Prototype information for the modeler

As a new model railroader, please answer some questions for me. What does the term "varnish" refer to? What does it mean to "pull a drawbar"? Thanks much.

Back when passenger cars were made of wood, heavy coats of varnish were applied to the premiere cars to make them gleam and shine.  Some old photos almost make them look like metal.  Compare to boxcars and other wood cars that might have had a bit of shine when new but would get chalky and dull with time.  The railroaders would refer to those premiere trains as "the varnish."

I suspect but don't know for sure, that the varnish was reapplied often to keep the cars looking nice.  References to "the varnish" might in part have been to the smell!

The drawbar is what the coupler is attached to.  It can swing from side to side a bit and there is slack in and out as well (less so for passenger cars); modern ones have cushioned springing action built in.  If the train was heavy on starting up the weakest link was often the drawbar's attachment to the car, so sometimes the whole thing would be yanked free -- pulling a drawbar.  It still happens from time to time.  In the early days of PRR electrification, the immediate horsepower being applied from the electric locomotive was higher than with steam, and over time cars and drawbars needed to be beefed up as a result.  Pennsy ended up converting some of their early electrics to pushers because they just kept pulling out drawbars.

Dave Nelson

mailman51:

What does it mean to "pull a drawbar"?

The drawbar, as described is the portion of the coupler that fits into the car end.

It can break, either from wear and fatigue or from being rapidly or overly stressed.  the engineer accelerates to rapidly or is going up a grade and there is too much weight on the drawbar (over 8000 tons) it can case it to fail.  If an air hose bursts or the train goes into emergency the slack forces in the train can cause a weak drawbar to fail.  Normally the knuckles fail before the drawbars.

The housing or center sill can fail and rip completely out of the car (known as "gutting" a car).

There is either a horizontal piece of metal (crosskey) or a vertical metal pin that keeps the drawbar in the center sill.  If the parts that keep the crosskey or pin in place break and the crosskey or pin falls out, the drawbar will come out.

The danger of a drawbar coming out is that is a very large piece of metal and if the train runs over it, it can derail the train, or the coupler can drop and wedge in the ties and "pole vault" the end of the car up in the air, derailing the train.

A crew cannot repair a drawbar failure, that takes heavy equipment and welders (as opposed to a knuckle which the crew normally can replace). 

If the drawbar fails in the leading end of a car, it is known as a "wrong end" drawbar because the train cannot couple back into the car to move it to a siding to set it out.  The crew has to chain or cable the the damaged car to the train and move it to the siding, or a following train has to couple into the rear and set the car out from the rear.  On the other hand a crusty old General Manager once pointedly told me there was no "right' end to get a drawbar.

Just a "small" addition...

If a knuckle breaks or a drawbar breaks/pulls out...

• it won't usually show up if the back part of the train is bunched up and "pushing" against the front part of the train... as when going down grade or slowing/stopping.
• when the train transitions from downgrade to level or up grade and/or from slowing to accelerating Or when the train is all being pulled... then the break will show up.
• It will show up by ceasing to do its job of keeping the train coupled together.
• As the train divides and space increases between the cars the coupled hoses for the automatic brake (in modern times an automatice air brake) will first stretch out... when they reach their length limit they will either be ripped apart or ripped from the end of the car with the weakest attachment.  (This might not be the car with the bust coupling).
• As soon as the brake pipe breaks all the air in the automatic system will be dumped causing a full application of the breaks in all cars in the train.  (An auto brake normally holds the brakes off to allow the car(s) / train to move... it automatically goes on if the air pressure falls too low... as when it all escapes through a broken pipe).
• The whole train should come to a shuddering halt.
• .
• I say "should" because brakes, like engineers, do not stop trains.
• Only two things stop trains... (1) friction between the brakes and the wheels (or discs) combined with friction between the wheels and the rails.  (2) anything larger and more solid than the train... like lumps of the planet.
• The difference between all the brakes going on and the train coming to a stand (which also depends on the weight and speed of the train and whether it is going uphill or down) is what allows lumps that have fallen off a car's drawgear to get under the wheels and derail the train or otherwise tip it off...
• however, if the derailment occurs before the train has stretched out and any part of the train "lands in the dirt" (i.e. hits the planet) the detached part of the train will usually be slowed down enough to stretch out the break in the train and snap the air pipes... dumping the air and putting the brakes on.
• It is possible for any derailed car to happily trundle along pretty much in line with the rest of the train for some distance... happily smashing up bits of the track...  until the derailed wheelset(s) hit something they can't smash out of the way... when they will deflect and there will be a pile-up...
• This is why there are things like bridge guard rails down the middle of the track on big bridges... they are there to stop derailed cars getting deflected more than an acceptable amount and smashing into the bridge structure.
• A pile-up will sever the brake pipe at some point along the train and put the brakes on.  In this scenario the break in the pipe may not be even close to the car that caused the problem... this will be something that investigators will be looking for after the event. 
•  
• So another problem that arises when a coupling breaks is that the air hoses will be damaged.  This makes problems for re-starting the train.
• If anything other than the flexible pipes are broken there is a real problem. 
• So long as it isn't needed for a FRED to operate correctly it is possible to "borrow" a hose off the back of the last car and fit it in place of a snapped hose.  This is a pain and takes time!  ... time on top of achieving getting the two parts of the train to stay together.
• If the brake can't be repaired the usual solution would be to cut the train at the break and deal with the two parts as seperate trains.  The front part would go forward as usual while the back part could be propelled forward or drawn back.
• That was simple wasn't it?
• So what happens if the drawgear has ripped out of the front of the car in the back part of the train and the metal pipe on the back of the front part of the train is damaged?
•  
• There is another factor to be considered...
• All automatically braked cars have a "brake release" which makes the car unbraked... allowing it to be moved... but it has no brakes with which to control it remotely.  It does still have its manual brake... so the brakes on it can be wound on by hand... which should be done when a car is spotted on its own...
• This means that if a train divides, can be hooked back together and the air brake can't be made right through from front to back... it can still be moved... but the back part of the train will not be braked... This was less of an issue when trains had a caboose at the back. It may not be allowed at all now???
• If a train moves with some of the brakes cut-out it will do so under specific working conditions and at reduced speed.

Hope this is useful.

Here is a gutted boxcar.

http://www.railpictures.net/viewphoto.php?id=244396&nseq=774 

Kadee #500000000000000000008 conversion.

dehusman:

You might want to actually do some research and understand how air brakes work before you post a tutorial.

Wasn't meant to be a tutorial.  Was based on working experience (if limited in some respects).  Sorry to offend you.

The one time I was close to a buckeye coupler failing the two parts of the train seperated very slowly (almost cartoon style) and the glad hands failed to part (sorry I thought that going into glad hands would be a bit too much)... the result was eventually an impressive bang as the metal pipe on one car snapped.

I did raise a query about whether a US train would be allowed to move at all with some defective brakes... But I'm left wondering how a defective car is set out without moving it if a train divides miles from the nearest spur or siding?

I would guess that ripped out drawgear was much more common in the early days when there were a variety of automatic brakes and (to soe extent) less rigid working methods.  Isn't this one of the many things that has lots of "era specific" elements?

Apologies for offense

This means that if a train divides, can be hooked back together and the air brake can't be made right through from front to back... it can still be moved... but the back part of the train will not be braked... This was less of an issue when trains had a caboose at the back. It may not be allowed at all now???

Dave-the-Train:

Wasn't meant to be a tutorial.  Was based on working experience (if limited in some respects).  Sorry to offend you.

No offense.   A bullet list seemed tutorial.  If you were describing UK practices that wasn't evident.  I know a lot of things mechanical are different in the UK than in the US.

The one time I was close to a buckeye coupler failing the two parts of the train seperated very slowly (almost cartoon style) and the glad hands failed to part (sorry I thought that going into glad hands would be a bit too much)... the result was eventually an impressive bang as the metal pipe on one car snapped.

The pipe was probably defective.  The first time a car is switched in a yard the air hoses part automatically .  A major US class one might switch 100,000 cars a day so the air hoses have to separate that many times  automatically.  Add in every time a train makes a cut to set out or pick up, the air hoses part automatically.  So its something that happens all the time.  Damaging the cars is very, very rare.

I did raise a query about whether a US train would be allowed to move at all with some defective brakes... But I'm left wondering how a defective car is set out without moving it if a train divides miles from the nearest spur or siding?

100% of brakes have to be working out of origin.  85% of the brakes have to be working at any given point.

If the air brakes are inoperative you can just cut out the air on that car and the rest of the train still has brakes.

If the train line is damaged then you will have to set the car out.  So you turn the angle cocks and move the car to a siding and set the car out.

The part that I was dis agreeing with was this paragraph:

 " This means that if a train divides, can be hooked back together and the air brake can't be made right through from front to back... it can still be moved... but the back part of the train will not be braked... This was less of an issue when trains had a caboose at the back. It may not be allowed at all now???"

Cutting the brakes out on the rear of the train isn't what they are supposed to do.  If the damaged car is like one or two cars from the rear they might move it far enough to set the car out, but the way I read it they could cut the air out on the rear of the train and go on.  That's not correct.

I would guess that ripped out drawgear was much more common in the early days when there were a variety of automatic brakes and (to soe extent) less rigid working methods.  Isn't this one of the many things that has lots of "era specific" elements?

Its era specific because in earlier eras the draft gear had less capacity when compared to newer cars, so draft gear designed for 40-50 ton cars was mixed with cars with draft gear made for 100 ton cars.  Modern high capacity  cars have high capacity drawbars and can be used in heavier trains without risking failures.  If you go really far back in the pre-WW1 era a lot of the cars had wood underframes and so were much weaker just because wood is weaker than steel.

 Air brakes work by sensing the difference between the pressure in the train line and pressure in the air reservoir on the car.

The air compressor charges air into the train line to a set pressure.  On each car there is a brake valve, a reservoir, an emergency reservoir and a brake cylinder.  If the pressure in the train line rises above the pressure in the reservoir, the brake valve senses the difference and the valve moves, releasing pressure from the brake cylinder and charging the reservoirs. 

When the train line reaches its set pressure the compressor stops charging the train line.  when the reservoir pressure equalizes with the train line pressure the valve centers and seals the pressure in the reservoirs.

When the brakes are set, the pressure in the train line is reduced, the valve on the car senses the difference in pressure and moves to send pressure to the brake cylinder.  When the reservoir and trainline pressures equalize the valve centers and traps the air in the cylinder and reservoir.

When the pressure increases in the trainline, the valve moves again and vents the cylinder pressure, and charges the reservoir.

If the pressure drops dramtically and the difference between the train line and reservoir gets too great the valve move far enough to vent the emergency reservoir into the brake cylinder, putting the train in emergency.

Each car has a valve that isolates the car's brake system from the trainline.  Each car has a valve that empties all the air out of the car's brake system.  Each car has a valve that allows only part of the brake cylinder pressure to be vented, it retains part of the pressure in the cylinder when the brakes are "released" (that's the retainer valve).  In addition there is a angle **** on both ends of the cars to shut off the train line on that end.

Modern brake valves have the ability to vent reservoir pressure into the train line when the brakes are released.  That accelerates the release on the train.  The down side is that if the crew has "bottled the air" (disconnected the engines from a cut of cars that has the train line charged and has the angle cocks closed on both ends) that sets up a situation that if something causes a pulse of air in the train line, that pulse can cause the brakes to begin to release on the cut.  A bad thing.

WOW!  Thanks for that explanation!  Lots of stuff that's very much the same but slightly different in there.

I think it's probably best if I leave it at that unless anyone wants us to go into more details... then I can be vague or get things wrong and you can correct me!    It's a long time since I worked directly with brakes.  Most of the time I just try to explain to completely non-rail people that if there is a problem on a train the brakes automatically come on in a "fail safe" manner... so long as the train has been put together correctly.

The risk of brakes leaking off is why we have schedules for how many cars in a cut left standing must have the brakes wound on by hand... naturally problems then arise when people don't unwind those brakes before moving the cut,,, this (as Dave will know) is how cars get flat spots on the wheels.

At the car works near me they don't just wind the brakes on but put wood wheelstops under the wheels at each end of any cut... some of the cars are probably there with brake defects anyway.

That gutted car http://www.railpictures.net/viewphoto.php?id=244396&nseq=774  is weird... How on earth did the centre sill get ripped out with no sign of damage to the sides?  I can guess that it's the sliding element of a cushion frame but it still seems weird to me.  I'd guess that the cars brake pipes got bust somewhere underneath the car!

Dave-the-Train:

I can guess that it's the sliding element of a cushion frame but it still seems weird to me.  I'd guess that the cars brake pipes got bust somewhere underneath the car!

The train line is attached to the sliding center sill.  At some point there is a "branch pipe tee" where the line from the train line branches off to the brake valve (the branch pipe).  On this type car that is a flexible hose.  When the retainers that limit the travel of the sliding centersill fail, the center sill slides out and the flexible hose branch pipe is severed.  So the train line isn't damaged, but the branch pipe is. Well sorta.  The trainline on the other end may be damaged where it was drug through the underframe.

Hopefully if your unlucky enough to have the trainling go bad on you, you have a run a round hose on your power. So that way you can cut the car out and just bypass that car's section of the trainline with your run a round and continue on your way. Another nifty lil part is a trainline repair clamp I have one in my grip that will temp fix up to a 2" hole. Either way then just tag the car and put it on the airslip as cut out and when it gets to the next terminal you can set it out.

Dave the train asked: did raise a query about whether a US train would be allowed to move at all with some defective brakes... But I'm left wondering how a defective car is set out without moving it if a train divides miles from the nearest spur or siding?

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In that case a car man would be called to fix the problems if we couldn't.98% of the time we fixed the problem since most brake problems was a busted air hose.

 Now looking at a busted draw bar-that seldom happen 99% of the time the coupler face would break before the draw bar since there is much more force on the coupler.

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The risk of brakes leaking off is why we have schedules for how many cars in a cut left standing must have the brakes wound on by hand... naturally problems then arise when people don't unwind those brakes before moving the cut,,, this (as Dave will know) is how cars get flat spots on the wheels.

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Not always..Some times the brakes won't release and the car is dragged..This is why the rear brakeman made a roll by inspection as the train departed the yard.Once on the main any crew waiting in a passing siding will make a roll by inspection and either radio you or give you a hand signal indicating you have sticking brakes.

BRAKIE:

Not always..Some times the brakes won't release and the car is dragged..This is why the rear brakeman made a roll by inspection as the train departed the yard.Once on the main any crew waiting in a passing siding will make a roll by inspection and either radio you or give you a hand signal indicating you have sticking brakes.

     Some roads may have used different hand signals, but one common hand signal for sticking brakes was to hold the hands together horozontally palm to palm and slide them together and then point to your body to indicate the location of the car in the train. Point to your head for the front, to your waist for the middle, to your knees for the rear of the train. Of course, at night it would be hard to see all this, so sometimes a stop signal would have to be given with a lantern.

Thank you.  I was about to issue a similar correction.  Saved me time and trouble.