In the journal Proceedings of Meetings on Acoustics, researchers explained that an air-water mix in vacuum-assisted toilets travels more than 483 kilometres per hour.
In some good news for frequent flyers, scientists have invented a vacuum-assisted toilet that is about half as loud as the regular airplane commode. It took researchers at the Brigham Young University (BYU) in the US two years of trial and error, three academic publications and thousands of flushes to figure out how to make toilets quieter.
“People have told us they don’t want their kids to be scared to use the bathroom on a flight. So, we have used good physics to solve the problem,” said lead researcher Kent Gee, a professor at BYU. It has been a really hard problem to solve, given the industry hasn’t been able to improve vacuum-assisted toilets over the last 25 years,” researchers said in a statement.
That is because getting airplane toilets to flush with very little water requires a partial vacuum, which at 38,000 feet, pulls air at nearly half the speed of sound. In the journal Proceedings of Meetings on Acoustics, researchers explained that an air-water mix in vacuum-assisted toilets travels more than 483 kilometres per hour. When things move at that speed, any disturbance at all to the flow — like the bend of a pipe or a valve — generates significant noise.
As newer airplanes come with much quieter interiors, toilet flushes reverberate much more throughout the cabin. It can make for very patchy sleep on a red-eye flight on a plane like the Airbus A380 that can have as many as 20 toilets, researchers said.
“Airline companies have always had standards for the toilet noise, but they have never met those and there has never been much pressure to do so,” said Scott Sommerfeld, one of the researchers. “Now with the reduced cabin sound levels, the sound of the toilet flushing is more noticeable and customers are pushing back,” Sommerfeld said.
To solve the problem, the BYU team focused on three valve conditions during the flush cycle. These were the initial noise level peak associated with the flush valve opening, an intermediate noise level plateau associated with the valve being fully opened and the final noise level peak associated with the flush valve closing. The researchers added additional piping to increase the distance between the toilet bowl and the flush valve and made the pipe attachment at the bowl more of a gradual bend as opposed to a sharp 90-degree angle.
Tests of the new contraption show noise dropped up to 16 decibels during the flush valve opening and about 5 to 10 decibels when the valve is fully opened. “It’s a great mix between physics and engineering,” said graduate student Michael Rose, lead author of the study. “The toilet is much quieter and now kids won’t think they’re going to get sucked out,” Rose said. Along with Scott Thomson, professor of mechanical engineering, the researchers have already filed three patents on the new toilet and are now working with an industry partner to bring it to market.