Tolerance design of multistage radial flow submersible pumps

Axial play between the impeller and its casing is one of the critical dimensions in a multistage submersible pump assembly. The axial play is introduced in the assembly using a coupling that connects the motor and pump sub assemblies. The length of the coupling could not be standardized by the industry where this analysis was conducted. Tolerance analysis is conducted on the pump sub-assembly to identify the causes of variation of coupling length. It has been found that there are n possible tolerance loops in a n stage pump. Since the tolerance design is to be conducted for the worst case, the assembly condition that yields the largest tolerance loop has been considered for the analysis. The methodology currently adopted by industry to overcome the problem of variation of coupling length involves machining operation during the assembly stage. It results in unreasonably longer assembly time. The concept of selective assembly is suggested in this paper to overcome the problem of coupling length variation.