HYDRAULICS

Hydraulic System

uses a liquid under pressure to move loads.

It increases the mechanical advantage of the levers in machines.

http://www.youtube.com/watch?v=6061BFXc1_M

Pressure in Fluids

Hydraulic systems work because they use fluids under pressure

Pressure

Remember from last unit-

Is a measure of the amount of force applied to a given area

A piston Creates Pressure

The force applied to the input piston creates pressure in the fluid. This pressure is transferred throughout the fluid and presses on the output piston. This creates a force on the output piston.

A Piston Create Pressure

When you push on the small input piston, it presses on the fluid, which presses up on the larger output piston which lifts the object

F input = 20N

Pressure and Mechanical Advantage

The reason that a hydraulic system has a large mechanical advantage is the ability of the fluid to transmit pressure equally

Can you remember what this is called

Pascal’s Law

When pressure is applied to a liquid in a container, the pressure and force is transmitted equally throughout the liquid

Formula

Pressure= Force (N) Area (m2)

What are the units? Pa

Let’s try this

A force of 350N is applied to the input piston of this hydraulic ram. The piston has an area of .15m2. How much pressure created?

P = F (N) A (m2)

Now you try

The Hydraulics in this Caddy uses 4000 N of force on hydraulic pistons with an area of 0.5 m2

P= F A

Let’s try A small piston has an area of 4 cm2 and the

force it applies to the fluid is 20 N. What is the pressure?

P=F/A= 20N/4cm2 = 5 N/cm2

We know from Pascal’s law that there is same pressure everywhere in the fluid, so pressure that you exert in the small piston is the same in the large piston.

SOOOOOOO.......

If the large piston has an area of 100cm2 What force is exerted on the large piston?

Think of the force and area at each piston as ratios that have to be equal. They both have to equal the pressure of 5 N/cm2. So the force of the small piston divided by the area of the small piston MUST equal the force of the large piston divided by the area of the large piston

Force of the small piston =Force of the large piston

= 5 N/cm2 Area of the small piston Area of the large piston

F small = F large A small A large 20 N = X____ = 500 N 4 cm 2 100 cm2

You all know what to do now....cross multiply then divide!!!

Last Example question

A thin pipe full of water connects two pistons. The first piston has a surface area of 20cm2. The second piston has a surface area of 15cm2. A force of 300N is applied to the first pistona) How much pressure does the first piston

create in the water pipe?b) What is the output force on the second

piston?

What is the shortcomings about hydraulic systems?

To increase the force on an output piston, the input piston has to move a greater distance