Technical Articles

Typical vertical pump types include turbine, mixed and axial flow. The Hydraulic Institute classifies these pumps as type VS (Vertically Suspended). Unlike horizontal pumps, these pumps typically have the pumping element (impeller, diffuser, column pipe and pump shaft) submerged in the pumpage. Therefore, the metallurgy of all pump components must be compatible with the pumpage to achieve adequate life (MTBF).

More than 15 years ago, a 160 in plate mill was experiencing significant maintenance problems with its descaling pumps; the typical mean time between repairs was only 6 to 8 months. Some rebuilt pumps even failed on start-up.
Descaling is one of the more severe, but critical, services in a steel mill. The pressures are high and the rapid changes in flows and pressures severely impact the pumps. At the same time, the pumps' performance can significantly impact the quality of the steel produced.

An 1,800 MW power station in the Midwest experienced constant trouble with four of its four-stage boiler feed pumps, which were driven by steam turbines and operated at variable speed to meet the required plant load. According to the plant, these pumps had always exhibited high vibration. In 2003, the plant approached an aftermarket service provider to resolve this problem. Unfortunately, the pumps were not fitted with vibration monitoring equipment, so vibration trends were not readily available. Since the problem existed on all four pumps, a systematic analysis was recommended to determine the root cause.