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As an example, the pressure loss (depending on the flow rate of the pump) is specified for different nominal sizes and materials of hoses in Figure 3 40. However, these data do not necessarily coincide with the actual pressure losses [FI-Hugo]. An additional increase of these pressure losses is to be expected, especially because, during use, one part of the hose is rolled onto the reel. In this case, the radius of the hose reel is decisive. The smaller … |
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The pressure loss in the high-pressure flushing hose can be reduced by adding flow accelerators. These are liquid substances that change the viscosity of water so that friction losses are minimised. The effect that can be achieved in this way is illustrated in the following example for hose lengths of 120 m and 240 m. The engine output constitutes the reference value of 100% [Ney2003]. |
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(Table: Pressure loss with and without a flow accelerator) |
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(Table: Pressure loss with and without a flow accelerator) |
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In addition to the friction losses occurring within the nozzle, there are also local losses due to a separation of the flow and a formation of dead spaces at points of discontinuity. Local losses are, e.g.:
[Geib2002] |
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In the cleaning nozzle, the water flow is deflected and distributed over the individual nozzle apertures and inserts. (Table: Different water jet deflections and their effect on the efficiency of the radial nozzle) |
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What does the optimal beam deflection mean in connection with cleaning nozzles? (Image: Beam deflection) |
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(Image: Nozzle with optimized beam deflection) (Image: Nozzle without optimized beam deflection) Effects of beam deflection within the nozzle to the formation of the jet (left: with optimized nozzle beam deflection, right: without optimized nozzle beam deflection). The greater the water flow rate is, the more important an optimized beam deflection inside the nozzle becomes. |
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(Table: Comparison of the current nozzle design characteristics from the company KEG) |
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The number of cleaning cycles depends largely on the
By increasing the volumetric flow rate and decreasing the pull-back velocity, the number of cleaning cycles can be reduced. |
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Moreover, the number of cleaning cycles is highly dependent on the condition of the nozzle. Besides the efficiency of the water jet deflection within the nozzle, missing or damaged nozzle inserts lead to a smaller jet area and thus reduced cleaning performance. (Image: Defective nozzle opening) |
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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.
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Furthermore, potential hazards for the sewer pipe occur when the cleaning nozzle impacts the pipe walls, when hard solid deposits are removed and mobilised, and when the cleaning nozzle pauses creating a point load. (Image: Nozzle impact) |
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The loads the pipe surface is exposed to are determined by the following influencing factors:
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(Image: Damage caused by high pressure cleaning) (Image: Nozzle in operation) (Image: High pressure cleaning vehicle) Channel
Nozzle
Cleaning
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May 15, 2012 Since the 1980s, many efforts have been made to develop test methods for determining the stress resistance of pipes, fittings and pipe joints exposed to high-pressure cleaning. In 08/2008, [DIN19523] was developed to cover this topic: Requirements and test methods for determining the resistance of sewer pipe components to HP jetting and flushing. |
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May 15, 2012 The tests according to DIN 19523 include:
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. |
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May 15, 2012 In material testing, a test track of 1.0 m length is placed under stress via a pressurised water jet that strikes the surface of the component part at an angle of 30° and a vertical distance between the surface under test and the centre of the nozzle insert of 10 mm. The minimum length of the component to be tested should be at least 1.30 m. Three test tracks with a lateral distance of not less than 10 cm are inspected. On these tracks, a set of three … |
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May 15, 2012 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. (Image: Investigation of the influence of high pressure cleaning on lateral service connections) (Image: The influence of high pressure cleaning on plastic pipes) |
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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 … |
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During high-pressure cleaning, there exists a risk of aerosol build-up, which is the formation of ultra-fine sewage droplets that are dispersed in the air. When an air flow is generated, these sewage droplets are transported via the manhole to the ground surface where they could pose a health hazard for the operating staff (Image: High emission of aerosols at the manhole) |
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