Vast proportions needed

Since the progressive cavity pumps to be implemented at Thames Water are needed to transport sewage sludge to a sewage treatment plant over a long distance, the combination of high pumping capacity and high pressure presented a special challenge to development engineers. Electric power of 250 kW had to be provided for a test run alone. The N 300–27TH pump built by seepex is undoubtedly one of the largest progressive cavity pumps in the world in terms of pumping capacity. It is designed to handle 180 m3/h under working conditions and operates against a pressure of 25 bar. This work requires 210 kW power – 250 kW were actually installed. The system is driven by a frequency converter. With a length of 11 m and a width of 1.3 m, each pump has an overall weight of 7.3 t (1.5 t for the electric motor and 700 kg for the impeller).

This large progressive cavity pump is based on the same technology as the seepex N family of basic pumps. Some parts had to be modified in order to withstand the extreme conditions and meet the specified requirements. The rotating unit, for example, must be able to transfer a torque of over 13,000 Nm and axial loads of more than 100,000 N. Special attention was given to easy handling during both assembly and servicing. The stator, for instance, is not a single standard component as is usually the case. It consists of two connected but separable parts. And instead of the normal tie bolts, an especially stable short-screw connection is used to join the stators and to connect them to the suction housing and the discharge branch.

Despite these dimensions, pump vibrations are minimal. This is due to the special design of the rotor geometry for this unique application and to the extremely rugged supporting structure. As a result of this development, the seepex progressive cavity pumps in the N family can now be supplied for capacities up to 500 m3/h and pressures up to 48 bar.

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