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.

Decentralised solid retention is defined to include “measures for the retention of solids in the place of their formation before the sewage is fed into the sewage system”.

In the opinion of many authors ( [Grott1991] [Giesl1997] [Kraut2000] [Stotz1998] [Somme2004a] [Somme2004] [Fraen2005] [Hilli2005] [SteinR05]) the runoff entering the sewage system from the surface via catch basins is the main source of mineral solids resulting in the formation of …

Catch basins with no sump and a direct invert discharge into the sewer line should use a perforated waste bucket as a sieve retaining coarse debris and floatables, before they enter the sewer system. Any particles that can pass through the waste bucket openings are able to reach the main sewer line via the lateral catch basin line [DIN4052:2006].

Catch basins with a sump retain solids in the sump space located between the bottom of the structure and the lateral invert. The disadvantage of this system is that floatables such as leaves cannot be retained and end up in the sewer system. This is also the case with debris in the sump which gets disturbed during heavy storm events [DIN4052:2006].

Catch basins which are currently in use are not appropriate for the targeted, let alone entire retention of the settleable solids carried along in the surface water. As shown in laboratory and in-situ trials run by Stein, as well as according to the experience of numerous sewer network operators, their performance capacity is very limited [SteinR08].

Owing to this knowledge, many authors ( [SteinR08] [Artie1988] [Sande1994] [Bromb1993] [Grott1991] [Giesl1997] [Kraut2000] [Stotz1998] [Somme2004a] [Somme2004] [Fraen2005] [Hilli2005]) recommend the replacement of conventional catch basins with new structures that have an improved cleaning function or solid retention. This improved separation of solids from the flow reduces operational requirements by increasing cleaning intervals.

Requirements concerning improved cleaning function are met by recently developed special catch basin systems described in the following tables.

Table: Structure, function and applications of various systems for decentralized solid retention [Somme2009]

Table: Structure, function and applications of various systems for decentralized solid retention [Somme2009] (Continued)

Table: Structure, function and applications of various systems for decentralized solid retention [Somme2009] (Continued)

The first separation step iconsists of an improved grate design as part of the cast iron frame and grate system “Multitop 500 PF” by the company ACO [FI-ACO].

It is constructed in accordance with DIN EN 124, and includes a shock absorbing riser which disperses traffic energy into the subsoil thus preventing localised settlement.

The second separation step is provided by the use of a waste bucket located just below the catch basin grate in accordance with DIN 4052-4. It has the same function as the bucket for a catch basin with invert outlet, that is, it acts as a sieve with predetermined slits and retains particles greater than 16 mm [DIN4052-4:2006].