_a._ Steam fire-pumps should be started, to limber them up, _at least_
once a week.
Although vulcanized India-rubber is much the best material yet used
for fire-pump valves, unfortunately the brass is sometimes corroded
by the free sulphur contained in the rubber, so that if the pump is
left standing for several weeks the rubber valve discs may become
stuck to their brass seats, and, if suction has a high lift, there
may not be vacuum enough to tear all the suction valves open when
pump is started.