194 Agricultural Mechanics and Technology Systems
Copyright Goodheart-Willcox Co., Inc.
be depressed before the gun will fi re. Sequential guns are much safer than
semiautomatic-fi ring, or bump-fi re, nail guns that fi re every time the trigger
is pulled without cycling a safety tip.
Safety Note
Nails driven by a nail gun have sufficient force to fully penetrate a board in a single
stroke. If the nail comes in contact with severely warped grain or a knot in the lumber,
the nail could be deflected as a dangerous projectile. Metal structures near wood
framing can produce the same result. Care must be taken to maintain appropriate
air pressure and to work around potential deflections. Large nail guns must be held
securely as they have the potential to kick back slightly when operating.
Hydraulic Jacks and Presses
A tool that uses hydraulic pressure is capable of exerting a tremendous
amount of pressure with a limited amount of input energy. The principle of
hydraulics uses an incompressible liquid to transfer and multiply force within
a closed connected system. Figure 8-18 illustrates this basic principle.
Hydraulic applications are used for tasks
such as lifting heavy objects, spreading
objects apart, and applying a squeezing
force to an object, as well as for other tasks.
Hydraulic jacks are low-profi le tools
capable of lifting heavy objects such as
vehicles and equipment. Bottle jacks are
vertical cylinders with a piston or ram that is
driven upward by the application of hydraulic
force, Figure 8-19A. Bottle jacks may be
operated by a manual or pneumatic-driven
pump. Jacks that lift from 2 to 20 tons are
common. The stroke, or distance the piston
travels, determines the amount of movement
a bottle jack can produce. Increasing the
diameter of the output piston multiplies the
output force a jack can produce. Bottle jacks
are small and portable.
Floor jacks use a horizontally mounted bottle jack that pushes against a
lever to lift the saddle arm and platform vertically, Figure 8-19B. This design
loses about three-quarters of the force produced by the standard bottle jack,
but results in a compact tool that can lift objects proportionally higher. The
wheels on the jack make it convenient to move on the shop fl oor, but most
fl oor jacks are heavy and lack portability.
When using a jack or jacks to lift a vehicle, you must physically block
the wheels that remain in contact with the ground to keep them from rolling.
Commercially made wheel chocks are available for this purpose, but wood
blocks of adequate size left over from other projects can also work.
Force
Piston
(plunger)
Load
Multiplied Force
Piston
(ram)
Goodheart-Willcox Publisher
Figure 8-18. Pascal’s law states that an increase in pressure at
any point in a confined fluid results in an equal pressure increase
at every other point in the connected system. When a downward
force is applied to the smaller piston in this illustration, the force
is multiplied due to the increased surface area of the larger piston.