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 (c) McGraw Hill Ryerson 2007

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 325 - 326 (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 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. High P See pages 326 - 327 Low 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. 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 (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 330 - 331 (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 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 station’s compressor filter was blocked, important messages could become lost. Take the Section 9.2 Quiz See pages 330 - 331 (c) McGraw Hill Ryerson 2007