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The advantage of the ejector technology in sewer operation is that a very high pump performance capacity can be exploited by feeding a water jet via the high-pressure cleaning vehicles that are already in use for sewer cleaning. This technology also displays health and safety advantages as it minimises the risk of hazardous blowouts. Furthermore, the equipment that is used in the day-to-day operation of sewer cleaning can be used without the need … |
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The ejector nozzle directs its kinetic energy towards the sewer invert. Thus, full contact between the pressurised water jets and the pipe wall is avoided. In specialist circles, this approach is also called "soft cleaning". (Image: Ejector nozzle) (Image: Ejector nozzle - top view) |
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To use an ejector nozzle, the cleaning vehicle must generate a volumetric flow rate of at least 320 l/min and a pump pressure of 150 bar. The water pressure at the nozzle, subsequently called nozzle pressure, must be between 40 to 60 bar to propel the relatively heavy nozzle. Compared to conventional high-pressure cleaning methods, using the ejector increases the volumetric flow rate of the pump by 3 to 5 times [FI-enz]. Ejector nozzles are used in … |
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High-pressure nozzles are equipped with interchangeable jetting inserts which help to extend the nozzles service life, and make it more versatile by being adaptable to different water flow and pressure rates. The inserts are easily screwed into the threaded bores of the nozzle. The nozzle inserts differ in:
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(Image: Ceramic nozzle inserts (JetMax, ceramic, max. 500 bar)) The cleaning nozzles inserts are made of
Ceramic and sapphire inserts show very low wear and have a high flow rate hence making them optimal in use with high-pressure cleaning vehicles with water reclamation technology. (Table: Nozzle inserts – Materials) |
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Sapphire and ceramic have proven to be very wear resistant materials, however, ceramics inserts have shown to have a longer life span when used with very contaminated flushing water.
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The nozzle inserts have a bore diameter of 0.3 to 4.0 mm or more. The number of nozzle inserts can be both even or odd. In the case of an odd number, only equally sized hole diameters are to be used to prevent the nozzle from drifting off in one direction. When using different hole diameters, their number has to be even and symmetrically placed. |
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Connection between cleaning and driving performance based on the number of nozzle inserts: (Image: Number of nozzle inserts) |
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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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