On 19/08/2010 21:13, Johannes Patruus wrote:

The latest piece in the Evening Standard has some more details from a
"leaked memo" - http://bit.ly/dufn0J

JP
I wonder if passengers on the train that was ordered to run would be
able to claim for that.

On Thu, Aug 19, 2010 at 09:48:11AM +0000, d wrote:

Surely it has some sort of handbrake? How else could it be parked safely
for long periods when the air will have all leaked out?

Uh, aren't railway brakes held *off* by vacuum, as opposed to being held
*on* by air?

That's fail-safe - lose power or burst a pipe and the vacuum goes away,
and the brakes go on. Of course, this doesn't help if you've
deliberately disabled the braking system, but I would expect the
operating procedures to only permit that if there is a hand-operable
braking system, even if it's just screwing a shoe down onto the wheels
and really ****ing up the wheels. I await the RAIB report with
interest. They're usually good reading as well as being informative.

--
David Cantrell | Hero of the Information Age

I remember when computers were frustrating because they did
exactly what you told them to. That seems kinda quaint now.
-- JD Baldwin, in the Monastery

On Fri, 20 Aug 2010, David Cantrell wrote:

On Thu, Aug 19, 2010 at 09:48:11AM +0000, d wrote:

Surely it has some sort of handbrake? How else could it be parked safely
for long periods when the air will have all leaked out?

Uh, aren't railway brakes held *off* by vacuum,

Once upon a time, but, UIVMM, not for several decades.

as opposed to being held *on* by air?

They're held both on and off by air. Pressure from a reservoir pushes them
on, and pressure from a brake pipe pushes them off. Whichever has the most
pressure wins.

The problem with the vacuum system is that you can never have more than
one atmosphere of pressure pushing the brake on, because that's all you
can ever muster to keep it off. Whereas with air, you can have as much
pressure as you like in the reservoir, as long as you can summon up the
same amount of pressure in the brake pipe to keep the brake off.

That's fail-safe - lose power or burst a pipe and the vacuum goes away,
and the brakes go on.

This is still the case with the current system - if the brake pipe comes
unstuck or the power to the compressor fails, its pressure drops, and the
pressure in the reservoir will overcome it, and apply the brakes.

The weakness, of course, is the reservoir. If it isn't filled (eg a train
has been parked for ages), or it runs out (eg a train has parked
recently), or it leaks or is vented by mistake, you've lost your ability
to apply the brake. I don't know how this is dealt with - i would guess by
making the reservoir quite large and very reliable (and it is, after all,
just a big tank with a pipe coming out of it), although this doesn't
address the cold start problem.

Of course, this doesn't help if you've deliberately disabled the braking
system, but I would expect the operating procedures to only permit that
if there is a hand-operable braking system, even if it's just screwing a
shoe down onto the wheels and really ****ing up the wheels.

Exactly. The sort of thing that in nuclear power engineering is called a
scram - a last-ditch, absolutely foolproof, not necessarily recoverable,
way of stopping a runaway.

tom

--
i know how they do it i think they just put on a song then the mario thing
plays it i think im not sure though im still looking on it -- darkcat102

On Thu, 19 Aug 2010, Paul Scott wrote:

"Tom Anderson" wrote in message
rth.li...
On Wed, 18 Aug 2010, martin wrote:

Something that I don't think had previously been released:

The crew of the grinding unit, who had no means of re-applying the
brake, jumped off the unit as it passed through Highgate station.

J. Jesus Krispy Kreme Christ on a Borisbike!

'no means of re-applying the brake' is a rather frightening phrase. I
would hope trains were not constructed in such a way that this could
ever be the case, but they are evidently not. Indeed, AIUI, air brakes
work by having a reservoir on each car that drives brake application
when the pressure in the brake pipe drops, but if there is no
compressor in action, as here, then this reservoir will be empty, and
there will be no pressure to apply the brakes even in the absence of
brake pipe pressure. Seems like a bit of a loophole in the fail-safety,
but i'm not sure what else you can do. Presumably a spring does not
supply enough force to apply the brakes!

Why assume it even has a conventional railway air brake system. We're talking
about a large item of yellow plant brought in to the system that is designed
to work independently?

I thought i'd read somewhere that it was a converted tube train, which
would suggest that it might have retained conventional brakes. However, i
now think i imagined that, and that it was this newish Schweerbau machine:

http://www.rtmjobs.com/rail-news/art...on-uk-railway/

Now, the RAIB press report talks about, at first, a train "designed for
re-profiling worn rails", but then about a "grinding unit", whereas this
is a milling machine, which is subtly different. However, the difference
is subtle, so it might get called a grinding machine by mistake, and i
have also seen it asserted that it is a combined grinding and milling
machine, so it might even be correct.

So, we know that the unit involved in the incident was (a) a rail
re-profiler of some sort, (b) operated by Tube Lines, (c) diesel powered,
(d) working on the Northern line, (e) similar-looking to a passenger tube
train, and all of those fit the train described in that article.

Reports earlier that it was an 'engineering train' and pictures of
normal LU battery locos aren't necessarily helping as far as I can see.
It's just as possible that it has never been designed to form part of a
'train' as everyone is assuming...

That is true.

tom

--
i know how they do it i think they just put on a song then the mario thing
plays it i think im not sure though im still looking on it -- darkcat102

In message . li, at
20:20:22 on Fri, 20 Aug 2010, Tom Anderson
remarked:
http://www.rtmjobs.com/rail-news/art...-rail-mounted-
milling-machine-trials-on-uk-railway/

Running rails on two stretches of the Northern line – above
ground between Colindale and Golders Green and in the tunnel
from Mornington Crescent to Warren Street – will be milled at
night using the specially developed machine.

Yes, that sounds a lot like what may have been going on.
--
Roland Perry

On 2010-08-20, David Cantrell wrote:
On Thu, Aug 19, 2010 at 09:48:11AM +0000, d wrote:

Surely it has some sort of handbrake? How else could it be parked safely
for long periods when the air will have all leaked out?

Uh, aren't railway brakes held *off* by vacuum, as opposed to being held
*on* by air?

Vacuum brakes are held off by the vacuum, if the air gets in they go on.

Air brakes are held off by the air pressure, and if the air gets out
they go on.

Both fail-safe, unless you try to mix them in the same train (in which
case you have to treat one lot as unbraked - there were rules about it).

Is there anywhere other than Britain where both were in use on the same
railway other than as a short transition period?

Eric

"Tom Anderson" wrote in message
rth.li...

I thought i'd read somewhere that it was a converted tube train, which
would suggest that it might have retained conventional brakes. However, i
now think i imagined that, and that it was this newish Schweerbau machine:

http://www.rtmjobs.com/rail-news/art...on-uk-railway/

Now, the RAIB press report talks about, at first, a train "designed for
re-profiling worn rails", but then about a "grinding unit", whereas this
is a milling machine, which is subtly different. However, the difference
is subtle, so it might get called a grinding machine by mistake, and i
have also seen it asserted that it is a combined grinding and milling
machine, so it might even be correct.

So, we know that the unit involved in the incident was (a) a rail
re-profiler of some sort, (b) operated by Tube Lines, (c) diesel powered,
(d) working on the Northern line, (e) similar-looking to a passenger tube
train, and all of those fit the train described in that article.

The (pretty small) picture on the RAIB investigation summary page:

http://www.raib.gov.uk/publications/...te_runaway.cfm

....seems to match this one more closely, the RGU 2000.

http://world.nycsubway.org/perl/show?65269

Compare the trapezoidal windows, rather than the new SFU machine's more
rounded shape:

Paul S

On 20 Aug, 21:47, Eric wrote:
On 2010-08-20, David Cantrell wrote:

On Thu, Aug 19, 2010 at 09:48:11AM +0000, wrote:

Surely it has some sort of handbrake? How else could it be parked safely
for long periods when the air will have all leaked out?

Uh, aren't railway brakes held *off* by vacuum, as opposed to being held
*on* by air?

Vacuum brakes are held off by the vacuum, if the air gets in they go on.

Air brakes are held off by the air pressure, and if the air gets out
they go on.

Both fail-safe, unless you try to mix them in the same train (in which
case you have to treat one lot as unbraked - there were rules about it).

Is there anywhere other than Britain where both were in use on the same
railway other than as a short transition period?

Eric

How does this fit with the case of the trucks that ran away into St
Pancras after the brakes had gone on automatically but eventually
released?

(This was the time that the brakes went on as the driver started to
pull away, and he went to the "back" thinking someone had nicked his
back light and opened the pipe, without it occurring to him that the
coupling had broken, leaving a couple of trucks further back.)

On Fri, 20 Aug 2010, MIG wrote:

On 20 Aug, 21:47, Eric wrote:
On 2010-08-20, David Cantrell wrote:

On Thu, Aug 19, 2010 at 09:48:11AM +0000, wrote:

Surely it has some sort of handbrake? How else could it be parked safely
for long periods when the air will have all leaked out?

Uh, aren't railway brakes held *off* by vacuum, as opposed to being held
*on* by air?

Vacuum brakes are held off by the vacuum, if the air gets in they go on.

Air brakes are held off by the air pressure, and if the air gets out
they go on.

How does this fit with the case of the trucks that ran away into St
Pancras after the brakes had gone on automatically but eventually
released?

(This was the time that the brakes went on as the driver started to
pull away, and he went to the "back" thinking someone had nicked his
back light and opened the pipe, without it occurring to him that the
coupling had broken, leaving a couple of trucks further back.)

Sounds like the main failure mode that air brakes have that vacuum brakes
don't: if you run out of air in your reservoir, then even in the absence
of pipe pressure, the brakes will release.

Again, i would have thought there would be a second-layer failsafe
mechanism that applies some other brake in the absence of reservoir
pressure (this could be as simple as a spring adding some air-independent
force to the brakes, requiring a surplus of pipe pressure over reservoir
pressure to release the brakes), but perhaps there isn't. Anyone know a
good book on railway brakes?

tom

--
Oh, and sometimes in order to survive you have to drink the irradiated
water from an old toilet. -- Jon, on Fallout

On Fri, 20 Aug 2010 19:46:24 +0100, Tom Anderson
wrote:

The weakness, of course, is the reservoir. If it isn't filled (eg a train
has been parked for ages), or it runs out (eg a train has parked
recently), or it leaks or is vented by mistake, you've lost your ability
to apply the brake. I don't know how this is dealt with - i would guess by
making the reservoir quite large and very reliable (and it is, after all,
just a big tank with a pipe coming out of it)

Part of it is additionally that trains tend to run with more than one
vehicle (not always, I know), and each has its own reservoir. Thus,
if in a 6-car train 2 cars lose their braking system completely, it
will still stop.

Exactly. The sort of thing that in nuclear power engineering is called a
scram - a last-ditch, absolutely foolproof, not necessarily recoverable,
way of stopping a runaway.

On the railway that's often handled off the vehicle by a set of catch
points, which are basically points that deliberately derail the train
and send it off into a sand drag or something. Not that useful on
LUL, though.

For engineering work, derailer ramps are often fitted at each end to
catch any runaway and stop it by sending it off the track in the same
sort of way. Maybe that's something LUL should look at doing - though
if it had happened here the two engineering staff on the runaway might
well not have survived the experience.

Neil
--
Neil Williams in Milton Keynes, UK
To reply put my first name before the at.