Some engineers call a steam gauge a "clock." I suppose they do this
because they think it tells them when it is time to throw in coal, and
when it is time to quit, and when it is time for the safety valve to
blow off. If that is what they think a steam gauge is for, I can tell
them that it is time for them to learn differently.
It is true that in a certain sense it does tell the engineer when to do
certain things, but not as a clock would tell the time of day. The
office of a steam gauge is to enable you to read the pressure on your
boiler at all times, the same as a scale will enable you to determine
the weight of any object.
As this is the duty of the steam gauge, it is necessary that it be
absolutely correct. By the use of an unreliable gauge you may become
thoroughly bewildered, and in reality know nothing of what pressure you
are carrying.
This will occur in about this way: Your steam gauge becomes weak, and if
your safety is set at I00 pounds, it will show I00 or even more before
the pop allows the steam to escape; or if the gauge becomes clogged, the
pop may blow off when the gauge only shows go pounds or less. This
latter is really more dangerous than the former. As you would most
naturally conclude that your safety was getting weak, and about the
first thing you would do would be to screw it down so that the gauge
would show I00 before the pop would blow off, when in fact you would
have I00 or more.
So you can see at once how important it is that your gauge and safety
should work exactly together, and there is but one way to make certain
of this, and that is to test your steam gauge. If you know the steam
gauge is correct, you can make your safety valve agree with it; but
never try to make it do it till you know the gauge is reliable.