In choosing the above-mentioned operating parameters, the pipe material, the wall thickness, and especially the structural condition of the sewer sections should be taken into consideration in addition to the parameters which result from the core task of cleaning.

With respect to the influence of the pipe material, experiments of the Civil Engineering Office in Zurich, Switzerland, have led to the conclusion that sewers made of asbestos cement, concrete, PVC and HDPE are not damaged in a high-pressure cleaning procedure using water pressure of up to 120 bar (at the cleaning nozzle) and a volumetric flow rate of 300 l/min [Züric1987][Steine1992].

In recent years, the further development of high-pressure cleaning (e.g. an increase of the performance capacity of cleaning vehicles) and its varying implementation in the individual European countries (e.g. in Great Britain, the sewers are not cleaned regularly, but only in the case of severe deposits or congestions, requiring high flushing pressures) have caused the European Committee for Standardisation (CEN) to examine the behaviour of pipes with respect to high-pressure cleaning more closely. Their objective was the creation of common rules regarding the determination of the pipe resistance and a damage-free implementation of cleaning measures.

In this context, the European standardization project "European Standard for determination of the Jetting Resistance of Drain and Sewer Pipes; Requirements and test methods" of CEN/TC 165 started in 1999, which makes a distinction between the standard operational cleaning measures for maintenance ("Cleaning") and cleaning measures to remove congestions ("Deblocking"). The latter implies a significantly higher stress level for the pipes as it usually requires very high flushing pressures [Zimme2000][CENTC165].

The scientifically supervised tests carried out by ETH Zurich lead to the following result: whereas all standard pipes in the "Cleaning" test weathered the 50 cleaning cycles (100 cleaning passes) to be expected within the usual service life more or less free of damage, i.e. without adverse effects on their function, stability and tightness, the "Deblocking" test according to the European draft standard turned out to be a technical requirement that could not be met by one single pipe under test, whether it was plastic or a ductile cast iron pipe.

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