TP25-09 Case Histories in Solving Natural Frequency

Vertical pumps servicing a cooling
tower at a co-generation facility were
experiencing premature bearing and
seal failures. The pump array, shown
in Figure 1, consisted of six 750 kW
(1,000 hp) units all discharging into a
common header. There were three
pairs of pumps, each pair supported
on a common flexible steel framing
system that spanned the walls of a
concrete sump pit. Provisions (pipe
stubs) were provided for future
expansion to include three additional
pumps, for an eventual total of nine
pumps. In the figure, six pumps and
nine discharge pipes can be seen. The
operating speed of the pumps was
900 rpm (15.0 Hz). A study was
conducted to determine whether vibration could be a contributing factor to the mechanical
problems that adversely affected the uptime of the pumps.