(c) McGraw Hill Ryerson 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

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 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 A 5000 N on a 0.5 m 2 piston = 10 kPa pressure Force applied at B 10 kPa applied on 5.0 m 2 piston = 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

(c) McGraw Hill Ryerson 2007 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

(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 Take the Section 9.2 Quiz 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.