sylphon
noun
syl·phon
| \ ˈsilˌfän\
plural sylphons
Definition of sylphon
: a thin-walled tubular bellows used in temperature and pressure regulators, bellows seals, and expansion joints
In between, a maze of valves, venturis (short tubes with constricted throats), and sylphons (pleated metal bellows) interacted with one another, maintaining conditions inside the airplane as outside pressure varied.— Nick D'Alto, Air & Space Smithsonian, September 2000
—formerly a U.S. registered trademark