi reduction is made on the automatic brake vavle.  Either the rear car's brakes have to be seen to apply or that pressure at the rear of the train has dropped 5 psi on the gauge/EOT.  When the air brake is released, the rear car's brakes must be seen to release or pressure has risen at least 5 psi on the gauge/EOT.

If departure is delayed, the air brakes need to be applied, but now it doesn't have to be by 20 psi.  Some railroads may have a specific minimum reduction.  We don't, but you want to set at least 10 psi to reduce the risk of sticking brakes when releasing.  You want to see the EOT drop when applying and rise when releasing, again it's to ensure brake pipe continuity.

We (other railroads may or may not have them) don't have any set requirement for how much brake pipe pressure or air flow there must be before movement can procede.  There are places with a heavy train once you release the air brakes the train is going to move way before the train is fully charged.  Things like that will be considered by the engineer.

If you're sitting on a steep grade with a heavy train and only going to move a short distance, following another train for example, it might be prudent to just stay where you're at until you can go further.

Jeff

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Posted by dehusman on Monday, February 13, 2023 8:27 PM

The way carmen worked at teh yards I was at (this is 20-30 years ago), the inbound train/cut would be yarded with air on it.

The track would be blue flagged, carmen would inspect the track and bleed off the air from each car.  Each car individually had to have the bleed rod pulled.  The carmen would check for defects to the carbody and safety appliances and worn brake shoes.  Plain bearings would be oiled, bearing oil pads/waste would be replaced, worn shoes replaced, bent grab irons straightened and any cars that could not be repaired in the recieving yard were bad ordered to be sent tot he RIP track.  

The bad order cars were giving to the yardmaster, the repairs and work done on the cars were given to the car foreman (to be billed to the car's owner) and then the track was released to teh yardmaster.

The track was switched.

When the outbound cut or train was assembled the cars would have air applied as Jeff described and the carmen would inspect the the cars again, this time focused on whether or not the brakes were working.

If there were no carmen, only the train crew, the crew switching the inboundcut/train would bleed off the air and make a cursory inspection for any obvious defects.  When the oubound train was assembled, the crew picking up or the outbound train crew would lace the hoses, and do the air test.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by gregc on Tuesday, February 14, 2023 5:44 AM

sorry if this is tedious, but if you were modeling brakes on a model ...

a train getting under way rarely have maximum brake pressure (e.g. 90 psi) either because it was stopped with brakes applied (e.g. ~10psi) or there was a brake test prior to departure from a yard.

brake line pressure would only build back up to max once the train is under way.   And this could take some time on long frieght where both the brake line and reservoirs in each car need to be pressurized to ~90psi

i assume an engineer attempts to maintain the speed of the train to avoid the need to apply brakes.

how attentive to brake line pressure is an engineer after applying brakes?

seems to me that brake application on a train is as much of an art, if not more so, as using throttle/reverser on a steam engine

greg - Philadelphia & Reading / Reading

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Posted by BigJim on Tuesday, February 14, 2023 9:08 AM

gregc

sorry if this is tedious, but if you were modeling brakes on a model ...

a train getting under way rarely have maximum brake pressure (e.g. 90 psi) either because it was stopped with brakes applied (e.g. ~10psi) or there was a brake test prior to departure from a yard.

The pressure on the rear car will depend on how long the train has been sitting after the Initial Terminal Brake Test is performed. Sometimes a train will be sitting for a very long time before departing and maximum trainline pressure will be achieved. Keep in mind that there is a pressure gradient throughout the trainline. The brake test cannot be performed until the pressure on the rear car is within 15psi of the feed valve setting on the locomotive. For example, if the feedvalve is set at 90psi, then, the rear car must have 75psi showing on the gauge.

brake line pressure would only build back up to max once the train is under way.   And this could take some time on long frieght where both the brake line and reservoirs in each car need to be pressurized to ~90psi

Again, it will depend on how long the train sits before departing.

i assume an engineer attempts to maintain the speed of the train to avoid the need to apply brakes.

Over the road, True.

how attentive to brake line pressure is an engineer after applying brakes?

For me, VERY!

seems to me that brake application on a train is as much of an art, if not more so, as using throttle/reverser on a steam engine

Yes, no matter what type of motive power is being used!!!

 

.

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