On Jul 29, 1:25*pm, Andy Dingley wrote:
On Jul 27, 7:14*pm, harry wrote:

Whether you could tell the difference as to whether steam or water was
present on opening the cock is an experiment I've never tried. *

This is basic operating practice for steam locos, as a backup for a
failed gauge glass.

There are two guage glasses. I have never known one to fail. They are
changed regularly, they get wire drawn from being blown down.
They are surrounded by a thick glass safety box to prevent accidental
damage and to protect the operator if the glass fails.
I have known a steam arm to block. We never found the reason for it
either.