Superior Signal Company LLC
AccuTrak
®
VPX-WR
User’s Manual
© 2015
8
Maximum sensitivity is normally used in locating very small leaks or leaks from far away. If you find
that too much background sound is coming in at the minimum sensitivity setting of the instrument,
the front must be muffled. The nose cone can do this very well. You can use the nose cone alone,
or with the flexible wave guide (a piece of PVC or Nylon tubing that fits in its front). This will extend
the reach of your instrument to very tight places.
If you are in a very loud area searching for small leaks you should shield or change the direction you
are using the VPX-WR if background noise
“floods” the instrument. Loud areas contain ultrasonic
sound which is unwanted noise. This noise is generated by leaks and other processes but it may
not be what you want to find at the point where you are but they may be leaks that you have not
found yet. Physically isolating this noise using the accessories and sometimes a piece of carton
can help you use the VPX-WR at a higher sensitivity to locate very small leaks in loud areas.
When you are searching for very low volume leaks in the order of 0.2 SCFH or less, the orifice is a
very important factor in determining the sound strength. If the orifice is "large" the flow may not be
turbulent thus generating very little sound. In these cases when you know by other means that
there is a leak, install the nose cone and move the instrument very slowly around the suspect areas,
along pipes or seams but with a tight zigzag along the path. This technique will help convert
laminar flows into a shock wave when the gas hits the edge of the fitting of the nose cone.
Generated ultrasonic sound will be detected by the VPX-WR and show the leak.
Use a spray bottle and spray water on the suspected area if the system permits it. Air flowing
through the water will generate bubbles which burst and create ultrasonic shock waves making it
easier to detect.
Another technique that may be applied,
conditions permitting,
is to cover a suspect spot with your
finger. Do not rub because your finger can make sounds too. Just cover an area for five seconds
then let it go. (This simply traps whatever gas or air is in the system and then lets it go, doing the
same thing as squeezing a bottle while holding it closed and letting it open.) The sudden release
again creates a shock wave that can be detected.
Leaks originating from cuts or holes in membranes, or other rubber type materials, are very difficult
to detect. The elasticity of the material makes the orifice smooth and reduces the turbulence to very
low values. Here again, the zigzag technique must be used to find the leak point.
Ultrasonic leak detectors will not indicate a leak if there is no flow producing sound when you check
for it. High concentrations of fuel fumes in a storage room, for example, might have been caused by
a leak when the temperature was high. Leaks of this nature are called static leaks, while leaks that
are caused in pressurized systems, (positive or negative) are called dynamic leaks.
Dynamic leaks are the leaks that do make sound and can be found with the VPX-WR. Make sure that
you fully understand this important distinction. When searching for leaks from combustible or
dangerous gasses you should also use other types of gas detectors like sniffers, which check for
concentrations in the atmosphere.
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, combustible gas, or other dangerous gas
leak, but you cannot find it with the VPX-WR, do not assume that it does not exist, as it
may not be turbulent at the time when you check for it. Use another method as verification
that there is no leaking dangerous gas present.
