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Waterjet Power Series
Optimizing Stand-off Distance
In the first installment of this three part series, we
looked at the effect of turbulence on waterjet power delivery. In this second installment, we examine how
the number of jets and the size of those jets affect cleaning
effectiveness. Directly related to the
size of the jets as they contact the surface is the distance from that surface
to the nozzle. This stand-off distance
has a profound effect on cleaning effectiveness. As we explained in the last E-Blast, the
further the waterjet is from the surface, the more likely that its
effectiveness will be compromised due to the effect of turbulence. It is important to try to achieve an optimum
distance from nozzle to surface. This
means that the nozzle end should be far enough away from the surface that
damage to the tool doesn’t occur from impact by either the nozzle itself or the
residual material as it is removed from the surface.
In
addition to the optimum stand-off distance, the orifices should be kept as
small as possible while maintaining the desired pressure and flow. In other words, the tool needs to have
orifices sized such that the impact from them will clean and flush the material
with as few orifices as possible and maintaining an optimum stand-off distance. In our final installment of this series
on Waterjet Power, we will look at the importance of correct jet velocity. For a given standoff distance, a larger
diameter jet will produce the greatest impact. At a 12 inch (305mm) standoff distance, a .032 inch (.8 mm) orifice will
have a ratio of 375, resulting in 40% performance, while a .063 inch (1.6 mm)
orifice will have a ratio of 190, with 55% performance. There are two ways to allow increasing the
orifice size- the obvious way is to increase the flow rate. The other is to use fewer nozzles in the
jetting tool without increasing the flow rate. This is why rotating tools are so effective- they allow complete
coverage with a fewer number of larger jets that hit harder. In our final installment of this series on
Waterjet Power, we will look at the importance of correct rotation speed when
using rotary tools.
You
can count on StoneAge to supply the
right tool for the job and StoneAge offers
a variety of extension nipples that will
help you optimize your stand-off distance. Additionally, we can fabricate custom length
extensions for special applications.
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