The tests according to DIN 19523 include:

• Material testing

• Testing under practical conditions

The hydraulic stresses imposed by the high-pressure flushing jet are modelled in material testing; the hydraulic and mechanical effects occurring during high-pressure cleaning are simulated in a test under practical conditions.

The practical test simulates the loads that are imposed by the pressurised water jets in combination with the mechanical loads caused by the flushing head and the hose during high-pressure cleaning.

Cleaning nozzles are to be used in such a way as to prevent them from turning around while in the channel.

This is achieved by ensuring that the selected nozzle is correctly dimensioned in proportion to the sewer size, and that a swivel joint is used between the nozzle and the flushing hose to prevent the hose from twisting. In the latter case, a bending-resistant extension (e.g. a section of rigid pipe) can also be used.

The rigid section has to …

Other preventive measures against the formation of aerosols and against their negative effects include:

• Use of invert nozzles in large sewer cross-sections,

• Reduction of the pump pressure approximately 10 m before reaching the starting manhole,

• Use of breathing- and eye protection

• Covering the manhole opening with a steel or plastic cover equipped with openings for the HP flushing hose and the suction tube.

[ATV1997]

Based on the practical experience and research findings of Prof. Dr.-Ing. Stein and Partner GmbH and literature research, the following suggestions and recommendations should be considered to ensure a professional use of high-pressure cleaning in order to avoid damages:

• In choosing the operating parameters (nozzle type, flow rate, angle of radiation, and pressure at the nozzle), the pipe material, the wall thickness, and especially the structural …

• In the case of damage-free sewers, the pressure at the nozzle should not exceed 120 bar. The corresponding pump pressure is to be determined and regulated considering the individual limiting conditions.

• When sewers are damaged, a much lower pressure has to be used at the nozzle. The load caused by the high-pressure water jets can be decreased by increasing the distance between the nozzle and the pipe wall, e.g. by using a guidance device (skids …

• Under no circumstances should the cleaning nozzle pause in one location while in operation, because the development or increase of damages in sewers, especially at joints and protruding side branches has to be avoided.

• Before the start of the cleaning measure, it has to be checked whether the nozzle apertures are clogged to avoid additional and uncontrolled reaction forces at the nozzle and increased stress imposed on the pipe walls.

• If the chosen …

• During the suction process, it has to be ensured that the suction tube is lowered into the shaft slowly to avoid damage to the gutter or benching.

• At temperatures of < 0° C, the cleaning vehicles are to be equipped with frost protection covers to avoid freezing of pumps and lines. The covers also provide a protective function against noise.

• Plastic hoses are preferred over rubber hoses due to their superior hydraulic characteristics and lower …

High-pressure cleaning often results in strong air flows. This interaction produces a high and low pressure jump at the nozzle., i.e. there is negative pressure in front of the nozzle (nozzle head) and positive pressure behind the nozzle (jet area). When the cleaning nozzle passes side branches (laterals), seal water can be blown out or sucked out from private drain traps (e.g. of toilets or washbasins) hence causing odour nuisances.

The pressure …

The following measures can reduce the occurrence of odours:

• Reduction of the pump pressure at the vehicle (resulting in a lower flushing pressure)

• Choosing the appropriate cleaning nozzle (large jet angles, low number of nozzle inserts)

• Reduction of the pullback velocity of the nozzle

• Cleaning of preferably short sections from manhole to manhole

• Regular removal of waste material within a section

• Improvement of the aeration (air inlet and outlet), …

A form of quality control carried out during the cleaning operation involves assessing the noise created by the deposits during suction and visually inspecting the flushing water.

Acoustic assessment: mud, rocks or solidified deposits cause noise as they are vacuumed up and hit the suction tube. This provides insights into the degree of contamination and the progress of the cleaning.

Visual assessment: A visual inspection of the flushing waters content and colour provides a general idea of the deposit situation and the cleaning progress.

Congratulations!

You have successfully finished this module.

Next you will have the opportunity to review the newly acquired knowledge with an interactive questionnaire.

You can of course still navigate back to any point in the modules if you wish to review a specific point or subject.

Stay curious!

An essential part of high-pressure cleaning are the cleaning nozzles.

This module covers the complex task of choosing the optimal cleaning nozzle for the respective application, as there are a multitude of nozzle types with different features available.

After completing this module, you will have a sound knowledge of:

• the physical mode of action of pressurized water jets;
• selection of cleaning nozzles depending on the cleaning task and
• assessment and recognition of application risks.

The possibility to reduce or even avoid the formation of deposits within the sewer system can be achieved through the implementation of constructive design measures used in the following scenarios:

• Semi-central sedimentation

• Decentralised retention of solids

Semi-central sedimentation includes “measures taken for the retention of solids within sewer networks”. For this purpose, sedimentation systems such as stormwater tanks or sedimentation shafts can be used to collect sediment from precipitation runoff and combined wastewater [SteinR08].

Where conditions permit, these systems can retain heavy solids through the use of settling basins while allowing lighter particles to pass.