Jacket - a sealed containment, either cast or welded, attached to a stuffing box or
a bearing housing containing a slightly pressurized water, or process liquid, to
provide some cooling to the seal or bearing.
In some instances steam is provided to provide some heating such as in
centrifugal pumps handling highly viscous liquids during winter season. Also
sometimes referred to as steam jacket.
Jet - a stream of liquid or gas forcefully shooting forth from a nozzle or orifice.
Jet pump - a type of pump employing a nozzle or orifice to move a stream of liquid
Jig - a plate, box, or frame for guiding a machine tool to perform its work or
Jockey pump - A small pump connected in parallel with a fire pump in a fire
sprinkler system. The jockey pump maintain the water pressure in the sprinkler
system at an elevated pressure such than when an sprinkler opens in the event of
a fire it will cause a pressure drop in the sprinkler system that can be detected by
the automatic controller at which time the fire pump will be activated. See fire
Joint - the location at which two parts are joined mechanically by welding, or by
the use of pin, or bolt.
Joule - the SI unit of work or energy; the work done by a force of one newton
multiplied by a distance of one meter.
Journal - the portion of a shaft contained or supported by a plain bearing.
Journal bearing - a sleeve bearing or sleeve-shaped bearing. It can be of plain,
elliptical (lemon-shaped), or of pressure-dam design depending on its intended
Journal box - a box or housing in a machine for containing a journal and its
F: glossary J1