Uptime Magazine - October/November 2008 - (Page 62)

ultrasound upload Leaks, Motors and Bearings Ultrasound is Well Suited for Many Varying Applications by Jim Hall T his is the first of a three part series of articles exploring the use of airborne ultrasound for leak detection, motor diagnostics, when and why we would use vibration with ultrasound and how the use of airborne ultrasound will greatly enhance your infrared program. This first article will discuss airborne ultrasound for leak detection and bearing analysis. There are numerous leak detection methods, applications, tips and tricks, some of which you may have never heard of before (Figure 3). Let’s talk about a few that will hopefully help improve your results with your instrument. Some Basics - Since airborne ultrasound occurs in wavelengths above 20 kHz frequency (wavelengths 20 kHz and below are sonic sound), you can go into a noisy (to your ears) environment with an ultrasonic instrument and detect an air leak several feet away. When you are unable to hear a leak, look at the instrument to make sure that the settings are correct. If your instrument is equipped with frequency select or frequency tuning, change the frequency to 38-40 kHz. This is the frequency range for air leaks. Be a Blocker - Use your hands, legs or whole body like a barrier, placing yourself between the competing sound and the target leak area (Figure 2). Then place the ultrasonic receiver in front of your body, effectively using your body to block the noise. Leak Detection The airborne ultrasound instrument is well known, and widely recognized as one of the most effective methods for detecting leaks, both airborne and underground. Most airborne ultrasound instruments are capable of sensing a 5 psig leak from a .050” opening at 50 feet away. Add a long range horn or a parabolic dish and extend that range even more. By adding either of these accessories you can define the leak within a couple of feet from quite far away. These instruments have been around for several years, and are simple to use. In fact, almost any person can simply grab a unit, go listen for air leaks, and will have at least some success finding them. However, becoming highly proficient at leak detection requires an interesting mix of science and art. With high quality training, and a lot of time with the instrument, you can become the Terminator for leaks in your facility. With the use of the aforementioned parabolic horns (both long and short range) and dishes, the distance at which a leak can be heard has grown greatly (Figure 1). Imagine being able to hear a leak in a compressed air system say, a 70 psig leak from a 1/8” (.125) opening from upwards of 100 feet away. No problem. Figure 2 - Competing ultrasound can be blocked by using a hand, clipboard, cardboards, etc. Figure 1 - Control air leaks found using ultrasound and rubber cone to narrow the focus and locate the leak. Vacuum Leaks - Vacuum leaks are ‘internal’ leaks, where the turbulence is internal. To detect these, you must be much closer than with an ‘external’ type leak. Wetting Solutions - You should become familiar with the use of “wetting solutions” when using airborne ultrasound to locate low-level leaks and those leaks october/november 2008 62

Table of Contents Feed for the Digital Edition of Uptime Magazine - October/November 2008

Uptime Magazine - October/November 2008 Contents Upfront Upclose: An Asset Management Oasis in the Desert Information Technology: Streamlining Through Simplicity Lubrication: Phases for Framing a Solid Foundation Infrared: Do Your Homework Before You Buy Maintenance Management: Get It Together by Getting Together Motor Testing: Key Elements in Motor Decision Making Precision Maintenance: Shedding Some Light on Tolerances Reliability: RCM & the Mortgage Meltdown Ultrasound: A Multidimensional Tool Vibration: The Whirling Pump Mystery, Solved with ODS Upgrade: Are You Looking in the Right Place for Your Wear Debris?

Uptime Magazine - October/November 2008

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