Understand Progressing Cavity Pumps Characteristics And A Void Abrasive Wear
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Progressing cavity pumps develop their pumping action by the meshing of the external threads of the elastomer stator and the internal threads of the metallic rotor. The special geometry, as characterized by the different pitches of stator and rotor threads and the eccentric motion of the rotor, is creating the displacement chambers, which are periodically discharging by superposition, a constant flow against the pressure differential. The authors report on the influencing parameters on pump performance with respect to flow-speed-characteristics, volumetric and energetic efficiency and starting toque. In all cases, the rotor/stator overlapping is featuring remarkable influences. Clearances between stator and rotor increase the internal leakages and decrease mechanical friction. Overlapping rotor/stator design yields internally tight pumps, but increased mechanical friction. With theoretical and experimental investigations, an understanding of the pump performance is presented. The tests clearly show an optimum of energetic efficiency to exist for a certain overlapping factor. The theoretical modelling of the pump performance proves to be very difficult, due to tolerances on clearance dimensions from manufacture and thermal or chemophysical expansion as well. But nevertheless, a first rule of thumb for estimating pump efficiency based on leakflow tests and determination of the friction coefficient u by means of a tribometer are given. Furthermore, hydroabrasive wear tests and possibilities of theoretical modelling are given. As progressing cavity pumps are frequently used for such applications as transporting abrasive suspensions and slurries, this subject is very important and implementing a new scientific approach. The tribological system in the pump in that service is dominated by sliding hydroabrasive wear. The wear mechanisms is explained and a model presented by considering the intermeshing geometry and the relative time interval for contact of a stator surface element. Field tests with progressing cavity pumps using quartz-suspensions and different materials selection demonstrate basically good correlation with the model, indicating clearly that the wear rate varies strongly with the local position on the rotor surface. A large number of tribological tests conducted with a special rotary sliding tribometer that is simulating the rotating and oscillating motion in the progressing cavity pump quite closely, delivered wear rates correlating quantitatively with field test results and, thus, offer a rough possibility for endurance prediction. Based on tribological tests with the adequate tribometer and the real pumping fluid, the optimum pump design may be elaborated.
Vetter, Gerhard; Wirth, Wolfgang (1995). Understand Progressing Cavity Pumps Characteristics And A Void Abrasive Wear. Turbomachinery Laboratories, Department of Mechanical Engineering, Texas A&M University. Available electronically from