Researchers invent a quieter airplane toilet

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Additional piping cuts flushing noise sharply without requiring a complete system replacement.

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Airplane toilets are loud but a group of Brigham Young University (BYU) physicists have figured out how to make them quieter.

After two years of trial and error, three academic publications and thousands of flushes, the BYU researchers have invented a vacuum-assisted toilet that is about half as loud as a regular airplane commode.

“People have told us they don’t want their kids to be scared to use the bathroom on a flight,” says lead researcher Kent Gee, BYU professor of physics. “So, we’ve used good physics to solve the problem.”

The industry hasn’t been able to improve vacuum-assisted toilets during the last 25 years because getting airplane toilets to flush with very little water requires a partial vacuum, which at 38,000ft, pulls air at nearly half the speed of sound (an air-water mix in vacuum-assisted toilets travels more than 300mph). When things move at that speed, any disturbance to the flow – such as the bend of a pipe or a valve – generates significant noise.

“Airline companies have always had standards for the toilet noise, but they’ve never met those and there has never been much pressure to do so,” researcher Scott Sommerfeldt says. “Now, with the reduced cabin sound levels, the sound of the toilet flushing is more noticeable, and customers are pushing back.”

To solve the problem, the BYU team focused on three valve conditions during the flush cycle:

  • Initial noise level peak associated with the flush valve opening
  • Intermediate noise level plateau associated with the valve being fully opened
  • Final noise level peak associated with the flush valve closing
  • The researchers added piping to increase the distance between the toilet bowl and flush valve, and made the pipe attachment at the bowl a more gradual bend instead of a 90° angle. Tests show noise dropped up to 16dB during the flush valve opening and about 5dB to 10dB with the valve fully opened.

    Grad student Michael Rose, lead author on the team’s most recent vacuum-assisted tech article in Proceedings of Meetings on Acoustics, says, “The toilet is much quieter and now kids won’t think they’re going to get sucked out.”

    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. Part of the lure of the BYU invention is that it works with existing airplane toilets – during a retrofit, only the elbow must be removed; the valve and bowl stay where they are.

    Brigham Young University