Failure analysis of the rainwater axial pumps installed in a wastewater pumping station

Abstract

A strategy of urban sewage centralized management is implemented in the most cities (e.g. Timisoara). All wastewater is collected and conveyed to a central location for treatment or disposal. In the urban area, the rainwater is embedded in the wastewater management. Seven rainwater pumps are installed in a wastewater treatment plant to protect it against flooding. This type of pumps is vertically installed in Timisoara’s wastewater treatment plant in order to pump the additional rainwater protecting it. Several catastrophic events have been occurred at the rainwater pumps tacking them out of service after a limited operation time. The fastening bolts of the blades are brittle broken due to the clog of the impeller with waste rag balls. The cumulated operation time is examined for each rainwater pump together with the catastrophic events identified in service. The mechanical properties of the waste fibres are experimentally determined with respect to it area in order to assess the clog/rag conditions corresponding to the clearance between the impeller blades and housing. Next, the inertial torque associated to the rotating parts of the rainwater pump is estimated to check the level when sudden locking occurs due to the impeller clogging. The maximum stress level of the fastening bolts is exceeded when the impeller is partially clogged or ragged. As a result, the root cause of the problem is associated with the ragging level of the impeller. A solution is proposed to avoid these problems.