Greetings once again.
All of you have been very helpful on my previous questions. Now we are in air brake class and the material they passed out is a bit technical and the diagrams suck.
So is there a web site that goes into detail for both freight and passenger air brakes?
Thanks once again
Gordon
Asst. Conductor {training}
Search engine: Westinghouse Air Brake Triple Valve
Considering the “triple valve” was outlawed in the 30’s or so, you might want to search for ABD or ABDW valve instead.
www.transalert.com sells railroad training material.
Dave H.
What do you need to know
Basics
A moving train contains energy, known as kinetic energy, which needs to be removed from the train in order to cause it to stop. The simplest way of doing this is to convert the energy into heat. The conversion is usually done by applying a contact material to the rotating wheels or to discs attached to the axles. The material creates friction and converts the kinetic energy into heat. The wheels slow down and eventually the train stops. The material used for braking is normally in the form of a block or pad.
The vast majority of the world’s trains are equipped with braking systems which use compressed air as the force to push blocks on to wheels or pads on to discs. These systems are known as “air brakes” or “pneumatic brakes”. The compressed air is transmitted along the train through a “brake pipe”. Changing the level of air pressure in the pipe causes a change in the state of the brake on each vehicle. It can apply the brake, release it or hold it “on” after a partial application. The system is in widespread use throughout the world.
The Principal Parts of the Air Brake System
Compressor
The pump which draws air from the atmosphere and compresses it for use on the train. Its principal use is for the air brake system, although compressed air has a number of other uses on trains. See Auxiliary Equipment.
Main Reservoir
Storage tank for compressed air for braking and other pneumatic systems.
Driver’s Brake Valve
The means by which the driver controls the brake. The brake valve will have (at least) the following positions: “Release”, “Running”, “Lap” and “Application” and “Emergency”. There may also be a “Shut Down” position, which locks the valve out of use.
The “Release” position connects the main reservoir to the brake pipe. This raises the air pressure in the brake pipe as quickly as possible to get a rapid release after the driver gets the signal to start the train.
In the "Runnin
Wow! This will take me all holiday time off to read and digest!
Thanx
Mookie
Hi, bigedd!
I see you explained correctly how the brakes work in the “Principal Parts of the…”, but in the “Basics” you said: "The vast majority of the world’s trains are equipped with braking systems which use compressed air as the force to push blocks on to wheels or pads on to discs. " In fact, the compressed air is used to push blocks AWAY from the wheels - make sure your teachers understand that you got it right (“The “Release” position connects the main reservoir to the brake pipe. This raises the air pressure in the brake pipe as quickly as possible to get a rapid release after the driver gets the signal to start the train.”) I’m not quite sure about the discs, but I guess it’s the same.
Good luck with your training and exams.
Stay safe,
Oliver
Oops, sorry, I should have addressed this previous one to Gordon, too!
Regards,
Oliver
Eh wot? I always understood that the air in the auxiliary reservoir (or emergency reservoir, if you had one) was routed by the valving (triple or otherwise) to the brake cylinders to apply the brakes when the trainline pressure dropped, and that the valving then restored the pressure in the reservoir(s) when the trainline pressure rose again (which is part of why partial releases can’t be done with older air brakes) – and which is why a series of small applications can run you out of air and out of luck on a downgrade. And why a car can have the brakes stick – weak return springs (among other reasons!)
Gordon -
Try going to wabtec.com and click on the “Review Tech Documents” link. Don’t know exactly what they have posted online but if anyone knows air brakes it’d be Wabec.
Hope that helps.
Brian
Oliver, air pressure is vented out of the brake cylinder through the triple valve and out of the vent at the retainer when the brakes are released. A spring in the brake cylinder pushes the piston back into the cylinder releasing pressure against the brake rigging and releasing the brakes. Air pressure is not used to force the piston back into the brake cylinder to release the brakes. The system that you are talking about where air pressure keeps the spring brake released is what is used on truck air brake sysytems.
JCHNHTFD, I may be wrong, but, I thought that the service portion of the reservoir was used to feed the brake cylinder. I agree, it is a bad thing if the engineer pisses away his air. If the brake pipe pressure drops below 40psi you cannot initiate an emergency application. Even when we do an over reduction (more than full service), we only draw off 40lbs. to secure the train. We have even used retainers to secure the train while we charged the train on a grade (this cannot be used to secure a train left unattended)
Ken
Ken it is 35lbs you cant make a emergency application. but if you **** that much air away you should have already stopped. for what ever reason.
The way he exsplained the brake operating system would make me confused. its much simpler than that . Mookie rember this the engineer ( not driver we dont have steering wheels) applys brakes by taking air away from the system. and releases brakes by giving air back. brakes in old days was applyed car by car slow and timely. with the triple valve it made applying brakes faster by allowing air to escape locally from each car rather than at the brake valve in the engine. this in turn made the brakes apply faster. Ken can correct me if i am wrong but if i remeber right it is only a fast drop of 3-5 lbs will set the train in emergency.
What are you trying to say Wabash? You have done plenty of correcting around here too.
A rapid change in brake pipe pressure… such as 20 lbs in one second
will set the system in emergency, and that discription of a brake valve
on the locomotive (handle positions) is old, very old, the newer valve is
self maintaining and dosnt have a “LAP” position, also the main reservior
is not connected to the brake pipe directly, MR normally runs at 130 to
140 lbs, brake pipe is normally 90 lb. air for braking the train is stored
in the aux. reservior and the emergency reservior on each car in the train
on a fully charged system the reserviors will be charged to the same as
the brake pipe, when the control valve on the car sinces a drop in brake
pipe pressure it will allow a volume of air to flow from the aux. res. to the
brake cylinder, with reductions over a minimum reductions about 2.5
pounds of air will flow into the brake cylinder for each pound of brake
pipe reduction, (dropping a 90 pound brake pipe to 70 pounds will
give 50 pounds of air in the brake cylinder 2.5 X 1 ratio )
with any brake pipe pressure, it can be multiplyed by .71428 to get the
car brake cylinder pressure (North American standard cars, dont know
about others). for an emergency application both the aux. and emergency
reserviors are vented into the brake cylinder (6 X 1 ratio) cylinder pressure
can be figured by multipllying brake pipe by .85714.
the car reserviors cannot be charged with air if the engineers brake valve
handle is in any position except release
Wow, and all this time I thought I was just going to have fun on the forums. Now I actually understand how air brakes work. Thanks!
[ps. Im NOT being sarcastic]
Ken it wasnt a correction it was a statement / question. I was told you couldnt put the train in emergency under 35psi . I have been in emergency on the side of a grade and started rolling at 42lbs. at 50 lbs i got 15 lbs and full dynamic and rode it out. stayed steady at 40 mph in a 25 mph zone. 9700 ton pushing me. I learned alot about air brakes that day on what they can and cant do ( or i didnt want them to do) that day i wont forget.
“J” that 9700 tons pushing you down the grade was what ? probably
75 to 100 cars in your train and most likely you were reading the 42 lb
of rising pipe pressure off of FRED (rear of train), most likely the head
20 or 30 cars had already released their brakes and there wasnt enough
brakes holding the train on the grade, good thing you had dynamics, also
the head part of the train probably had “some” brake because of your
15 lb reduction
In North American Trucks there is a chamber at each brake that is fed with air from the supply to force the pad against the wheel. This is controlled by the driver’s foot pedal. Now my training is a bit dated but if you empty the air supply there are springs in the chamber which then will apply the brakes for you. A constant reliable supply of clean, dry and useable air is vital. When you hear a trucker park there is a large “flatuance” of air from the entire vehicle. That is the entire working air supply being dumped so the springs lock the vehicle in place. Federal standards states that the brakes must be able to hold the vehicle on any grade, on ice and snow.
To lap brakes on a train imagine a trucker going down a mountain grade you see his tail lights go on and stay on while the truck keeps a steady speed (Hopefully slow) all the way down. If done right the shoes will cool off to the wheel drums (or disks) and that heat will be exchanged with the airflow in a even manner. If there is too much braking too long and insufficient heat exchange the brakes will over heat, glaze (turn to glass) smoke and finally burn. To the unfortunate driver a escape ramp or a long run out at the bottom are only options.
We use “Jacobs” brakes by creating a resistance against the outflow of exhaust thru the valves hence the famous blubblubblublub sound. Locomotives in Trains will try to generate alot of current (resistance) via the motors which are sent thru grids at the top of the engine and dumped as heat “Dynamic Braking”
The reason for use of Air rather than “Brake Fluid” is heat. Cars and light trucks can get away with fluids as in larger brakes will literally boil off the fluid due to high tempratures.
I hope this helps.
Lee
I passed my exam and now I’m out in the yard observing/participating in the daily activities. Your combined comments did help explain the material, Thanks Again, Gordon
Jack flash
nope i was moving as soon as i released them to get some air up. the equilizer was at 42. that is what i glaced at. i didnt have much for dynamic only a dash 9 and a somewhat inoperartable sd50. ( meaning it was either full dynamic or nothing. as soon as you come out of set up) I cant recall what the eot was reading as i was fairly busy trying to stay in controll of the train. the amount of cars i had wasnt that many ( if memory serves me ) this train is always short and heavy . tank cars and covered hoppers make up the biggest part of this train. and i will agree with you that the brakes on the head end was what was operating. even drawing air off the train the rear never seen a change ( is my guess) but the head end was doing all the work. Either way the lesson learned was that even with the small amount of air i had I knew i couldnt wizz it away as there was not another chance of getting it pumped back up. get enough to hold and maybe a pound or 2 more to help slow down and ride it out. there is no room for second chance.