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Pfeiffer <strong>Vacuum</strong><br />
Page 128<br />
1) Clamping flange<br />
2) Clamp<br />
3) Collar flange<br />
4) Fixed flange<br />
5) Base plate /<br />
housing wall<br />
6) Claw<br />
7) Circlip<br />
<strong>Vacuum</strong> <strong>Technology</strong><br />
Fixed flanges and clamping flanges<br />
Standard ISO 1609.4 / DIN 28404 specifies fixed flanges for nominal diameters of DN 10 –<br />
1000 ISO-F and clamping flanges for nominal diameters of DN 10 – 630 ISO-K. The small<br />
flange components are usually preferred for nominal diameters of DN 10 – 50. As in the case<br />
of small flanges, fixed and clamping flanges with centering rings have a seal between the<br />
flat mating surfaces of the flanges. The flanges are fastened by means of special clamps<br />
(clamping flanges) or by means of screws or pins (fixed flanges). By using a collar flange that<br />
is held in a groove on the clamping flange by means of a retaining ring or claws, it is also<br />
possible to connect clamping flanges to fixed flanges. When installing turbomolecular pumps<br />
with clamping flanges, the manufacturer’s special instructions in the operating manuals<br />
must be observed for reasons of safety.<br />
Figure 6.6: Clamping and fixed flange connections<br />
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DIN flanges<br />
Since fixed and clamping flange connections are not designed for overpressure applications<br />
and because there are process technologies in which the connections are charged with both<br />
vacuum as well as overpressure, DIN flanges continue to be used. DIN 2501 (ND 6) and<br />
DIN 2502 (ND 10) specify the flange pattern of these flanges. One flange with o-ring groove<br />
and one flange with a smooth mating surface must be paired for each connection. Another<br />
disadvantage of these flanges relative to the ISO flanges consists of their significantly higher<br />
material and space requirements.<br />
UHV flanges<br />
Flanges with cutting edges and copper gaskets, (also referred to as Conflat ® or CF flanges)<br />
are used for UHV applications. A copper ring is placed between two flanges. The concentric<br />
peripheral cutting edges of the flanges penetrate into the copper to form a metallic seal<br />
that is characterized by an extremely low leakage and permeation rate, as well as by high<br />
temperature resistance. These flanges are standardized in accordance with ISO TS 3669.<br />
A sufficient number of screws ensure the necessary high contact pressure. Once used,<br />
copper gaskets cannot be reused.<br />
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