BS ISO 3669:2020 pdf download.Vacuum technology —Dimensions of knife-edge flanges.
This document specifies the dimensions of fixed or rotatable bolted knife-edge flanges used in vacuumsystems for pressures ranging from atmospheric to as low as 10-11 Pa.
2Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:-ISO online browsing platform: available at http://www.iso.org/obp
—IEC Electropedia: available at http://www.electropedia.org/
3.1 knife-edge flange
metal sealed flange used for high and ultra-high vacuum service
Note 1 to entry: Sandwiching one metal gasket between two knife-edge flanges and securely bolting thesetogether makes a vacuum tight joint. The seal is made when the identical circular (triangular profile) knife-edgesare bolted together.A deformable metal gasket captured between the knife-edge flanges establishes the sealingsurface.
Note 2 to entry: Originally developed as ConFlatRflanges. The widespread and continued use of knife-edgeflanges has made these a de facto international standard, codified by this document.
3.2 nominal bore
value intended to both identify the flange and specify the largest practical size of tubing that can beaccommodated by the flange
Note 1 to entry: See Table 1, in which the convention of identifying original flanges by the outside diameter of theflange (historically in inches) has been maintained.
3.3 leak check groove
groove machined into the seal side of the flange to facilitate the free passage of trace gas from the outerperimeter of the flange to the seal zone near the metal gasket
5Requirements
5.1Materials
5.1.1 Flange
The selection of the material shall be compatible with the requirements for the flanges.Considerationsmay include service temperature, sealing capacity, corrosion resistance, magnetic permeability, type ofseal gasket used and dimensions.
NOTE Austenitic stainless steel is commonly used, but it is not the intent of this document to specify or limitthe choice of flange material to austenitic stainless steel.
5.1.2 Bolt holes
The flange may have either clearance or tapped bolt holes.
NOTE As a number of flanges in use currently originated in the United States, the tapped flanges often haveEnglish tapped holes.Of increasing use are flanges with metric threads.Both are presented in this document (seeTable 1).
5.1.3 Grooves
Leak check grooves should be used.The grooves shall be arranged equidistantly between the bolt holes.5.1.4 Gasket
In general, the gasket should be softer than the flange to avoid dulling of flange knife-edge.
NOTE Oxygen-free high conductivity (OFHC) copper is commonly used, but it is not the intent of thisdocument to specify or limit the choice of gasket material to OFHC copper.
5.2 Dimensions
Flange dimensions are shown and specified in Figures 1 to 3 and in ‘Table 1 and Table 2.See Figure 4 forthe recommended dimensions of leak check grooves.BS ISO 3669 pdf download.

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