Design of a new-concept conical positive displacement slurry pump for continuous de-clogging

Abstract

Slurry pumps are extensively used in the construction industry while positive displacement screw pumps are used in most mobile concrete pump applications. The aggregate size is known to significantly affect pump performance in terms of clogging. Large aggregates tend to be trapped against the stator-rotor interface, blocking the continuous and smooth operation of the screw pump. In order to avoid the development of excessive stress values able to damage the rotor-stator mechanism of the pump, the typical de-clogging mechanism deployed by most positive displacement screw slurry pumps includes reversing the rotation of the pump driving motor thus allowing the aggregates to be carried away with the mixture, so that the pump can soon resume its operation. This procedure causes frequent start-stops of the pump resulting in dis-continuation of the pumped mixture lasting a few seconds, that while being of little importance in most construction applications, can be of significance in applications requiring higher levels of accuracy and continuous mixture flow. In the context of this work, a novel concept of positive displacement screw slurry pump is presented, including a continuous de-clogging mechanism, without the need to reverse the rotation of the driving motor. This de-clogging operation is achieved through the modification of the geometry of both the rotor and stator introducing a conical form along the axial direction. This configuration of the rotor-stator, allows for small displacements along the axial direction, which in turn increases the size of the cavities facilitating the de-clogging of the pump. Variable pitch is also introduced to both the rotor and stator in order to ensure constant mass flow of the mixture throughout the length of the screw pump covering for the velocity increase as a result of the conical geometry. The axial movement of the rotor in relation to the fixed stator, is achieved through the elastic support of the rotor in the axial direction, that allows for small axial displacements, when stresses induced from trapped aggregates exceed the stiffness of the support. The proposed concept comprises a passive real-time de-clogging mechanism that greatly reduces pump idle time compared to the conventional mechanism described earlier, providing smoother operation and stable mass flow of the mixture.