Basic Vacuum Technology
|
What is a vacuum ? A vacuum is a negative pressure or depression - which means that the pressure is lower than the atmospheric (also called ambient) pressure that surrounds us all. Pressure is the relationship between a Force and the Area on which it acts. The following formula is the basis of calculations: P = F/AIn practice when talking about vacuum in industrial handling applications we use the term % of atmospheric pressure.
A little bit of history : About 1630 Torricelli, (who gave us the torr measurement system), discovered that atmospheric pressure at sea level would maintain a column of mercury of 760 mm high. Since this value can fluctuate with weather conditions the value adopted was the pressure which a column of mercury of 760 mm exerts on a flat surface -that, is 1013.25 millibars. The French physicist Bar gave us the bar and millibar (mbar) measurement system which is largely used in vacuum technology today. Pascal gave us the Pascal (Pa) and kiloPascal (kPa) units 0.001bar = 1 mbar = 100Pa = 0.1kPa For handling systems relatively low vacuum levels are generally used - 50% to 60% vacuum The table below shows the different vacuum values compared to millibars :
A simple reminder is that 1 bar = 1000millibars = 10100 Pa = 100kPa = no vacuum Atmospheric pressure is 1013.25 mbars (standard as per DIN 1343). It may vary according to climatic conditions. Atmospheric pressure decreases with altitude – by approximately 12,5 mbars each 100 meters.
These differences affect how vacuum handling systems will work – as an example if a vacuum system can move 10Kg at sea level, it could only move 8,92 Kg at 1000 meters altitude. That is why calculations are most frequently made for suction cup vacuum handling systems using % vacuum. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||