If the accident of low water occurs at a time where it is important to
continue operations with the least possible delay, a pine plug may be
driven in the opening left by the melting of the fusible metal. In any
event it is but a short job to renew the fusible cap, it being only
necessary to unscrew the nut and insert a new cap, the rest of the
device remaining intact.
The plug should be renewed occasionally and the surface exposed inside
the boiler be kept free from scale and deposit. It is to be understood
that the fusible portion extends entirely through the shell of the
boiler and when melted out makes a vent for the water or steam.
All marine boilers in service in the United States are required to have
fusible plugs, one-half inch in diameter, made of pure tin, and nearly
all first-class boiler makers put them in each boiler they build.