Also found in: Dictionary, Wikipedia.
A controllable butterfly valve in the exhaust pipe of a reciprocating engine equipped with a turbocharger. The valve controls the amount of exhaust gases that can be forced through the turbocharger. The valve gradually closes with height until it is rated at full-throttle or another selected value is reached when it is fully closed. At this time, all exhaust gases must pass through the turbocharger. See also butterfly valve.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved