ISO 3669:2026

Overview

ISO 3669:2026 - Vacuum technology - Dimensions of knife-edge flanges is an international standard that defines the dimensional specifications for fixed and rotatable bolted knife-edge flanges used in vacuum systems. These flanges are engineered for reliable sealing in vacuum environments, supporting pressure ranges from atmospheric conditions down to ultra-high vacuum levels as low as 10⁻¹¹ Pa. This fourth edition of the standard revises and harmonizes dimensions to ensure interchangeability and compliance with other international norms, aiming to support the seamless integration of components in diverse vacuum applications.

Key Topics

• Knife-Edge Flanges: Metal-sealed flanges featuring a knife-edge design, widely used for establishing tight, leak-free joints in high and ultra-high vacuum systems.
• Dimensional Specifications: Detailed dimensions for various flange types, covering parameters such as outside diameter, bolt holes, bolt circle, seal recess, and gasket size.
• Material Guidelines: Recommendations for flange and gasket materials to ensure optimal sealing performance, corrosion resistance, and compatibility in demanding vacuum environments. Austenitic stainless steel is commonly used for flanges; OFHC copper is typical for gaskets.
• Thread Standards: Inclusion of both metric and English tapped threads to accommodate global industry practices and legacy installations.
• Interchangeability: Compatibility with established flange types such as ConFlat®, and harmonization with ASTM E2734M, enabling seamless integration across systems.
• Leak Check Grooves: Recommendations for the placement and dimensions of leakage detection grooves to enhance operational reliability.

Applications

Knife-edge flanges standardized by ISO 3669:2026 are essential in applications where vacuum integrity is critical. Practical applications include:

• Scientific Research: Commonly used in particle accelerators, synchrotrons, and space simulation chambers where contamination-free environments are essential.
• Semiconductor Manufacturing: Employed in vacuum process chambers to enable precise fabrication steps requiring ultra-high vacuum conditions.
• Pharmaceutical & Chemical Processing: Applied where controlled atmospheres are needed for sensitive chemical reactions or substance handling.
• Vacuum Equipment Manufacturing: Flange dimensions defined by ISO 3669:2026 are critical for manufacturers of valves, vacuum pumps, and analytical instruments to ensure device compatibility and modular assembly.
• Fusion and Nuclear Research: Utilized in fusion reactors and other nuclear research facilities, where high-strength, dependable vacuum seals are necessary.

Related Standards

To support a consistent and international approach to vacuum flange design and manufacturing, ISO 3669:2026 references and aligns with the following standards:

• ASTM E2734M: Covers dimensions of knife-edge (ConFlat®-type) flanges, harmonized for gasket and flange compatibility.
• ISO 965-1: Governs tolerances for ISO general purpose metric screw threads, ensuring thread compatibility and interchangeability.
• ISO 286: Establishes a system for tolerances on linear sizes, relevant to ensuring the dimensional accuracy of flanges.
• ISO 1609: Specifies dimensions for non-knife edge vacuum flanges, complementing this standard for broader vacuum technology applications.

Practical Value

By adhering to ISO 3669:2026, manufacturers and end users benefit from:

• Guaranteed Component Compatibility: Enables global users to source and integrate vacuum system components from different manufacturers with assured fit and function.
• Enhanced System Reliability: Standardized flange dimensions and gasket recommendations minimize risk of leaks and failures in critical vacuum applications.
• Simplified Maintenance & Upgrades: Consistent interface dimensions streamline system maintenance, expansion, or retrofitting, reducing downtime and operational costs.
• International Trade Facilitation: Uniform flange specifications remove technical barriers, supporting cross-border equipment supply and project collaboration in vacuum technology sectors.

ISO 3669:2026 is essential for anyone engaged in the design, specification, procurement, or maintenance of vacuum systems requiring robust and standardized knife-edge flange connections.