The flushing shield is secured and guided by a steel cable in order to control its velocity and prevent the flushing pipes from colliding with the sewer debris. In the target manhole, the device is stopped by a stopper and manually retrieved. The waste material that is moved forward by the flushing shield has to be extracted by suction vehicle in the respective manhole.

The flushing shield for rectangular sewer profiles used in the German city of Leipzig has a similar construction to the one used for oval sewer profiles. Due to its larger dimensions, it cannot be brought into the sewer via a standard shaft, requiring special access points.

(Image: Self-guided flushing shield for rectangular sewer profiles)

Operating experience with flushing shields (cont.)

• Due to its design, the flushing shield cannot be used to clean the air space of the pipe. Thus, this method is not appropriate for cleaning prior to inspections or rehabilitations.

• Solidified deposits are not mobilised.

• The flushing shield can get jammed or stuck on lateral pipe connections. In this case it has to be manually repositioned.

• By backing up the sewage behind the flushing shield, the …

Operating experience with flushing shields (cont.)

• Generally, a team of 4-5 people is required for the assembly, operation and removal of the flushing shield. The cleaning performance per day strongly depends on the local limiting conditions. It varies between just a few metres in the case of low water levels and large deposit amounts to several hundred metres in the case of favourable water levels and small deposit amounts. The daily performance …

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In addition to an introductory overview of the various flushing methods and the criteria that must be taken into account when selecting these measures.

This module focuses thematically on the physical properties of shafts and the different designs of flushing methods.

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

• process sequences in surge flushing;
• influences on the efficiency of bed-load and suspension waves;
• differentiation of surge flushing devices according to their constructive design or technical equipment;
• process sequences in back-up flushing and their application limits.

In the case of large sewers with long sections and large deposit amounts, a combination of the following cleaning methods is recommended:

• Manual cleaning with auxiliary tools and devices

• Special cleaning systems

Removal of extensive solidified or crystalline deposits:
Solidified or crystalline deposits are loosened and removed by means of pickaxes, compressed air hammers, selective blasting as well as mini-excavators or skid steer loaders.

The waste material can be removed manually using wheelbarrows, suspended monorail containers, skid steer loaders, or by suction hoses.

For the cleaning of large profiles with extensive and solidified deposits, the following special cleaning systems are available:

• Cleaning system from the company CSM BESSAC
• Cleaning system “Sielwolf”
• Automatic cleaning system SVM-RS

The cleaning system from the company CSM BESSAC combines the removal, loading and transportation of debris in one efficient operation. All system components are housed on a diesel engine driven pneumatic-tyred chassis, which also utilises a catalytic exhaust treatment system [FI-CSM].

For safety reasons, the cleaning system is operated and controlled from a pressurized control station. From here, the machine operator also has direct access to the spiral conveyor for manual removal of waste material components that cannot be transported (large stones and bulky material).