During the development of sewage pumps their functionality and efficiency have been continuously improved. Different impeller types have been developed; types to reduce clogging, types for associated maintenance during the various stages of the wastewater transport system, and types to increase the efficiency of the pumps.

In the current market, energy requirements and efficiency play an increasingly important role. The design of pump impellers with the aim of improving efficiency may increase the susceptibility of clogging. So far there is no test describing both the energy efficiency and the wastewater pumping functionality. Operators can only describe in tenders, a desired efficiency and the indication of plausible experience with respect to the impeller geometry: the impeller shape and the ball passage.

It is generally assumed that the susceptibility of clogging can be derived from the impeller shape and the ball passage (or freely passable space). Under this assumption, the vortex impeller should have the lowest susceptibility to clogging. With single and dual-channel impellers, accordingly, the largest possible ball passage points to a low susceptibility of clogging. Both, the hydraulically disadvantageous form of the vortex impeller and an enlargement of the ball passages beyond the hydraulic requirements leads to a significant reduction of efficiency. Generally, it is inferred from these circumstances that clog-free pumps are associated with low efficiency. This assumption, which is also found in the literature, requires a uniform test procedure for the objective assessment of the clogging behavior of sewage pumps. Such a test did not exist.

At the Chair of fluid system dynamics, TU Berlin a test stand was developed to examine such assumptions to investigate the functionality and the clogging behavior of sewage pumps.

More than 30 different wastewater pumps were tested in this procedure. The results may suggest a correlation between the susceptibility to clogging and the shape of the impeller or ball passage of various sewage pumps. Based on investigations already carried out at the Chair of fluid system dynamics, TU Berlin, the following conclusions are drawn from the measurements:

• the superordinate impeller form (Vortex, Channel, etc.) gives no evidence about the susceptibility to blockages,

• the ball passage does not indicate the susceptibility to blockages.

From these observations it can be deduced:

• a sewage pump with an appropriate efficiency may have a low susceptibility to clogging.

It can therefore be concluded that the ball passage and the type of impeller are not appropriate parameters to characterize the functional performance of a sewage pump.

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