Ultra-high Vacuum Fittings: What Are Flanges Used For?

Posted by Paul Dabrowski (Nowvac) on Jan 14, 2022 8:20:40 AM

Despite how commonplace vacuum technology is, it can be difficult to know what fittings and parts are needed to create ideal vacuum environments. Here, we explore what vacuum flanges are and what they may be used for. Let’s start by looking at how flanges are used to create vacuum systems.

What Are Vacuum Flanges?

Flanges connect components. For instance, flanges are used to connect lenses to cameras or to connect the pipes in your wall. Within vacuum systems, flanges are fittings that connect vacuum chambers, pumps and tubing. 

While flanges are designed to keep pieces of a system in place, they also allow for a system to be assembled and disassembled. This is a benefit for vacuum experiments that require regular system rearranging or the fitting of additional pieces. The ability to disassemble vacuum components is especially useful when maintaining, cleaning and monitoring your system. While consistent maintenance is useful in reducing system downtime, it is also one of the key rules for working under high-vacuum and ultra-high vacuum conditions.

Are There Different Flange Types?

There are a multitude of flange standards, sizes and attachment mechanisms, with each type being suited for different vacuum regimes. But searching for the right flange is complicated by the fact that different manufacturers use their own naming schemes to identify their flanges. Fortunately, knowing the different standards will help you understand these manufacturer naming differences. We unpack the different flange standards below:

KF/QF flanges

Klein Flansche (KF) or Quick Flange (QF) vacuum flanges are an ISO standard quick release flange. These flanges may also be referred to as NW or DN flanges. 

Adopted by ISO, DIN and Pneurop, the KF flange features a chamfered back surface that is set against an elastomeric O-ring. KF flanges are enclosed and attached with a circular clamp and a metal centring ring that fastens objects in place. The KF range is also defined by its diameter size which ranges from 10mm up to 50mm. KF flange sizes of 10, 20 and 32mm are not common as they are Renard numbers. 

Providing versatility, these flanges may share clamps with other sizes within the KF standard. This makes it possible to connect KF flanges of varying sizes with the same clamp and by using an adapter.

ISO flanges

The ISO large flange standard is also called the LF, LFB, or the MF. The ISO standard uses an elastomeric O-ring and a centring ring and clamp. ISO flanges feature an additional spring-loaded circular clamp that fastens larger O-rings in place during mounting. Larger than the KF flange, ISO flanges support tube diameters of 63mm to 500mm.

ISO flanges come in two main types. The first is called the ISO-K or ISO LF and it features double-claw clamps that make use of a groove. ISO-F or ISO LFB, the second type, uses holes and bolts to secure the connection. But both these ISO types can be joined using single-claw clamps on the ISO-K side and bolts on the ISO-F side. 

CF flanges

CF or Conflat ("ConFlat") flanges are used for ultra-high vacuum seals and they come in sizes of 10mm to 250mm in Europe and Asia. In North America, the size of a CF flange is measured in inches and they range from one inch to 16.5 inches.

CF flanges use oxygen-free, high thermal conductivity copper gaskets and a knife-edge flange to create airtight seals. This metal-to-metal seal is much stronger than other types of seals because the metal gasket deforms around the cutting edge of the flange. This provides an operating range of down to 10-13 mbar. 

To protect the knife edge, a CF flange recesses it in a groove on each side. This holds the gasket in place and assists in aligning the two flanges when connected. This also reduces gasket expansion in operation, and temperatures up to 450 degrees Celsius are possible with the right gasket material. CF flanges have the benefit of being interchangeable, especially as they have no female or male orientations.  

Quick CF flanges

Quick CF, also called the QCF flanges, combine the CF's knife-edge mounting principle with the ease of clamp chains. This fitting is well-suited for fastening pumps in ultra-high vacuum environments. Instead of the CF's tricky attachment process, QCF flanges and attachments can be assembled at a faster rate. Quick CF flanges are also smaller and easier to work with than CF flanges and QCF components can be connected to any vacuum system through the use of adapters. This makes them a highly versatile vacuum flange.

Wheeler and ASA flanges

Wheeler flanges are large, wire-seal flanges that are common with larger vacuum chambers.

Due to a name change in the organisation, the American Standards Association (ASA) flange is also called the American National Standards Institute (ANSI) flange. While they are the same flange, the ANSI standard measures flange sizes by the inner diameter — these range from one to 10 inches. Conversely, the ASA standard measures the flange’s outer diameter, and these range from 4.25 inches to 16 inches.


Why Gaskets Are Crucial to Flange Operation

No flange would function without the right gasket. These gaskets ensure that flanges maintain a vacuum seal after connection. Vacuum gaskets are commonly made out of Teflon, silicone rubber, Viton fluoropolymer, or Buna rubber. Gaskets are kept in place with a centring ring, a groove, or by being held in place with separate metal rings. 

When ultra-high vacuums are needed, the rubberized gasket is replaced by a soft metal gasket that fastens the connecting flanges via knife-edges. In CF flanges, this metal gasket is copper, though other metal gaskets can be made from gold or indium.


Learning More About Vacuum Systems

In this post, we’ve highlighted the key role that flanges play in connecting a vacuum system. But there’s always more to learn about vacuum technology. 

Like flanges, choosing the right pump is a critical factor in guaranteeing the optimised performance of a vacuum system. As these pumps come in many forms, we’ve written a free guide to understanding the different types of vacuum pumps. In it, we discuss:

  • The most common types of vacuum pumps
  • The advantages and disadvantages of different types of vacuum pumps
  • How to select the right vacuum pump for your application
  • The impact of vacuum pumps on vacuum processes and application 


Click on the link below to grab your copy:


Filed Under:

Vacuum Pumps, flanges