9.2 Constructed Fluid Systems

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
2
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
• 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 325 - 326
3
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 326 - 327
Low P
High P
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 50 000 N
See page 421
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
6
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
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 email attachments and
faxes? This Rohrpoststation used pneumatics to
shoot tubes with rolled up documents around
large building like factories. If the stations
compressor filter was blocked, important messages
could become lost.
See pages 330 - 331
Take the Section 9.2 Quiz