The overall-fitted man marching around the Ford Stamping Plant in Geelong, Victoria, with earphones on is not listening to the latest gig by the Red Hot Chili Peppers or the Hot House Flowers.  Instead of rocking around the plant, the fitter is using an ultrasound detector to find compressed air leaks and saving Ford $2,000 every week and this saving could increase to $5,000 per week in the near future!  The device is an Ultraprobe 2000, which was supplied by Jonathan Orban of Duff and Macintosh from Hornsby in Sydney.  Because it picks up the noises made by leaks in the ultrasound range, it can be used in a busy factory where normal operating sounds make leaks impossible to detect by ear.  Jonathan said that when he visited the Ford factory he could hear nothing except the stamping machinery banging out car body parts above a background hiss of compressed air being used.

Press Operations Maintenance Superintendent, Doug Richards, told me "compressed air was a significant part of the factory's costs."  In fact he is about the only plant manager I have ever met who knew how much the compressed air was costing and could estimate the value of wastage through leaks in the system  !Doug put on the earphones and then pointed the detector at compressed air lines.  I watched him grin with delight as he realized he could hear and locate individual leaks he'd suspected were there but had been unable to find by other means.   The combination of the earphones blocking out the background noises and the directional signal of the Ultraprobe, enabled him to hear exactly where various leaks were coming from ... even on the 50 ton stamping machines when they were operating!  Doug zeroed in on the floor and in no more than a few seconds, found a reflected signal made by a significant air leak from the base of a stamping machine!   "All the attachments on this machine would have made it impossible to find the leak in any other way," Jonathan said.  Doug Richards walked around finding leaks that he thought would have been impossible to find and he then began passing the instrument to other people and telling them to "pull the trigger and zero in on the leak."  They did and have been doing so ever since.

Within a week, Ford had bought its first Ultraprobe and the cost of the instrument was recovered in the first month!  In large factories, the plant compressor is usually set to maintain a nominated pressure and when feeding a leaky system, it has to run harder and longer to maintain the pressure.  This extra operating time is often overlooked or just considered a normal part of the cost of running a business but few people realize just how high that expense can be.  A 600 kPa system that provides air at a cost of only five cents per cubic meter can lose over $22,000 worth of air per year from a total plant leakage equivalent to that from a 12 mm diameter hole!   With hundreds of meters of piping and scores of connections, the system loss in a large plant can easily exceed that level.  Many plants have regulated pressures beyond 600 kPa and in these the cost of wasted air could be much higher!

Ultrasonic leak detection is based on the principle that forcing a fluid through a small opening creates turbulence on the downstream side.  The turbulence generates "white noise" that has an extremely strong ultrasonic component.   Most of the audible sounds of a leak might be masked but the ultrasonic signals will be readily detectable, even when loud ambient noise is present.  The directional locating ability of the Ultraprobe also helps find leaks during a plant shutdown when the audible level sounds from several leaks can make it difficult to pinpoint the location of each single leak.  Airborne ultrasonic testing instrumentation is usually battery operated and compact to ensure portability and ease of use.  The detector's electronic circuitry converts ultrasound to audible sound through the earphones.  In scanning mode, the detector can be used at a safe distance from pipes carrying superheated steam or dangerous gas.  As it detects sound, it can be used on systems carrying any sort of gas or fluid.  As well as pressure leaks, the Ultraprobe can be used to detect vacuum leaks into a system, leaking valves or even changes to a machine's "sonic signature" which could indicate impending failure and allow a simple maintenance job to prevent major machine damage and an expensive shutdown.