First of all, I want to say thanks to everyone here for the contributions. I have often referred to this site when I had a "head scratcher". I also consider this an excellent forum for "continuing education".
Anyhow, this is more of an FYI post, for ultrasonic leak detectors, specifically the Accutrack-VPE.
I had a med temp 404A walk in compressor replacement (RTU) a couple of days ago, and I needed to do some re-piping. Quite a few fittings were needed, Suction and liquid line driers, new site glass, etc. Anyhow, I pulled a little vaccum to see if she would hold. Got to less than 27 in on the gauge, but no further, so I knew something was amiss. Mine will usually go down to 30" if I am on the right track. IF it does, I atttach my old and faithful Themal Engineering Vacuum gauge. Anyhow, I got out the vpe and went to work. This was my first attempt at using it. Started "sniffing" around the fittings, and wouldnt you know behind a 3/8" shrader fitting it starts making a "rushing sound". I was really surprised because I looked directly at that spot several times with my inspection mirror. To be honest, I thought the VPE was wrong and was somehow hearing the turbulence through the piping from the vacuum pump, or whatever.
This unit sensitivity is adjustable, so if its too high, you can even hear the vacuum pump huffing and puffing from a few feet away, which sounds pretty weird.
What I did was shut the vacuum pump off, and played around a little. Since the leak was so small, I got to test the sensitivity and so forth. There is also a volume control on the headset as well. The VPE honed right in on that leak, no problems. If the sensitivity is higher, it will hone in on the general vicinity. Then, you can adjust sensitivity to hone in closer.
Got to say, I am impressed. No fiddling with trace gases, pressurizing with nitrogen needed (THIS TIME!). I had previously looked right at the point several times with my inspection mirror and couldnt see a thing. The VPE found it.
This little unit is light weight and simple, so there will be times on a windy day where it might be useful for you. It was for me.
BY the way, I was trying to decide between this one and the Amp Probe, which is somewhat more expensive. (eBay prices ) So, I called tech support because I needed a plastic extender tube, which is a small attachment that goes on the end to siphon the sound. I spoke to engineering directly and was told that this is the same sensor as used in their 1000 dollar model, just without the logging. That was the deal clencher for me.
99.00 on ebay, new they're about 250-275.
Hope this helps anyone wondering about Ultrasonic leak detectors.