Vacuum Science and Technology (VST), e-chapter 9 Sealing techniques and system components
This chapter gives an overview of demountable and permanent vacuum sealing techniques and commercially available system parts. Demountable joints in vacuum technology usually are flange connections between metal components. Numerous types of connections and elastomer or metal gasket sealings are available today. Vacuum tight permanent sealing is made by welding, brazing, soldering or gluing. Different welding and brazing techniques are compatible with vacuum tight sealing. Pros and cons of these techniques are amply discussed.
If we want to transmit electricity, motion, liquids or optical radiation into a vacuum environment, we must somehow ‘pass through the vacuum wall’. To this end a variety of electrical feedthroughs, motion feedthroughs and manipulators, liquid feedthroughs and viewports are on the market. In order to connect or disconnect different vacuum sections, valves are available in a variety of configurations for manual, electromagnetic or pneumatic operation. Important components in each valve are the sealing construction and the actuation mechanism. Apart from dimensional considerations, the choice of the sealing construction and the actuation mechanism, as well as the choice of materials for the valve body and the sealing are determined by the pressure range in which the valve is to be used.
To provide in a controlled gas atmosphere, it is necessary to be able to adjust the pressure in a vacuum system or to regulate and hold the inlet rate of a gas in the vacuum system at the desired value. Gas admission valves are used to admit controlled quantities of gas from a source external to the vacuum. For this purpose we can distinguish needle valves, bakeable UHV precision dosing valves, permeation valves and mass flow controllers. The control range of these systems depends on the valve type and its exact dimensioning.
When small or large movements are needed, the influence of pump vibrations should be muted or oversizing compensated, the application of metal bellows forms an appropriate solution. According to their manufacturing method and properties we distinguish corrugated bellows and diaphragm bellows.