Vacuum Technology

The Most Popular Vacuum Flange Types

This article is to introduce some common vacuum flange types.

A vacuum flange is used to connect a vacuum pump, hose and vacuum chamber to each other. There’re several different standards for vacuum flange which may bring confusions to end users and even professionals. Below are the vacuum flange types popularly used in the vacuum industry.

Let’s take a look and make it clear.

1. ISO-KF (NW) Flange

ISO-KF (NW) is a quick release flange. A circular clamp with a centering ring and an O-ring is used to combine two KF flanges. The full size range includes DN10, 16, 20, 25, 32, 40 and 50.

For rotary vane vacuum pumps, the most popular sizes are KF16, KF25 and KF40, also known as DN16/25/40 or NW16/25/40. The connecting hose size for KF25 is 25.4 mm (diameter)*1.65 mm (wall thickness).

The flange is basically made of stainless steel 304 or 316.

2. ISO Vacuum Flange

The ISO flange standard is also known as LF, LFB or MF. There are two types of ISO standards.

ISO-K: Two single flanges are connected with the help of double-claw clamps, that clamp to a groove on the tubing side of the flange.

ISO-F: This type is commonly used for gate valves or wall mounting. The connection is also made by flange, O-ring and centering ring. The ISO-F flanges have holes so that they can be attached with bolts.

The smallest ISO flange is 63 and the connecting hose is 50.8 mm (diameter)*1.65 mm (wall thickness).

3. JIS VF/VG Flange

It is basically a Japanese standard (JIS B 2290). The flanges are mainly used in vacuum distribution pipes and chambers.

The letter V means Vacuum, F means Flat, and G means Gasket. See the figure to understand how to connect those flanges.

4. CF Vacuum Flange

The CF, or ConFlat flange, is used for ultra high vacuum (UHV) application. CF flange is usually made of stainless steel (304 or 316), for which baking temperature of 450 °C can be achieved. The flange size includes DN10, 16, 25, 40, 50, 63, 75, 100, 125, 160, 200 and 250.

Sealing is achieved by a gasket of oxygen-free thermal conductivity copper (OFHC) or Viton or PTFE. The gasket needs to be replaced once the flange is disassembled for systems with high vacuum requirement.