Pressure relief

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As a pressure relief , the slackening of is pressure to a solid or a fluid designated, for example by a decrease in the air pressure or by reducing the applied load .

In physics , materials and geosciences , pressure relief is the cause of numerous phenomena and an important cause of volume changes and the processes that result from them. In the case of gases , the volume increases sharply - in accordance with the gas laws - which is used for technical purposes in cooling systems , for example , but in the extraction of crude oil can cause natural gas to escape unexpectedly from the underground. In technology, pressure vessels are relieved of pressure in certain work phases or automatically through safety valves - e.g. B. in steam boilers , pressure cookers or venting a nuclear reactor.

If a liquid is under atmospheric or other gas pressure , the rate of evaporation increases as it decreases , which in extreme cases can lead to rapid sublimation into the gaseous state even below freezing point . If, on the other hand, gases are dissolved in liquids under pressure, then - as Robert Boyle already established in 1670 - gas bubbles form when the pressure is suddenly released . The diving physics therefore has various safety systems to the dreaded bubble of gas embolism to prevent (decompression), which occurs when divers ascend too quickly.

In the case of solids and rocks , each pressure relief results in only a small change in volume , but this can be expressed in cracks, fissures and other phenomena through the expansion of the volume . When deep rocks rise (or erosion of rocks above them), crevice systems are created which accelerate weathering on the earth's surface . This special form of concentric fissure formation and the associated weathering is called exfoliation . Granitic rocks like the Sugar Loaf of Rio de Janeiro or the Half Dome in California's Sierra Nevada owe their distinctive shape this process.

literature

  • Wilhelm Westphal: Physics. A textbook . 22.-24. Edition, Springer-Verlag, Berlin / Göttingen / Heidelberg 1963 (713 pages, Chapters III, VI and VII).
  • Dieter Richter: General Geology. 3rd edition, De-Gruyter Verlag, Berlin / New York 1985, ISBN 3-110-10416-4 .