Severe Suction Bell Damage In Large, Open Impeller, Vertical Turbine Pumps

Abstract

Sixteen (nine 1500 hp and seven 500 hp) single stage, vertical turbine, cooling water pumps suffered massive metal loss within two years of installation. All pumps had cast iron suction bells and semiopen, manganese bronze impellers. An accounting of the conditions that resulted in the perforation of the 2 in thick suction bells (one suction bell separated form the pump and fell to the bottom of the pit), including photographs, is given in this case history. Conclusions on how the damage occurred are given and other theories are considered. A description of the modifications to the pumps is given, as are the results of the followup inspections showing only normal wear. The large pumps were converted to enclosed impeller designs, but retained cast iron as the suction bell material. The smaller pumps still have open impellers, but the suction bells have been fitted with aluminum bronze inserts. This case history is given to show that current industry practice for general purpose (not utility class) water pumps is not adequate for larger size pumps.