AccuTrak
VPE-2000
8
Principle of Operation
The principle of operation of the AccuTrak is based on the turbulent flow of fluids
and gasses. Turbulent flow has a high content of ultrasound. This is sound
which is above the human hearing range, but can be heard with the AccuTrak,
and traced to its source.
Imagine air leaking from a tire. Because this is such a
large
leak, your ear
can
detect this sound, however your ear hears only about 1/3 of the actual spectrum
of sound which exists. The sound of small leaks is mostly ultrasonic which your
ear can
not
detect.
It is important to remember this example... A piece of straight tubing connected
to a gas supply and left free to exhaust into the atmosphere will not generate
sound if the volume of gas through it is such that turbulence does not take place.
Yet for that same flow, an opening as small as 0.005 of an inch could generate
enough sound to be heard several feet away.
For a leak to happen there must be an opening in the system that carries a gas
or fluid. Normally, these openings are not clean smooth holes, but passages
through cracks with many jagged edges and internal chambers. Fluid or gas
escaping through an "orifice" like this, is forced into turbulence, random
circular-like motions. Inside a tube where a gas may be flowing, the flow is
normally laminar which means that a given layer of gas does not mix with layers
above it or below it. This condition happens in a straight long tube when the
velocity of the fluid is not high. A gas leaking out of a straight and long tube will
not generate as much sound as if it were leaking out of a small crack because
the flow is not turbulent.
The intensity of sound generated at a leak is a very complex function of the
viscosity, the temperature, the speed the fluid is moving, the Raynolds number,
the pressure differential across the leak, and the physical dimensions and
characteristics of the orifice. This is why it is impossible to
quantify
the size of a
leak with ultrasonic technology. A smaller leak may generate more sound than a
larger one!
What this all means...
The AccuTrak detects ultrasound NOT the presence of a specific gas. It is NOT
a gas “sniffer”. Because of this fact, the AccuTrak can function in areas where
heavy wind or a concentration of fumes renders other detectors useless.
WARNING
Ultrasonic detectors will not indicate a leak if there is no turbulent flow producing sound
when you check it. If you suspect a toxic gas, natural gas, or other combustible gas
leak, and do not detect it with the AccuTrak, do not assume that it does not exist as it
may not be turbulent. Use another method as verification that there is no leaking gas
present.
