Train Brakes: How do they work?

You had better buy a book on the subject. they are trying electric brakes now, too.

http://www.railway-technical.com/brake2.shtml

Well, the old head steam Engineers would have told you they work like this: Psssst, they're on; psssst, they're off.

But it is much more involved than that.  Basically, each car and locomotive has brake equipment that applies and releases the brakes in response to a signal sent from the locomotive brake valve, through the continuous brake pipe, which decreases air pressure (to apply) or increases air pressure (to release) the brakes.  The locomotive air brake valve also provides air to the reservoirs of each car, so that the cars can respond to the pressure signal to apply or release the brakes.

Read the link that NCJOE posted.  It clearly explains the details.  It was written by a fellow who posts on these forums and has a gift for explaining complicated railroad subjects in a way that those who are not railroaders can understand.

The Evolution of the Air Brake, the same way on your Subway Trains.

https://www.youtube.com/watch?v=9E9Vlpw6cnM

Gary - Cheers from The Detroit and Mackinac Railway ��

Electro-pneumatic braking (air brakes with electric controls) is nothing new.  It has been used for decades on both "heavy" and "light rail" multiple unit electric passenger equipment.  The biggest drawback is that all cars need to be connected with electrical cables in addition to air piping. 

If someone should come up with a fully integral (and inexpensive) brake operating and control system, ie no cables OR air pipes required, it would be a true quantum leap! 

All you engineering geniuses, put on your thinking caps.

Number 90 posted:

Well, the old head steam Engineers would have told you they work like this: Psssst, they're on; psssst, they're off.

ROTFL!  That's how they work on the 765...

Seriously, this is a good question. Folks who don't know about how train brakes work have a hard time grasping the concept of how LOWERING air pressure APPLIES the brakes.

The Wabco You Tube video is a long one - 1 hour - but it pretty much covers everything you would ever want to know about train brakes.

After reading about train brakes (link above) and then thinking about the terrible accident at Lac-Megantic, Quebec, when the brake system ran completely out of air, why do the train brakes fail to off and not to on or full stop? Since they can't proceed down the track until the air pressures are all correct anyway, it seems like they could be spring loaded or something to stop the train on complete air loss?

I am sure this has been thought of and considered before and there is probably something obvious I am missing here? It also seems like fail to stop would prevent runaways as well, as were described in the article link, when the brakes were applied too many times in a short period of as when going down steep grades? I also plan to watch the video, but don't have time right now.

Here's some history for you, including the early competition between air and vacuum braking for trains. 

http://www.midcontinent.org/ro...nary/eamesbrakes.htm

http://www.catskillarchive.com/rrextra/chapt22.Html

http://www.catskillarchive.com/rrextra/chapt21.Html

rtr12 posted:

After reading about train brakes (link above) and then thinking about the terrible accident at Lac-Megantic, Quebec, when the brake system ran completely out of air, why do the train brakes fail to off and not to on or full stop? Since they can't proceed down the track until the air pressures are all correct anyway, it seems like they could be spring loaded or something to stop the train on complete air loss?

I am sure this has been thought of and considered before and there is probably something obvious I am missing here? It also seems like fail to stop would prevent runaways as well, as were described in the article link, when the brakes were applied too many times in a short period of as when going down steep grades? I also plan to watch the video, but don't have time right now.

What happened at Lac-Megantic is that the air leaked down at such a slow rate that it didn't trigger the control valve to put the brakes on, keep in mind that for whatever reason the engineer left the air brakes in release position. If it had leaked down a little faster the control valve should have reacted and applied the brakes and the cars not run away. I really can't explain the science involved, but, it has happened to me while moving and I can attest that it will happen. Not very reassuring, eh?

I'll give it a shot. There is an on board air reservoir ( this holds air when not attached to train) once filled with air pushes against a diaphragm and spring at say 80 psi  that engages the cars brakes. When a loco or rail mover is attached to car and air hooked up and turned on the pressure pushes the diaphragm in the other direction at 120 psi releasing brakes. So dropping air or coming uncoupled the loose of air pressure reengages the car brakes. If system is not working due to a leak or sticking brakes the only way to apply is with hand brake which mechanically applies the car brakes. If we can't get the brakes to release on car when we hook our track mobile and have all ready applied air and verified  valves and hand brake are released we pull valve  to dump the air reservoir the internal spring pushes the diaphragm the other direction on car which will also releases the car brakes ( which we do when we used pay loader to move cars when track mobile is broke down) . I assume a loco operates like track mobile pushing throttle speeds up and pulling back engages loco/track mobile brakes then the air valve for train brakes fully open brakes are disengaged closing back valve applies cars brakes. Only difference is track mobile is like car so when can down shift transmission to also help slow down. I think that basically covers it . How did I do?

Thank you for all of the response guys. Simply put, air brakes work with a reservoir of air that is compressed on the train cars, and when air is released, braked shoes create friction on the wheels until they stop or the brakes are taken off. Anyways, I assume that the independent brake works the same, just on an engine. So what about dynamic brakes. What do they do?

A few years ago I got to use the portable UP train simulator during the 150th celebration of the Pacific Rail Act in Houston.  I had a SD40-2 for power and a 700' train.  I was getting "greens" on the 35 MPH part of the Portland Sub along I84 east of Steel Bridge.  The I got a "yellow".  So I cut back on the throttle from run 8 to 1 one "number" at a time.  Expecting a "red", I started to use the air around 15 MPH.  It is amazing how slow a train slows, even using the air.   And I got the train stopped before the Red without dumping the air.

After that event, I can see the pool of knowledge a train engineer needs to run a train safely, including the air.  Diesel, steam, pure electric.

Maxrailroad posted:

Thank you for all of the response guys. Simply put, air brakes work with a reservoir of air that is compressed on the train cars, and when air is released, braked shoes create friction on the wheels until they stop or the brakes are taken off. Anyways, I assume that the independent brake works the same, just on an engine. So what about dynamic brakes. What do they do?

Dynamic brakes are a form of electrical braking that isn't just restricted to railroads. A DC motor is a generator if it's rotated mechanically. If there's high-momentum equipment rolling along like a diesel-electric locomotive (or mine-hoists and large mining trucks, where it's also been used), the generating power of the DC traction motors (made by the wheels turning the motors) can be used to slow the train down. The power produced is routed through a bank of resistors, creating a load on the "generators" i.e. the motors.

It can get quite warm around dynamic brake resistor grids, so cooling fans were part of the parcel. There's also a regenerative type of dynamic braking where the power produced is fed back into a supply system. I think the Milwaukee RR used it on their electrified sections, but maybe our experts can chime in on that.

Here's a pic of some dynamic brake resistors from a mine hoist: http://tinyurl.com/hcv3mck

Maxrailroad posted:

I assume that the independent brake works the same, just on an engine.

I don't know about diesels, but the brakes on a steam locomotive use straight air; i.e., the air pressure from the reservoirs on the engine is used to apply the brake shoes to the wheel. When you release that air, a large spring inside the brake cylinder releases the brake.

smd4 posted:

Maxrailroad posted:

I assume that the independent brake works the same, just on an engine.

I don't know about diesels, but the brakes on a steam locomotive use straight air; i.e., the air pressure from the reservoirs on the engine is used to apply the brake shoes to the wheel. When you release that air, a large spring inside the brake cylinder releases the brake.

Correct. Works the same way on diesels, and/or electrics.

The genius of the technology is that the engineer controls an entire train by controlling the pressure in a reservoir no much bigger than a football. The science of managing air pressure and the skill of a knowledgeable  engineer are simply marvelous to behold.  Science and Art!     

ReadingFan posted:

In theory, a steam locomotive could slow a train by admitting steam to the cylinders with the valve gear set in reverse [or in forward if a locomotive were running in reverse].

Putting a steam locomotive into reverse when moving forward is a good way to do terrible damage to the locomotive. Just ask Ed Dickens. He flattened all of the 844's drivers by doing just that.

It is not an acceptable way to brake a steam locomotive under ANY circumstances.

The true genius of the air brake system devised by George Westinghouse is that it takes air from the atmosphere, compresses it, stores it in reservoirs, uses it as needed, then returns it back to the atmosphere. It is fundamentally the same today as it was when he designed it. Granted, vast improvements in the control valves, both locomotive and car, but the pipe diameters, train line, branch pipe, etc. and principals are still the same.    

Whoa! This is confusing. Some are saying air pressure RELEASES the brakes while others say air pressure APPLIES the brakes. Which is it? Or is it opposite for cars and engines?

Both. Reducing the brake pipe pressure causes the triple valve to operate and admit compressed air stored in the reservoir of each car to the brake cylinders of that car, applying the brakes directly. Restoring brake pipe pressure to normal actuates the triple valve again, this time allowing the brakes to release by venting the compressed air in each brake cylinder to atmosphere and allowing the brake pipe air to recharge the reservoir. The triple valve is an ingenious part of the system.

B Smith posted:

Both. Reducing the brake pipe pressure causes the triple valve to operate and admit compressed air stored in the reservoir of each car to the brake cylinders of that car, applying the brakes directly. Restoring brake pipe pressure to normal actuates the triple valve again, this time allowing the brakes to release by venting the compressed air in each brake cylinder to atmosphere and allowing the brake pipe air to recharge the reservoir. The triple valve is an ingenious part of the system.

Now that's a great explanation! Thanks!

We can always thoroughly confuse the issue by stirring up Westinghouse's air brake vs. Eames' vacuum brake, but then again, maybe not.......

The operation of the triple valve is hard to explain without a diagram, but its function is to (1) apply the brakes using air stored in the car's air reservoir when the valve detects a drop in brake- pipe pressure relative to the pressure normally maintained in the reservoir, (2) vent the air from the brake cylinders when brake pipe pressure is increased again and (3) allow brake-pipe air under pressure from the locomotive's air compressors to recharge each car's reservoir. The genius of Westinghouse's design is that each car carries its own reservoir of compressed air to operate the brakes, which can be triggered fairly rapidly in each car along the whole length of the train by a small reduction of the brake-pipe pressure and the resulting operation of the triple valve. So, a break anywhere in the brake-pipe or the hoses between cars automatically causes the brakes to be set for the whole train. On the other hand, the air reservoir in each car only holds a finite volume of compressed air, and all that air can bleed off slowly over an extended period of time because of normal leakage in the system if the car (or cut of cars) is left standing without a continuing source of air to recharge the reservoir. That was partly what happened at Lac Megantic: the locomotive's air compressors stopped charging the brake-pipe because the local firemen shut down the engines when they first arrived on the scene, then the air reservoirs went empty from normal system leakage, the brakes slowly released, and because the crew had not set adequate hand brakes (assuming the engines would continue to run and keep the brake reservoirs charged after they left) to hold the train on the slight grade, it started to roll away.

madmax posted:

I'll give it a shot. There is an on board air reservoir ( this holds air when not attached to train) once filled with air pushes against a diaphragm and spring at say 80 psi  that engages the cars brakes. When a loco or rail mover is attached to car and air hooked up and turned on the pressure pushes the diaphragm in the other direction at 120 psi releasing brakes. So dropping air or coming uncoupled the loose of air pressure reengages the car brakes. If system is not working due to a leak or sticking brakes the only way to apply is with hand brake which mechanically applies the car brakes. If we can't get the brakes to release on car when we hook our track mobile and have all ready applied air and verified  valves and hand brake are released we pull valve  to dump the air reservoir the internal spring pushes the diaphragm the other direction on car which will also releases the car brakes ( which we do when we used pay loader to move cars when track mobile is broke down) . I assume a loco operates like track mobile pushing throttle speeds up and pulling back engages loco/track mobile brakes then the air valve for train brakes fully open brakes are disengaged closing back valve applies cars brakes. Only difference is track mobile is like car so when can down shift transmission to also help slow down. I think that basically covers it . How did I do?

Wel, madmax, I'll buy you a cold beer for your courage in attempting the locomotive air brake exam "cold", i.e., without studying the Enginemen's Air Brakes and Air Systems on Locomotives and Cars book.  However, I regret to inform you that you have failed with a score of 5%.  The only correct answer was that there is an on-board air reservoir, and I actually gave you that one.  The desired answer is that there are two reservoirs aboard the locomotive and a duplex reservoir aboard cars.  But you deserved something for at least trying.

Locomotive air brake systems are manually controlled by two brake valves which work together but have different functions, and (both when in controlling or trailing position in a locomotive consist) automatically in response to reductions in brake pipe pressure initiated by any cause other than use of that locomotive's brake valve.  Thankfully, coupler buff and draft forces do not activate locomotive air brakes, although this was tried by the Louisville & Nashville on remote unmanned helper consists for throttle control.

Please review Wyhog's essay on air brakes, and we will look forward to success at your second sitting for the air brake examination.

rtr12 posted:

After reading about train brakes (link above) and then thinking about the terrible accident at Lac-Megantic, Quebec, when the brake system ran completely out of air, why do the train brakes fail to off and not to on or full stop? Since they can't proceed down the track until the air pressures are all correct anyway, it seems like they could be spring loaded or something to stop the train on complete air loss?

Well, you have to step back and look at the total picture concerning Lac-Megantic.  If the Engineer had secured the train with enough hand brakes before leaving it unattended, It would not have rolled downgrade when the air brakes leaked off.  That was the root cause.  There were other, contributing causes, but, if the train had been properly secured by hand brakes, the train would have remained standing in spite of the contributing causes.

Yes, some type of spring brake could have been built into the air brake systems of the cars, as is done on highway truck trailers, but this is unnecessary, as each rail car also has a hand brake for assuring that -- regardless of the status of the air brakes -- the car will remain stationary.  This is a low-maintenance, easy to operate appliance that, if properly maintained and used, can be relied on without reservation.  Truck trailers lack this feature, and thus have a spring brake which must be overcome by air pressure when the truck driver intends to begin movement.  A spring backup for rail car air brakes would add significant maintenance expense and would be difficult to test in the field when leaving equipment unattended.

One man crew as well... Terrible way to run a railroad... especially leaving an unattended train on top of a grade.  There's still a lot of unanswered questions to terrible event....If there was a fire in the lead unit,  was it usable for the next trip or did someone switch  the units around...  ??  

OGR Webmaster posted:

Putting a steam locomotive into reverse when moving forward is a good way to do terrible damage to the locomotive. Just ask Ed Dickens. He flattened all of the 844's drivers by doing just that.

It is not an acceptable way to brake a steam locomotive under ANY circumstances.

In fact, it was quite common to stop locomotives this way back in the 19th century. It is actually done today on the Walt Disney World steam engines, which are not equipped with brakes.

Gary E posted:

Whoa! This is confusing. Some are saying air pressure RELEASES the brakes while others say air pressure APPLIES the brakes. Which is it? Or is it opposite for cars and engines?

Yes, it's the opposite for cars and engines.

A reduction in pressure applies the brakes on the train cars; an application of pressure applies the brakes on an engine.

There are two brake levers in a locomotive--the automatic (train) brake lever, and the independent (or locomotive only) brake lever.

 When using the automatic brake with a train, both the car brakes and locomotive brakes are applied at the same time. When releasing the automatic brake, the brakes on the cars back off, but the brakes on the locomotive stay applied. Those brakes are "bailed off" using the independent (locomotive) brake lever.

smd4 posted:

OGR Webmaster posted:

Putting a steam locomotive into reverse when moving forward is a good way to do terrible damage to the locomotive. Just ask Ed Dickens. He flattened all of the 844's drivers by doing just that.

It is not an acceptable way to brake a steam locomotive under ANY circumstances.

In fact, it was quite common to stop locomotives this way back in the 19th century. It is actually done today on the Walt Disney World steam engines, which are not equipped with brakes.

iam not a mechanical engineer of any sort, but going in reverse while moving forward just sounds like a real bad idea to me...Jim

Gregg posted:

One man crew as well... Terrible way to run a railroad... especially leaving an unattended train on top of a grade.  There's still a lot of unanswered questions to terrible event....If there was a fire in the lead unit,

Technically, the fire was in the lead unit's engine room, i.e. a typical fuel nozzle high pressure line leak, which was common on older GE units. Someone called the local fire dept., and upon arrival at the "scene of the fire", a Firefighter pushed the Emergence Fuel Cut-off, which shut the unit down. Since that was the only unit running, and maintaining air pressure in the main reservoirs, when it was shut down, to put out the fire, there was no longer any method to maintain brake pipe pressure, and eventually the air leaked away and the brakes were released.

Had the proper number of hand brakes been applied, and PROPERLY tested, the train would NOT have rolled away. The proper, and REQUIRED, method for setting and testing hand brake applications is:

1) While the air brakes are set on the whole train, apply the "recommended" amount of hand brakes for that size of train at that location on the railroad.

2) Release the air brakes on the train AND the independent brakes on the locomotive consist.

3) With the brakes fully released, wait for ANY movement of the train.

4) If/when ANY movement is detected, immediately reapply brakes and begin to apply more hand brakes.

5) Keep repeating steps 2 and 3 until there is no longer ANY movement of the train after all air brakes have been released.

6) The train is then PROPERLY "tied down"!

  was it usable for the next trip or did someone switch  the units around...  ??  

Number 90 posted:

Yes, some type of spring brake could have been built into the air brake systems of the cars, as is done on highway truck trailers, but this is unnecessary, as each rail car also has a hand brake for assuring that -- regardless of the status of the air brakes -- the car will remain stationary.  This is a low-maintenance, easy to operate appliance that, if properly maintained and used, can be relied on without reservation.  Truck trailers lack this feature, and thus have a spring brake which must be overcome by air pressure when the truck driver intends to begin movement.  A spring backup for rail car air brakes would add significant maintenance expense and would be difficult to test in the field when leaving equipment unattended.

How would testing spring brakes be any more difficult?

I would guess that the crew verifies hand brakes by giving the car a little tug with the locomotive before uncoupling. The same could be done with a spring brake system after disconnecting the air line.

If the hand brakes are "tested" by the fact that the car doesn't roll away when uncoupled, then the same "test" could be performed on a spring brake system with no additional effort.

Spring brakes would remove the human element from the equation. As clearly evidenced, all it takes is one lapse of procedure for a disaster to happen. It doesn't matter how many times the procedure is drummed into a person's head; sooner or later someone's going to have a brain fart or a fit of complacency. Spring brakes are automatic.

Obviously, this is armchair quarterbacking because there is absolutely no way to add spring brakes to the entire rail fleet. It would not only bankrupt every railroad in the nation, it would bankrupt the nation.

Jim Berger posted:

smd4 posted:

OGR Webmaster posted:

Putting a steam locomotive into reverse when moving forward is a good way to do terrible damage to the locomotive. Just ask Ed Dickens. He flattened all of the 844's drivers by doing just that.

It is not an acceptable way to brake a steam locomotive under ANY circumstances.

In fact, it was quite common to stop locomotives this way back in the 19th century. It is actually done today on the Walt Disney World steam engines, which are not equipped with brakes.

iam not a mechanical engineer of any sort, but going in reverse while moving forward just sounds like a real bad idea to me...Jim

Well, prior to George Westinghouse's invention of "air brakes", that was the ONLY way to slow & stop a locomotive from, say the 1830s thru the 1880s. Train cars, both freight and passenger, had manually operated mechanical brakes, i.e. "hand brakes", which would be applied by the Brakemen, sometimes one on each passenger car or one per 2 or 3 freight cars (that was why freight cars had vertically mounted brake staffs, and walkways in the roofs).

Also remember that the steam locomotives of that era were NOT the huge behemoths of the  early 1900s and later, plus the rolling stock was not as heavy, nor were the freight trains that long.

Jim Berger posted:

iam not a mechanical engineer of any sort, but going in reverse while moving forward just sounds like a real bad idea to me...Jim

You don't just throw the Johnson bar into the back corner as you're moving forward under steam.

It's pretty straight forward: When moving forward, you CLOSE the throttle. Then you put the Johnson bar in reverse. After that, you SLOWLY open the throttle, admitting just a bit of steam. That pressure will slowly bring the locomotive to a halt.

Like I said...perhaps the technique is obsolete, but it was a common way of stopping locomotives before air brakes. You may think it's a "real bad idea," but the steam engineers in the mid-19th century saw otherwise.

The engineman could have been there all day tying on hand brakes and walking back and forth to the engine to test whether he had enough brakes on...  When the engineman  leaves the engine to go back  and tie on hand  brakes  does he make a full train  brake application?  shut off generator field, put reverser in neutral ? 

It's just crazy having a one crew in my  humble  opinion. I'm  suppose on a hundred car train on a downgrade at least 40 hand brakes would need to be applied   and then tested.  Yep rules is rules.

Hot-  ever had an unintentional brake release on a freight.

I see ads for portable derailers in the train mags, so why not clamp one or two in front of some wheels somewhere near the front of the train; something like the chocks used for trucks and airplanes.  I don't know the physics of portable derailers and the locomotive wheels... maybe they would just shatter them due to the diesel's weight.  But if you would get a car or two on the ground, I don't see a stopped train dragging everybody with it as it slowly begins to move.  But maybe I'm wrong; I know moving trains can have a cars on the ground and keep moving like nothing's wrong.  There was a video on here sometime back where some cars derailed and everything kept moving until finally the cars rerailed  themselves at a crossing or someplace and all continued on their way.  I believe the video showed the railroad retracing the route of the train to figure what had happened. Just a thought from a railfan, not an expert by any means.

Gregg posted:

The engineman could have been there all day tying on hand brakes and walking back and forth to the engine to test whether he had enough brakes on... 

Yes,,,,,,and your point is……?

When the engineman  leaves the engine to go back  and tie on hand  brakes  does he make a full train  brake application? 

Yes, of course. Otherwise the train would not be stopped,,,,,right.

shut off generator field, put reverser in neutral ? 

Yes, and yes.

It's just crazy having a one crew in my  humble  opinion.

I don't disagree one bit!

I'm  suppose on a hundred car train on a downgrade at least 40 hand brakes would need to be applied   and then tested. 

It definitely depends on the grade, but you are correct.

Yep rules is rules.

Hot-  ever had an unintentional brake release on a freight.

Not on a train that I was on. However, I was in the area when a UP loaded coal train that was stopped on the grade just south Naco Junction, on the Powder River Joint BN/UP coal line in Wyoming. The temperature was about 30 degrees BELOW zero, at about mid-night, with clear sky and moon, and while the loaded coal train was stopped waiting for the reared pusher (a nice bran new GE) to come up the grade and tie onto the rear for assistance up the grade (1.75%), suddenly every single "bathtub coal gon., all 135 of them, released their brakes! The BN Road Foreman of Engines happened to be driving on the RR access road when it happened, and immediately got on the radio and alerted everyone within ear shot of the run-a-way. The headend crew jumped off, when they realized what had happened, and the helper Engineer immediately stopped and told his bran new lady Conductor, to grab all her cold weather gear, get off, and start running up the embankment. The Engineer, who I had worked with a number of times on the new SD70MAC units, was right behind her. After they both had covered a good distance, and were well up the embankment, he hollered for her stop and turn around, "You are about to see something that you will NEVER, EVER forget!".

Shortly the blinking FRED on the rear coal gon came roaring downgrade and slammed into that nice new GE, and continued down the grade and a pretty fast speed! At the bottom of the grade, is Antelope Creek, where the BN/UP were building two new bridges so there would be individual access across the creek for each of the three main tracks. Apparently, the GE pusher unit had been derailed when crashed into by the run-a-way coal train, as it didn't make it all the way through the turnouts at the still single track bridge. At that point, the whole entire coal train went into Antelope Creek! In the daylight, the next morning, there was over 18,000 tons of coal plus mangled nice new aluminum coal gons piled two stories high in the creek!   

FJ posted:

I see ads for portable derailers in the train mags, so why not clamp one or two in front of some wheels somewhere near the front of the train;

Those are generally only for protecting a track, or for one or two cars in an industrial spur.

something like the chocks used for trucks and airplanes.  I don't know the physics of portable derailers and the locomotive wheels... maybe they would just shatter them due to the diesel's weight.

Yes, you are correct.

 But if you would get a car or two on the ground, I don't see a stopped train dragging everybody with it as it slowly begins to move.

You would be amazed at what a heavy loaded freight train can move or drag.

 But maybe I'm wrong;

Right.

I know moving trains can have a cars on the ground and keep moving like nothing's wrong.  There was a video on here sometime back where some cars derailed and everything kept moving until finally the cars rerailed  themselves at a crossing or someplace and all continued on their way.  I believe the video showed the railroad retracing the route of the train to figure what had happened. Just a thought from a railfan, not an expert by any means.

smd4 posted:

In fact, it was quite common to stop locomotives this way back in the 19th century. It is actually done today on the Walt Disney World steam engines, which are not equipped with brakes.

The little tea kettles at Disney World are a world apart from a modern Super-Power 2-8-4 or 4-8-4.

Mr. Dickens tried this once with UP 844. It did not end well.