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(Image: Radial nozzle - Removal of loose deposits) (Image: Rotary nozzle - Rear and side jetting) (Image: Penetrator nozzle) |
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The placement of the nozzle inserts and the specific angle (exit angle β) of the rear discharging jets determine how efficiently the nozzle propels itself, and the HP hose, upstream through the sewer channel. (Image: Effects of the jet angle on the propulsion of the nozzle as per [FI-Mülle]) |
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The jet angle (also called exit angle) represents an essential parameter in high-pressure cleaning. It is the angle between the pressurised water jet and the pipe axis or longitudinal axis of the sewer, and may range between 0° and 90°. Equation: (Formula: Berechnung der Zugkraft) with: FZ = Pulling force FSt = Jet force β = Jet angle n = Number of jets (nozzle inserts) Equation: (Formula: Berechnung der Reinigungskraft) with: |
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From a mathematical point of view, the force of the nozzle jets can be split vectorially into cleaning and pulling force components (drive force), meaning that the energy distribution for these two reactions changes depending on the jet angle. (Image: Nozzle jets pressure output represented vectorially by propulsion and cleaning components) |
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(Image: Jet angle - Effect on driving force and cleaning performance) |
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(Image: Jet angle selection) Achieving the above results is dependent on the free jet length. |
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(Image: Beam Angle - Influence of the pipe diameter) |
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May 15, 2012 BE-05 Cleaning: Cleaning Nozzles Pulling force – Water jet force, Number of nozzle inserts, Jet angle The pulling force (drive force) generated by the high-pressure water jets is dependent on:
(Image: Nozzle jet pressure test) |
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May 15, 2012 BE-05 Cleaning: Cleaning Nozzles Pulling force – Water jet force, Number of nozzle inserts, Jet angle Correlation between cleaning and driving performance based on the number of nozzle inserts and the beam angle: (Image: Effect of jet angle and number of nozzles) |
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May 15, 2012 BE-05 Cleaning: Cleaning Nozzles Pulling force – Water jet force, Number of nozzle inserts, Jet angle The jet force at the nozzle is dependent on:
It can be calculated using the following equation: (Formula: Equation to calculate the jet force) pdyn = dynamic pressure at the nozzle opening ρwater = water density v0 = water velocity at nozzle opening [Geib2002] |
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May 30, 2012 BE-05 Cleaning: Cleaning Nozzles Pulling force – Water jet force, Number of nozzle inserts, Jet angle The cleaning performance and driving force can be further enhanced by mounting the nozzle onto a sleigh or skid, thus avoiding direct contact between the cleaning nozzle and the pipe wall. (Image: Centric positioning of the nozzle through the use of a sleigh) (Image: Mounted nozzle) (Image: Cleaning nozzle with a skid) |
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For an effective use of high-pressure cleaning, a precise knowledge of the occurring pressure losses is very important. A distinction is drawn between:
Both nozzle pressure and volumetric flow rate can be optimised by choosing the appropriate high-pressure flushing hose, nozzle and nozzle inserts. Given an equal pump output, the required … |
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In the line between the high-pressure pump outlet and the high pressure hose inlet on the reel, there exists a large number of valves and fittings. The pressure losses at the vehicle are therefore dependent on the particular type of set up, and are equal to 5 % of the total loss or 12 – 15 bar [Geib2002]. |
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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 the following equation: (Formula: Druckverluste im Hochdruckspülschlauch) with: hv = Friction loss height [m] or pressure loss [bar] l = Hose length [m] d = Internal diameter of the hose [m] vm = Average flow velocity [m/s] in the hose l = Pipe coefficient of friction [-] |
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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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