After the cleaning measures are completed, a quality control is carried out in step 4. Subsequently, the cleaning services and results are documented. This ensures that inadequately or insufficiently performed cleaning measures can immediately be detected, and the service provider can be asked to undertake improvements. Furthermore, quality control inclusive of appropriate documentation (Table 3‑2) ensures a constant update of the much needed operational …

(Image: Overview of the drain and sewer cleaning methods as per [Führb1980])

There exist numerous methods for the cleaning of drainage systems (Image 3‑14). They are applied based on the cleaning objective and the structure specific, local, structural and hydraulic limiting conditions. Selection of cleaning measures must be in accordance with EN 14654-1 [ [EN14654-1:2005]], and should also take into account the technical feasibility and economic viability …

High-pressure cleaning is the use of high-pressure equipment to remove obstacles and deposits in drains and sewers [ [EN14654-1:2005]]. This universal method, which is applied in about 90% of all sewer cleaning measures in Europe, is also used as a preparatory action prior to an inspection (section 4.1.2 - in progress) or a rehabilitation (2^nd volume of Rehabilitation and Maintenance of Drains and Sewers - in progress) [ [Geib2002]].

The process of …

The high-pressure cleaning process utilises different types of vehicles depending on the limiting conditions and site location (Image 3‑17) [ [SteinD00]].

(Table: Vehicle types for high pressure cleaning)

The flushing water required for cleaning is taken from the water supply network via stand pipes and sand filters. A direct connection to a hydrant is prohibited. Generally, a permission under the Water Act and a specially equipped high-pressure flushing …

Depending on the vehicle type, there exist

• high pressure pumps,
• vacuum pumps

or both types of pumps can be used at the same time (Image 3‑20).

The pumps are arranged behind the driver's cab and are driven by a gear-independent auxiliary drive directly by the vehicle's motor using a v-belt (Image 3‑21).

(Image: Pumps drive system)

The high-pressure pump is used to generate the flow rate and pressure for the …

Hoses

The hoses used for high pressure cleaning are divided into

• high pressure flushing hoses and

• suction tubes.

High pressure flushing hoses

(Image: Arrangement of the large and small hose reel on the combined high pressure flushing and suction vehicle with water recovery technology )

High pressure flushing hoses, subsequently also called HP-flushing hoses or hose, serve to transport the flushing water under high pressure to the nozzle, and have to …

Suction tubes (Image 3‑26) are used to extract the waste material collected in the manhole.

(Image: Extraction of the waste material from a manhole using a suction tube)

In practice, abrasion-proof rubber tubes are used for this purpose. They have to meet the following requirements [ [Geib2002]]:

• Resistance to internal and external abrasion
• Ability to withstand the maximum negative pressure generated by the vacuum pump
• Low internal frictional resistance

The nozzle is described in [ [Brock1952]] as the mouthpiece of the pipe which is used to narrow the flow channel, thus transforming pressure into velocity (pressure nozzle) or velocity into pressure (suction nozzle).

Nozzles used for cleaning purposes (subsequently also called cleaning nozzles) serve to generate the required jets of liquid (pressurised water jets, in literature often called high-pressure water jets) to

• Propel the flushing hose from …

Fluid jets, which also include pressurised water jets, are free jets by definition, because they form a fluid flow that passes through a nozzle that is then emitted into the open air without restrictions [ [Kraat1989]] [ [Rinal2003]] [ [Freim1998]]. The following case involves circular non-restricted turbulent free jets (water jets) in the medium of air. They are characterised by exchanges that are triggered by the turbulent diffusion at the edges …

Cleaning nozzles are designed depending on the type and quantity of sedimentations and deposits, or rather the type of obstacle, the cross sectional shape of the sewer, and the cleaning objective (Table 3‑13). They are categorised into:

1. Radial nozzles (pressurised water jets emerge radially backwards, distributed along the length/extent of the nozzle)

2. Rotary nozzles (like radial nozzle, in addition, the cleaning nozzle rotates)

3. Penetrator nozzles (…

In recent years, special forms of cleaning nozzles have been developed in addition to the above-mentioned standard nozzle types in the attempt to expand the range of high-pressure cleaning application.

One such special nozzle is referred to as the invert cleaner or seeing nozzle as it allows for both cleaning and inspection (Image 3‑36) [ [SteinR04]]. This so-called invert cleaner is used to remove deposits in drains and sewers with the assistance …

For an effective use of high-pressure cleaning, a precise knowledge of the occurring pressure losses is very important. A distinction is drawn between:

• Pressure loss at the vehicle,
• Pressure loss in the high-pressure flushing hose and
• Pressure loss in the nozzle.

According to [ [Orth2008]], depending on the cleaning nozzle and the nozzle inserts, as well as the characteristics of the high-pressure flushing hose (material, nominal size, length), …

The highest pressure losses can be found in the high pressure flushing hose. According to [ [Geib2002]], the calculation of these losses, resulting from the turbulent flow, is performed using Equation 3‑7.

(Formula: Pressure loss in the high-pressure flushing hose)

According to this equation, the pressure loss in the high-pressure flushing hose is inversely proportional to the internal diameter and the hose length, the squared mean flow velocity and …

In the cleaning nozzle, the water flow is deflected and distributed over the individual nozzle apertures and inserts. Image 3‑41 indicates how three different cleaning nozzles deflect water jets differently. The latter are significantly determined by both the form and design of the nozzle, and hence the flow conditions prevailing there.

(Table: Different water jet deflections and their effect on the efficiency of the radial nozzle)

In addition to the …

When high pressure cleaning is performed incorrectly, the pressurised water jets can cause damage in the form of grooves, flakes, cracks or holes in the pipe walls and linings (Image 3‑42) (Image 3‑43).

Furthermore, potential hazards for the sewer pipe occur when the cleaning nozzle impacts the pipe walls, when hard solid deposits are removed …

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 …

Flushing methods

Flushing is considered to be one of the oldest sewer cleaning methods [ [Frühl1910]] [ [Gürsc1921]], it is divided into

• Surge flushing and

• Back-up flushing.

Both methods can be used to remove loose, unconsolidated deposits and require a free discharge line. The flushing systems can either be installed permanently or temporarily.

Surge flushing

Surge flushing is defined as the creation of a temporarily increased discharge to remove …

Currently, there are several different surge flushing devices used for surge flushing of drains and sewers as well as local drainage structures. According to [ [Dettm2004a]], these devices are categorised into four groups with respect to their structure and technical equipment (Image 3‑47):

• Wastwater volume activated flushing system,
• Flushing using a tipping bucket,
• Flushing using a flushing chamber and
• Surge manhole flushing system.

(Table: Schematic …

Wastewater volume activated flushing systems have sealing devices that are especially arranged perpendicularly to the flow direction in the sewer to back up the wastewater in the upstream sewer sections for flushing. Depending on the type of the sealing device, the sewer cross section is blocked entirely or partly. The flush gate, arched flush gate, flushing weir, flush sluice, inflatable pipe plug and rotating elbow are counted among the sewer volume …

Flushing systems with a tipping bucket serve for the automatic cleaning of stormwater storage basins (e.g. stormwater sewer, stormwater overflow basin, etc.). The flushing water is stored in a comparatively small flushing tank in the form of a tipping bucket or pivoting drum and released abruptly.

The emptying of the flushing tank is automatically triggered by a shift in its centre of gravity as it reaches the maximum filling level. An example of …