Soap and water have been the standard tools for spotting a leak in a compressed air or gas line for decades. If you hear or even suspect a leak, put a drop of dish soap in a bucket of water and spread the solution up and down the line. Bubbles foaming up indicate a leak.

That might be practical for a single line in your home garage. But when you’re in a manufacturing facility with multiple compressed air lines and noisy machinery that masks the sounds, finding and fixing compressed air leaks can be so time-consuming that it's rarely a priority.

“Until acoustic imaging emerged, finding and fixing compressed air leaks has always been too manual and too time intensive to throw a lot of labor at,” said Justin Sheard, principal engineer for new product solutions at Fluke Corporation. “It just didn’t make business sense to try and save your energy dollars by sending someone on a wild good chase. Facilities learned to live with the inefficiency of those leaks.”

Oft-cited data from the U.S. Department of Energy suggests leaks cost 20% to 30% of a compressor’s output. This can result in:

• Inefficient production, as weaker or inconsistent system pressure renders tools less effective
• Increased energy costs, as more energy is required to run the compressors – or more compressors are added to make up for the inefficiency
• More carbon dioxide emissions, which are a no-no for companies with an eye on sustainability goals

In addition, there can be sustainability and safety issues when the leaks involve gases that could be flammable.

From Ultrasonic Detection to Acoustic Imaging

Ultrasonic technology has made it easier to find leaks, even in large facilities. When air or gas escapes, it may emit sound waves at frequencies that humans can’t hear. Special microphones can pick up these ultrasonic waves and filter out other noises to identify leaks.

Non-imaging ultrasonic detector tools work by translating the inaudible ultrasonic waves into an audible signal that a trained professional can use to determine a leak’s approximate location. This technology, which came into use in the last 20 years or so, has been valuable for some situations but not enough to become mainstream.

“It made it better than soap and water, but it didn’t make it good enough and fast enough that everyone wanted to go out and fix all their leaks,” Justin said. “The tool still didn’t tell you exactly where the leak was coming from nor was it easy to use.”

Acoustic imaging, which emerged around 2019, uses ultrasonic microphones and integrates the results with a hand-held digital camera. Thanks to advances in computing power, this combination can hear the leak and then translate it to a visual representation overlaid on the image from the camera.

“It gives you a picture and you can pinpoint the source of sound, maybe it’s the threads and there’s something wrong with the tape or there’s something wrong with the gasket and you know right where to fix it,” Justin said. “Then after repairing the leak, you can scan the same area with the camera and see, is it really fixed? All those elements play into a much more efficient process.”

Leaks are commonly found in locations such as hoses, fittings, regulators and filters as well as in the overhead distribution system. Because the leak could be in a location tight among other equipment, it’s important to be thorough, even with the new technology.

“You want to scan with the camera from different angles because that tells you more about exactly where the leak is coming from, and it also confirms that it's not a reflection,” Justin said. “Sound bounces off floors and walls. You may want to circle the area or take pictures from different views. And if the sound stays fixed on that spot, then it confirms it's real.”

Acoustic imaging tools can detect and create an image for anything emitting ultrasonic sound, not just air leaks. Justin called out two other notable applications:

• Partial discharge from electrical components
• Mechanical issues in other equipment

Compressed Air Audits

Acoustic imaging can also be a tool in preventive maintenance via a compressed air audit. An audit will cover more than leaks and may review usage, piping quality and structure, the working environment and other factors to help determine an overall approach to improve efficiency and save money.

A more comprehensive audit might require enlisting a vendor experienced in the work, but with the right tools, a high-level, in-house audit could uncover opportunities for saving time and money. This includes completing work during planned downtime, rather than being surprised by a sudden failure that forces an unplanned shutdown.

And comprehensive audits might even call for less use of compressed air.

“It’s about using that air effectively and efficiently,” Justin said. “Sometimes compressed air is used to do things that can be more effectively and efficiently done a different way. You want to look at your overall facility. What pressure do I need at places, why do I need that equipment there, is that the best way of doing that action?

“Maybe it was the best thing 10 years ago to use compressed air, but now I don’t want to have that compressed air running all the time just to dry off a part.”