QUALITY GOVERNING – Power developed is governed by varying the quantity of fuel injected while the quantity of air sucked in is almost the same. The air fuel ratio in the combustion chamber is different at different loads.

QUICK SILVER – Metallic mercury.

QUENCHING – Rapid cooling of a metal in a bath of fluid during heat treatment after it has been heated to a given temperature, thus trapping the molecules of the metal in the desired structure.

QUICK CHANGE GEARBOX – A cluster of gears on a machine tool arranged in such a way that a sliding gear can be moved by a lever to mesh with anyone of the gears in the cluster to obtain desired ratio of speeds, feeds or thread pitches.

QUICK RETURN MECHANISM – A mechanism on various machine tools to give a table, ram or other movable part a rapid movement during the return or non-cutting stroke.

QUILL – A hollow shaft that revolves on a solid shaft, carrying pulleys, gears or clutches. When the clutch is closed, the quill and shaft revolve together.

QUICK RETURN MECHANISM – The mechanism used in machine tools such as shapers and power driven saws for the purpose of giving the reciprocating cutting tool a slow cutting stroke and a quick return stroke with a constant velocity of the driving crank.

QUENCH – The space in some combustion chambers which absorbs enough heat to quench or extinguish the combustion flame front as it approaches a relatively cold cylinder wall. This prevents detonation of the end gas but results in hydrocarbon emission.

QUALITY OF STEAM – Refers indirectly the amount of water or unevaporated moisture in steam.

QUASI-STATIC PROCESS – is a process which is carried out in such a manner that at every instant the system departs only infinitesimally from the thermodynamic equilibrium state.