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Glossary J
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The following definitions are intended to give basic understanding of the terms
commonly used in the pump industry. Some industry standards, or customer
specifications, may have specific meaning of certain terms that may be different
from their common usage - in such case the terms should be interpreted in the
context of the standards, or specifications, being referred to.
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 under pressure.

Jig - a plate, box, or frame for guiding a  machine tool to perform its work or
function.

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 pump.

John Crane - a commercial brand of mechanical seals and sealing elements
widely used in pumps.
John Crane is a registered trademark by its owner.

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 use.

Journal box - a box or housing in a machine for containing a journal and its
bearing.
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