This constant vigilance on the part of
operators was trying, so feedwater
regulators were developed which control
the flow automatically as the water in the
boiler drum rises and falls. These are very
helpful even with small boilers but in the
case of modern high-pressure boilers they
are almost imperative. A large highpressure
boiler, evaporating in the neighborhood
of a million pounds of water per
hour would run dry in about 90 seconds
if the water supply was suddenly cut off.