by saying, "I thought I had plenty of water." You may be fooled in
another way. You are aware that when a boiler is fired up or in other
words has a steam pressure on, the air is excluded, so when the boiler
cools down, the steam condenses and becomes water again, hence the space
which was occupied by steam now when cold becomes a vacuum.

Now should your boiler be in perfect shape, we mean perfectly tight,
your throttle equally as tight, your pump or injector in perfect
condition and you were to' leave your engine with the hose in the tank,
and the supply globe to your pump open, you will find on returning to
your engine in the morning that the boiler will be nearly if not quite
full of water. I have heard engineers say that someone had been
tampering with their engines and storm around about it, while the facts
were that the supply being open the water simply flowed in from
atmospheric pressure, in order to fill the space made vacant by the
condensed steam. You will find further on that all check valves are
arranged to prevent any flowing out from the boiler, but nothing to
prevent water flowing in. Such an occurrence will do no harm but the
knowing how it was done may prevent your giving yourself away. A good
authority on steam boilers, says: "All explosions come either from poor
material, poor workmanship, too high pressure, or a too low gauge of
water." Now to protect yourself from the first two causes, buy your
engine from some factory having a reputation for doing good work and for
using good material. The last two causes depend very much on yourself,
if you are running your own engine. If not, then see that you have an
engineer who knows when his safety valve is in good shape and who knows
when he has plenty of water, or knows enough to pull his fire, when for
some reason, the water should become low. If poor material and poor
workmanship were unknown and carelessness in engineers were unknown,
such a thing as a boiler explosion would also be unknown.