Brake vans - why?

[CAF397]

The mk5 sleeper stock, yes it's the seated coach.
Not sure about the mk5a stock but it would make sense for it to be the driving trailer.

No handbrake in the driving trailer. An electrically applied parking brake button which controls only the parking brake on the Class 68, and every vehicle has spring applied, air released parking brake.

 

[trebor79]

Because the vacuum brake will leak off over a period of time.

The engine running will maintain the vacuum,

No, it won't, not on the side of the cylinder that is never open to atmosphere unless the handle is in the "release" position.
Loomat a diagram of a vacuum brake cylinder to understand why this is the case.
There was even a Mk1 dmu that ran away whilst on the move because the distracted driver had left the brake handle in the lap position and hence the vacuum had leaked off.

 

[Ken H]

The engine running will maintain the vacuum, but if unattended there is always the risk that the engine will stop and nobody will notice. That was also contributory to Lac Megantic - the one locomotive left with engine running caught fire and the engine was shut down by the fire brigade, after which the air brakes leaked off and not enough hand brakes had been applied to hold the train.

So basically, an unattended train should have a parking brake put on? Is that in the rule book today, or do modern trains not have this issue?

 

[edwin_m]

So basically, an unattended train should have a parking brake put on? Is that in the rule book today, or do modern trains not have this issue?

It's been in the rule book from time immemorial, although as mentioned above modern multiple units have a parking brake that applies automatically if the air leaks off.

No, it won't, not on the side of the cylinder that is never open to atmosphere unless the handle is in the "release" position.
Loomat a diagram of a vacuum brake cylinder to understand why this is the case.
There was even a Mk1 dmu that ran away whilst on the move because the distracted driver had left the brake handle in the lap position and hence the vacuum had leaked off.

That seems a fairly serious defect in the two-pipe vacuum system, which I believe doesn't apply to the two-pipe air brake.

 

[driverd]

And I thought modern train brakes were "fail safe" - leaky pipe means loss of compressed air (or vacuum) means brakes come on. So how can the brakes on a parked train with no power source leak off?

Precisely the question that I asked at the start of the thread (perhaps in different words) & is as yet not completely answered.

So to be more specific.

1. Does the above principle (aka - spring applied air released) apply to mk1/2/3/4 stock (intended as a question for each type of stock)

If not, what's the fail safe incase of a train division?

2. If this principle does apply to any of the above trains, why do we bother with a brake van when there are parking brakes?

3. If these vehicles don't have a parking brake, why not? Surely it's sensible, given its a principle that's been used on DMUs and EMUs for a good 40 years.

 

[trebor79]

That seems a fairly serious defect in the two-pipe vacuum system, which I believe doesn't apply to the two-pipe air brake.

Vacuum brakes are a one pipe system.

 

[AndrewE]

Vacuum brakes are a one pipe system.

Apart from 1st generation DMUs which were 2-pipe for quicker release.

 

[Bill57p9]

Vacuum brakes are a one pipe system.

First generation DMUs had 2 vacuum pipes. I believe the second one was the vacuum reservoir, in a parallel to the 1vs 2 pipe air brake system.

 

[edwin_m]

1. Does the above principle (aka - spring applied air released) apply to mk1/2/3/4 stock (intended as a question for each type of stock)

No, no, no and no.

If not, what's the fail safe incase of a train division?

Each coach has an air reservoir. If the train is divided, pressure in the train pipe drops to zero and this causes a valve on each coach to operate, sending air from the reservoir into the brake cylinders to apply the brakes. However if there is no operational compressor (only on the locomotive in a loco-hauled train) the air will gradually leak off and this brake becomes ineffective after a period of hours. Springs aren't really strong enough to apply a brake with enough force to stop a moving train, but they can hold a train that's already stopped.

2. If this principle does apply to any of the above trains, why do we bother with a brake van when there are parking brakes?

The only parking brake is one applied by hand in the brake coach.

3. If these vehicles don't have a parking brake, why not? Surely it's sensible, given its a principle that's been used on DMUs and EMUs for a good 40 years.

Discussed above, but probably down to cost and "we've always done it that way".

 

[Ashley Hill]

brakes in the power car which shoule be the adjacet vehicle in the train

The guards van used to be in the power cars and the hand brake controls,brake setter and gauge are still in them. After NUR intervention due to complaints of excessive noise and rough riding some of the mk3 HST cars were converted to TGS vehicles but with only a PassCom provided.

 

[Trackman]

No, it won't, not on the side of the cylinder that is never open to atmosphere unless the handle is in the "release" position.
Loomat a diagram of a vacuum brake cylinder to understand why this is the case.
There was even a Mk1 dmu that ran away whilst on the move because the distracted driver had left the brake handle in the lap position and hence the vacuum had leaked off.

Was that the Football special at Preston? Think he was distracted by the organiser who sat up front.

 

[43096]

After NUR intervention due to complaints of excessive noise and rough riding some of the mk3 HST cars were converted to TGS vehicles but with only a PassCom provided.

The TGS vehicles were built new, they weren't conversions.

 

[driverd]

No, no, no and no.

Thank you for such a succinct response - I won't quote the whole reply but its very much, appreciated that you answered all my questions!

Final question is, when a train is divided for shunting purposes, does isolation of the MRPIC at the end of each carriage prevent the air loss than applies the emergency brakes? Or does something else need to be isolated to enable shunting without a compressor?

Many thanks again!

 

[Gloster]

The guards van used to be in the power cars and the hand brake controls,brake setter and gauge are still in them. After NUR intervention due to complaints of excessive noise and rough riding some of the mk3 HST cars were converted to TGS vehicles but with only a PassCom provided.

The TGS were new builds, not conversions of existing coaches, although they were based on the normal TS design. It is just possible that the numerically first vehicle (44000) used a vehicle that had been originally been intended to be a TS.

 

[43096]

The TGS were new builds, not conversions of existing coaches, although they were based on the normal TS design. It is just possible that the numerically first vehicle (44000) used a vehicle that had been originally been intended to be a TS.

44000 used the last vehicle originally ordered under lot 30939 (which would have been 42306). Lot 30953 was issued for the change.

 

[PupCuff]

Thank you for such a succinct response - I won't quote the whole reply but its very much, appreciated that you answered all my questions!

Final question is, when a train is divided for shunting purposes, does isolation of the MRPIC at the end of each carriage prevent the air loss than applies the emergency brakes? Or does something else need to be isolated to enable shunting without a compressor?

Many thanks again!

No, the main reservoir pipe just 'tops up' the auxiliary reservoir on each vehicle. Isolation of the main reservoir pipe would just mean that the auxiliary reservoirs on any vehicle affected by the isolation would get filled via the brake pipe instead (single pipe working).

If you're shunting without a compressor then you'd be shunting without brakes. Your brake pipe should already have been discharged, applying the brakes, prior to the train being divided. You'd then hook on a locomotive and build up the air in the brake pipe again to release the brakes. Vehicles are fitted with a control to release the air from the brake cylinders if you needed to run the vehicle unbraked however shunting unbraked carries a lot of risk (eg the train becoming detached and being unable to be stopped as it doesn't have working brakes).

 

[Ken H]

I need a memory jog. I seem to remember reading a precis of an accident report in Modern railways some years ago. There was something about yard staff 'pulling a string' to release pressure in the brake reservoir. I think it was to allow loose shunting. It caused some sort of runaway incident.
And are brake continuity tests still a thing in todays railway? and if not, why not? There was another accident report I read about a train running away because some brake cocks were left closed and there was not enough brake force to control the train on a falling gradient. Again I am working from memory.

 

[hexagon789]

I need a memory jog. I seem to remember reading a precis of an accident report in Modern railways some years ago. There was something about yard staff 'pulling a string' to release pressure in the brake reservoir. I think it was to allow loose shunting. It caused some sort of runaway incident.
And are brake continuity tests still a thing in todays railway? and if not, why not? There was another accident report I read about a train running away because some brake cocks were left closed and there was not enough brake force to control the train on a falling gradient. Again I am working from memory.

Certainly for loco-hauled trains, the runaway at Edinburgh Waverley with the Caledonian Sleeper in August 2019 was directly related to the order in which the brake test was performed in relation to other duties that necessitated working at track level.

Essentially on splitting the Glasgow and Edinburgh portions, the brake test was performed satisfactorily. However, afterwards an ETS jumper was connected up and issues with trying to connect this jumper were thought likely to have resulted in the accidental closure of a brake pipe cock, isolating the coach brakes from the loco and leading to the failure to comply with certain speed restrictions at Haymarket and Waverley and overruning the platform at Waverley as only the locomotive brakes were able to be operated by the driver.

There's also running brake tests as well to ascertain how the brakes are actually performing in terms of retarding the train.

 

[Bletchleyite]

I would guess that they had so much portion working, with odd through coaches being dropped off and attached all over the place, that you couldn't rely on a braked vehicle (or a pilot loco) being coupled to any particular portion all the time, so each individual coach needed its own handbrake.
We used to have it (to a more limited extent) but continental trains retained through coaches to a wide variety of destinations long after BR went to the single "block-train" principle for passenger trains as well as freight.

Yes, true, a RIC coach is very much treated as a self-contained thing, a bit more like an unpowered Class 153 than the way the UK has used LHCS in recent years.

 

[edwin_m]

I need a memory jog. I seem to remember reading a precis of an accident report in Modern railways some years ago. There was something about yard staff 'pulling a string' to release pressure in the brake reservoir. I think it was to allow loose shunting. It caused some sort of runaway incident.
And are brake continuity tests still a thing in todays railway? and if not, why not? There was another accident report I read about a train running away because some brake cocks were left closed and there was not enough brake force to control the train on a falling gradient. Again I am working from memory.

I don't recall your first incident but the "string" is the predecessor of the control to release the air as mentioned by @PupCuff.

Your second one may be this: https://www.gov.uk/raib-reports/rep...trol-on-a-sleeper-train-approaching-edinburgh

The driver was unable to stop the train because the brake pipe isolating cock on the leading end of the leading coach was closed. This prevented the brakes on all the coaches from operating when demanded by the driver, although the driver still had control of the brake systems on the locomotive.

The isolating cock became closed during coupling operations when the Edinburgh train was split from the Glasgow train at Carstairs station; this happened after the mandated brake continuity test had been completed. The closure of the valve was therefore undetected prior to the train’s departure from Carstairs.

The isolating cock is used to seal the brake pipe at the end of the train.

 

[trebor79]

Was that the Football special at Preston? Think he was distracted by the organiser who sat up front.

That's the one.

Vehicles are fitted with a control to release the air from the brake cylinders if you needed to run the vehicle unbraked however shunting unbraked carries a lot of risk (eg the train becoming attached and being unable to be stopped as it doesn't have working brakes)

Doesn't it just. Many years ago I was a volunteer at a small preserved railway. One non-operating day we were going a fairly lengthy shunt in the yard, which involved using the main running line as a headhshunt. Line was at a 1 in 42 gradient shortly after leaving the yard.
So there's 18 year old me driving the 03, with several coaches, a dogfish ballast waggon, crane, crane runner and a dead 4-6-0 tender steam locomotive in tow. Some vehicles were unbraked and for convenience we'd pulled the cords on the vacuum braked stuff as it was in the middle of the consist and loose couple everything.
So I'm a fair way onto the running line when I get the stop signal from the shunter, the far end of the consist having cleared the points. Put the air brake in and for a moment nothing happened. Then I became aware of actually accelerating as the momentum overcame the brakes. There was a bit on an "oh ****" moment and I started wondering what to do. Fortunately I'd been sensible enoght to only be at walking pace in the first place, and a severe bend and slight easing of the gradient was just enough to stop, eventually. Starting back up the hill was also interesting.
That was pretty scary on a clear single line. The guy at the front of the runaway CS or Preston football special must have experienced panic of many multiples what I did that day.

 

[cjmillsnun]

Automatic brakes ( Vacuum or Westinghouse ) were mandated in the UK in 1889.
Not sure of the exact date on the continent but there was a runaway of a heavy passenger train in France in 1917 that only had the Westinghouse brake on the first 3 coaches.

I think you are referring the the Saint-Michelle-de-Maurienne derailment of 12 December 1917. 675 dead and still France’s worst railway accident.

 

[83G/84D]

Where I used to work a Mk 3 sleeper ran away a short distance down a siding after the brakes bled off. The wheels were not chocked as they should have been.

 

[The Lad]

In the 1st generation DMUs as indeed in other coaching stock the Vacuum holding the brake on, is in the top of the cylinders and is only replenished when the brakes are released. The intention of the two pipe system was to provide a source of high vacuum to give a quick release rather than to maintain the brake.

 

[driverd]

Thank you all all the very informative replies!

In the 1st generation DMUs as indeed in other coaching stock the Vacuum holding the brake on, is in the top of the cylinders and is only replenished when the brakes are released. The intention of the two pipe system was to provide a source of high vacuum to give a quick release rather than to maintain the brake.

Having never worked with vacuum stock, am I correct in thinking the vacuum holds the brakes off (assuming springs apply them?) - the fail safe being loss of vacuum applies the brakes? Or is this completely incorrect?

 

[Annetts key]

Incorrect configuration of a locomotive braking system when coupled to an air braked train can also result in a runaway train. That happened to a mail train, where only the brakes on the locomotive were operational. The train ran into the back of a freight train at Lawrence Hill, Bristol. The driver jumped out of the cab as he saw the road over rail bridge “approaching”, but the cab stopped just in time...

Look at these You Tube videos:

 

[hexagon789]

In the 1st generation DMUs as indeed in other coaching stock the Vacuum holding the brake on, is in the top of the cylinders and is only replenished when the brakes are released. The intention of the two pipe system was to provide a source of high vacuum to give a quick release rather than to maintain the brake.

I understood the other consideration was the DMUs used belt-driven exhausters, so when the engines were at idle the exhauster speed would be slower and thus the brake release would be very slow. Adding the high-vacuum resolved this.

Thank you all all the very informative replies!



Having never worked with vacuum stock, am I correct in thinking the vacuum holds the brakes off (assuming springs apply them?) - the fail safe being loss of vacuum applies the brakes? Or is this completely incorrect?

There are no spring applied brakes on vacuum stock.

The loss of vacuum does indeed apply the brakes, creating a vacuum releases them, but as with air braked stock natural leaks will bleed the brakes off over time and so when parked up use of a handbrake (and if necessary chocks) is needed.

 

[Bletchleyite]

Vacuum braking does use springs, at least in its most basic form. The vacuum holds them off, the springs apply them.

 

[Efini92]

I need a memory jog. I seem to remember reading a precis of an accident report in Modern railways some years ago. There was something about yard staff 'pulling a string' to release pressure in the brake reservoir. I think it was to allow loose shunting. It caused some sort of runaway incident.
And are brake continuity tests still a thing in todays railway? and if not, why not? There was another accident report I read about a train running away because some brake cocks were left closed and there was not enough brake force to control the train on a falling gradient. Again I am working from memory.

Brake continuity tests aren’t required on EP braked trains as to get brake release proves the system has continuity.
Air braked trains are still required to have a brake test.

 

[hexagon789]

Vacuum braking does use springs, at least in its most basic form. The vacuum holds them off, the springs apply them.

The springs in brake cylinders push the pistons back and thus take the brake blocks out of contact with the wheel rims - ie releasing the brakes.