In article , (Roland
Perry) wrote:

In message , at
08:00:08 on Wed, 18 Aug 2010, remarked:

That makes me wonder why they didn't attempt the rescue with a battery
loco or something else with compatible braking equipment.

Where would the nearest battery loco be at that time of day, and
would there be anything between it and the train needing to be
rescued (for example, some service trains).

Well, the right answer would be for the railgrinder to have a compatible
braking system or a way of adapting it. No brakes is inherently unsafe.

--
Colin Rosenstiel

In article ,
wrote:
Well, the right answer would be for the railgrinder to have a compatible
braking system or a way of adapting it. No brakes is inherently unsafe.

Or to have crew in position to re-enable a disabled braking system
while the train is in motion.

--
Mike Bristow

In article , (Mike
Bristow) wrote:

In article ,
wrote:
Well, the right answer would be for the railgrinder to have a
compatible braking system or a way of adapting it. No brakes is
inherently unsafe.

Or to have crew in position to re-enable a disabled braking system
while the train is in motion.

If they have no air and no power to get any, re-enabling will hardly help,
surely?

--
Colin Rosenstiel

On Thu, 19 Aug 2010 04:24:05 -0500
wrote:
In article , (Mike
Bristow) wrote:

In article ,
wrote:
Well, the right answer would be for the railgrinder to have a
compatible braking system or a way of adapting it. No brakes is
inherently unsafe.

Or to have crew in position to re-enable a disabled braking system
while the train is in motion.

If they have no air and no power to get any, re-enabling will hardly help,
surely?

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?

B2003

On 19/08/10 10:48, d wrote:
On Thu, 19 Aug 2010 04:24:05 -0500
wrote:
In , (Mike
Bristow) 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?

Perhaps it had a sprung parking brake, of the kind that automatically
engages when the pressure in the main reservoir is low? If it was
impossible to pressurise the air brake, such a parking brake would need
to be disabled...

-roy

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 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.

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

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.)