1. 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.
By using pumps and levees, New Orleans is usually kept dry. When Hurricane Katrina overwhelmed their fluid-control systems, however, tragedy occurred.
See page 324
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2. Fluids at Rest and in Motion
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
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
Air moving faster over the wing creates higher pressure underneath = lift force
See pages
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3. Hydraulics = study of pressure in liquids
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 than 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
A pump (top) first creates low pressure to draw water in, then high pressure to pump it out.
See pages
Low P
High P
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4. 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.
A small area applying pressure can cause a large force to be exerted over a large area.
Pressure applied at A
5000 N on a 0.5 m2 piston = 10 kPa pressure
Force applied at B
10 kPa applied on 5.0 m2 piston = N
See page 421
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5. 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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6. 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
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7. 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 become inefficient
What did we do before 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.
See pages
Take the Section 9.2 Quiz
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