Influence of Abrasive Wear on Pump Behaviour of Rotary Lobe Pumps

Abstract

Double shaft rotary lobe pumps are often used for conveying slurries in liquid manure, biogas and sewage plants. Increasing abrasive wear enlarges the gaps and decreases the backflow leakage accordingly. The effects on the pump characteristic of helical toothed rotary lobe pumps were systematically analyzed and the influence factors were valuated. The research is carried out on the test stand for pumps at ATB (Fig. 1). The most important influence factors are the dimensions of head gaps and front gaps (Fig. 2, 3) as well as the viscosity of fluid. The effect of viscosity on the gap flow rate is considerably important (Fig. 4). The gap leakage rate is reduced due to increasing liquid viscosity. The effective flow rate as well as the total efficiency (Fig. 5) increases with increasing viscosity. This effect makes clear that enlarged gap dimension should be taken into consideration when pumping high viscous fluids. The effect of the pump speed on the leakage rate is negligible. Gap flow rates meas- ured on a blocked pump therefore can be taken as the leakage rates of a running pump. The effect of lobe shape (straight or helically toothed) on the leakage rate is nearly insignificant. Helically toothed lobes with high number of wings have better pump behavior then lobes with less number of wings. At high pump pressure double-side bearing rotary lobe pumps should preferably applied instead of pumps with cantilevered shafts (Fig. 6). Double-side bearing pumps have less abrasion at the lobe’s wing tips and better suction behaviour (Fig. 7). The pressure-flow characteristic curve p = f (n p ) plotted at closed discharge pipe (Fig. 8) or the direct measurement of leakage flow QS = f (p) is able to describe the pump’s wear status. Based on these tests the real pump characteristic curve can be calculated (Fig. 9).