Flange Systems Overview

What are Flanges?

In vacuum technology, flanges are semipermanent connections to join parts that:

• (a) are frequently or occasionally disassembled;
• (b) are light enough to be moved with available equipment; or
• (c) cannot be welded due to heat sensitivity or replacement needs (e.g., valves, pumps, or gauges).

There are many flange designs:

• Formal standards (e.g., ISO, KF/QF/NW, ASA/ANSI flanges)
• De facto standards (e.g., CF/ConFlat® flanges)
• Some are best described as conforming to manufacturer's standards (wire-seal flanges and ASA—as adapted for vacuum use), that is, two flanges from one manufacturer will mate, but may not if from different manufacturers.

Commonly used flange designs have a soft gasket squeezed between harder flange surfaces to form a leak-free seal. The various gasket materials are rubbers, elastomers (springy polymers), soft polymers covering a springy metal (e.g., PTFE covered stainless steel), and soft metal (copper or aluminum). Each flange design has merits.

When planning a new vacuum chamber, the designer should compare all the flange designs available and choose that which:

• Matches the vacuum conditions required
• Matches the temperature conditions required
• Is unaffected by the process's starting materials or products
• Matches OEM fittings and components added to the system
• Is easiest to use in that particular system
• Has the lowest total costs

But note, the CF and ISO/KF types are so convenient, low cost, and widely available that they predominate in practical vacuum systems. Mixing flange types using adapters is possible but not recommended unless necessary to match existing components or fittings. However, using one flange type for chamber-mounted components and another for foreline components is common practice.