(c) McGraw Hill Ryerson 2007

9.2 Constructed Fluid Systems

• By controlling fluids, humans attempt to do work or protect development. Hydraulics = create pressure in fluids to do work Pneumatics = create pressure in gases to do work Humans attempt to control natural water movements

through the use of pumps and barriers like levees.

See page 324

By using pumps and levees, New Orleans is usually kept dry. When Hurricane Katrina overwhelmed their fluid-control systems, however, tragedy occurred.

(c) McGraw Hill Ryerson 2007

Fluids at Rest and in Motion

• Fluids at rest Pascal discovered the concept of static pressure Squeezing a fluid at one point transmits force everywhere Static pressure is created when an enclosed fluid is

squeezed Static pressure can then apply a force somewhere else• Eg. Squeezing a tube of toothpaste, brakes on a car

See pages 325 - 326

Fluids at Rest and in Motion

• Fluids in motion Bernoulli discovered the concept of dynamic pressure Fluids in motion cause a decrease in pressure

perpendicular to the direction of motion Dynamic pressure is created when fluid moves

(c) McGraw Hill Ryerson 2007

Air moving faster over the wing creates higher pressure underneath =

lift force

(c) McGraw Hill Ryerson 2007

Hydraulic Systems

• Hydraulics = study of pressure in liquids Hydraulic systems create pressures that travel through a

fluid Pressure applied to an enclosed fluid creates a force that

can be used anywhere A pump is generally used to provide pressure at one point

Everywhere in the system then has a usable force• This is why we have pressure in our taps and faucets

Pumps may create high or low pressure to move fluids

See pages 326 - 327

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

A pump (top) first creates low pressure to draw water in, then high pressure to pump it out.

Low P

High P

(c) McGraw Hill Ryerson 2007

Valves and Hydraulic Multiplication

• Valves are used to control the movement of fluids Therefore, valves control the location of fluid

pressure Check valves only allow fluids to flow in one

direction• Hydraulic multiplication allows small changes in

pressure to do large amounts of work.

See page 421

A small area applying pressure can cause a large force to be exerted over a large area.

(c) McGraw Hill Ryerson 2007

Valves and Hydraulic Multiplication

See page 421

Pressure applied at A5000 N on a 0.5 m2 piston = 10 kPa pressure

Force applied at B10 kPa applied on 5.0 m2 piston = 50 000 N

(c) McGraw Hill Ryerson 2007

Problems in Hydraulic Systems

• Hydraulic systems must be designed carefully Minimize twists and turns to allow fluid to flow freely Connect pipes and seams well to avoid leakage Pressure in the system is affected by the size of the pipes

and the smoothness of the inside of the pipes. Pressures can be dangerous if fluids allowed to escape

through broken pipes or lines. Pressure-relief valves re often used to control pressures

Fluids are often poisonous

See page 329

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Pneumatic Systems

• Pneumatic systems use a gas under pressure Same idea as hydraulics, except gases can be compressed,

whereas fluids do not compress much. Compressors are used in pneumatic systems, not pumps

Compressors build up pressure, then quickly release it in a small area to produce large forces

Pneumatics can be used in large and small systems Pneumatics and hydraulics are often used together

See pages 330 - 331

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

(c) McGraw Hill Ryerson 2007

Pneumatic Systems and their Problems

• Pneumatic systems must have unblocked air flow to work efficiently.

Because air is usually brought into a compressor to increase pressure, filters clean the air to keep the compressor clean

If the filters are not cleaned, the pneumatic system becomes inefficient

See pages 330 - 331

Take the Section 9.2 Quiz

What did we do before email attachments and faxes? This Rohrpoststation used pneumatics to “shoot” tubes with rolled up documents around large building like factories. If the station’s compressor filter was blocked, important messages could become lost.