Ex*pan"sion (?), n. [L.
expansio: cf. F. expansion.] 1.
The act of expanding or spreading out; the condition of being
expanded; dilation; enlargement.
2. That which is expanded; expanse; extend
surface; as, the expansion of a sheet or of a lake; the
expansion was formed of metal.
The starred expansion of the
skies.
Beattie.
3. Space through which anything is expanded;
also, pure space.
Lost in expansion, void and
infinite.
Blackmore.
4. (Com.) Enlargement or extension of
business transactions; esp., increase of the circulation of bank
notes.
5. (Math.) The developed result of an
indicated operation; as, the expansion of (a +
b)2 is a2 + 2ab +
b2.
6. (Steam Engine) The operation of
steam in a cylinder after its communication with the boiler has been
cut off, by which it continues to exert pressure upon the moving
piston.
7. (Nav. Arch.) The enlargement of the
ship mathematically from a model or drawing to the full or building
size, in the process of construction. Ham. Nav.
Encyc.
&fist; Expansion is also used adjectively, as in
expansion joint, expansion gear, etc.
Expansion curve, a curve the
coördinates of which show the relation between the pressure and
volume of expanding gas or vapor; esp. (Steam engine), that
part of an indicator diagram which shows the declining pressure of
the steam as it expands in the cylinder. -- Expansion
gear (Steam Engine). a cut-off gear. See
Illust. of Link motion. -- Automatic
expansion gear or cut-off, one that
is regulated by the governor, and varies the supply of steam to the
engine with the demand for power. -- Fixed expansion
gear, or Fixed cut-off, one that
always operates at the same fixed point of the stroke. --
Expansion joint, or Expansion
coupling (Mech. & Engin.), a yielding joint or
coupling for so uniting parts of a machine or structure that
expansion, as by heat, is prevented from causing injurious
strains; as: (a) A slide or set of rollers,
at the end of bridge truss, to support it but allow end play.
(b) A telescopic joint in a steam pipe, to permit
one part of the pipe to slide within the other.
(c) A clamp for holding a locomotive frame to the
boiler while allowing lengthwise motion. -- Expansion
valve (Steam Engine), a cut-off valve, to shut
off steam from the cylinder before the end of each stroke.
