Vacuum Fitting

Overview and Selection Guide

Introduction

All vacuum systems require connections with either pumping systems or with different peripheral accessories such as vacuum gauges, valves, and hoses. While these connections must preserve vacuum integrity, vacuum fittings must also be modular to allow for flexibility, maintenance, and repair of the vacuum system. The type of vacuum fitting used depends on the requirements of vacuum system and its application. All vacuum applications involve flanges and fittings with stringent requirements regarding the vacuum fitting material, dimension, tightness, and conductance.

Vacuum fittings come in various standards, configurations, materials, and sizes.


The three most popular types of fittings are:
•    ISO-KF Flanges and Fittings
•    ISO-K Flanges and Fittings
•    CF Flanges and Fittings


Based on the ISO-KF, ISO-K, and CF standards, there follows an expansive range of fitting configurations such as elbows, tees, 4-way crosses, flexible couplings, reducers, and specialized or custom adaptors that convert from one standard to another. Within these configurations, fittings are further divided into material types (i.e., stainless steel, aluminum) and sizes.  For vacuum fitting sizing, the normalized nominal diameters are generally used for each fitting standard type. 


Vacuum fittings are selected on the following criteria:
•     Working pressure
•     Required connective tightness
•     Required conductance
•     Connective size
•     Required material for vacuum application


ISO-KF Flanges and Fittings
ISO-KF flanges and fittings are ideal for vacuum systems and applications requiring a quick release and tight connections from 10 to 50 mm nominal diameters. Typically, two flanges are coupled together by a centering ring with an O-ring and a clamp.

This type of connection provides the following advantages:
•     Easy and quick mounting
•     Assembly without any tools
•     Unlimited orientation
•     Easy interchangeability

ISO-KF Stainless steel fittings are ideal for high vacuum, corrosive or high temperature applications and offer a large range of high performances, according to seal material (see Table 1).

Table 1: ISO-KF Stainless Steel Fitting Seal Performances


Seal type       
•NBR O-ring:        
Specifications                  
 Baked temperature: 80 °C
 Pressure range: 10-7 mbar

Seal type
•FPM O-ring:       
Specifications                        
 Baked temperature: 150 °C
 Pressure range: 10-7 mbar


Seal type
•Metal seal (Aluminum, Braided aluminum, Indium)*
Specifications 
 Baked temperature: 200 °C
 Pressure range: 10-9 mbar
 Maximum overpressure: 5 bars

*Due to metallic seal characteristics, special clamps such as chains or half flanges without centering rings are required.


Connections between different diameters ISO-KF Flanges

ISO-KF flanges also offer sizing compatibility that lends to simple connections. For example, 10, 20 and 32 mm nominal diameter flanges have the same external dimensions as 16, 25 and 40 mm, making the 10/16, 20/25, 32/40 connections compatible with the use of an adaptor ring and O-ring. A metallic seal also lends to easy connections because they are centered on the flange outside diameters. For different diameters, a conventional reducer must be used.

ISO-K Flanges and Fittings
The ISO-K flanges and fittings range includes 6 diameters from DN 63 to DN 250. Made of stainless steel, the ISO-K component range includes weld flanges, elbows, tees, 4-way crosses, and nipples and offers the following advantages:
•    High conductance
•    Easy assembling
•    360° orientability
•    Baked to 80 or 150 °C

According to the seal material, the ISO-K coupling provides the following performances (see Table 2).

Table 2: ISO-K Stainless Steel Fitting Seal Performances

Seal type            
Buna-R O-ring:
Specifications
 Baked temperature: 80 °C
 Pressure range: 10-7 mbar

Seal type
FPM O-ring:
Specifications        
 Baked temperature: 150 °C
 Pressure range 


Double claw clamp connection
Ideal for the 10-7 mbar pressure range, the double claw clamp ISO-K connection includes two of the same nominal diameter flanges, one centering ring with O-ring, and according to the nominal diameter, 4 or 6 double claw clamps.

Rotatable flange connection
Including two ISO-K flanges coupled together by two rotatable flanges with retaining ring, a centering ring with O-ring and, a bolts set, this kind of connection allows an easy angular orientation.

CF Flanges and Fittings
CF type flanges and fittings are ideal for ultra high vacuum applications. CF flanges use a copper gasket compressed between the knife edges of CF flanges which provides perfect tightness from atmosphere to 10-13 mbar.  In this pressure range, there is not any leak detectable on a mass spectrometer with sensitivity a of 2.10-10 mbar.l/s (std cc/sec). Including stainless steel flanges and copper seal, Ultra High Vacuum CF couplings can be baked to 450 °C.

Range of Flanges and Fittings
Rotatable flange coupling CF flanges in are available in rotatable as well as non-rotatable versions. The rotatable version allows better mounting with an easier angular orientation of the component. In addition to the thru-hole flanges, tapped-hole flanges allow a fewer number nuts and washers. These tapped-hole flanges are available with metric or US Standard tapping.