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The general adoption of rotary valves in the place of poppet valves in combustion engines was prevented by the issue of sealing. Poppet valves have a seal around the tapered flange of the opening, and this seal improves with increased working pressure in the combustion chamber because the pressure forces the valve shut.
Radial shaft seals, also known as lip seals, are used to seal rotary elements, such as a shaft or rotating bore. Common examples include strut seals, hydraulic pump seals, axle seals, power steering seals, and valve stem seals.
A Bendix drive is a type of engagement mechanism used in starter motors of internal combustion engines.The device allows the pinion gear of the starter motor to engage or disengage the ring gear (which is attached to the flywheel or flexplate of the engine) automatically when the starter is powered or when the engine fires, respectively.
The pinion pairs only mesh for the part of their length between the two spur gears, and rotate in opposite directions. The remaining length of a given pinion meshes with the nearer spur gear on its axle. Each pinion connects the associated spur gear to the other spur gear (via the other pinion).
Labyrinth seals are also found on pistons, which use them to store oil and seal against high pressure during compression and power strokes, as well as on non-rotating shafts. In these applications, it is the long and difficult path and the formation of controlled fluid vortices plus some limited contact-sealing action that creates the seal.
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A rack and pinion has roughly the same purpose as a worm gear with a rack replacing the gear, in that both convert torque to linear force. However the rack and pinion generally provides higher linear speed — since a full turn of the pinion displaces the rack by an amount equal to the pinion's pitch circle whereas a full rotation of the worm screw only displaces the rack by one tooth width.
Axial run-out causes the tip of the tool or shaft to rotate off-centre relative to the base. Axial run-out will vary according to how far from the base it is measured. In addition, irregular run-out is the result of worn or rough bearings which can manifest itself as either axial or radial run-out.