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Post by jamesb on Jun 30, 2017 11:14:58 GMT
My questions (prompted by reading (possibly incorrect) reports that an emergency brake application caused a NYC subway train to derail recently as discussed in another thread):
What is the maximum safe braking rate of a tube train? Is '4 bar' the standard brake cylinder pressure that is applied across all LU trains during emergency brake applications?
How is the maximum safe braking rate determined?
What lead me to ask the question:
The 'brake cylinder pressure gauge' (may not be right term) located under the seats at one end of each carriage on the central line seems to jump up to '4 bar' during emergency brake applications. The train comes to an abrupt halt.
On the metropolitan line recently, two failed signals between Liverpool Street and Moorgate required the driver to 'apply the rule' to pass the signals at danger. I observed that the brake cylinder pressure gauge jumped to '4 bar' as we came to an abrupt stop.
I know that on older trains, one door in each double leaf can be 'pushed back' a few centimeters to free small obstructions like a coat toggle which could still be trapped despite the doors being proved shut. The force required to push the door back has to be easy enough to overcome to free an obstruction, but not so easy that it would be pushed back by the forces generated by an emergency brake application. I recall that when the 2009ts was being designed, emergency braking could have caused spring loaded doors to 'push back' during maximum deceleration, so sensitive door edges was a solution to enable the doors to be locked tight shut but mitigate the risk of a passenger to be dragged.
I imagine that the rate of deceleration needs to balance the need to stop the train as quickly as possible, against the risk of damaging the wheels / injuring the passengers / keeping the train on the tracks?
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Post by trt on Jun 30, 2017 11:19:31 GMT
I imagine that the rate of deceleration needs to balance the need to stop the train as quickly as possible, against the risk of damaging the wheels / injuring the passengers / keeping the train on the tracks? I think that's the definition of regular braking. I would infer that the 'emergency' part means simply stopping the train in the shortest possible distance. |
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Post by jamesb on Jun 30, 2017 11:29:38 GMT
But the driver cannot choose how much brake to apply in an emergency as such, they just select the 'emergency brake' position and there is nothing more that they can do ?
How much brake is applied in emergency mode must be pre-determined?
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class411
Operations: Normal
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Post by class411 on Jun 30, 2017 13:10:06 GMT
Don't forget that the absolute maximum braking rate is determined by when the wheels start to slip.
With anti-lock brakes, I dare say that the maximum rate is whatever the system can apply before the anti-lock mechanism begins limiting action.
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North End
Beneath Newington Causeway
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Post by North End on Jun 30, 2017 13:12:20 GMT
I imagine that the rate of deceleration needs to balance the need to stop the train as quickly as possible, against the risk of damaging the wheels / injuring the passengers / keeping the train on the tracks? I think that's the definition of regular braking. I would infer that the 'emergency' part means simply stopping the train in the shortest possible distance. Emergency braking gives an extra rate of braking over and above full service, but there are some other features. The emergency position on the handle is hard wired and fail safe, whereas the service braking positions are designed to a lesser level of integrity. Also rheostatic braking is inhibited in emergency braking for the same reason- although this can be a mixed blessing as if you've misjudged your braking and select emergency on something like a 95 stock there will be a noticeable time lag of a second or two where you get less braking, as the rheo cuts out and you wait for the friction brake to become effective. Once that happens the extra braking becomes obvious, but the general feeling is it is often better to leave the train in full service and hold one's nerve relying on the rheo brake which is normally pretty effective. For those watching the brake cylinder gauges beware that these will not reflect any rheostatic braking. Typically one will see a spike when the brakes are first applied, which will disappear when the rheo takes hold. Then you will see nothing until the friction brake again comes into play for the final stop when the rheo fades out. This may differ if there is extra friction braking for whatever reason. |
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Post by trt on Jun 30, 2017 13:18:31 GMT
Oh, I see what you mean. Well at all but the highest speeds, I believe the regular braking on the S-stock is regenerative. The amount of brake pressure available in an emergency application will depend on the amount of air or vacuum in the reservoirs, but the actual force applied is determined by the sort of requirement given in this document which defines the requirement purely as a stopping distance for the class of train, the type of route it is on and the speed it was doing when the brakes were applied. |
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North End
Beneath Newington Causeway
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Post by North End on Jun 30, 2017 13:25:39 GMT
Don't forget that the absolute maximum braking rate is determined by when the wheels start to slip. With anti-lock brakes, I dare say that the maximum rate is whatever the system can apply before the anti-lock mechanism begins limiting action. Yes. This has been discovered by some unwitting folk at places like Totteridge southbound on the first train in leaf fall season on a damp windy morning when attempting to brake from 45 mph. In one case I think every wheel set on the train was damaged beyond repair! |
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Post by jamesb on Jun 30, 2017 15:14:59 GMT
Oh, I see what you mean. Well at all but the highest speeds, I believe the regular braking on the S-stock is regenerative. The amount of brake pressure available in an emergency application will depend on the amount of air or vacuum in the reservoirs, but the actual force applied is determined by the sort of requirement given in this document which defines the requirement purely as a stopping distance for the class of train, the type of route it is on and the speed it was doing when the brakes were applied. Thanks - interesting stuff. I suppose that these standards have to be taken into account when designing a new train. |
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Deleted
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Post by Deleted on Jun 30, 2017 21:45:50 GMT
This reminds me of an incident around 1994, whereby one Piccadilly Line driver hung something heavy on the traction controller, had no pilot light, and got off to close the open door in the second car, this completed the pilot light circuit, and the train shot off at 60 miles per hour from Kings Cross towards Caledonian Road, however the home signal was at red at Caledonian Road, so the train got tripped on the train stop whilst doing 60 miles per hour, I bet that all 24 wheelsets of that train were damaged beyond repair, following such an incident. The emergency braking from 60 miles per hour through a raised trainstop would have probably ruined all 24 wheelsets by way of two inch flats on every axle. www.independent.co.uk/news/uk/runaway-tube-driver-jailed-1445495.html |
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Post by fish7373 on Jun 30, 2017 22:18:59 GMT
This reminds me of an incident around 1994, whereby one Piccadilly Line driver hung something heavy on the traction controller, had no pilot light, and got off to close the open door in the second car, this completed the pilot light circuit, and the train shot off at 60 miles per hour from Kings Cross towards Caledonian Road, however the home signal was at red at Caledonian Road, so the train got tripped on the train stop whilst doing 60 miles per hour, I bet that all 24 wheelsets of that train were damaged beyond repair, following such an incident. The emergency braking from 60 miles per hour through a raised trainstop would have probably ruined all 24 wheelsets by way of two inch flats on every axle. www.independent.co.uk/news/uk/runaway-tube-driver-jailed-1445495.htmlThe wheels had flats but did not get up to 60 mph then a mod was done to stop this called re stroke mod to the pilot light. FISH7373 81C NFP |
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Post by fish7373 on Jun 30, 2017 23:09:40 GMT
73 T/STOCK BRAKEING PRESSURES are and the gauges in car are not very good to say FISH7373 81C NFP
MOTOR CAR TRAILER
SERVICE 1 1.1 1.4
SERVICE 2 1.4 1.7
SERVICE 3 1.7 2.1
SERVICE 4 2.1 2.4
EMERGENCY 2.4 2.7
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Deleted
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Post by Deleted on Jul 1, 2017 12:07:07 GMT
There is a predetermined figure, but can't remember off the top of my head. Thought it was 1.2mps or something
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Deleted
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Post by Deleted on Jul 1, 2017 16:37:55 GMT
This reminds me of an incident around 1994, whereby one Piccadilly Line driver hung something heavy on the traction controller, had no pilot light, and got off to close the open door in the second car, this completed the pilot light circuit, and the train shot off at 60 miles per hour from Kings Cross towards Caledonian Road, however the home signal was at red at Caledonian Road, so the train got tripped on the train stop whilst doing 60 miles per hour, I bet that all 24 wheelsets of that train were damaged beyond repair, following such an incident. The emergency braking from 60 miles per hour through a raised trainstop would have probably ruined all 24 wheelsets by way of two inch flats on every axle. www.independent.co.uk/news/uk/runaway-tube-driver-jailed-1445495.htmlYes his bag |
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Post by firestorm on Jul 4, 2017 17:41:36 GMT
My questions (prompted by reading (possibly incorrect) reports that an emergency brake application caused a NYC subway train to derail recently as discussed in another thread): What is the maximum safe braking rate of a tube train? Is '4 bar' the standard brake cylinder pressure that is applied across all LU trains during emergency brake applications? How is the maximum safe braking rate determined? What lead me to ask the question: The 'brake cylinder pressure gauge' (may not be right term) located under the seats at one end of each carriage on the central line seems to jump up to '4 bar' during emergency brake applications. The train comes to an abrupt halt. On the metropolitan line recently, two failed signals between Liverpool Street and Moorgate required the driver to 'apply the rule' to pass the signals at danger. I observed that the brake cylinder pressure gauge jumped to '4 bar' as we came to an abrupt stop. I know that on older trains, one door in each double leaf can be 'pushed back' a few centimeters to free small obstructions like a coat toggle which could still be trapped despite the doors being proved shut. The force required to push the door back has to be easy enough to overcome to free an obstruction, but not so easy that it would be pushed back by the forces generated by an emergency brake application. I recall that when the 2009ts was being designed, emergency braking could have caused spring loaded doors to 'push back' during maximum deceleration, so sensitive door edges was a solution to enable the doors to be locked tight shut but mitigate the risk of a passenger to be dragged. I imagine that the rate of deceleration needs to balance the need to stop the train as quickly as possible, against the risk of damaging the wheels / injuring the passengers / keeping the train on the tracks? The maximum safe braking rate on the S-Stock is dependant on what type of car it is (DM, M1 M2(D) etc), which end of the car and the passenger loading which is monitored by the load weigh system. There are set braking parameters which the train must be able to achieve, from tare weight to crush load. Without going into too much detail, here are the figures for Emergency braking in tare conditions: DM - A end 4.01 - 4.39, D end 3.22 - 3.60 M1 - A end 3.38 - 3.75, D end 3.53 - 3.90 M2 - A end 3.04 - 3.42, D end 3.04 - 3.42 M2D - A end 3.12 - 3.50, D end 3.20 - 3.58 MS - A end - 3.25 - 3.63, D end 3.25 - 3.63 For crush load conditions in Emergency braking: DM - A end 5.58 - 5.96, D end 5.58 - 5.96 M1 - A end 5.23 - 5.61, D end 5.45 - 5.83 M2 - A end 5.06 - 5.44, D end 5.06 - 5.44 M2D - A end 5.21 - 5.59, D end 5.29 - 5.67 MS - A end - 5.09 - 5.47, D end 5.24 - 5.61 There are also figures for maximum service brake, under tare and crush load conditions. The train has a EP (Electro Pneumatic) Valve of some sort monitoring each bogie and will determine the the rate of braking depending on the above factors. |
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Deleted
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Post by Deleted on Jul 4, 2017 18:18:54 GMT
My questions (prompted by reading (possibly incorrect) reports that an emergency brake application caused a NYC subway train to derail recently as discussed in another thread): What is the maximum safe braking rate of a tube train? Is '4 bar' the standard brake cylinder pressure that is applied across all LU trains during emergency brake applications? How is the maximum safe braking rate determined? What lead me to ask the question: The 'brake cylinder pressure gauge' (may not be right term) located under the seats at one end of each carriage on the central line seems to jump up to '4 bar' during emergency brake applications. The train comes to an abrupt halt. On the metropolitan line recently, two failed signals between Liverpool Street and Moorgate required the driver to 'apply the rule' to pass the signals at danger. I observed that the brake cylinder pressure gauge jumped to '4 bar' as we came to an abrupt stop. I know that on older trains, one door in each double leaf can be 'pushed back' a few centimeters to free small obstructions like a coat toggle which could still be trapped despite the doors being proved shut. The force required to push the door back has to be easy enough to overcome to free an obstruction, but not so easy that it would be pushed back by the forces generated by an emergency brake application. I recall that when the 2009ts was being designed, emergency braking could have caused spring loaded doors to 'push back' during maximum deceleration, so sensitive door edges was a solution to enable the doors to be locked tight shut but mitigate the risk of a passenger to be dragged. I imagine that the rate of deceleration needs to balance the need to stop the train as quickly as possible, against the risk of damaging the wheels / injuring the passengers / keeping the train on the tracks? The maximum safe braking rate on the S-Stock is dependant on what type of car it is (DM, M1 M2(D) etc), which end of the car and the passenger loading which is monitored by the load weigh system. There are set braking parameters which the train must be able to achieve, from tare weight to crush load. Without going into too much detail, here are the figures for Emergency braking in tare conditions: DM - A end 4.01 - 4.39, D end 3.22 - 3.60 M1 - A end 3.38 - 3.75, D end 3.53 - 3.90 M2 - A end 3.04 - 3.42, D end 3.04 - 3.42 M2D - A end 3.12 - 3.50, D end 3.20 - 3.58 MS - A end - 3.25 - 3.63, D end 3.25 - 3.63 For crush load conditions in Emergency braking: DM - A end 5.58 - 5.96, D end 5.58 - 5.96 M1 - A end 5.23 - 5.61, D end 5.45 - 5.83 M2 - A end 5.06 - 5.44, D end 5.06 - 5.44 M2D - A end 5.21 - 5.59, D end 5.29 - 5.67 MS - A end - 5.09 - 5.47, D end 5.24 - 5.61 There are also figures for maximum service brake, under tare and crush load conditions. The train has a EP (Electro Pneumatic) Valve of some sort monitoring each bogie and will determine the the rate of braking depending on the above factors. Welcome to the forum! =) Thanks very much  |
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Post by superteacher on Jul 4, 2017 19:23:55 GMT
That must be a contender for the most technical first ever post! Welcome along firestorm!
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Post by fish7373 on Jul 4, 2017 20:01:15 GMT
 Brake info of rolling stock.
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Post by jamesb on Jul 6, 2017 18:13:42 GMT
Thank you so much - this is all fascinating stuff! I don't know why I find it so fascinating... Thats why I love this forum so much!
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