Hydraulic Basics PDF
Hydraulic Basics PDF
Hydraulic Basics PDF
From backyard log splitters to the huge machines you see on construction
sites, hydraulic equipment is amazing in its strength and agility! On any
construction site you see hydraulically-operated machinery in the form of
bulldozers, backhoes, shovels, loaders, fork lifts and cranes. Hydraulics
operates the control surfaces on any large airplane. You see hydraulics at
car service centers lifting the cars so that mechanics can work underneath
them, and many elevators are hydraulically-operated using the same
technique. Even the brakes in your car use hydraulics!
In this drawing, two pistons (red) fit into two Air in the System
glass cylinders filled with oil (light blue) and It is important that a
connected to one another with an oil-filled hydraulic system
pipe. If you apply a downward force to one contains no air bubbles.
piston (the left one in this drawing), then the You may have heard
force is transmitted to the second piston about the need to "bleed
through the oil in the pipe. Since oil is the air out of the brake
incompressible, the efficiency is very good -- lines" of you car. If there
almost all of the applied force appears at the is an air bubble in the
second piston. The great thing about hydraulic system, then the force
systems is that the pipe connecting the two applied to the first piston
cylinders can be any length and shape, gets used compressing
allowing it to snake through all sorts of things the air in the bubble
separating the two pistons. The pipe can also rather than moving the
fork, so that one master cylinder can drive second piston, which has
more than one slave cylinder if desired. a big effect on the
efficiency of the system.
The neat thing about hydraulic systems is that it is very easy to add force
multiplication (or division) to the system. If you have read How a Block
and Tackle Works or How Gears Work, then you know that trading force
for distance is very common in mechanical systems. In a hydraulic
system, all you do is change the size of one piston and cylinder relative to
the other, as shown here:
The piston on the right has a surface area nine times greater than the
piston on the left. When force is applied to the left piston, it will move
nine units for every one unit that the right piston moves, and the force is
multiplied by nine on the right-hand piston.
To determine the multiplication factor, start by looking at the size of the
pistons. Assume that the piston on the left is 2 inches in diameter (1-inch
radius), while the piston on the right is 6 inches in diameter (3-inch
radius). The area of the two pistons is Pi * r 2. The area of the left piston is
therefore 3.14, while the area of the piston on the right is 28.26. The
piston on the right is 9 times larger than the piston on the left. What that
means is that any force applied to the left-hand piston will appear 9 times
greater on the right-hand piston. So if you apply a 100-pound downward
force to the left piston, a 900-pound upward force will appear on the
right. The only catch is that you will have to depress the left piston 9
inches to raise the right piston 1 inch.
In cross section, the splitter's important hydraulic parts look like this:
High-pressure oil from the pump is shown in light blue, and low-pressure
oil returning to the tank is shown in yellow.
In the figure above you can see how the valve can apply both forward and
backward pressure to the piston. The valve used here, by the way, is
referred to as a "spool valve" because of its resemblance to a spool from a
spool of thread.