Hydraulic
Power
basics
Pascal’s Law
Pressure exerted at any point on
a confined liquid is transmitted
undiminished in all directions.
Hydraulic Terms
Hydraulic
Piston
Shaft
PSI
Pneumatic
Stroke
Check valve
Spool valve
Pump
Seal
Rockshaft
Cylinder
Hydraulic
motor
Singleacting
Doubleacting
Input /
Output
Hydraulic
Tool or equipment
powered by the
movement of fluid
under pressure.
Examples are brakes,
Pneumatic
Tool or equipment
powered or supported
by the movement of
compressed air.
PSI
Pounds per Square Inch
determines amount of force
GPM
Gallons per Minute
determines speed of action
Basic
principle
Pressure applied to piston “A” is
transferred equally to a piston of the same
size “B” because PSI is the same
throughout the system.
hydraulic
advantage
If the surface area of piston “B” is 10 times
the surface area of piston “A”, then the force
applied to piston “A” is multiplied 10 times as
the force exerted on piston “B”. PSI is equal
throughout the system.
Input / Output
Force input on a hydraulic
system or component results
in transfer of power to output
of force by the system or
component.
Pump
Functions in a hydraulic
system by pressurizing
and moving fluid from one
part of the system to
another.
Hydraulic pumps are usually one
of four types:
PISTON
GEAR
VANE
INTERNAL ROTOR
Piston Pumps
• Work well at PSI’s of 2000 or more
• Single piston pump used in bottle jacks
• Require several pistons working together to
generate enough volume for tractor
applications
• Necessarily involve many moving parts
Gear Pumps
• Work well at 1500 PSI and below
• Work with a minimum of moving
parts
• Less expensive to manufacture
than piston type pumps
Gear
Pump
driven gear
idler gear
Hydraulic Motor
Receives power from
moving fluid to
transfer hydraulic
power to mechanical
Cylinder
Piece of equipment that
transfers hydraulic power
into mechanical
movement in one or two
directions only.
Hydraulic Cylinder
Single-acting
Refers to a hydraulic
cylinder that works in one
direction only.
Double-acting
Refers to a hydraulic
cylinder that pushes and
pulls.
Single-acting
cylinder
Double-acting
Cylinder
Piston
Internal component of a
hydraulic cylinder that is
moved in a linear motion by
the action of fluid introduced
into the cylinder.
Shaft
The polished round bar that
is extended from and
retracted into a hydraulic
cylinder.
Stroke
The length of movement that a
hydraulic cylinder is capable
of producing.
Seal
Found in hydraulic
components; function is to
keep fluid from leaking
between moving and nonmoving parts
Check Valve
Restricts flow of fluid to only
one direction; allows pressure
to build up or be maintained.
Spool Valve
Controls direction of flow of
fluid in a hydraulic system to
cause the different parts of
the system to function.
The first hydraulic power lift for a
tractor was introduced in 1935 by
John Deere. This unit only had two
positions, up and down, but the
hydraulic action cushioned the
lowering of the implement.
Rockshaft
Rotating shaft on a modern
tractor powered by an internal
hydraulic cylinder; used to
transfer power to the
implement lift.