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Storage of Seals, Continued
C-shaped  Bourdon  Tube

Fluid Power - Intro to Hydraulics, Pneumatics, and how it all works
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CHAPTER 8 MEASUREMENT AND PRESSURE CONTROL DEVICES For  safe  and  efficient  operation,  fluid  power systems  are  designed  to  operate  at  a  specific pressure  and/or  temperature,  or  within  a  pressure and/or  temperature  range. You have learned that the lubricating power of  hydraulic  fluids  varies  with  temperature  and that  excessively  high  temperatures  reduce  the  life of   hydraulic   fluids.    Additionally,   you   have learned  that  the  materials,  dimensions,  and method of fabrication of fluid power components limit  the  pressure  and  temperature  at  which  a system operates. You have also learned of means of   automatically   controlling   pressure   in   both hydraulic  and  pneumatic  systems. Most  fluid  power  systems  are  provided  with pressure  gauges  and  thermometers  for  measuring and indicating the pressure and/or the tempera- ture  in  the  system.  Additionally,  various  tempera- ture  and  pressure  switches  are  used  to  warn  of  an adverse pressure or temperature condition. Some switches  will  even  shut  the  system  off  when  an adverse  condition  occurs.  These  devices  will  be discussed in this chapter. PRESSURE  GAUGES Many   pressure-measuring   instruments   are called  gauges.  However,  this  section  will  be restricted  to  two  mechanical  instruments  that contain  elastic  elements  that  respond  to  pressures found in fluid power systems—the Bourdon-tube and  bellows  gauges. BOURDON  TUBE  GAUGES The majority of pressure gauges in use have a  Bourdon-tube  as  a  measuring  element.  (The gauge is named for its inventor, Eugene Bourdon, a French engineer.) The Bourdon tube is a device that senses pressure and converts the pressure to displacement.  Since  the  Bourdon-tube  displace- ment is a function of the pressure applied, it may be  mechanically  amplified  and  indicated  by  a pointer.   Thus,   the   pointer   position   indirectly indicates pressure. The   Bourdon-tube   gauge   is   available   in various tube shapes: curved or C-shaped, helical, and  spiral.  The  size,  shape,  and  material  of  the tube depend on the pressure range and the type of  gauge  desired.  Low-pressure  Bourdon  tubes (pressures  up  to  2000  psi)  are  often  made  of phosphor  bronze.  High-pressure  Bourdon  tubes (pressures above 2000 psi) are made of stainless steel   or   other   high-strength   materials.   High- pressure Bourdon tubes tend to have more circular cross  sections  than  their  lower-range  counterparts, which  tend  to  have  oval  cross  sections.  The Bourdon   tube   most   commonly   used   is   the C-shaped metal tube that is sealed at one end and open  at  the  other  (fig.  8-1). Figure 8-1.—Simplex Bourdon-tube pressure gauge. 8-1







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