Oil Train

[Euclid]

tree68

You're sounding a little schizophrenic here.  In one post you note that your concept of how "adjustable braking" works agrees with what Al Krug wrote - braking force is added to loaded cars.

But then you write

 

2)    Add a load sensor that causes the pneumatics of the brake system to reduce the brake force when the car is empty.    

 

 While this is more or less correct, it reverses the role of the load sensor.  If the sensor Al describes fails to actuate, braking will remain at "stock" levels.  This would  result in lesser braking effort, but would minimize the possibility of sliding wheels.  If the sensor you describe fails to actuate, the car will operated at increased braking levels at all times, increasing the probability of sliding wheels.  You're making this a lot more complicated than it really is.  

You are leaving out my item #1, which is, the pneumatic modification to raise the brake force for the car by changing to a different reservoir. 

You are right that if the load sensor fails to actuate, braking will remains at stock levels, as you say.  But that stock level has been increased with the change of the reservoir.  Then from that increased level, the load sensor reduces it for empty cars. 

The basic point is to increase load brake pressure, and this is done by changing the car reservoir.  That change then requires the load sensor to protect empties from wheel slide.

Therefore if a load sensor were to fail on an empty car, that higher stock level of braking force would not be reduced for that car, and the wheels most definitely slide. 

[zugmann]

Euclid

. But that is not the basic, underlying reason for adding a load sensor to a freight car. The basic reason is to get more braking power on the loads.

But the load sensor has no way of doing that.  All it can do is exhaust air from the cylinder.  It can't create more air and therefore, more pressure and braking effort. It can only reduce.

 

 

[Euclid]

From the Al Krug reference on load sensors:

“The first step [which correlates to my item #1 above] was to put larger reservoirs on the cars so that the traditional 2.5 to1 ratio of reservoir volume to brake cylinder volume was greater. This will result in higher brake cylinder pressures for any given brake pipe reduction. The problem is that higher pressure will slide the wheels of an empty car. So a pressure limiting valve is attached to the brake cylinder which will vent any excessive pressure to the atmosphere thus limiting braking effort. The exhaust of this limiting valve is open to atmosphere on an empty car allowing it to vent excess pressure. On a loaded car it is closed off so it cannot vent any pressure from the brake cylinder thus taking advantage of the higher pressure which results in higher braking effort.”

 

Clearly the intent is to provide higher braking effort on the loads, although it does also entail reducing the pressure for empties.  But if you did not install this system and raise the braking force as it requires, there would be no need to protect the wheels from sliding on empties. 

[Euclid]

Larry and zugmann,

I understand what you are saying, and this has been a point of confusion through most of the previous page.  The following explanation is as clear as I can explain my understanding:

My understanding of load sensors has been this:   They are intended to provide greater braking power for loads. This goal is accomplished by two modifications to a freight car as follows:

1)    Modify the pneumatics of the brake system to increase the maximum brake force to as high as possible when the car is loaded.

 

 2)    Add a load sensor that causes the pneumatics of the brake system to reduce the brake force when the car is empty.    

So adding a load sensor is not fundamentally intended to prevent wheel slide on empties, although this point can be confusing because in item #2, load sensor does do that in order to achieve the basic goal of item #1. 

So the purpose of the load sensor itself is to reduce the empty car brake force in order to prevent wheel slide.  But that is not the basic, underlying reason for adding a load sensor to a freight car.  The basic reason is to get more braking power on the loads.

 

 

 

[tree68]

Euclid

The only way this load sensing/enhanced braking makes sense to me is if all railroads agreed to install this on all of their cars.

Since the railroads no longer own the majority of the cars running on their lines, this point is really moot.

You're sounding a little schizophrenic here.  In one post you note that your concept of how "adjustable braking" works agrees with what Al Krug wrote - braking force is added to loaded cars.

But then you write

2)    Add a load sensor that causes the pneumatics of the brake system to reduce the brake force when the car is empty.    

 While this is more or less correct, it reverses the role of the load sensor.  If the sensor Al describes fails to actuate, braking will remain at "stock" levels.  This would  result in lesser braking effort, but would minimize the possibility of sliding wheels.  If the sensor you describe fails to actuate, the car will operated at increased braking levels at all times, increasing the probability of sliding wheels.  You're making this a lot more complicated than it really is.  

[zugmann]

Euclid

What I am talking about does not amount to a choice between those two options. It is a choice between replacing worn out brake shoes or not needing to. As I said, the point of adding the load detector is not to prevent empty car wheel slide.

From the catalogs and patents I read, the load detector doesn't increase braking force.  It is a device for reducing it for empites.

[zugmann]

Here's Wabtec's patent:

 

https://patents.justia.com/patent/20100283316

 

Brake equipment for railway freight cars typically employs dual capacity empty/load equipment which adjusts the brake application force according to the empty or loaded conditions of the freight car. In such dual capacity empty/load equipment, a two-setting control is provided where normal brake pressure is realized under full load conditions and a reduced or modulated brake pressure is realized under an empty load condition. In contrast, single capacity brake equipment, which produces a brake application force independent from the load condition of the car loading, is susceptible to wheel lock and sliding wheels due to the same brake force being applied to an empty car as a loaded car. Sliding wheels undesirably cause flat spots on the wheels as well as decreased brake performance. By modulating the brake pressure under empty load conditions using dual capacity empty/load equipment, the occurrence of sliding wheels is reduced or eliminated

[Euclid]

zugmann

 

Euclid

  As I said, the point of adding the load detector is not to prevent empty car wheel slide. 

 Source?

 

It is here:

 

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

[zugmann]

Euclid

  As I said, the point of adding the load detector is not to prevent empty car wheel slide. 

 

Source?

[Euclid]

Posted by zugmann on Monday, March 30, 2015 10:27AM   [QUOTE]                     

Euclid [said]

So your improved car is working extra hard and wearing out brake shoes faster, but with little net benefit to the other guy’s train, and no benefit to you.

zugmann said:

It's a lot easier, quicker, and cheaper to replace worn brake shoes than to replace wheels. Sliding wheels = flat spots.

-----------------------------------------------------------------

What I am talking about does not amount to a choice between those two options.  It is a choice between replacing worn out brake shoes or not needing to.  As I said, the point of adding the load detector is not to prevent empty car wheel slide. 

[zugmann]

Euclid

So your improved car is working extra hard and wearing out brake shoes faster, but with little net benefit to the other guy’s train, and no benefit to you.

 

It's a lot easier, quicker, and cheaper to replace worn brake shoes than to replace wheels.   Sliding wheels = flat spots.

[Euclid]

My understanding of load sensors has been this:   They are intended to provide greater braking power for loads. This goal is accomplished by two modifications to a freight car as follows:

1)    Modify the pneumatics of the brake system to increase the maximum brake force to as high as possible when the car is loaded.

 

2)    Add a load sensor that causes the pneumatics of the brake system to reduce the brake force when the car is empty.    

 

So adding a load sensor is not fundamentally intended to prevent wheel slide on empties, although this point can be confusing because in item #2, load sensor does do that in order to achieve the basic goal of item #1. 

So the purpose of the load sensor itself is to reduce the empty car brake force in order to prevent wheel slide.  But that is not the basic, underlying reason for adding a load sensor to a freight car.  The basic reason is to get more braking power on the loads.

So this gets back to my earlier question asking why you would want to add this system to your freight car.  It will have more braking power, but most likely, this will be realized when your car is operating in someone else’s train.  And even then, your improved car may be the only such car in that train.  So your improved car is working extra hard and wearing out brake shoes faster, but with little net benefit to the other guy’s train, and no benefit to you.

The only way this load sensing/enhanced braking makes sense to me is if all railroads agreed to install this on all of their cars.    

[Paul_D_North_Jr]

tree68

Al Krug provides the answer.  Scroll down to "Some Other Embellishments." 

Direct URL to that section, since it's not at Krug's usual website:

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

See why some of us like Al so much ?

- Paul North.  

[Euclid]

Okay, my understanding of load sensors conforms to that described by Al Krug.  So the point is to add more brake force rather than to prevent wheel slide that would occur with the typical brake system without the load sensor. 

[Euclid]

Wait—I did not explain my understanding properly.  My understanding, like yours, would have the device derate the braking force for empties like you say.  It does say that in the report. 

But my understanding also is that adding this device would also entail the raising of the default braking force to maximum for loads instead of being maximized for empties as is the case on all cars without this device.  I suspect that default braking force would be raised by changing the brake mechanism.    

In that sense, the device itself would not directly increase brake force for loads.  But it would allow a higher default braking force for loads, and thus increase load braking in that indirect way by being able to reduce that higher braking force for loads to the point where it can apply to empties without sliding the wheels.  The point would be to provide greater braking force for loads.

So that is at least the proper explanation of my understanding of how the device works, although that may be incorrect in the case of this ELX-B 60 mechanical-pneumatic device that we have been discussing.  Maybe what I am talking about has not been invented yet.  I will look further into this.   

I will take a look at the Krug link, and a couple other things here. 

[Wizlish]

tree68

 

 

Euclid

Basically, it sounds like you and BaltACD are saying the load sensors are intended to prevent wheel slide on empties.  Whereas, my understanding is that load sensors are intended to provide more brake force on loads than would be the case on cars without load sensors.      

 

 

Al Krug

provides the answer.  Scroll down to "Some Other Embellishments."

Well, what do you know, I had it exactly backward!

[tree68]

Euclid

Basically, it sounds like you and BaltACD are saying the load sensors are intended to prevent wheel slide on empties.  Whereas, my understanding is that load sensors are intended to provide more brake force on loads than would be the case on cars without load sensors.      

Al Krug

provides the answer.  Scroll down to "Some Other Embellishments."

 

[Euclid]

My understanding is that without load sensors, freight car air brakes apply the highest braking force possible that does not exceed the wheel slide point of empty cars.  So when the cars are loaded, they could take more braking force without sliding, but none is available, so the loaded cars are under-braked.

In other words, I thought the point of load sensors was to distinguish between loads and empties in order to apply maximum braking force on empty cars, and then apply the higher maximum force on loaded cars.  The point would be better stopping power of the train to the extent that it has loads in it. 

Maybe this is not the correct interpretation.  My next question would have been to ask how the load sensing system in my understanding would add more brake force.

However, you are saying the opposite of my understanding when you say, “The valve only derates braking force when the car is empty, so that the wheels will not slide.”  You may be right, but if this were the case I would think that braking normally maximized for loads will always be excessive for empties.  If that is the case, how can equipment go without this load sensor option?  I would think wheels on empties would be sliding all the time during heavy brake applications if the brakes defaulted with maximum force for loaded cars no matter whether they are loaded or empty. 

Basically, it sounds like you and BaltACD are saying the load sensors are intended to prevent wheel slide on empties.  Whereas, my understanding is that load sensors are intended to provide more brake force on loads than would be the case on cars without load sensors.      

[Wizlish]

OK, I think I see where this is going off the trolley a bit.

I don't believe these valves are used to INCREASE braking force above the 'usual' default calibration for a car, which is going to be for close to the nominal loaded weight.  The valve only derates braking force when the car is empty, so that the wheels will not slide.

The analogy with load-leveling is that the control is only applied in one direction; do not be confused by the fact that load leveling applies more force to create its effect, while railcar load-sensing reduces force to create its effect.  In both cases, the system usually doesn't compensate 'in the other direction' -- in load leveling, there usually isn't any active 'kneeling' action to force the rear of the vehicle down if, say, negative tongue load were applied to a hitch.

Some passenger train braking systems were set up to provide an increased level of braking at high speed -- the Decelakron, if I remember correctly, used a sliding inertial weight to give a control input for the physical rate of deceleration, and modulated the braking effort to achieve the higher brake cylinder pressure needed to produce that rate at higher speed.*  I wouldn't expect such a system to be of practical use on freight consists, even if it could be adjusted and maintained effectively in typical interchange service.

My understanding of how the antislide valve is calibrated is that it keeps braking effort 'well enough' below where wheels will slide for any expected combination of car weight and adhesion.  It's difficult to implement 'antilock brakes' on a foundation-braked car -- that's one of the reasons passenger cars went to truck-mounted cylinders with short actuating levers to the tread or disc-brake shoes.

 

*There was much more 'stuff' involved in a brake system with a Decelakron, including variable calibration of braking ratio, for example in four steps from 250% above 90 mph down to 100% below 20 mph on Union Pacific in the '30s.  I'm just illustrating how the control proportionality was done.

[Euclid]

BaltACD

The benefit of load sensor equipment on cars would manifest itself as decreased billing for wheel change out from slid flat wheels.

But why would load sensors help prevent wheel slides?  Do they reduce braking force to less than it would be on empty cars without load sensors?  I thought that they only increased braking force on the loads. 

[BaltACD]

Euclid

Wizlish

I understand those benefits and see their value.  I also definitely see your point about mandating load sensors on oil trains as being low hanging fruit in the current politics of the issue.  But my question is to ask why a railroad company would decide to add load sensors to a purchase of say 50 new freight cars.  If say two of those cars happen to be running in another company's train containing 100 cars without load sensors, it would be a slight benefit to that train, and no benefit to the railroad company that owns the two cars with the sensors.  In other words, why would a company spend money improving the stopping performance of another company's train?

This thought leads to another question:

Say you have a mixed consist train of loaded 100 cars, and there are 25 cars with load sensors and 75 cars without them.  Say the 25 cars with sensors are all together in the train.  Wouldn’t the extra brake force on the 25 cars have a bad effect on train handling? 

 

Car owners pay for repairs to their cars, even when the repairs are made on another railroad.  There is and has been in place a uniform system for repairs to be billed back to the owner at at standard price for each type of repair made.  The benefit of load sensor equipment on cars would manifest itself as decreased billing for wheel change out from slid flat wheels.

In train handling, from the engineers perspective, he feels total train retardation - no matter how it is generated within the train.  So long as no wheels are sliding he doesn't care how the train retardation is being accomplished.  Handling freight train air brakes is not like braking ones automobile, as the only brake modulation that is available is to increase braking pressure or to fully release the brakes.

[Euclid]

Wizlish

I understand those benefits and see their value.  I also definitely see your point about mandating load sensors on oil trains as being low hanging fruit in the current politics of the issue.  But my question is to ask why a railroad company would decide to add load sensors to a purchase of say 50 new freight cars.  If say two of those cars happen to be running in another company's train containing 100 cars without load sensors, it would be a slight benefit to that train, and no benefit to the railroad company that owns the two cars with the sensors.  In other words, why would a company spend money improving the stopping performance of another company's train?

This thought leads to another question:

Say you have a mixed consist train of loaded 100 cars, and there are 25 cars with load sensors and 75 cars without them.  Say the 25 cars with sensors are all together in the train.  Wouldn’t the extra brake force on the 25 cars have a bad effect on train handling? 

[Wizlish]

Euclid

Why would a railroad company choose to install these devices on their rolling stock?

The principal use for freight is on cars with a sizable difference between loaded and unloaded weight.  A good representative example was the car illustrated in the accident report, a center-beam flatcar used for lumber products.

With developments in reducing tare weight, the importance of adjusting NBR on loads vs. empties, in as automatic and 'car-specific' a way as possible, has taken on more significance.  The key has been to accomplish that in ways that best fit contemporary railroading practice.

It is also becoming more and more important to avoid even momentary wheelslide on low-tare-weight trains with high axle loading -- two examples being stack trains and coal-gon unit coal trains.  I think it is easy to comprehend why the use of 'automatic' proportioning would be of value on those consists.

Conversely, the advantage would be 'lower' for the specific case of oil trains built to increasingly armored standards, operated at lower speeds.  I'd still find the technology valuable, of course ... and would also think it would be political low-hanging fruit to mandate the use of brake proportioning on these "dangerous" consists in order to improve "safety".

[Paul_D_North_Jr]

cx500

[snipped - PDN.] . . . I have no idea when the value for NBR was established so it may be a legacy of past experience.  Perhaps it can be raised to reflect the current more modern cars but in reality the brake/wheel/rail interfaces have changed very little in the past 100 years.

Per Sec. 1.14.2 of the TSB report, the NBRs were set at least once in 1999, then raised in 2004.  The quoted 2004 AAR Air Brake Association paper indicates that the Canadian Class 1's had been exceeding those values "for many years" to assure adequate performance. 

- Paul North. 

[Paul_D_North_Jr]

Euclid

[snipped - PDN] . . .

 

Are you determining the number of cars derailed correlating with the length of those cars in relation to the stopping distance?  I wonder if there may be other factors such as the resistance effect of the derailing cars. 

Yes.  The scenario behind my example was simple: a car ahead derails, comes to a complete stop instantly, and becomes an immovable object.  How many of the trailing cars will crash into it or each other before the rest of the train is stopped by braking force only ?  That's basically the distance traveled by a car subject only to that braking force.  As you imply, there are other forces that might reduce that distance, as a practical matter: the 1st derailed car might roll or slide ahead a little ways until it comes to a halt, providing a slight additional stopping distance; it and the subsequent derailed cars will experience further deceleration as they plow through the track structure and the ballast; and until they become uncoupled or jack-knife at 90 deg. to each other, the couplers and frames will transmit some additional reaction/ pushback force towards the other cars at the rear of the train. 

 

 

Euclid

As I understand it, you are comparing stopping distance of ECP brakes with or without the maximization of brake force appropriate for loaded cars.  If that is correct, what then happens if you compare ECP brakes to conventional air brakes with that same maximized braking for the loads; and then factor in the instant application of ECP brakes versus the timed propagation of conventional air brakes?  

Not quite.  I was comparing the effect on stopping distances on the basis of a former typical Net Braking Ratio, then 2 recent/ current maximum NBRs, and then 1 greater than is now currently specified, presuming it could be obtained with a more sophisticated empty /load device, faster-acting brakes, and a more powerful braking system. - regardless of the kind of controls used.  That likely would be ECP, but not necessarily - after all, someone could invent a way to do that with conventional brakes . . .  

I did not directly compare ECP vs. conventional because of the complexities of the conventional systems - all of which make them slower to react than the ECP.  I acknowledge those complexities as a qualitative issue, but quantifying them is beyond the scope of what I was trying to illustrate.   

- Paul North.

[cx500]

Paul North's calculations provide a fascinating comparison of the results of increasing the Net Braking Ratio to what is achievable in ideal conditions.  In less salubrious situations, as he also mentions, the reult may be a train of flatted wheels, still cheaper than a major derailment.  The flipside to this, and perhaps why the NBR is kept low, is that from time to time a train may experience an undesired emergency brake application due to a faulty brake valve somewhere on the train.  No derailment prevented, but still a lot of flatted wheels to deal with.

Locomotives can deal with varying factors of adhesion by their wheel slip sensing system.  In theory you could do something similar on each freight car (it was used on some passenger cars such as CPR's The Canadian) but the cost would be staggering to provide it on the North American freight car fleet.

I have no idea when the value for NBR was established so it may be a legacy of past experience.  Perhaps it can be raised to reflect the current more modern cars but in reality the brake/wheel/rail interfaces have changed very little in the past 100 years.

[Euclid]

Wizlish

Previous posts have referred to one existing method of adjusting load/empty braking force for air-braked cars. 

How common is the use of these load sensors on North American freight cars?  Why would a railroad company choose to install these devices on their rolling stock?

[zugmann]

BroadwayLion

Nope, not at all. Oil Trains require a sand car between the Oil Cans and the Locomotive. That is your transition car, it holds all of the necessary electronics, batteries, generators, terminals, and etc. for the operation of the train. It has a trainline coupler on one end, and a regualr coupular on the other. It could transpit wirelessly to a console in the locomotive (lap top or rugged tablet) used by the conductor.

 

Hazmat placement regulations restrict certain loaded hazmat cars (I think oil qualifies without looking at the chart) from being coupled next to cars with internal combustion engines (aka generators).

[BroadwayLion]

dehusman

So your automatic couplers not oly require a new car they require a new engine to pull the car, one that is equipped with the new couplers, air system, control system, computer interface, etc. etc.

Nope, not at all. Oil Trains require a sand car between the Oil Cans and the Locomotive. That is your transition car, it holds all of the necessary electronics, batteries, generators, terminals, and etc. for the operation of the train. It has a trainline coupler on one end, and a regualr coupular on the other. It could transpit wirelessly to a console in the locomotive (lap top or rugged tablet) used by the conductor.

Use any locomotives you wish, use locomtoives at both ends.

couplers open with a key rather than with a lift bar. Simple adapters on each car will connect iron to iron as necessary for shop, yard or setout movements.

ROAR

 

[Wizlish]

Why is this discussion going all over the place with lasers and load cells in the suspension?

Previous posts have referred to one existing method of adjusting load/empty braking force for air-braked cars.  This uses a mechanical method similar to that used on some systems of automatic load-leveling for automobiles.  Here is an illustration of the mechanism:

This is from the Canadian accident report that was referenced earlier in this thread.  Referenced in that thread is the need for a 'sensor plate' to be attached to the truck frame -- this is not an active load cell or anything sophisticated that requires electricity or the communication of logic signals, it is just a solid flat surface that the 'sensor arm' of the apparatus bears on as the truck rotates relative to the car on curves. 

I found it interesting that so many of these plates were found damaged or missing when the accident investigation in 2007 was progressing.  This suggested to me that the preparation or welding operation used to attach them was somehow deficient -- I don't immediately see how any normal or even accidental force would tear such a plate, in such a location, loose from a sideframe, so I would have to suspect corrosion damage, or little more weld integrity than that for tack welds.  I can see how the assumption could be made that these plates only see minimal force applied to them in service, and that extensive welding on the sideframes themselves might cause HAZ damage.

There is little doubt that a setup like this could be adapted to oil-train service, and with little additional work it could be made to have multiple stages of actuation or even be made proportional.  In such a setup, the integrity as well as the proper setup of the sideframe reference plates becomes an issue for attention.

(Yes, I thought it was interesting that the improper 5/8" setup height of the plates was noted to counteract the effect of the plate breaking off with respect to actuation of the ride-height valve in the Lillooet accident!)