Hydraulic Power

basics

Pascal’s Law

Pressure exerted at any point on

a confined liquid is transmitted

undiminished in all directions.

Hydraulic Terms

Input / Output

Double-acting

Single-acting

Hydraulic motor

CylinderRockshaftSealPump

Spool valveCheck valveStrokePneumatic

PSIShaftPistonHydraulic

HydraulicTool or equipment powered by the movement of fluid under pressure. Examples are brakes, jacks & tractor lifts.

Pneumatic

Tool or equipment powered or supported by the movement of compressed air.

PSIPounds per Square Inch

determines amount of force

GPMGallons per Minute

determines speed of action

Pressure applied to piston “A” is transferred equally to a piston of the same size “B” because PSI is the same throughout the system.

Basic principle

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.

hydraulic advantage

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:

PISTONGEARVANE

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 MotorReceives power from moving fluid to transfer hydraulic power to mechanical rotating force.

Cylinder

Piece of equipment that transfers hydraulic power into mechanical movement in one or two directions only.

Hydraulic Cylinder

Single-actingRefers to a hydraulic cylinder that works in one direction only.

Double-actingRefers 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.

StrokeThe 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 non-moving 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.