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Thrust Bearing Load Observations on Enclosed Lineshaft Geothermal Production Pumps
AuthorReede, Christopher Ladd
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This thesis reports the experimental observations of thrust bearing load on deeply set enclosed lineshaft pumps operating at various shaft speeds. In an effort to validate the accuracy of techniques commonly used to estimate such loads, a load cell was installed between the lineshaft connection and the motor thrust bearing of two identical make and model pumps. The first pump operated with an open lineshaft in the manufacturer’s test lab and the second pump operated in the field with an enclosed lineshaft. The load cell allowed for real-time online measurement of impeller down-thrust encountered on the surface. The thrust measurements were normalized into thrust coefficient curves, also known as Kt curves, for various shaft speeds. At lower speeds, it is observed that both the lab pump and field pump Kt curves are in agreement. However, the curves begin to diverge as shaft speed is increased above 1,600 RPM. More specifically, Kt curves measured in the field at 1,320 RPM closely followed those measured in the lab, while Kt curves taken in the field at 2,200 RPM were up to 58% lower than the lab measured curves. The experimental data indicates that motor thrust bearings on pumps operating at the usual speed of 1,800 RPM may be loaded significantly less than expected. In addition, the impeller relative movement, with respect to pump bowls, may be significantly less than expected. Overall, the data represents a comparison between a well-established lab-tested Kt curve and the Kt curve of a single pump running in the field. Repeatability of the findings needs to be further validated through testing of additional field pumps. Further modeling is also necessary to understand and model the up-thrust mechanisms present in the enclosing tube. Such further validation is expected to highlight general conclusions, allowing for the formulation of useful correlations which account for thrust error. Such correlations will allow operators of similar pumps to better determine motor thrust bearing loads and impeller movement to ultimately increase the production of fluid on the surface.