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.)