Boiler glossary

Boiler glossary J


JACK -- A flag flawn at the bow of a ship.
JACK BOX -- A box containing switches or connexions for changing circuits.
JACKET -- An outer casing or cover constructed round a cylinder or pipe, the space being filled with a fluid for either cooling or heating the contents, or with insulating material for keeping the contents at substantially constant temperature, e.g., the water jackets of an I.C. engine.
JACK SHAFT -- An intermediate shaft used in locomotives having collective drive; the jack shaft is geared to the motor shaft and carries cranks which drive the coupling rod on the driving wheels.
JERK-PUMP -- A timed fuel-injection pump in which a cam-driven plunger overruns a spill port, thus causing the abrupt pressure rise necessary to initiate injection through the atomizer.
JACOBS'S LADDER -- Vertical belt conveyor with cups or buckets.
JET CONDENSER -- A condenser in which exhaust steam is condensed by jets of cooling water introduced into the steam space.
JET PUMP -- A pump working by entraining a fluid in a jet of steam. See injector, ejector.
JOINT COMPOUNDS -- Non-hardening materials used on pipe threads to insure a proper seal.
JOINT EFFICIENCY -- The ratio, expressed in per cent, of the strength of a section of riveted or welded joint to the strength of an analogous section of solid plate.
JOULE -- J. The SI unit of work or energy, equal to the work done by a force of one newton when its point of application moves through a distance of one meter in the direction of the force.
JOULE EFFECT -- Production of heat solely arising from current flow in a conductor.
JOURNAL -- That part of a shaft that is in contact with, and supported by, a bearing.
JUMPER -- A wire used to connect two electrical terminals or nearby rails.
JUNK RING -- A metal ring attached to a steam-engine piston for confining soft packing materials; or for similarly holding a cast-iron piston-ring in position.