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Waterjet Power Series
The Effect of Turbulence
High-pressure waterjet tools have been used with excellent results for several years, but the science and technology behind these tools continues to evolve. This first in a series of three E-Blasts aims to simplify some of the concepts behind waterblast tool technology and make you more familiar with how these tools work most effectively. When it comes to delivering the most power, there are three concepts that are most important: 1) Controlling turbulence, 2) Optimizing stand-off distance, and 3) Optimizing dwell time.
At the exit of the nozzle, the high pressure water becomes a high velocity waterjet. The surrounding air begins to break down the jet into droplets, first occurring at the edges, leaving a powerful core that continues to carry the power of the jet. With increasing distance travelled through the air, the core is ultimately broken down to the point of being ineffective for cleaning.
Even though the laws of physics make the water jet less effective the further it gets from the tool, there are some things that can be done to minimize that effect. The two things that affect the power of the jet are upstream conditions before the nozzle and the design of the nozzle itself. The ideal upstream condition before the nozzle is a straight, smooth bore pipe with no elbows, bends or adapters. The optimum length of this straight section is fifty times the inner diameter of the tube. Unfortunately, most of the time, this is not possible, such as in small pipe cleaning. Even an extension nipple as small as two inches long will add some improvement to jet performance. Another method of improving the jet power is the use of flow-straightening vanes installed in the nozzle itself. StoneAge Attack Nozzle Tips use a flow-straightening vane behind the orifice that recovers about half the power lost to upstream turbulence.
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