Exhaust manifold

Exhaust manifolds, or exhaust ports, are components of starships responsible for venting plasma from the vessel's propulsion systems into space. Exhaust manifolds could often get clogged with EM residue, and required periodic purging. Vectored exhaust ports, as those installed on the Delta Flyer II, lent themselves to increased speed and maneuverability. 

In 2151, the experienced a number of malfunctions as a result of an unexplained constriction in the flow of the ship's plasma exhaust. Enterprise's chief engineer, Charles Tucker, initially suspected the constriction was due to EM residue buildup in the exhaust ports, however, upon checking, discovered that was not the case. 

In 2152, upon discovering a a vessel from the 31st century, initial scans indicated no signs of any plasma exhaust ports, leaving the Enterprise crew confused as to the vessel's method of propulsion. 

In 2154, after a devastating attack by the Xindi, T'Pol ordered Commander Tucker to make inspecting the damage done to Enterprise's exhaust manifolds a priority, as it was crucial that impulse drive be restored as soon as possible, in order to facilitate their mission of locating the Xindi weapon. 

In 2373, Captain Janeway assigned Neelix the task of scrubbing the USS Voyagers exhaust manifolds for a period of two weeks, as punishment for his unauthorized attempt to trade some of Voyagers warp plasma for a map of the Delta Quadrant beyond the region known as "the Nekrit Expanse." 

In 2375, the crew of a duplicate version of Voyager, created by a substance known as the "Silver Blood," attempted to purge their warp field of interstellar dust with which it had become contaminated, but was unable to do so as the vessel's exhaust manifolds had disintegrated, due to exposure to a form of subspace radiation.