my understanding is air-brakes affect the brake cylinder in the locomotive.
what happens when independent brakes are applied while the air brakes are also applied?
can the independent brake setting release as well as increase the locomotive brake cylinder pressure?
what would need to be done to return control to the air-brakes? Does the "Relay Valve" shown in the diagrampass whichever pressure source is higher?
greg - Philadelphia & Reading / Reading
As I understand it (lots of reading and some playing with the real thing -- newer 26L brake setups with self-lapping independents) the independent brake valve literally lets the locomotive brakes work independently of the rest of the train (controlled by the automatic brake valve).
You can apply the locomotive brakes independently of the train brakes (by moving the independent handle with the train brakes released), or release the locomotive brakes while the train brakes are applied (by pushing down on the IBV handle -- "bailing off"). The latter could happen, I believe, if the operator was trying to stretch the train by applying both power and some train brake.
What would happen if you made an IBV application with the train brakes applied? I believe if the pressure commanded by the IBV exceeded that from the ABV, you'd simply get more locomotive brake. It's been a LONG time since my last cab ride, but I believe I saw engineers do this to bring the train to a halt. Train brakes cannot be partially released, only completely released, so using locomotive brakes would let you modulate your stops a little better, as they can be released and reapplied quicker than the train brakes.
I am not a locomotive engineer so take what I say with a grain of salt. :)
Aaron
gregcmy understanding is air-brakes affect the brake cylinder in the locomotive.
More on this -- it's not so straightforward. (And forgive/ignore me if I'm telling you something you know.)
The independent brake valve does, I believe, directly control the movement of air into the brake cylinders. The automatic brake valve works differently. There is a line of air that runs throughout the train -- the brake pipe (consisting of all the lines, pipes, etc). Each car has its own air reservoir, a valve (triple valve, I believe it's called), and a brake cylinder.
The locomotive charges the brake pipe, and from this pipe the individual cars pump up their individual air reservoirs. When the brakes are to be released, the pipe is pumped up to a certain pressure (I believe it used to be 90 psi for freight trains, 110 for passenger). This can only happen once the air reservoirs, etc. are full. The pressure moves the triple (?) valve to the release position, causing each car to release air from its own brake cylinder.
When the engineer wants to apply the brakes, she makes a reduction in brake pipe pressure -- say, venting the pipe from 90 down to 80 psi. This causes the triple valve on each car to move to an apply position and admit some air from the individual air reservoir to the brake cylinder. When the pressure is restored to the brake pipe, the valve on each car causes the brake to release, and the reservoir restores its pressure from the pipe. (This is why it takes a while to release the brakes on a train.)
If the engineer puts the brake in Emergency, the rapid reduction in pressure causes each car to apply its brakes immediately, IIRC.
The beauty of this system is that if the train comes apart and the brake hoses separate, the pipe loses pressure and the train goes into emergency. It also allows emergency application from simple valves in the loco or caboose. BUT -- if a car is left to sit and all of the air bleeds out of it, the brakes won't be stuck on; with no pressure in the car's reservoir, they release. (Unlike a truck or bus which requires air pressure to release the brakes.) Pretty cool system!
Autonerdif the pressure commanded by the IBV exceeded that from the ABV, you'd simply get more locomotive brake.
does the "Relay Valve" simply pass the greater of the (2) pressures from the independent brake valve and air brakes control valve?
can the IBV reduce the brake cylinder pressure to less than what the air brake control (triple) valve provides? (i think no)
The independent brake valve does not directly control the pressure in the brake cylinders. It controls the pressure sent to the relay valve on each locomotive in a consist. The relay valves are calibrated to then send the proper pressure to the brake cylinders on each locomotive. This is done because of the different cylinder pressures required by various braking setups on locomotive trucks. As I recall 72, 45, and 36 pounds are used. If 72 lbs. were sent to a loco designed for 45 or 36 lbs. the wheels might slide or the brake rigging be damaged.
The IBV can reduce the brake cylinder pressure on the locomotive below what the automatic brake calls for by what is called "bailing off" the brakes. This is done by depressing the IBV handle. All or any portion of the automatic application on the locomotive can be released by bailing off.
Mark
mvlandswIt controls the pressure sent to the relay valve
mvlandswThe IBV can reduce the brake cylinder pressure on the locomotive below what the automatic brake calls for by what is called "bailing off" the brakes.
but if the IBV only controls the relay valve, can there be brakes without the air brakes being applied
The IBV can apply or release the locomotive brakes entirely independently(thus its name) of the automatic train brakes.
An application of the automatic train brakes will also apply the locomotive brakes, but that application of the locomotive brakes can be released, either fully or partially by bailing off the IBV.
mvlandswThe IBV can apply or release the locomotive brakes entirely independently(thus its name) of the automatic train brakes.
mvlandswThe independent brake valve does not directly control the pressure in the brake cylinders. It controls the pressure sent to the relay valve on each locomotive in a consist.
can you describe IBV positions that would increase and decrease brake cylinder pressure with and without air brakes being applied?
On modern equipment (24, 26, 30, and the newfangled electronic "valves"), there are no real "positions" other than release (all the way left) and fully applied (all the way right).
Hold down the handle (regardless of position), and the engine brakes are "bailed off" (from brake pipe application), pressure can be increased/decreased/released regardless of brakes on train.
You could be just rolling on a light engine, hold the independent brake valve down in the release position... and then... put the auto brake valve into emergency. Brake pipe will go to zero, but engine will keep rolling because you "bailed off" loco brake cylinder pressure from building up. At least that's how it worked on "real air" (when moving the brake handles actually controlled air pressure directly).
Nowadays everything goes "through the computer", and there's a slight "lag" between where you put the handle and how cylinder pressure responds. Maybe they've gotten it to work better since I was there.
OldEnginemanYou could be just rolling on a light engine, hold the independent brake valve down in the release position... and then... put the auto brake valve into emergency. Brake pipe will go to zero, but engine will keep rolling because you "bailed off
does this mean that the independent brakes only have effect -- overriding the air brakes -- when the IBV is pressed down?
No it means that the independent brake applies the brakes on the engine when it is applied, but it can release the brakes independent of the automatic brake setting. The brakes on the engine can be controlled independent of the train brakes.
Dave H. Painted side goes up. My website : wnbranch.com
how?
it's not clear what position the IBV must be in for the air-brakes to solely affect the loco brakes and what position(s, including holding it down the IBV affects the loco brakes regardless of the air brake application: some or no braking?
doesn't the loco control (triple?) value maintain the loco brake cylinder pressure based on the drop of the brake line pressure?
if the IBV isn't increasing (apply) or decreasing (release) pressure in brake cylinder, would the control valve restore it?
can the IBV maintain the brake cylinder pressure at less pressure than the control value initially set it to?
gregcit's not clear what position the IBV must be in for the air-brakes to solely affect the loco brakes and what position(s, including holding it down the IBV affects the loco brakes regardless of the air brake application: some or no braking?
I think you're missing the bigger picture here: The IBV is a seperate lever from the ABV.
Here's a pic that shows 26L brake gear with two handles (and describes their position): http://www.sdrm.info/faqs/brakes/control/26stand.html
The IBV does exactly what it says it does -- controls the loco brakes independently of the train brakes. Push it forward and it applies; pull back and it releases, and if the train brakes are applied, pushing down on the handle releases the locomotive brakes.
Positions depend a bit on the equipment. Newer self-lapping indepenent brakes work a bit like the brake pedal on your car. The father you move it forward, the more braking effort you get.
Older non-self-lapping brakes have an apply position, which gradually applies the brakes, a lap position, which holds the application, and a release position that (duh) releases them.
IIRC (and others here can correct me), with a self-lapping brake, let's say you're running a light locomotive and want a moderate loco brake application. You'd move the independent handle to its half-way-or-so mark, and that's that. To release, you move the handle back to the release position, and maybe press down (bail) for good measure.
With a non-self-lapping brake, you'd move the handle forward to Apply and watch the brake cylinder pressure gauge until it reached the pressure you wanted, then move it back to Lap, which would lap off the flow of air. To release, you'd pull the handle back to the Release position.
How the independent and automatic interact depends on what you want. If you want to apply both power and train braking (say to keep the train stretched on uneven territory), you'd make your train brake application with the automatic brake valve, and press down on the independent brake valve (bail) to release the loco brakes. (Presumably with the throttle open to put tension on the train.) If yuo wanted some additional braking from the locomotive, with an application already made on teh train brakes, you'd simply push the IBV forward to get more braking force from the locomotive.
AutonerdThe IBV is a seperate lever from the ABV.
Autonerd If you want to apply both power and train braking (say to keep the train stretched on uneven territory), you'd make your train brake application with the automatic brake valve, and press down on the independent brake valve (bail) to release the loco brakes.
AutonerdIf yuo wanted some additional braking from the locomotive, with an application already made on teh train brakes, you'd simply push the IBV forward to get more braking force from the locomotive.
and i understand that if there are no air brakes, the IBV can release pressure from the brake cylinder thru the relay valve (as shown)
what i've read is that the IBV can
but can the IBV be used to "partially" reduce the brake cylinder pressure due to air brakes, other than "bailing off"? (no)?
what happens when the IBV is in the release position when air brakes are applied? (no effect)?
greg,
The illustration above shows an OLD brake valve assembly, obsolete for many decades (although you might still find them in use on old engines).
Same with the piping. It looks NOTHING like more recent equipment.
26 brake equipment (underneath the engineer's seat) would have a "rack", with a control valve, "J-type" relay valve, A-1 charging cutoff valve, P2a switch, etc.
The brake "equipment" on new engines is all electronic, not sure what they're like.
The most "modern" freight engine I ran was an SD50. I did climb up on an SD60 once at Selkirk, to see what it was like...
gregc
The use of this diagram is very misleading because it is incomplete not showing the independent system.
.
BigJimThe use of this diagram is very misleading because it is incomplete not showing the independent system.
does that prevent answering the question of can the IBV "partially" reduce the locomotive brake pressure when the air brakes are applied without releasing the brakes complete by "bailing off"?
gregc BigJim The use of this diagram is very misleading because it is incomplete not showing the independent system.
BigJim
No, but, you don't seem to be able to comprehend how the two systems work together in applying and releasing the locomotive brakes
of course i don't understand how they work, that's why i'm asking questions. (as an EE, i don't assume i understand, i try to verify that i completely understand)
i had the impression from someone else, that the IBV has both a quick and slow Release position. i'm guessing this is wrong? brakes can never be partially released
the above quote suggests that the loco brakes can be released (i.e. completely) by moving the IBV to the release position to release the brakes due to the IBV but that the handle has to be depressed to release the brake due to air brakes.
gregci had the impression from someone else, that the IBV has both a quick and slow Release position. i'm guessing this is wrong? brakes can never be partially released
I'm somewhat familiar with the #6 ET brakes used on a USRA Mikado.
The independent brake lever had a "running" position that the handle was left in for nearly 95% of the time. Upon a reduction in brake pipe pressure using the automatic valve the engineer would push the handle of the independent further past and into the release position (quick release) this was a spring return so the handle came back to the running position.
IF you wanted to "partially" apply the engine and tender brakes you could move the independent toward the apply position. There really wasn't a detent for a lap position but you could leave the independent handle in a neutral position between apply and release and your ET brake cylinder pressure would stay where you wanted it even if that was "partially applied".
Likewise, on the apply side there was a "quick apply" that would then provide increased air flow into the locomotive and tender brake cylinders. This position was also a spring return back to the apply position.
It didn't take long to apply full pressure to the brake cylinders therefore you really didn't have to hold the handle in quick apply for very long. You had to use your experience and feel to know where that sweet spot was to get maximum stopping force (if that's what you wanted) without sliding the wheels. Normally, running the light engine you certainly anticipated where you were going to stop and you made incremental applications to the independent.
While running with a train you "bailed off" the independent (placed the lever in the quick release, spring return position) several times during the automatic reduction. You could hear the brake cylinder exhaust from the independent so you knew (plus the gauge needle) that the brake cylinders were vented.
Especially on steam you didn't want to overheat the driver tires causing them to loosen on the wheel nor did you want to excessively wear the shoes which were more costly to replace.
When running with a train it was preferable to keep the engine slack tight, therefore keeping a bit of throttle open and keeping the engine brakes released until after the speed reduction or stop.
Think about how often you vary the pressure on your foot when you "apply" your automobile brakes. You don't even think about it but you constantly make adjustments based on speed, road conditions, how soon you have to stop, are you on a grade — up or down, how heavy is your vehicle (are you alone in a Yugo or have a full load of stone in a pickup. Not much different on a locomotive, conditions are rarely the same and experience and knowing the equipment features or limitations is what will get you through the day.
I forgot more than I ever knew about air brakes but I'm pretty sure of the above.
Regards, Ed
As others have mentioned above it is important to pinpoint an "era" for your study since there have been lots of later developments especially with "blending" the independent and automatic with dynamic braking and more electronic controls.
Here is some basic background on the #6 which was a pretty good system for quite a while, later the #8 made a few improvements but was largely similar.
6_ET-brakes_text by Edmund, on Flickr
You can reference the handle positions of the independent valve below:
6_ET-brakes_independent positions by Edmund, on Flickr
And here's an overall look at the valve.
6_ET-brakes_valve by Edmund, on Flickr
Rugged simplicity and reliability. If you want a simpler system to study there is the Westinghouse A-1 which predated the #5-6-7-8 ET ewuipment. I have some documentation on the A-1 which does use the simplified, plain "triple" valve. This is from the K brake era.
This diagram shows the late 1800s A-1 straight air locomotive brake system. It works in conjunction with the automatic brakes and it is the "double check valve" that separates the two.
A-1-brakes_Straight-air by Edmund, on Flickr
greg asks: "does that prevent answering the question of can the IBV "partially" reduce the locomotive brake pressure when the air brakes are applied without releasing the brakes complete by "bailing off"?"
I can apply or reduce whatever brake cylinder pressure I want on the engine (or engine consist) by holding down the independent handle and moving it within the quadrant.
What the brake pipe happens to be set at (and what cylinder pressure is "in the cars") doesn't matter.
That's why it's called the INDEPENDENT brake.
i understand that the IBV is "independent" of the AIR brake,
but the way the IBV controls the brakes is opposite the way AIR brakes control the brakes.
train brakes are applied when the AIR brake valve reduces the brake line pressure and the train brakes are completely released when the AIR brake valve starts increasing the brake line pressure
the IBV applies the brake by providing increased pressure to the loco brake cylinder but the comment below suggest the IBV can partially reduce the loco brake cylinder pressure by unpressing the IBV handle before completely venting the loco brake cylinder pressure (??)
gmpullmanWhile running with a train you "bailed off" the independent several times during the automatic reduction.
moving on ... it's not clear to me why the IBV handle in the RELEASE position needs to be pressed down to "bail off" the air brakes but based on my understanding doesn't need to be pressed down when used independent of the AIR brakes
do the AIR brakes need to be "bailed off" before the IBV can directly affect (reduce) the loco brakes?
Maybe listen to this guy to get a little better grasp of the system:
I said you bailed off the independent several times is because while controlling train speed and slack without running the risk of depleting your air the automatic valve can be manipulated many times in just a short distance. All the while you're looking out for crossings, signals, track conditions, other people plus a whole lot of other "stuff".
Unless you are constantly watching your brake cylinder gauge, which you almost always are but if you glance away you might find the engine's brake cylinder pressure creeping up. Bailing off the independent somewhat frequently gives the engineer the reassurance that they are released. It is just a good habit to get into when making an automatic reduction.
Good Luck, Ed
thanks
gmpullmanUnless you are constantly watching your brake cylinder gauge, which you almost always are but if you glance away you might find the engine's brake cylinder pressure creeping up.
gregcof course the air brakes need to be "bailed off" if no loco brakes are desired,
Sometimes, depending on how long ago those rotary valves have been rebuilt, some brake cylinder pressure might start to creep up even with the handle in running position. I made it a habit to push the handle over to quick release every now-and-then just to make sure there's no residual pressure in the cylinders.
Again, this was on old 6-ET brakes. Later brake designs overcame some of these shortcomings.
Ed
wasn't sure you might be suggesting the various valves may leak a little.
LA-6-P Independent Brake Valve
This is a self lapping type independent brake which will maintain against leakage when applied. This valve has two positions, release at the extreme left of the quadrant and full application at the extreme right. Between these two positions is an application zone where movement to the right will increase brake cylinder pressure and movement to the left will decrease brake cylinder pressure. Depressing or bailing down on the handle in release position will release the brakes quickly regardless of the source of the application.
gregcbut the way the IBV controls the brakes is opposite the way AIR brakes control the brakes.
Nope.
The train brakes apply when the brake valve on the cars sents air to the car brake cylinders.
The engine brakes apply when the brake valve on the engine sends air to the engine brake cylinders. Same thing.
The train line is a dual communication line and an air supply line.
gregctrain brakes are applied when the AIR brake valve reduces the brake line pressure and the train brakes are completely released when the AIR brake valve starts increasing the brake line pressure
You are leaving out the brake valve on the car. The brake valve on the car is the valve that increases the pressure in the brake cylinder or releases the pressure in the cylinder. The automatic brake controls the pressure in the train line and the changes in pressure cause the brake valves on the CARS to change the pressure in the brake cylinders using the air stored in the reservoirs on the cars. The automatic brake valve doesn't directly apply or release the brakes, the pressure in the train line doesn't directly apply or release the brakes. The train line communicates the "instruction" to the brake valves on the cars and then when teh brakes are released, the brake valve on the car uses the train line to recharge the reservoirs.
The part you are missing is that the IBV is basically performing the same function of the brake valve on the car. The IBV is controlling the air going to the engine brake cylindrs (just like the brake valve on the car is controling the air to the brake cylinders on the car).
It is possible to "bail off" the brakes on an individual car too, but it's an entirely manual process and can't be done on the fly. If you cut out the brakes (shut off the connection between the train line and the car brake valve) and pull the bleed rod you can release the brakes on an individual car.
The IBV is more or less equivalent to the the brake valve on a car, but it is set up to allow more manual control and to exercise that control while moving.