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Re: More info for the interested
Author: SP5103
Date: 06-20-2014 - 23:55
The article is far too simplified and out of date in my opinion. Some of what is mentioned was used on some prototypes. I remember seeing remnants of parts on a ECP test train over 15 years ago on some BN grain cars interchanged to us in Minnesota.
There is a real difference between electro-pneumatic (EP) and electronically-controlled-pneumatic (ECP) brakes. EP dates back to the origins of the Westinghouse air brake, and if you recall ol' George was familiar with electricity also. The holy grail of North American railroad air brakes is to have instantaneous application and release (electrons are faster than air molecules) and to have graduated release. Almost every major proposed air brake change over the last century has specified graduated release, but there has never been a practical pneumatic design that consistently worked on trains over about 24 cars.
EP (and ECP) does potentially provide instantaneous control and graduated release. There have been numerous EP systems over the last century, none of them really standard but several common ones. Those familiar with the U12 control valve common on heavyweights may not realize that the from blanking plate was for the E-P magnet valves. A typical system required four wires to control three magnet valves - application, release and emergency. (The DL&W MU cars had this system.) The magnet valves would release air locally from the brake pipe at each control valve, or add air to the brake pipe from a main reservoir line depending upon the position of the engineers brake valve. When the lightweight streamliners first appeared, many used a confusing combination of straight air controlled by EP that controlled brake cylinder pressure directly. Another common system is the PS-68 (MBTA still uses?). The typical magnet valves are used to control the brake pipe pressure with some twists. The cars are equipped with ABD or similar freight valves without the accelerated release portion. The engineer's brake valve is a 26E (and there is a similar 30 type) which is a pressure maintaining position valve that is not self lapping. In release everything is familiar. To make a reduction, the engineer moves the brake valve to application then back to lap. A diaphragm valve between the brake pipe and equalizing reservoir pressures trips the application or release magnets as required. Between the lap and release position is a holding position which recharges the brake pipe to normal pressure but another magnet valve on each car closes its brake cylinder exhaust. By moving the handle between lap and release, the engineer can get a graduated release while recharging the brake system at the same time. There must be something that limits brake cylinder pressure, but I don't recall off the top of my head how they do it.
There are two very important points to remember about EP brakes. First - the entire system will only work properly if full continuity is maintained between the controlling engine and all the cars. This was the problem George had trying to develop it in the infancy of air brakes, and has been the problem ever since. Second - almost all the EP systems I have instruction manuals on are overlay systems - the EP system works with the regular automatic brake system. The initial terminal air test includes the requirement to test both systems. If the EP system fails, the air brakes will still apply normally though slower than if under EP control. The train can still move and brakes controlled in the conventional manner.
The Decelostat and similar systems typically used a multi diaphragm relay valve. During a brake application at high speed the system would develop say 100% of the brake cylinder pressure the reduction was calling for. As speed decreased, the system would transfer control to smaller control relay diaphragms maybe only being at 40% prior to stopping. The lower the speed, the more likely wheels are to slide under heavy braking, especially with cast brake shoes.
The AAR sets the required minimum and maximum braking ratios. On engines and passenger equipment where the weight range stays within a small range, the equipment can be braked at a fairly high ratio with sliding only a real concern due to poor rail conditions. On freight cars, too high of a braking ratio and a car will slide when empty, too low and it won't stop when loaded. Imagine driving your pickup around empty and if your hit loose gravel braking hard the rear wheels will usually skid (unless the ABS jumps in). Now load the bed full and pull a loaded unbraked trailer and you will be hitting the brakes hard and heavy coming up to a stop. These are all single capacity brake systems. As a general rule, engines and passenger cars are braked at about twice the ratio of an empty freight car, and a loaded freight car has less than half the braking effort when empty.
Sometimes the difference between an empty or tare weight and loaded weight of a car, a single capacity brake cannot be used. There are also some heavy haul cars where more braking effort when loaded is desired. In these instances, an empty-load system is used. These date clear back to K triples where different brake cylinders were used depending on whether a change over valve was set to loaded or empty. Modern systems use a sensor valve that either measures truck spring deflection or a diaphragm the load presses against. Modern systems typically add an extra volume to the brake cylinder resulting in a lower brake cylinder pressure when empty. Most rules allow an empty-load car to be counted as 1-1/2 effective brakes when loaded when figuring tons per brake. A good portion of new rail cars I have seen are required to have empty-load brake equipment.
Many transit systems use other brake and propulsion control systems than used on heavy rail, and also have variable load systems that adjust braking for passenger loads, or magnetic track brakes to decrease emergency stopping distances. Transit is from another world entirely, and I am not qualified to go there.
Now to ECP. The original concept and tests years ago were for a wireless control system. To solve the power issue I know there was one patent for a standard size railroad axle roller bearing that included a generator. In testing, terrain, tunnels and surrounding electrical noise resulted in a loss of continuity. This was abandoned in favor of a hard wired system, but the problem became who was going to connect the multi conductor cable, an electrician, carman or trainman? The refinement of digital sytstems has made a working ECP system a possibility. First, as if connecting air hoses isn't bad enough (especially the new wide flange ones with wide lip gaskets), the air hose to be used now includes a two conductor contact added on the top. This carriers the braking signal throughout the train, something like 160vac? (a friend said it was a common voltage in communications) I believe (and I am probably wrong) is that it is similar to the DCC systems used in model railroading. A square wave AC voltage is generated which goes through a dropping transformer on each car and then a rectifier bridge, and as noted also charges a small battery on each car. By altering the pulse width of the AC, a digital signal is created which is read by each control valve. The brake pipe becomes a simple supply line, and the ECP control valve acts to release the brakes, recharge the reservoirs off the brake pipe supply line or apply the brakes according to signal. Each control valve "talks back" to the engineer's control unit to confirm its status and indicate any problems. I am guessing this is some kind of serial or USB bus operating on its own carrier frequency. (An alternative might be the basic signal is a steady square wave with the digital commands on another carrier frequency.) The control system must recognize the FRED talking to it to prove ECP continuity at all times.
Two ECP systems have been proposed - the first is a dual system so the the car can be used in standard or ECP mode. The second, much cheaper option, is for an ECP system only eliminating the standard pneumatic control valves. Because of the HUGE initial first cost, the FRA is pushing the cheaper option in an effort to justify the change. Over half of the freight cars in the US are now owned by non-railroad owners, so it will be the leasing companies and private car owners that will share the financial pain but not few of the benefits. Part of the FRA's justification is that there will be far less wheel wear and damage (agreed), and the shorter stopping distances will allow railroads to increase capacity on the same track. Slack issues are supposed to be greatly reduced. If all these benefits would truly be realized and create such an economic benefit, why haven't the railroads themselves pushed the AAR to adopt them as a standard instead of it becoming an FRA requirement?
I am a pessimist by nature, so here are the reasons I don't think the current incarnation of ECP will prove to be a fiasco and eventual failure:
1. The problem with EP and ECP has for the last century and will always be maintaining continuity. We are still dependent upon two circuits between each car making consistent continuity. The higher voltage AC will help, but now be a hazard to the crew. Will the ECP system have to be disabled like HEP every time someone goes in between?
2. The impending ECP system does not overlay the standard brake pipe control, but is its own stand alone system. If it fails or even burps, the standard control valve (assuming the car has the dual system) is not providing a backup control like with most EP systems. What happens when electronic systems aren't happy? They shut down and pout. The loss of continuity or any malfunction will result in the ECP valves defaulting to a penalty application.
3. As a last resort, the venting of the brake pipe due to a break in two, engineer's brake valve or conductor's valve will still result in a pneumatic emergency as always. So the benefits of an ECP emergency will only result if the ECP system is fully functioning on the entire train. For a system that is supposed to eliminate UDE applications, it seems to me that it might actually invite more.
4. Don't just grab a wrench and a spare air hose. A burst or ripped off air hose will now require the ECP wires to also be connected or spliced in.
5. And how long will it take to resolve an ECP issue in the yard or on the road? Assuming the system tells you the last car talking to it, you have to hike back and either repair the system (doubtful), kick the air hose connection (checking first for weed weasels) or install a jumper cable around the affected car. In the meantime, all those extra trains that the system allowed to closely follow you are slammed to a halt blocking crossings until you can get going again.
6. Is it reasonable to expect every carmen will now become an electrician? Even if all they have to do its parts swapping, how long will the electronics and batteries last on each car? And we won't even mention software updates or trying to replace recalled units.
The phase in of ECP is supposed to start with unit trains, then to intermodal. Finally to the rest of the general car fleet. This will be misleading, as has the testing, because unit or captive service cars do not typically get switched out, go over humps, and have the ECP electrical contacts connected and disconnected numerous times. What happens when a low ECP air hose drags through some pile or pond of aromatic sludge on an industry track? And if the car owners and railroads standardize on the stand alone ECP installation as the FRA is pushing instead of the dual system due to cost, then that means every single industrial locomotive, trackmobile, Brandt, etc. will have to be retrofitted with ECP controls or switch everything without air brakes. If the dual system is used, then there is a way to revert to the antique but proven air system when the ECP fails. Maybe the reason the FRA is pushing the standalone ECP system is if it proves to be unreliable, uneconomical, unsustainable or unsafe - and most of the fleet is equipped with the standalone system, then there is no going back.
This will be the first time in the last century since automatic air brakes and knuckle couplers became required that the North American railcar fleet will not be fully compatible with the next generation.
There is a real difference between electro-pneumatic (EP) and electronically-controlled-pneumatic (ECP) brakes. EP dates back to the origins of the Westinghouse air brake, and if you recall ol' George was familiar with electricity also. The holy grail of North American railroad air brakes is to have instantaneous application and release (electrons are faster than air molecules) and to have graduated release. Almost every major proposed air brake change over the last century has specified graduated release, but there has never been a practical pneumatic design that consistently worked on trains over about 24 cars.
EP (and ECP) does potentially provide instantaneous control and graduated release. There have been numerous EP systems over the last century, none of them really standard but several common ones. Those familiar with the U12 control valve common on heavyweights may not realize that the from blanking plate was for the E-P magnet valves. A typical system required four wires to control three magnet valves - application, release and emergency. (The DL&W MU cars had this system.) The magnet valves would release air locally from the brake pipe at each control valve, or add air to the brake pipe from a main reservoir line depending upon the position of the engineers brake valve. When the lightweight streamliners first appeared, many used a confusing combination of straight air controlled by EP that controlled brake cylinder pressure directly. Another common system is the PS-68 (MBTA still uses?). The typical magnet valves are used to control the brake pipe pressure with some twists. The cars are equipped with ABD or similar freight valves without the accelerated release portion. The engineer's brake valve is a 26E (and there is a similar 30 type) which is a pressure maintaining position valve that is not self lapping. In release everything is familiar. To make a reduction, the engineer moves the brake valve to application then back to lap. A diaphragm valve between the brake pipe and equalizing reservoir pressures trips the application or release magnets as required. Between the lap and release position is a holding position which recharges the brake pipe to normal pressure but another magnet valve on each car closes its brake cylinder exhaust. By moving the handle between lap and release, the engineer can get a graduated release while recharging the brake system at the same time. There must be something that limits brake cylinder pressure, but I don't recall off the top of my head how they do it.
There are two very important points to remember about EP brakes. First - the entire system will only work properly if full continuity is maintained between the controlling engine and all the cars. This was the problem George had trying to develop it in the infancy of air brakes, and has been the problem ever since. Second - almost all the EP systems I have instruction manuals on are overlay systems - the EP system works with the regular automatic brake system. The initial terminal air test includes the requirement to test both systems. If the EP system fails, the air brakes will still apply normally though slower than if under EP control. The train can still move and brakes controlled in the conventional manner.
The Decelostat and similar systems typically used a multi diaphragm relay valve. During a brake application at high speed the system would develop say 100% of the brake cylinder pressure the reduction was calling for. As speed decreased, the system would transfer control to smaller control relay diaphragms maybe only being at 40% prior to stopping. The lower the speed, the more likely wheels are to slide under heavy braking, especially with cast brake shoes.
The AAR sets the required minimum and maximum braking ratios. On engines and passenger equipment where the weight range stays within a small range, the equipment can be braked at a fairly high ratio with sliding only a real concern due to poor rail conditions. On freight cars, too high of a braking ratio and a car will slide when empty, too low and it won't stop when loaded. Imagine driving your pickup around empty and if your hit loose gravel braking hard the rear wheels will usually skid (unless the ABS jumps in). Now load the bed full and pull a loaded unbraked trailer and you will be hitting the brakes hard and heavy coming up to a stop. These are all single capacity brake systems. As a general rule, engines and passenger cars are braked at about twice the ratio of an empty freight car, and a loaded freight car has less than half the braking effort when empty.
Sometimes the difference between an empty or tare weight and loaded weight of a car, a single capacity brake cannot be used. There are also some heavy haul cars where more braking effort when loaded is desired. In these instances, an empty-load system is used. These date clear back to K triples where different brake cylinders were used depending on whether a change over valve was set to loaded or empty. Modern systems use a sensor valve that either measures truck spring deflection or a diaphragm the load presses against. Modern systems typically add an extra volume to the brake cylinder resulting in a lower brake cylinder pressure when empty. Most rules allow an empty-load car to be counted as 1-1/2 effective brakes when loaded when figuring tons per brake. A good portion of new rail cars I have seen are required to have empty-load brake equipment.
Many transit systems use other brake and propulsion control systems than used on heavy rail, and also have variable load systems that adjust braking for passenger loads, or magnetic track brakes to decrease emergency stopping distances. Transit is from another world entirely, and I am not qualified to go there.
Now to ECP. The original concept and tests years ago were for a wireless control system. To solve the power issue I know there was one patent for a standard size railroad axle roller bearing that included a generator. In testing, terrain, tunnels and surrounding electrical noise resulted in a loss of continuity. This was abandoned in favor of a hard wired system, but the problem became who was going to connect the multi conductor cable, an electrician, carman or trainman? The refinement of digital sytstems has made a working ECP system a possibility. First, as if connecting air hoses isn't bad enough (especially the new wide flange ones with wide lip gaskets), the air hose to be used now includes a two conductor contact added on the top. This carriers the braking signal throughout the train, something like 160vac? (a friend said it was a common voltage in communications) I believe (and I am probably wrong) is that it is similar to the DCC systems used in model railroading. A square wave AC voltage is generated which goes through a dropping transformer on each car and then a rectifier bridge, and as noted also charges a small battery on each car. By altering the pulse width of the AC, a digital signal is created which is read by each control valve. The brake pipe becomes a simple supply line, and the ECP control valve acts to release the brakes, recharge the reservoirs off the brake pipe supply line or apply the brakes according to signal. Each control valve "talks back" to the engineer's control unit to confirm its status and indicate any problems. I am guessing this is some kind of serial or USB bus operating on its own carrier frequency. (An alternative might be the basic signal is a steady square wave with the digital commands on another carrier frequency.) The control system must recognize the FRED talking to it to prove ECP continuity at all times.
Two ECP systems have been proposed - the first is a dual system so the the car can be used in standard or ECP mode. The second, much cheaper option, is for an ECP system only eliminating the standard pneumatic control valves. Because of the HUGE initial first cost, the FRA is pushing the cheaper option in an effort to justify the change. Over half of the freight cars in the US are now owned by non-railroad owners, so it will be the leasing companies and private car owners that will share the financial pain but not few of the benefits. Part of the FRA's justification is that there will be far less wheel wear and damage (agreed), and the shorter stopping distances will allow railroads to increase capacity on the same track. Slack issues are supposed to be greatly reduced. If all these benefits would truly be realized and create such an economic benefit, why haven't the railroads themselves pushed the AAR to adopt them as a standard instead of it becoming an FRA requirement?
I am a pessimist by nature, so here are the reasons I don't think the current incarnation of ECP will prove to be a fiasco and eventual failure:
1. The problem with EP and ECP has for the last century and will always be maintaining continuity. We are still dependent upon two circuits between each car making consistent continuity. The higher voltage AC will help, but now be a hazard to the crew. Will the ECP system have to be disabled like HEP every time someone goes in between?
2. The impending ECP system does not overlay the standard brake pipe control, but is its own stand alone system. If it fails or even burps, the standard control valve (assuming the car has the dual system) is not providing a backup control like with most EP systems. What happens when electronic systems aren't happy? They shut down and pout. The loss of continuity or any malfunction will result in the ECP valves defaulting to a penalty application.
3. As a last resort, the venting of the brake pipe due to a break in two, engineer's brake valve or conductor's valve will still result in a pneumatic emergency as always. So the benefits of an ECP emergency will only result if the ECP system is fully functioning on the entire train. For a system that is supposed to eliminate UDE applications, it seems to me that it might actually invite more.
4. Don't just grab a wrench and a spare air hose. A burst or ripped off air hose will now require the ECP wires to also be connected or spliced in.
5. And how long will it take to resolve an ECP issue in the yard or on the road? Assuming the system tells you the last car talking to it, you have to hike back and either repair the system (doubtful), kick the air hose connection (checking first for weed weasels) or install a jumper cable around the affected car. In the meantime, all those extra trains that the system allowed to closely follow you are slammed to a halt blocking crossings until you can get going again.
6. Is it reasonable to expect every carmen will now become an electrician? Even if all they have to do its parts swapping, how long will the electronics and batteries last on each car? And we won't even mention software updates or trying to replace recalled units.
The phase in of ECP is supposed to start with unit trains, then to intermodal. Finally to the rest of the general car fleet. This will be misleading, as has the testing, because unit or captive service cars do not typically get switched out, go over humps, and have the ECP electrical contacts connected and disconnected numerous times. What happens when a low ECP air hose drags through some pile or pond of aromatic sludge on an industry track? And if the car owners and railroads standardize on the stand alone ECP installation as the FRA is pushing instead of the dual system due to cost, then that means every single industrial locomotive, trackmobile, Brandt, etc. will have to be retrofitted with ECP controls or switch everything without air brakes. If the dual system is used, then there is a way to revert to the antique but proven air system when the ECP fails. Maybe the reason the FRA is pushing the standalone ECP system is if it proves to be unreliable, uneconomical, unsustainable or unsafe - and most of the fleet is equipped with the standalone system, then there is no going back.
This will be the first time in the last century since automatic air brakes and knuckle couplers became required that the North American railcar fleet will not be fully compatible with the next generation.
