Very low-pressure gas - Vacuum speaker accessories

Readers are referred to all the articles in this section, and in particular to :

• [B 4 020] Very low pressure gases. General information.

• [B 4 050] Vacuum chambers.

For pressure gauges, flowmeters and tightness testing, readers are referred to the specialist articles in the Mesures et Contrôle treatise.

The vacuum range is very wide, from atmospheric pressure to interstellar pressures, from 10 ⁵ to 10 ^–16 Pa. The means used to create vacuum are very diverse; so there are a great many accessories that are either indispensable (piping, valves, seals, etc.) or used as part of this or that process (movement passages, portholes, electrical passages, etc.). The list is long, and the catalog is never definitive, as it varies with needs and technical advances. As a result, we can't draw up an exhaustive list of all existing equipment, so we'll confine ourselves to giving the principles of accessories, numerous examples and the most comprehensive list possible of equipment manufacturers and importers.

It is customary to distinguish between several pressure ranges: coarse vacuum, medium vacuum, high vacuum and ultra-high vacuum. From a strictly utilitarian point of view, we divide them into two domains:

• the industrial vacuum comprising the coarse vacuum and part of the medium vacuum, from about 10 ⁵ Pa to 10 ² Pa ;

• classic vacuum, i.e. the rest, including high vacuum and ultra-high vacuum (below 10 ² Pa).

The requirements are different. For example, in industrial vacuum, gas flows are often high, so leakage can be tolerated. This is not the case in high vacuum, and even less so in ultra-high vacuum, so accessories are very different.

Remember that at any given moment, the gas flow to be pumped comes from the decrease in the number of molecules in the enclosure, the flow due to desorption, that due to leakage and permeation, that backscattered by the pumps and, finally, that imposed by the process (see the General section on gases at very low pressure [B 4 020] ). This flow must be absorbed by the pumping system.

At any given time :