Seal, permanent, vacuum

Seal, permanent (vacuum technology) A seal that is designed so as not to be easily disassembled. Example A weld or braze joint. 

PTFE taps usually have two different types of seal as shown in Fig. 2.6. Seal E is produced by a vertical pressure of the key, whereas seal D is the result of a lateral pressure from the body of the key. The latter seal tends to be the weaker and the more temperature-sensitive, and this should be considered when planning the orientation of the tap in the system the better seal E should always be used to close the more permanent vacuum. 

The counter was sealed permanently into a vacuum system and provisions for reducing the aliquot of the sample being counted by a series of expansions and dilutions with inert carrier are described for cases where the activity is initially too great. 

Seal, demountable (vacuum technology) A seal designed to be disassembled and reassembled easily using a gasket. The sealing gasket may be reusable or replaced each time the seal is disassembled. Also called a Non-permanent seal. 

A handlamp is essential for all jobs that cannot be conveniently rotated in the bench burner flame. For example, it is used to seal off test-tubes containing samples which must be kept cool, or which should not be disturbed. It is indispensable if additions have to be made to glassware which is part of a complicated and semi-permanent apparatus, such as a vacuum line, and for sealing-off evacuated vessels. 

Mechanical failures occur when the part is exposed to some t5q)e of force that exceeds its capability. A part may be exposed to three different t5q)es of forces tensile, compression, and vacuum-generated stresses. Many processes require super- or subatmo-spheric pressure. In a fluoropol5mier-Iined vessel or a stand-alone vessel at elevated pressure, the walls are subjected to tensile stress. Compression stress develops in parts such as seals and gaskets where force is applied to the part, for instance, by placing it between bolted flanges. Vacuum can be a permanent or transient feature of a process and subjects a part to complex forces which could be a combination of tensile and compression. 

Another glue-free design uses Tefzel gaskets to seal the two microscope slides together [99]. The slides can also be held in a Kel-F (transparent fluoropolymer) clamp and lowered into a completely vacuum-tight cell [100]. Detailed descriptions of the vacuum procedures are provided [101]. For a less permanent seal, wax (such as that used in hair removal) may be used, though it does eventually succumb to solvent attack [102]. 

Non-permanent joint (vacuum technology) A vacuum seal made so as to allow easy disassembly. The seal is made using an elastomer, a deformation metal seal, a shear gasket, or some other reusable or disposable material. See also Permanent joint. 

To facilitate the movement, as well as increase the gasket and the lifetime of the plunger, silicone grease is used on the O-rings (better known as vacuum grease) because it is not soluble in water and prevents corrosion. In other words, a light film of a lubricant made with silicone grease was used that both sealed and acted as a permanent lubricant to reduce friction. 

For test applications, it is only necessary to obtain an outgassing rate low enough that the pressure will remain at an acceptable level during the test. Many deliverable packages are permanently sealed, and the vacuum must remain at an acceptable level for periods up to 15 years. The required engineering and processing are fairly complex, and are treated as highly proprietary by most companies. 

Example Consider a small permanently sealed dewar that must have a pressure of 0.05 torr or less for acceptable performance. If the dewar vacuum is to last for 10 years (3.15x10 s), and if the dewar contains no getters, it must have a net... 

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