Jack (device)

The personal name Jack, which came into English usage around the thirteenth century as a nickname form of John, came in the sixteenth century to be used as a colloquial word for 'a man (of low status)' (much as in the modern usage 'jack of all trades, master of none').

The first attestation in the Oxford English Dictionary of jack in the sense 'a machine, usually portable, for lifting heavy weights by force acting from below' is from 1679, referring to 'an Engine used for the removing and commodious placing of great Timber.

'[2] A scissor jack uses the mechanical advantage of a leadscrew and 4-bar linkage to allow a human to lift a vehicle by manual force alone.

The jack shown at the left is made for a modern vehicle and the notch fits into a jack-up point[3] on a unibody.

When the plunger pulls back, it draws oil out of the reservoir through a suction check valve into the pump chamber.

When the plunger moves forward, it pushes the oil through a discharge check valve into the cylinder.

At this point the suction ball within the chamber is forced shut and oil pressure builds in the cylinder.

Floor jacks usually include casters and wheels, allowing compensation for the arc taken by the lifting pad.

This mechanism provides a low profile when collapsed, for easy maneuvering underneath the vehicle, while allowing considerable extension.

The screw version of the bottle jack works by turning a large nut running on the threaded vertical ram at the neck of the body.

This eliminates the need for the user to actuate the hydraulic mechanism, saving effort and potentially increasing speed.

Sometimes, such jacks are also able to be operated by the normal hydraulic actuation method, thereby retaining functionality, even if a source of compressed air is not available.

The jack's versatility stems from its use for such applications as lifting, winching, clamping, pulling and pushing.

It is this versatility, along with the long travel it offers and its relative portability, which make the farm jack so popular with off-road drivers.

Selection of the standard is an agreement between the purchaser and the manufacturer, and has some significance in the design of the jack.