quick-disconnect coupling (fluid lines). A fluid line coupling that automatically seals the line when it is disconnected. Hydraulic pumps are normally connected into the hydraulic system with quick-disconnect
couplings. This allows the pump to be removed for maintenance without air getting into the system. External hydraulic power sources can be connected into the system through quick-disconnect couplings.
quicksilver. Another name for mercury. See mercury.
quiescent current. Current flowing in an electronic circuit when there is no signal on the input.
quill shaft (generator coupling). A type of shaft used to couple an intermittent load, such as a generator to an engine. A quill shaft is a long, thin, hardened steel shaft with splines on each end. One end splines into the engine and the other end splines into the generator.
When an electrical load is suddenly applied to the generator, the quill shaft absorbs the load by twisting. This prevents the load being applied to the gear train of the engine as a sudden shock.
quill shaft (torsional vibration damper). A form of torsional vibration damper used between the engine crankshaft and the propeller reduction gears. The quill shaft is a hardened steel shaft with splines on both ends. One end splines into the crankshaft and the other end into the drive gear of the propeller reduction gear system. Torsional vibration is absorbed by the twisting of the quill shaft.