Broken Down Freight Train Near Bushey

[najaB]

Or maybe it doesn't happen very often and we're getting this out of perspective.

Yeah, maybe 'we' are.

 

[cf111]

Maybe the lessons of continuous brakes were learned. In which case it's a shame that the railway is still being let down by basic eqiupment failures now. Ever heard of engineering tolerances? or brake valves/regulators set up wrongly?
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no confirmation of the cause on that thread...
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Just saying that in the last 20 years or so I can't remember a journey spoilt by brake problems. Maybe I've just been lucky, or maybe it's that dragging brakes are very rare in a railway that is remarkably reliable in the first place.

I will dig around for accident enquiries that put the cause down to dragging brakes.

They happen - I've had one cause a HST to be cancelled between Darlington and Newcastle and they are maintained to the highest standards. It's the only time I can remember it happening in all my travels and with the best will in the world, sometimes machines will fail.

 

[ComUtoR]

Aren't they powered to come off as well as on (even if only by a spring return?)
Maybe I ought to patent a stronger spring.

I thought they were "spring applied, air released"

 

[RichmondCommu]

Assuming that a wheel set change is required along with repairs to the brakes is this something that could be carried in Wembley Yard with the train then being sent on its way? Or will the wagon have to be unloaded and sent away to a repair facility? Just curious that's all

 

[najaB]

I thought they were "spring applied, air released"

That's my understanding as well. If they were spring released then they could get stuck 'off'! hock:

 

[AndrewE]

definitely applied by compressed air pressure (which is why at 125 - 140 psi they are so much more powerful than vacuum, which can only be 1 atmosphere/14.7 psi by definition)
See the Wikipedia page and the Westinghouse / triple valve bit.

 

[DarloRich]

Assuming that a wheel set change is required along with repairs to the brakes is this something that could be carried in Wembley Yard with the train then being sent on its way? Or will the wagon have to be unloaded and sent away to a repair facility? Just curious that's all

A wheel set change on a freight wagon is pretty common "in the field". The maintainers should be able to do it quite easily in normal circumstances. The issue will be getting the vehicle somewhere you can do the work.

 

[najaB]

definitely applied by compressed air pressure...

So a train will roll if it loses air pressure?

 

[DarloRich]

Maybe it's because most of my journeys nowadays are on Pendolinos, a few Voyagers, LM EMUs on the WCML or EMUs and DMUs in the west midlands.

The same thing will have happened to everyone of those units to varying degrees. Perhaps not so bad they become welded to the track but they will have all had dragging brakes

 

[talltim]

Bearing in mind this is still subject to investigation dragging brakes can happen on any stock at any time no matter how many pre-departure checks one does.

Dragging disc brakes don't damage the tyres in the same way tho.

 

[Domh245]

That's my understanding as well. If they were spring released then they could get stuck 'off'! hock:

Indeed. I would be shocked if the railway (which prides itself on safety) had anything other than a fail-safe mechanism on brakes. I've found a RAIB bulletin into a derailment caused by dragging brakes, which might be an interesting read. It seems to suggest that the dragging brakes were caused by the distributor not working properly - I don't think that RAIB will investigate this incident however.

It is also worth noting that modern passenger units will tend to have less failures of this kind than old freight stock. How much of this is down to less stringent requirements or just poor design, I don't know

 

[talltim]

So a train will roll if it loses air pressure?

Yes, hence handbrakes. See the Lac Megantic crash for a classic example.
Most have no springs, held off by air, held on by air. I believe HST power cars have spring applied handbrakes

 

[westcoaster]

So a train will roll if it loses air pressure?

Yes which is why they have handbrakes or parking brakes.

On a 319 the parking brakes ( spring loaded) apply when the main res drops drops low, and releases when it charges.

 

[furnessvale]

I thought they were "spring applied, air released"

They are air applied AND air released. Thus, when required, the release cords can be pulled to completely release all the air and the wagon becomes unfitted.

 

[najaB]

Yes, hence handbrakes. See the Lac Megantic crash for a classic example.

Sorry, I didn't make it clear that I meant a train in service, rather than when stopped and parked (using the handbrake).

My understanding is that air pressure is used to release the brakes against the spring force that would otherwise apply the brake. A train that loses pressure while in service would stop rather than roll, would it not?

 

[doningtonphil]

That's my understanding as well. If they were spring released then they could get stuck 'off'! hock:

I think you are refering to the parking brake in the loco. Air brakes are compressed air working against the force of the spring in the brake cylinder. The spring keeps the piston unextended which through the rigging keeps the brake block off the wheel. As the brake applies air is forced into the cylinder which forces the piston out, moving the rigging which foreces the block against the wheel.

Most often, dragging brakes are caused by 'faulty' distributors. They respond to very small changes in air pressure signals. Sometimes if there is a fault, the distributor doesn't 'see' the pressure change so doesn't respond to the signal so doesn't release the brake block from the wheel when it should. The wheel is therefore either dragged along without turning or the brake blok has moved someway away from the wheel allowing it to turn but is still rubbing against it- causing a heat through friction

 

[najaB]

Ah, never mind - being stupid.

 

[ComUtoR]

They are air applied AND air released. Thus, when required, the release cords can be pulled to completely release all the air and the wagon becomes unfitted.

My traction manual is very wrong then because it states that the brakes are spring applied. Dumping all the air out the system in the event of a failure applies the brakes.

As I understand it the current system uses a series of electrical wires to do all the magic jiggery pokery with valves and governors etc working along side.

See the Wikipedia page and the Westinghouse / triple valve bit.

Again, I'm getting confused. Aren't we using Westcode EP brakes ?

We also have rheo brakes. If I remember rightly, ours is refereed to as being a "dynamic" brake as we have rheo and friction.

 

[GB]

Perhaps I ought to be glad that most of the trains I travel on don't suffer dragging brakes, but I thought this problem had been sorted out several times since the invention of continuous brakes...

Dragging brakes that damage wheels to this extent is rare. This sort of damage is normally caused by a handbrake being left on which isn't the case here.

Passenger trains do suffer dragging brakes from time to time but due to the shorter length of passenger trains it is usually picked up on pretty quickly due to either the feel of the train, the driver looking back and seeing, being reported from the lineside or station, or smell. Some modern stock have indicators in the cab.

The problem with this train is at 2300ft long the driver is not going to feel it or see it (especially when its at the rear). Being in the middle of the night no one line side or on the platforms.

We shouldn't have an intensively-used 21st century network stitched up by what sounds like a basic technical failure.
The railway's problem is that the whole system (and all customers) get stuffed by almost any lack of attention to detail by any one of the thousands of people who have to "do it right." On the road network there are a million potential culprits and no single participant gets the blame; On the railway no-one really gets blamed but the system suffers a serious reputational blow every single time.

Sorry, but blame is apportioned where due on the railways....or are you after a public flogging?

 

[axlecounter]

AFAIK, the only spring-applied brake in modern railways is the parking brake on locos and "modern" trains. This works as said, air pressure keeps the spring compressed and avoids the parking brake to be applied. When air pressure is not enough the spring extends and applies the brake, thus avoiding roll away of stock, as opposed to handbrakes, where the force is applied by... hand. This is not the same brake used in service.

The brake used for braking the train in service works with air pressure only. Air from the main reservoir pipe is stored in the brake cylinder reservoir and gets ordered in or out of the brake cylinder thus applying, reducing or releasing the brakes. This is either done mechanically with a distributor sensing air pressure changes in the brake pipe or electrically like in the EP system.

 

[AndrewE]

Sorry, but blame is apportioned where due on the railways....or are you after a public flogging?

Interesting that it wasn't a handbrake left on. Also interesting comment by Doningtonphil that faults in brake distributor valves are often the cause, in which case you would hope that technical investigations would manage to find the underlying problem and get it sorted.

Public flogging? I think that the railway industry generally tries to discover the root cause of a failure and ensure it is not repeated. Delay attribution (blame) may be a new industry in its own right, but prosecutions and punishments are rare.

Of course, now that we have so many separate businesses involved and hence potential compensation claims, there is less chance of full and open participation. (Unlike the time when there were only the Chief Mechanical and the Chief Civil Engineers' tribes blaming each other!)

 

[Deepgreen]

Well - I'm glad I asked!

 

[furnessvale]

Sorry, I didn't make it clear that I meant a train in service, rather than when stopped and parked (using the handbrake).

My understanding is that air pressure is used to release the brakes against the spring force that would otherwise apply the brake. A train that loses pressure while in service would stop rather than roll, would it not?

No springs involved. Initial air pressure charges up the reservoir on each wagon. Once each reservoir is full, reducing the pressure in the train pipe allows the reservoir air to apply the brakes. Increasing air pipe pressure blows the brakes off again.

A wagon disconnected from a train will initially have a full brake application. Over time, the reservoir air will leak off releasing the brakes which is why there is a separate handbrake fitted.

 

[najaB]

No springs involved. Initial air pressure charges up the reservoir on each wagon. Once each reservoir is full, reducing the pressure in the train pipe allows the reservoir air to apply the brakes. Increasing air pipe pressure blows the brakes off again.

A wagon disconnected from a train will initially have a full brake application. Over time, the reservoir air will leak off releasing the brakes which is why there is a separate handbrake fitted.

Yup, like I said - I was being stupid. This is what happens when you think out loud.

 

[Tomnick]

So a train will roll if it loses air pressure?

Indeed. I would be shocked if the railway (which prides itself on safety) had anything other than a fail-safe mechanism on brakes.

Sorry, I didn't make it clear that I meant a train in service, rather than when stopped and parked (using the handbrake).

My understanding is that air pressure is used to release the brakes against the spring force that would otherwise apply the brake. A train that loses pressure while in service would stop rather than roll, would it not?

As others have explained, the various braking systems are fail-safe in as much as that they should stop a train if there's a loss of air pressure, using the air pressure in the brake supply reservoir to do so. On a single-pipe air system, where the reservoir is charged from the brake pipe, the loss of air in the brake pipe will (through the distributor, as though it was responding to a brake application initiated by the driver) cause the brakes to be applied. On a twin-pipe system, where the reservoir is normally charged from the (higher pressure) main reservoir pipe, a loss of pressure in that pipe will effectively (and automatically) make the system revert to single-piped by a couple of non-return valves. On an EP system, where the air pressure to apply the brakes is controlled by electrical signals along the train, a drop in main res pressure below a certain level is detected, causing the brakes to apply along the length of the train (again using the air in the brake supply reservoir that's charged from the main res). In all cases, that'll at least bring the train to a stand.

(a good chance for some revision, thanks!)

My traction manual is very wrong then because it states that the brakes are spring applied. Dumping all the air out the system in the event of a failure applies the brakes.

As I understand it the current system uses a series of electrical wires to do all the magic jiggery pokery with valves and governors etc working along side.

Again, I'm getting confused. Aren't we using Westcode EP brakes ?

I don't know what traction that is, but it'll be very different to the system on wagons such as these! As above, the brakes are applied using air pressure, with a 'fail-safe' system to bring the train to a stand if the air supply is lost. Once it's at a stand, with no main res (or brake pipe) air to recharge the system, the brakes will gradually leak off. That's where the spring applied parking brake on units comes into play - normally held off by main res pressure - on units, once the main res drops below a certain level. I doubt it'd be strong enough to bring the train to a stand from any sort of speed though (hence the 5mph restriction in the Rule Book for any movement with the brakes on the leading or trailing vehicle isolated, with certain exceptions, where you'd be relying on the application of the parking brake to stop the vehicle in an emergency, i.e. if the train becomes divided). There's no such thing on wagons, coaching stock etc. though, hence the reliance on a handbrake or otherwise securing the train.

 

[doningtonphil]

Interesting that it wasn't a handbrake left on. Also interesting comment by Doningtonphil that faults in brake distributor valves are often the cause, in which case you would hope that technical investigations would manage to find the underlying problem and get it sorted.

Public flogging? I think that the railway industry generally tries to discover the root cause of a failure and ensure it is not repeated. Delay attribution (blame) may be a new industry in its own right, but prosecutions and punishments are rare.

Of course, now that we have so many separate businesses involved and hence potential compensation claims, there is less chance of full and open participation. (Unlike the time when there were only the Chief Mechanical and the Chief Civil Engineers' tribes blaming each other!)

Investigations often do go on into why a distributor caused a brake drag. The distributor is tested on a rig and then dismantled methodically. The tiny components and springs that make up a distributor and the relatively small changes in air pressure they are designed to detect and respond to means that it can be a very small component issue that causes the problem. This might be caused by a tiny bit if contamination from the air supply, or a component not moving as freely as it should.

With the age of a lot of the valves on locomotives and wagons, often it has to be put down to 'one of those things'. No blame can be attached.

Distributors are something operators of wagons and coaching stock like to keep a few spares of on the shelf. They are a 'hot swap' item which cause very little surprise if they don't last the full length of an overhaul period