Tightness

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Tightness , also impermeability to a substance , gas , liquid , radiation or the like, is a property of material structures.

Tightness is a relative term. There are no absolutely sealed parts. The requirement for tightness always relates to given framework conditions. For example, a water pipe is watertight up to a certain internal pressure with a permissible leak rate .

The material properties of the building material and the quality properties of the structure (joints, cracks, air pockets, etc.) are always decisive for the tightness of an overall construction. The tightness is verified by means of a tightness test.

Application examples

General reviews: air tightness , water tightness , dust tightness

  • Airtightness of residential buildings: If residential buildings are not sufficiently airtight, this leads to increased energy consumption , undesirable drafts , moisture damage from condensation and condensation, and deterioration in sound insulation .
  • Airtightness of chimneys: overpressure boilers must be tight against the installation room so that the combustion gases do not escape into the installation room. Fireplaces that are operated as natural draft boilers only with negative pressure do not need to be completely airtight. In the event of leaks, room air can flow into the fireplace, but exhaust gas cannot escape.
  • Gas and radiation tightness of storage facilities: Castor containers, for example, have to guarantee tightness over the entire transport and storage period. For this purpose, the container body, together with the double-lid sealing system, forms a tight enclosure for the radioactive content . The function of the double lid system is continuously monitored during long-term interim storage.
  • Tightness of concrete structures against gases and liquids: sluices , dams , structures in the groundwater ( white tub ), tunnels
  • Leak tightness of supply lines: gas tightness of gas pipes, water tightness of water pipes, oil tightness of oil lines ( pipelines )
  • Leak tightness of housings: According to their degree of protection (IP class), housings offer a certain degree of tightness against particles (dust) and moisture. Depending on the requirements, housings must also be gas-tight (e.g. with an internal vacuum) in order to fulfill their protective function.
  • Leak tightness of fuel tanks at car filling stations is monitored by the indicator liquid level in the space between the double jacket.
  • The tightness of the fuel tank of a motor vehicle must be maintained even when the vehicle is heated, rolled over and crushed.
  • Leak-tightness of primary cells and batteries is common today and is limited by pressure relief valves to be on the safe side.
  • Tightness of X-ray bulbs: In order to maintain the highest possible vacuum in the X-ray sources for a longer period of time, housings made of borosilicate glass can be used, for example , which are fitted using a glass-metal connection .
  • Cellophane , softened when damp, stretched over a preserving jar with jam, when dried forms a very gas-tight seal that preserves the contents against spoilage due to atmospheric oxygen. However, water vapor is selectively absorbed by cellophane and can diffuse through the membrane along a concentration gradient. In glasses that have been stored dry for a long time, the volume of the filling material shrinks due to evaporation of water, the external air pressure increasingly dents the membrane and can cause it to tear.
  • Light tightness for the protection of light-sensitive materials and sensors in photography is created by blinds, matt black coloring, tight overlapping, filling of joints, with foam rubber or velvet.
  • District heating pipes and heating circuits made of metal are "squeezed off" with water. The compressive strength against bursting is tested under test pressure. Holding the pressure indicates the tightness of the system.
  • Vacuum apparatuses are " leak tested" after each modification to ensure that the leakage rate is sufficiently low for operation .
  • Compressed air and high-pressure gas systems, devices and lines are pressurized and the critical joints are coated with a foam-forming soap solution when the gas escapes.
  • A tire inner tube of a bicycle, or the part of a tire, is filled with a certain pressure and submerged under water and examined for any air bubbles that may escape.
  • For tightness of clean rooms against dust, ingress of cold air at windows, unwanted spreading of smells or toxins, for example also in case of fire, the pressure conditions between pipes, rooms, locks and doors are often a determining factor. Often tightness is only required in one direction of flow.

literature

  • Wolfgang Tietze (Hrsg.): Manual sealing practice. 3. Edition. Vulkan Verlag, Essen 2003, ISBN 3-8027-3301-0 .
  • Herbert Wittel, Dieter Jannasch, Joachim Vossiek, Christian Spura: Roloff / Matek Machine elements: standardization, calculation, design - textbook and table book . 24th edition. Springer Vieweg , 2019, ISBN 978-3-658-26280-8 , pp. 504-507 .

See also

Web links