Development of a conceptual test rig for an adaptive mechanism in wastewater pumps : Design and evaluation of a test setup for impellers with adaptive mechanisms at Xylem

Sammanfattning

Wastewater pumps function in harsh environments filled with debris and larger objects such as gravel and wet wipes. Fibrous materials prevent the pump impeller from rotating, causing clogging, leading to increased operational and maintenance costs. To reduce clogging, Xylem has developed an adaptive mechanism within the impeller that allows larger flow to pass through the pump. The purpose of this thesis was to develop a conceptual test rig capable of recreating the damages inflicted on the adaptive mechanism, but within an accelerated timeframe. Currently at Xylem a method has been developed to test the mechanism within an existing pump. However, this method is labour intensive, time consuming and very loud. One of the department’s focus areas is the development of the adaptive mechanism, leaving limited time to develop a separate test rig. Their current method does not identify which specific motion on the impeller causes what damage in the mechanism. First, the damage caused by long time use of the impeller was examined. Then forces acting on the mechanism were identified and tied together with the relevant damage. Different test rigs at the company were explored, with the aim to find inspiration. The concept development followed an iterative process, where several concept generation methods were used. The multiple concepts were then compared to the requirement specification to select one of the concepts. The selected test rig concept was further developed through material and component selection, three-dimensional modelling, simplified laboratory testing and solid mechanics calculations. The final concept is called a repetitive movement test rig allowing for two different accelerated damage tests. One recreates the linear collisions caused by objects passing through the pump, and the other recreates misalignment of the impeller as these objects passes through. In the linear test a centrally aligned linear actuator applies axial loads on a simplified version of the impeller. During the misalignment test the linear actuator will be moved along linear guide rails to apply the force near the outer diameter of the impeller. After either of these tests has been conducted, the adaptive mechanism will be removed from the simplified impeller, and any damages will be studied and noted. Together these tests allow the user to identify what motions contribute to specific damage within the adaptive mechanism. Building on this conceptual design, the continued construction of a less labour intensive test rig can be done by the development department at Xylem.