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Braking issue on Caledonian Sleeper causes train to "run away" at Edinburgh

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Surreytraveller

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Yes, but to make the applications, the driver would have to have control over the system. I don't see how the driver can have control over the system if it's isolated from the loco.
If the brake pipe cock was open and the reservoir cock was closed it would enable the driver to have control of the brakes until the air was depleted
 
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a_c_skinner

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So static and running brake tests would not detect brake pipe open but reservoir cock closed?
 

O L Leigh

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If the brake pipe cock was open and the reservoir cock was closed it would enable the driver to have control of the brakes until the air was depleted

The brake pipe would replenish the air reservoirs but only slowly, hence the need for the second main air pipe. The issue comes where the driver needs to make a lot of brake applications, such as on approach to a major station, and the air gets depleted faster than it can be replenished. But this is precisely what I believe happened.

So static and running brake tests would not detect brake pipe open but reservoir cock closed?

Nope. It would show that the brake pipe was complete from front to rear and it's likely that there was still more than sufficient air pressure left to give a normal-feeling running brake test. Indeed, it's possible that the train might have got the whole way to Waverley without problems had there been sufficient air to provide for the remaining brake applications needed to observe speed restrictions, signal aspects and the final stop into the platform.

Seems odd to me that the driver didn't go for the emergency brake before the TM did. I wonder how accurate that report might be.
 

GB

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If the brake pipe cock was open and the reservoir cock was closed it would enable the driver to have control of the brakes until the air was depleted

The brakes are still fully operational with the brake pipe open/operational but the main res pipe isolated, all it does is become a single piped train.
 

hexagon789

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Assuming the main res was isolated and only the brake pipe was still connected normally, with the brake pipe being subsequently depleted, how did the TM manage to make an emergency application if there was no air left?

Or is this suggestion wrong and was indeed stopped purely on the loco brake, that's what I don't understand.
 

O L Leigh

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Assuming that the TM even did this at all...

Some vehicles have an emergency brake reservoir that contains a certain amount of compressed air for just this situation. Whether or not the Mk5s do, I couldn't say.
 

GB

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Assuming the main res was isolated and only the brake pipe was still connected normally, with the brake pipe being subsequently depleted, how did the TM manage to make an emergency application if there was no air left?

Having only the brake pipe connected doesn't deplete the system. Even constantly applying and releasing the brakes won't deplete the entire system, it just makes the brake release slower. If you keep applying and releasing the brake you will come to a stand before you have a chance to fully recharge and release. The only way to fully deplete the system is to either let the air escape naturally over a period of hours or days (ie leak off) or purposely vent each vehicle in turn.

You can't run out of air to the extent that the brakes fail to apply, they just don't work like that.
 

Robertj21a

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Having only the brake pipe connected doesn't deplete the system. Even constantly applying and releasing the brakes won't deplete the entire system, it just makes the brake release slower. If you keep applying and releasing the brake you will come to a stand before you have a chance to fully recharge and release. The only way to fully deplete the system is to either let the air escape naturally over a period of hours or days (ie leak off) or purposely vent each vehicle in turn.

You can't run out of air to the extent that the brakes fail to apply, they just don't work like that.

Thanks - I hope you don't come to regret that statement !! :D
 

O L Leigh

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I'd suggest having a look at this page and read down to the section headed "Successive Applications" which explains some of the problems associated with a single pipe train. It's not necessary to run out of air entirely for the brakes to fail to work.
 

axlecounter

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Having only the brake pipe connected doesn't deplete the system. Even constantly applying and releasing the brakes won't deplete the entire system, it just makes the brake release slower. If you keep applying and releasing the brake you will come to a stand before you have a chance to fully recharge and release. The only way to fully deplete the system is to either let the air escape naturally over a period of hours or days (ie leak off) or purposely vent each vehicle in turn.

You can't run out of air to the extent that the brakes fail to apply, they just don't work like that.
As pointed out, you might though, get to a situation where you don’t have enough braking force to stop the train where intended.
 

Erniescooper

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If the main res was isolated and then depleted topping up the brake pipe then why did the spring applied parking brakes not apply?
 

EE Andy b1

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If the main res was isolated and then depleted topping up the brake pipe then why did the spring applied parking brakes not apply?

I asked a while back if the Mk5 sleepers were fitted with spring applied parking brakes, so if they are as you say then as you say if the air was insufficient in the reservoirs why did these not apply and bring the train to an emergency stop? Class 390s have this system.

Plenty speculation on here as usual, we will find out for sure in the future, peoples lives and jobs are on the line here.
 

O L Leigh

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I'm not sure about loco-hauled stock, but spring-actuated parking brakes are normally associated with MUs which use electro-pneumatic brakes (Cl390s included).
 

Tomnick

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The brake pipe would replenish the air reservoirs but only slowly, hence the need for the second main air pipe. The issue comes where the driver needs to make a lot of brake applications, such as on approach to a major station, and the air gets depleted faster than it can be replenished.
Forgive my possible ignorance, possibly misunderstanding the finer details of the braking system on these vehicles relative to a conventional two-pipe system, but does the air on the reservoir side of the diaphragm get depleted to any significant extent? It should be maintained at a (nearly?) constant pressure if my understanding is correct, the brake application being controlled by varying the air pressure on the brake pipe side and the main res pipe (or supply from the brake pipe if the main res isn't present) only being required to maintain the pressure lost through the inevitable leakage.
 

EE Andy b1

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Mk5 has a spring applied parking brake on each bogie

What is a spring parking brake?

Spring brakes for emergency braking and parking.

Spring parking brakes are not air applied like service brakes. They apply when air pressure leaves the brake chamber and release when air pressure builds up in the chamber.

So cannot understand why the parking brakes didn't apply!!
Did these sprung parking brakes have anything to do with the earlier brake problems on the Mk5 sleepers?
Hope they've not been isolated! Just my speculation.
 

Erniescooper

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What is a spring parking brake?

Spring brakes for emergency braking and parking.

Spring parking brakes are not air applied like service brakes. They apply when air pressure leaves the brake chamber and release when air pressure builds up in the chamber.
And the Mk5 has one of these spring applied parking brakes attached to one of the four callipers on each bogie.
 

O L Leigh

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Forgive my possible ignorance, possibly misunderstanding the finer details of the braking system on these vehicles relative to a conventional two-pipe system, but does the air on the reservoir side of the diaphragm get depleted to any significant extent? It should be maintained at a (nearly?) constant pressure if my understanding is correct, the brake application being controlled by varying the air pressure on the brake pipe side and the main res pipe (or supply from the brake pipe if the main res isn't present) only being required to maintain the pressure lost through the inevitable leakage.

I'm not sure I fully understand the question. The role of the main res pipe is to replenish the brake reservoirs directly (and, therefore, more quickly) than from the brake pipe alone. Air is lost from the system as the brakes are used and is replaced by the loco's compressor.

Mk5 has a spring applied parking brake on each bogie

I can only assume that the pressure in the brake pipe never fell low enough for these to engage. Even if they had, the retardation effect is generally very slight. They are, after all, only parking brakes and designed to prevent an uncoupled, unattended coach from wandering off on it's own.
 

Tomnick

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I'm not sure I fully understand the question. The role of the main res pipe is to replenish the brake reservoirs directly (and, therefore, more quickly) than from the brake pipe alone. Air is lost from the system as the brakes are used and is replaced by the loco's compressor.
On a conventional two-pipe system, the air from the main res pipe isn’t “used” as such - that side of the diaphragm in the brake cylinder is maintained at a constant pressure, the brakes being released as pressure is admitted into the adjacent chamber from the brake pipe (equalising the pressure in the two) and applied as pressure is released (creating a differential) - if I’m not mistaken (it’s been a while...).
 

diffident

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What is a spring parking brake?

Spring brakes for emergency braking and parking.

Spring parking brakes are not air applied like service brakes. They apply when air pressure leaves the brake chamber and release when air pressure builds up in the chamber.

So cannot understand why the parking brakes didn't apply!!
Did these sprung parking brakes have anything to do with the earlier brake problems on the Mk5 sleepers?
Hope they've not been isolated! Just my speculation.

This is what I was thinking. Wasn't it the brakes locking on whilst the train was moving that caused the well-discussed wheel flat episode with the Mk5's a few months back??
 

Parham Wood

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I agree with this. I do not trust that just because the problem is understood, it is presumed to be solved. I am sure those of you in the industry know mistakes or problems arise from technical failures or human ones. They both have a probability (and hence certainty) of failing at some point. Protocols and technical solutions rely then on double checks to minimise the probability of something slipping through. This sleeper incident has happened out of relatively few occasions of this particular train being split, so that indicates a vulnerability with a potential high disasterous outcome. It needs a certain assurance (through RAIB ?) of an additional protocol and/or technical double check.
Of interest:
Boeing maintains that 737 Max disasters were a complex product of probability of events. The view from others is that their new system of stabilisation of the 737 Max to level it in flight depends on only one sensor, which when failed caused the plane to push nose down. Boeing 737Max have already flown massively larger numbers of times and more hours, before the probability of failure kicked in, and then in disasterous ways. The solution looks like quietly to be installing two sensors. Corporate culture and economics are not always open to being respondent to risk.
Solution should be three sensors for such a safety critical component which is standard in the air industry. Sorry off track but could not let it go!
 

hexagon789

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Having only the brake pipe connected doesn't deplete the system. Even constantly applying and releasing the brakes won't deplete the entire system, it just makes the brake release slower. If you keep applying and releasing the brake you will come to a stand before you have a chance to fully recharge and release. The only way to fully deplete the system is to either let the air escape naturally over a period of hours or days (ie leak off) or purposely vent each vehicle in turn.

You can't run out of air to the extent that the brakes fail to apply, they just don't work like that.

So that only affects a traditional single-pipe air brake with triple valves rather than a twin-pipe with distributors working as a single pipe then?
 

Bromley boy

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on a train on which the brakes don't make the train stop, nobody knows that until they try to make the train stop and that is all fine because it is not a technical error it is just some other problem that is to he expected from time to time.

I can only assume you have been reading a different thread. Nobody has said anything of the sort on this one!
 

edwin_m

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If the problem was the reservoir pipe not being connected leading to loss of reservoir pressure over multiple brake applications in quick succession, then the obvious solution would be to do a continuity test on that pipe as well when coupling up the train. That wouldn't protect against the reservoir pipe getting disconnected in transit, though the driver would presumably be alerted to that by the loss of air pressure. I've read about it in the context of big American freight trains descending long grades, but I have no recollection of this been mentioned as a cause in a UK accident report - and I've read most of them.
 
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