Tightness


Also found in: Dictionary, Thesaurus, Legal, Financial, Idioms, Wikipedia.

Tightness

 

the ability of the shell of a body or of its separate elements and joints to block the exchange of gases or liquids between the environments separated by the shell. Tightness is a necessary working condition for many systems, apparatus, and instruments. The required tightness of a covering (the permissible exchange) is determined from the conditions necessary for the normal course of the process for which the tightness is created. The degree to which a covering is hermetic is characterized by the quantity of a substance passing through it per unit of time and is measured for liquids in liters per sec (l/sec) or grams per sec and, for gases and vapors, in grams per sec or liters · mm Hg/sec (l · mm Hg/sec). A covering is considered hermetic if the liquid or gas exchange through it does not exceed the permissible level.

Tightness is an important property of objects and must be considered in planning sealed objects meant for prolonged keeping and use. The quantitative characteristics of an object’s hermetic properties determine its reliability and durability. Calculations are made to establish the probable period of time within which, given certain usage conditions (fluctuations in pressure, temperature, load, and so on), liquids or gases may flow through the entire covering or parts of it and destroy the hermetic properties.

Gas or liquid exchange—that is, the reason for disruption of the hermetic state—can be caused by the permeability of the material of the covering or of a joint with intact structure, which is taken into consideration during construction, or leaks in the structure of the material or joints, which are detected by vacuum technology. There is large-scale production of so-called hermetic castings for parts of motors, turbines, and water-supply and heating systems.

Other objects that must be hermetic include the bodies of aircraft and spacecraft, submarines, diving suits, and caisson chambers. A high degree of tightness is necessary to maintain a superhigh vacuum in the cavities of thermonuclear devices, accelerators, and space simulators. The normal operation of such systems can be disrupted by leaks as slight as 10-7 to 10-8 /· mm Hg/sec. Even more stringent tightness requirements exist for the casings of electrovacuum and gas-filled miniature instruments, in which the pressure or composition of the gaseous medium must not change perceptibly during prolonged storage or in the process of use. For example, to maintain working pressure in an electrovacuum instrument with a volume of 100 cm3 that does not contain a getter, the leak in its shell must not exceed 3 x 10-12 1·mm Hg/sec during a one-year storage period.

The hermetic properties of oil and gas boreholes play an important part during the drilling process in deposits with high formational pressure. Surfaces are sealed while opening oil strata when there is a danger of blowout or open gushing. It is also necessary for surfaces to be hermetic while working oil and gas deposits to prevent small leaks of the mineral between the place where it is drilled and the refinery. The maintenance of hermetic seals is obligatory during many technological processes in the chemical, food, pharmaceutical, and canning industries when it is necessary to maintain high pressure, a vacuum, or sterile conditions. It is necessary to seal industrial machinery and instruments that are exposed to the action of moisture, gases, dust, dirt, aggressive chemical substances, or instruments emitting radioactive rays. If temperature-moisture and sanitary conditions must be observed in places of work, hermetic production buildings are constructed.

REFERENCES

Smirnov, A. I., and A. A. Sotnikov. Liteinoe proizvodstvo, 1964, no. 4, p. 25; no. 6, p. 27.
Lanis, V. A., and L. E. Levina. Tekhnika vakuumnykh ispytanii, 2nd ed. Moscow-Leningrad, 1963.

L. E. LEVINA

References in periodicals archive ?
President Trump, who has commented few times on OPEC artificially bumping up the prices, could decide to take action by releasing SPR barrels in order to offset the tightness in the market.
Because both a limited number of observations and important unobserved aggregate factors affect labor market tightness and wage growth simultaneously, the causal link between labor market tightness and wage growth is difficult to estimate.
As mentioned above, the two key drivers of raw material prices are feedstock/ oil prices and supply tightness. Oil prices went up 14 percent in 2017 versus 2016.
Plotting the U/V ratio against wage growth as measured by the employment cost index (ECI) provides insight into the relationship between labor market tightness and wages.
With rest, ice, compression, and elevation, the muscle will heal, and function will be restored; however, more severe or improperly treated injuries lead to muscle tightness that extends beyond the 4- to 6-week window of typical resolution.
"It's probably precautionary, just a little bit of tightness."
Any decrease in the flexibility of hamstrings or tightness can cause hamstring injuries which are the most common type of injury among athletes and have a slow recovery rate, make health expenditures high and also decrease the performance level of the athlete.
For most of the patients with isolated long flexor tightness following exercises are taught:
* Sizes from 3/8" to 2" (DN 10--DN 50), standards include ISO 9393 for tightness and EN 12266 for leak rating
Loop length and tightness factors together with twist multipliers have an effect on air permeability property of single jersey and 1 x 1 rib knitted fabrics.
"At the end of training on Tuesday Robbie felt a tightness in his hamstring and when we had it scanned, there was a little bit of blood there," said Schmidt.
We restrict the scope of this note to two variables that described the curvature of a squirrel's tail: Tightness and Portion Bent.