loco6625 So am I correct that the main reservoir on each car has 2 compartments divided equile, one side for service application only, and one side for emergency,
So am I correct that the main reservoir on each car has 2 compartments divided equile, one side for service application only, and one side for emergency,
The reservoir on the car is divided into two sections, however, there is a cone placed inside that makes the emergency side much larger than the service side. so when emergency is applied, both reservoirs dump through the triple valve and into the brake cylinders for the higher brake shoe pressure. What you have to realize is that an emergency brake application is not a "wham-bam-thank you- maam" operation. The control valve controls which side of the reservoir opens and at what time in order to get the higher braking effort.
so when emergency is applied, both reservoirs dump through the triple valve and into the brake cylinders for the higher brake shoe pressure.
The best way that I have found to visualize what happens comes from WABCO and involves barrels of water. Draw three tall rectangles (barrels) side by side. Color the first two blue to represent the Emergency and the Service side of the air reservoir fully filled TO THE SAME LEVEL. This level represents the feed valve setting or brakepipe pressure that fills the reservoirs. Leave the third one blank to represent the brake cylinder.
On the first two, draw something on the bottom to represent a valve that can be opened. Now, from each valve, draw a line to represent a pipe and connect it to the barrel representing the brake cylinder.
Now, fully open the valve on the Service barrel. The water, representing the air, will drain into the empty brake cylinder barrel until both levels equalize. Do you see and understand this? No more pressure can be put into the brake cylinder from the service side of the reservoir. The pressures have equalized.
Now, fully open the valve on the Emergency barrel. Note that since it is fully filled, some of the water will drain into the brake cylinder barrel until they too equalize at the same level. This level is higher than the level before and represents the additional brake pressure attained in an emergency application. Savvy?So when the triple valve pull rod is pulled in hump or flat yard switching operations, does it dump both sides of the air reservoir, or maybe only the emergency side,In switching operations, only the brake cylinder needs to be exhausted. When the bleed rod (depending on the type) is given a short pull, for the most part it only releases the air in the brake cylinder. If the entire reservoir needs to be exhausted, then you need to push/pull & hold the bleed rod until all of the air is exhausted. so when the air hoses uncouple, there is still air left in the service side? When a train line separates, air remains in both reservoirs because not all of the air in athe reservoirs is needed to apply the brakes. If so, would the air left in the service side help when the train is made up and the air test time would be shortened?When the engineer releases the brakes after an application, the control valve will sense the rise in pressure and use a little bit of the air from the emergency reservoir to help recharge the trainline.
So when the triple valve pull rod is pulled in hump or flat yard switching operations, does it dump both sides of the air reservoir, or maybe only the emergency side,
so when the air hoses uncouple, there is still air left in the service side?
If so, would the air left in the service side help when the train is made up and the air test time would be shortened?
.
Quoting xrrman: "Actually the engine brake is quite similar to the car brake. When an automatic brake application is made the engine brakes react and apply just like a car brake. Since this is usually undesirable the engineer must "bail off" or actuate the independent brake lever to release the brakes on the locomotives. The engine brakes will remain released until either a further automatic brake or an independant brake application is made."
True--but the engine brake is still straight air. That the engine brake is set when the train brake is set and is bailed off at the engineer's discretion has long been a feature on locomotives, dating from steam engine days.
Johnny
Deggesty I appreciate the willingness of those in actual railroad service to share their knowledge with those who have an interest in railroading. After more than sixty years of absorbing such knowledge, I still know that I have much to learn. However, in the discussion of engine brakes, I feel that one important factor has not been stressed: the independent, or engine braking, system does not have the same kind of valve that is present on every car in the consist, but depends on a direct, or straight, application of air from the engine's reservoir. There is no separate air reservoir for the engine's braking system, so when the air leaks out of the engine's braking system and the air pump does not kick in, there is no air to keep the engine brakes applied. BigJim, a thought occurred to me; am I right that the brakes on a steam engine's tender were also set by straight air? And, I recall the account of the rookie fireman who, when told, "that pipe is for the straight air," wondered how straight air could be put into such a crooked pipe. Actually the engine brake is quite similar to the car brake. When an automatic brake application is made the engine brakes react and apply just like a car brake. Since this is usually undesirable the engineer must "bail off" or actuate the independent brake lever to release the brakes on the locomotives. The engine brakes will remain released until either a further automatic brake or an independant brake application is made.
I appreciate the willingness of those in actual railroad service to share their knowledge with those who have an interest in railroading. After more than sixty years of absorbing such knowledge, I still know that I have much to learn.
However, in the discussion of engine brakes, I feel that one important factor has not been stressed: the independent, or engine braking, system does not have the same kind of valve that is present on every car in the consist, but depends on a direct, or straight, application of air from the engine's reservoir. There is no separate air reservoir for the engine's braking system, so when the air leaks out of the engine's braking system and the air pump does not kick in, there is no air to keep the engine brakes applied.
BigJim, a thought occurred to me; am I right that the brakes on a steam engine's tender were also set by straight air?
And, I recall the account of the rookie fireman who, when told, "that pipe is for the straight air," wondered how straight air could be put into such a crooked pipe.
loco6625 So am I correct that the main reservoir on each car has 2 compartments divided equile, one side for service application only, and one side for emergency, so when emergency is applied, both reservoirs dump through the triple valve and into the brake cylinders for the higher brake shoe pressure. So when the triple valve pull rod is pulled in hump or flat yard switching operations, does it dump both sides of the air reservoir, or maybe only the emergency side, so when the air hoses uncouple, there is still air left in the service side? If so, would the air left in the service side help when the train is made up and the air test time would be shortened?
So am I correct that the main reservoir on each car has 2 compartments divided equile, one side for service application only, and one side for emergency, so when emergency is applied, both reservoirs dump through the triple valve and into the brake cylinders for the higher brake shoe pressure. So when the triple valve pull rod is pulled in hump or flat yard switching operations, does it dump both sides of the air reservoir, or maybe only the emergency side, so when the air hoses uncouple, there is still air left in the service side? If so, would the air left in the service side help when the train is made up and the air test time would be shortened?
When cars are bled off for flat switching or humping - there is no air left in either air resevoir.
Never too old to have a happy childhood!
they only have one line, not 2 like trucks, It would take an extra air line to release the spring brake. That is why there are hand brakes on each car to set up if its being left unattended.
Just to verify some verbage, Independant brakes are only on the Locomotives and do not hook up to the train cars. The trainline hooks the cars to the loco and uses a reduction in pressure to set up the train car brakes.
pajrr Hi, In keeping with this theme of air brakes, how are the car brakes released so that a car can roll freely through a hump yard? Do the yard engines pump up the trainline and the individual angle cocks closed? Are the brakes slowly bled off so that no air remains in the system to set the brakes? In watching humping operations I notice when the air hoses part there is no popping sound. I have always wondered about this. Thanks for any info you can give me.
Hi, In keeping with this theme of air brakes, how are the car brakes released so that a car can roll freely through a hump yard? Do the yard engines pump up the trainline and the individual angle cocks closed? Are the brakes slowly bled off so that no air remains in the system to set the brakes? In watching humping operations I notice when the air hoses part there is no popping sound. I have always wondered about this. Thanks for any info you can give me.
The car department or crew will manually bleed all air out of the system of each car by pulling the bleed rod. This makes the car a free rolling weight.
10000 feet and no dynamics? Today is going to be a good day ...
beaulieu John Urtz I, too, find it odd that the train was not left with at least a full service application, if not an emergency application. The reason to not make an Emergency application to secure the train is because if the train is left like that for more than 4 hours, then you have to do a full Terminal Air Test on the train. That test requires the Trainline Air to be pumped up to full operating pressure, the pressure differential between Controlling Locomotive and rear car to be measured and not more than 10 psi difference, then an application of the Automatic air brakes are to be made and the train walked to make sure the brakes have applied on every car, followed by a release and the train walked again to make sure every car's brakes have fully released. Yeah sure that's going to happen. In any case the Automatic Air brakes on the train are going to fully release very shortly after the outbound Engineer starts to put air back in the Trainline. Of course the report says that the railroad lacked a Safety Culture so maybe they would skip the air test and just go. They could always just cross their fingers for Luck. Read the full report. TSB Report
John Urtz I, too, find it odd that the train was not left with at least a full service application, if not an emergency application.
I, too, find it odd that the train was not left with at least a full service application, if not an emergency application.
The reason to not make an Emergency application to secure the train is because if the train is left like that for more than 4 hours, then you have to do a full Terminal Air Test on the train. That test requires the Trainline Air to be pumped up to full operating pressure, the pressure differential between Controlling Locomotive and rear car to be measured and not more than 10 psi difference, then an application of the Automatic air brakes are to be made and the train walked to make sure the brakes have applied on every car, followed by a release and the train walked again to make sure every car's brakes have fully released. Yeah sure that's going to happen. In any case the Automatic Air brakes on the train are going to fully release very shortly after the outbound Engineer starts to put air back in the Trainline. Of course the report says that the railroad lacked a Safety Culture so maybe they would skip the air test and just go. They could always just cross their fingers for Luck.
Read the full report.
TSB Report
Not in Canada. It has to be off air for more than 24 hours.
CN, in Canada, before this accident, fully relied on the air to hold a train and had a handbrake exemption for leaving trains - with the exception of heavy grade territory. I never liked it but those were our rules. CP and the MMA it appears never had this exemption.
In this situation, if the air was not set and the engines were dead (which they were), there would be nothing to set the air up, other than leakage, on the train as the RSC would be disabled. The report said there were handbrakes on the engines, RCL caboose and one car. Locomotive handbrakes are garbage from what I have noticed.
Also, this is Canada. After a train has been given an air test by the car department, the train doesn't need another test unless it has been OFF AIR for MORE THAN 24 hours.
I found this from a couple of old air brake and train handling manuals I have in my collection. The current railroad issued ones I have don't go into the same amount of detail as the old ones.
"When the pressure on the brake pipe side of the piston is reduced faster than the air in the auxiliary reservoir can flow back into the brake pipe through the feed groove the auxiliary reservoir pressure, then being a few ounces greater than brake pipe pressure, forces the piston to move to the left toward the lower brake pipe pressure."
From the above, and also a diagram of a (admittedly outdated) type of triple valve, when the brakes are in the release, charging position, there is a feed groove that always allows air to flow from the brake pipe to the auxiliary reservoir. When the brake pipe pressure is reduced, say by the engineer making a brake application, air starts to flow back into the brake pipe. It can't flow back fast enough, so the triple valve senses the pressure difference, and the piston moves, etc.
So if I understand this right, if the rate is such that air can flow back into the brake pipe fast enough, the auxiliary reservoir itself depletes at that slow rate, leaving an equal pressure on both sides of the piston.
Jeff
The triple-valve brake system is rate sensitive. That is it has a piston that leaks air from one side to the other of the piston. If the brake pipe pressure reduces slowly, the pressure on both sides of the piston is equal and it won't move. If the brake pipe pressure falls quickly the piston pressure on one side exceeds the other and reservoir pressure in each car is directed into the car's brake cylinder. If the brake pipe pressure drops very quickly, the piston moves further and puts emergency air reservoir pressure into the brake cylinder as well.
Now you ask why? Well, brake pipe pressure will go up and down slightly as the locomotive brake system senses a drop in pressure from train leaks. This modulation is slight and slow enough that it doesn't set off the triple valve. For that reason, the brake system is rate and not absolute pressure sensitive. Additionally, being rate sensitive means that the brakes will apply from any initial brake pipe pressure as long as the drop is fast enough. The triple valve can run at any brake pipe pressure within a reasonable range and respond the same.
EuclidSo when the train was running away, all of its car reservoirs were sill charged.
Probably so... and with no way, by the end, to send the control-air signal to the valves which would cause them to direct the air in those reservoirs to the brake cylinders. (This is a problem with a one-pipe Westinghouse system)
Remember that the 'straight' independent would have been (slowly) leaking off to the point the train started to roll while there was still technically 'plenty' of pressure to allow the differential control-air signal; the blued treads on 'more than the handbraked wheels' confirm that the actual leakdown of pressure continued to be slow even as the train gained considerable speed.
As I read section 2.6.2, there was indeed pressure in the reservoirs AND enough air left in the trainline to send the control signal to apply the brakes, although I have no way to assess how much of the 'deceleration' was due to the effect of the derailing consist itself vs. contribution from the train brakes applying after 'the brake pipe pressure went to zero'. (I believe there are some time-classified brake-pipe pressure readings in the report, but I cannot find them right now.)
Randy Stahl Euclid Randy Stahl Euclid After reading the report on the Lac Megantic wreck, I have the same question as the original poster. The report says that when the train was secured at Nantes, the engineer left the automatic brake fully released with 94 psi in the train line (brake pipe). Only the independent brakes were set with air. It is reported that, as the train line leaked down, the loss of pressure corresponded to an equal loss of pressure in the locomotive independent brake cylinders. Eventually the independent brake cylinder pressure dropped to the point where they would not hold the train. HOWEVER: As the train line leaked down, why would not the automatic brakes apply on all the cars? They apply when there is a reduction in train line pressure. I cannot imagine that there would be so much leakage from the cylinder/reservoir side of the system that it would totally lose cylinder pressure in so short of a time. Because it leaked slowly enough not to set the brakes. I don’t understand that. You have a fully charged brake pipe and car reservoirs. If the brake pipe leaks down, won’t the triple valve send air from the charged car reservoir to the brake cylinder? Are you saying that if the brake pipe leaks slow enough, the triple valve will take no action and simply leave the reservoir air bottled up? That's exactly what I'm saying. Even with an air turbine rear marker the brake pipe leakage may not set the brakes.
Euclid Randy Stahl Euclid After reading the report on the Lac Megantic wreck, I have the same question as the original poster. The report says that when the train was secured at Nantes, the engineer left the automatic brake fully released with 94 psi in the train line (brake pipe). Only the independent brakes were set with air. It is reported that, as the train line leaked down, the loss of pressure corresponded to an equal loss of pressure in the locomotive independent brake cylinders. Eventually the independent brake cylinder pressure dropped to the point where they would not hold the train. HOWEVER: As the train line leaked down, why would not the automatic brakes apply on all the cars? They apply when there is a reduction in train line pressure. I cannot imagine that there would be so much leakage from the cylinder/reservoir side of the system that it would totally lose cylinder pressure in so short of a time. Because it leaked slowly enough not to set the brakes. I don’t understand that. You have a fully charged brake pipe and car reservoirs. If the brake pipe leaks down, won’t the triple valve send air from the charged car reservoir to the brake cylinder? Are you saying that if the brake pipe leaks slow enough, the triple valve will take no action and simply leave the reservoir air bottled up?
Randy Stahl Euclid After reading the report on the Lac Megantic wreck, I have the same question as the original poster. The report says that when the train was secured at Nantes, the engineer left the automatic brake fully released with 94 psi in the train line (brake pipe). Only the independent brakes were set with air. It is reported that, as the train line leaked down, the loss of pressure corresponded to an equal loss of pressure in the locomotive independent brake cylinders. Eventually the independent brake cylinder pressure dropped to the point where they would not hold the train. HOWEVER: As the train line leaked down, why would not the automatic brakes apply on all the cars? They apply when there is a reduction in train line pressure. I cannot imagine that there would be so much leakage from the cylinder/reservoir side of the system that it would totally lose cylinder pressure in so short of a time. Because it leaked slowly enough not to set the brakes.
Euclid After reading the report on the Lac Megantic wreck, I have the same question as the original poster. The report says that when the train was secured at Nantes, the engineer left the automatic brake fully released with 94 psi in the train line (brake pipe). Only the independent brakes were set with air. It is reported that, as the train line leaked down, the loss of pressure corresponded to an equal loss of pressure in the locomotive independent brake cylinders. Eventually the independent brake cylinder pressure dropped to the point where they would not hold the train. HOWEVER: As the train line leaked down, why would not the automatic brakes apply on all the cars? They apply when there is a reduction in train line pressure. I cannot imagine that there would be so much leakage from the cylinder/reservoir side of the system that it would totally lose cylinder pressure in so short of a time.
After reading the report on the Lac Megantic wreck, I have the same question as the original poster. The report says that when the train was secured at Nantes, the engineer left the automatic brake fully released with 94 psi in the train line (brake pipe).
Only the independent brakes were set with air. It is reported that, as the train line leaked down, the loss of pressure corresponded to an equal loss of pressure in the locomotive independent brake cylinders. Eventually the independent brake cylinder pressure dropped to the point where they would not hold the train.
HOWEVER: As the train line leaked down, why would not the automatic brakes apply on all the cars? They apply when there is a reduction in train line pressure. I cannot imagine that there would be so much leakage from the cylinder/reservoir side of the system that it would totally lose cylinder pressure in so short of a time.
Because it leaked slowly enough not to set the brakes.
I don’t understand that. You have a fully charged brake pipe and car reservoirs. If the brake pipe leaks down, won’t the triple valve send air from the charged car reservoir to the brake cylinder? Are you saying that if the brake pipe leaks slow enough, the triple valve will take no action and simply leave the reservoir air bottled up?
That's exactly what I'm saying. Even with an air turbine rear marker the brake pipe leakage may not set the brakes.
I need clarification on one more point. When the air slowly leaked out of the train line, the triple valves did not respond in any way. So once, the train line was fully exhausted, all of the car reservoirs were still fully charged, and car brake cylinder pressure was at zero. So when the train was running away, all of its car reservoirs were sill charged.
Strictly as an observer, I have seen that the reservoir on each car is bled off to release the car brakes before a cut is pulled out for flat switching or pushed over the hump.
Dave is correct to this day. Railroading 101. You NEVER rely on air (that includes emergency) to hold a parked train. It only takes a pound or two increase in a brakepipe to initiate a release. And using emergency to hold a parked train is not a good idea. Better be 100% absolutely positively extra sure any handbrakes or loco brakes can hold you, or else you are going for a wild ride when you release to recharge.
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
Of course there is a valve at each car. The triple-vavle concept, with reducing air pressure in the train line applies brakes, rather than the reverse, rapidly replaced the orginal Westinghouse "straight=air" concept, which was retained for nearly all streetcars (not most of them equipped for mu) and even some mu electric trains. And the original triple-valve has been replaced by more sohpisticated systems.
Read thhe above for why the brakes won't apply with a slow leak.
In winter weather, at least on the B&M some 60 years ago, we would not rely on an emergency applicaton to hold the brakes as applied on a standing train with the engine shut down. Hand brakes were always a requirement.
Randy Stahl Euclid Big Jim, No I had not yet read that. It does explain it clearly. I did not know that it is possible for the brake pipe to leak to zero and not cause a set up of the train brakes. I didn't either until I saw it happen
Euclid Big Jim, No I had not yet read that. It does explain it clearly. I did not know that it is possible for the brake pipe to leak to zero and not cause a set up of the train brakes.
Big Jim,
No I had not yet read that. It does explain it clearly. I did not know that it is possible for the brake pipe to leak to zero and not cause a set up of the train brakes.
I didn't either until I saw it happen
I didn't either, but looking back, I have actually had it happen to me while the train was moving. What happened was our train had been going downhill for a while and I noticed the EOT pressure reading dropping. It continued to drop, but, the train didn't feel like the drop in pressure was having any effect.
As it continued to drop, I mentioned to the conductor that I thought we might have an anglecock crossed back in the train. I stopped the train with the automatic air and had the conductor drop off. Then, I slowly pulled the train by him as he looked for a crossed anglecock. Sure enough he found one maybe 40 - 45 cars back.
This, not putting the brake on, is something that the FRA needs to look into and all engineers need to be aware of!
EOT's can be very different from one another. SOP after hanging an EOT is to close the anglecock ahead on the same car, then flipping the HOT switch to check to make sure the EOT will put the trainline into emergency. Some EOTs will exhaust the air before an emergency signal makes it pop, most will hold.
Still, my opinion is that if the engineer of that train had left the train with a proper automatic brake application (among other things) it would never have run away.
Euclid,Did you read down into the report this far?
"1.14.4 Testing of the sense and braking unit
Testing was conducted on a rail car to evaluate how the rate of brake pipe leakage affected the car’s air brake system. Following simulated brake pipe leakage, the car’s brake pipe pressure dropped 5 psi (to 85 psi) in 7 minutes. The car’s air brakes did not engage. The car was then recharged to 90 psi, and the test was repeated. In this test, the brake pipe was reduced by 80 psi (to 10 psi) in 75 minutes. The car’s air brakes again did not engage.
A turbine-equipped SBU,Footnote26 similar to the one used on MMA-002, was then tested to determine what effect the brake pipe air lost through the SBU would have on the car’s air brake system. The venting of air through the SBU caused the air brakes on a single car to engage almost immediately.
Testing was then conducted with a turbine-equipped SBU on a train with 2 locomotives and 71 cars. The test showed that a similar rate of brake pipe air loss through the SBU would initiate a brake application on a train that was 5 cars or fewer, but not on a train longer than 5 cars. Similar to the single-car test, this test demonstrated that brake pipe air pressure on an entire train can be reduced to 0 psi at a slow rate and result in no brake application on the cars."
Well .. the UP just had ANOTHER head on collision with two employees killed. Safety culture indeed..
It is the triple valve on each car that senses the brake pipe reduction and, in turn, causes the brakes to apply using air from the service reservoir on each car. The air has to leave the brake pipe at a certain rate (the service rate) in order for the triple valve to properly detect the signal and apply the brakes. The automatic brake valve in the locomotive cab allows air out of the brake pipe at the service rate. A slow leak is insufficient to trigger the triple valve. A rapid reduction in the brake pipe (from a break-in-two) causes an emergency application. In an emergency application, air from both the service and emergency reservoir are used, resulting in higher braking force than can be achieved using the service reservoir alone.
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