Hoffman D.M., Singh B., Thomas J.H. (Eds). Handbook of Vacuum Science and Technology

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412

Chapter 4.2: Flange

and

Component Systems

Fig.l.

A beaded-edge face-sealed

coupling.

The

gasket

usually copper

nickel.

Flanges

Male

Nut

Gasket

4.2.3.1 Beaded-Edge Face-Sealed Flanges

Figure 1 illustrates a coupling frequently used on gas supply lines and for gauge

attachment. It is made up of two identical flanges, a gasket, and a male and a fe-

male nut. The nuts are installed before the flanges are welded into place. On the

face of each flange is a raised bead of semicircular cross section. The seal is made

when the beads penetrate a gasket as the nuts are tightened. Flanges of this style

are available from many manufacturers, and are often interchangeable. Some man-

ufacturers refer to the flanges as glands. Elbows, Tees, crosses, and various adap-

tors in this system are commercially available.

Viton®, copper, nickel, and stainless steel are common gasket materials. Some

gaskets have a groove in each side to help align the flanges. In some situations,

gaskets with retaining clips can aid installation. Gaskets incorporating sintered

filter elements that are capable of trapping particles as small as a few microns are

useful for applications where particulates could cause damage.

Table 2 gives dimensions of these flanges. The couplings for j- and y-inch

O.D. tubing are those most commonly encountered in vacuum work, although

flanges are made for up to

1.0-inch

tubing. Fittings with electropolished internal

surfaces are available for use in ultra-clean applications.

Advantages of these flanges are that they do not require axial clearance to in-

stall components, that they are suited to automated welding methods, and that

they will tolerate high overpressures. Disadvantages are that the sealing area on

the raised bead is not tolerant of scratches or other damage, and that the large

sizes require considerable tightening torque to achieve mass spectrometer leak-

tight seals.

4.2.3 Common Flange Systems

413

Table

Typical Dimensions of Beaded-Edge Face-Sealed Flanges; Flanges of this type are not

standardized within the vacuum industry, and some dimensions may vary

)»>}»»n»>m

mmM

j/////mmm.

"'""""•'"^''"'"i

W/M//M//M

Nominal

Tube Size

(in)

0.125

0.25

0.375

0.50

0.75

1.0

Maximum

Body Diameter

/ in \

V(mm);

0.20

(5.1)

0.35

(8.9)

0.47

(11-9)

0.60

(15.2)

0.80

(20.3)

1.19

(30.2)

Hex Size,

Male Nut

(in)

i-fe

Hex Size,

Female Nut

(in)

iTk

Outside

Diameter

of Gasket

/ in \

V(mm)y

0.25

(6.3)

0.48

(12.2)

0.61

(15.5)

0.78

(19.8)

1.14

(28.9)

1.40

(35.6)

4.2.3.2

ISO

O-Ring

Sealed Flanges

The International Standards Organization (ISO) in Geneva, Switzerland, has pub-

lished dimensional standards for two different series of

0-ring

sealed vacuum

flanges. The smaller series is often referred to as ISO-KF and the larger one as

ISO-MForlSO-K.

ISO-KF flanges are covered by ISO Standard

2861/1

— "Vacuum technology—

Quick release couplings—Dimensions" and are available for tubing sizes up to

2.0 inches. The system originated in Europe and the KF comes from the German

414

Fig.

Chapter 4.2: Flange and Component Systems

Clamp

Centering Ring

Flange 0-Ring Flange

Flange

Clamp

^0-Ring

Centering Ring

(a) A joint using KF

flanges

is made with two identical flanges, an 0-ring carried on a center-

ing ring, and a clamp. The centering ring limits compression of

the

0-ring and provides align-

ment of

the

flanges, (b) The assembled KF joint. (Reproduced with the permission of the HPS

Division of

MKS

Instruments, Inc., Boulder, Colorado.)

word Kleinflansch, meaning "small flange." These flanges are also called "QF,"

"quick flanges" or "NW" flanges by some manufacturers. "NW" was mistakenly

picked up from European flange tables, where it was used as the abbreviation for

Nennweite, meaning "nominal diameter."

A KF

flange

joint is illustrated in Figure 2.

joint consists of two identical and

infinitely rotatable flanges, a centering ring with seal, and a clamp. The centering

ring centers and spaces the flanges, retains the 0-ring seal, and limits the 0-ring

compression. The clamp holds the joint together and provides the sealing force.

Some clamps are closed with a wingnut, others with a toggle lever. Lever-closed

clamps are convenient when the joints are frequently disassembled. Clamps are

correctly tightened when the flange faces contact the spacer portion of the center-

4.2.3 Common Flange Systems

415

ing ring. This contact is necessary to make reliable

joints.

Wingnut-closed clamps

should be tightened until a sudden, sharp increase in closing torque is felt. Lever-

closed clamps require some spring means to provide the correct sealing force and

ensure flange to centering ring contact in any situation.

A second series of

0-ring

sealed flanges is described by ISO Standard 1609,

"Vacuum Technology—Flange Dimensions." Of the flanges described by this

standard, only those for nominal tubing sizes of 2.5 inches and larger are in

common use. This system is variously called ISO-MF, ISO-Universal, ISO-K, or

PNEUROP. They too are sealed with an

0-ring

mounted on a centering ring, and

the flanges are sexless. Figure 3 shows the hardware used in this system.

Rg.X

Flanges and hardware fasteners belonging to the larger ISO

(International Standards Organization) O-ring-sealed flange system.

Multi-Fastener

(MF) Flange

r— Bolted Flange

Retaining

Ring

Spacer Ring .

0-Ring

Centering

Ring

Single

Claw Clamp

The names

are

for descriptive purposes

and do not

reflect

any

universally accepted

name.

(Repro-

duced with the permission of

the

HPS Division of

MKS

Instruments, Inc., Boulder, Colorado.)

416

Chapter 4.2: Flange and Component Systems

Fig.

The various ways tlie larger ISO (International Standards Organization)

O-ring-sealed flanges can be held together.

(A)

(B)

(C)

(D)

(Reproduced with the permission of the HPS Division of MKS Instruments, Inc., Boulder,

Colorado.)

The various larger flange styles and the ways of holding them together are il-

lustrated in Figure 4. The ISO-MF name came about because of the several meth-

ods of fastening these flanges together, "MF' standing for "Multi Fastener flange."

Both flanges can be infinitely rotatable, held together with double-claw clamps as

in Figure 4(a), or they can be bolted as in Figure 4(d). Bolted flanges are primar-

ily found on components such as gate valves, where there is not space for a clamp.

Nonbolted flanges can be joined to a tapped flange by using single-claw clamps,

as in Figure 4(c), or with the addition of a rotatable bolt ring that fits over the out-

side diameter of the flange, as illustrated in Figure 4(b). Flanges held together

with clamps or rotatable bolt rings have the advantage of infinite rotatability. The

centering ring and the seal region for a given size flange are always the same. As

with the ISO-KF flanges, MF flange joints are correctly tightened when the seal

surfaces contact the spacer portion of the centering ring.

Table 3 gives dimensions of common KF flanges, and Table 4 dimensions of

4.2.3 Common Flange Systems

417

Table

KF Flange Dimensions: Stub dimensions suitable for welding

to inch-sized tubing are given. All other dimensions in the table are according

to the ISO (International Standards Organization) or PNEUROP Standards.

The ISO standard specifies a minimum length of 10 mm (0.39 inches).

(Reproduced with the permission of HPS Division of MKS Instruments, Inc.,

Boulder, Colorado.)

-J\

L-

o-''^

Nominal

Size

(mm)

Nominal U.S.

Tube Diameter

Outside

Diameter

Counterbore

Diameter

0.50

(12.7)

0.75

(19.0)

1.00

(25.4)

1.50

(38.1)

2.00

(50.8)

Dimensions:

1.18

(30)

1.18

(30)

1.57

(40)

2.16

(55)

2.95

(75)

inch

0.48

(12.2)

0.68

(17.2)

1.03

(26.2)

1.62

(41.2)

2.05

(52.2)

(mm)

Table

Dimensions of the Larger ISO (International Standards Organization)

0-Ring-Sealed

Flanges.

The weld socket dimensions are typical for flanges made to fit inch-sized tubing. All other dimensions

in the

figure

are according to the ISO standard. (Reproduced with the permission

of HPS Division of MKS Instruments, Inc., Boulder, Colorado.)

ISO Bolted Flange

ISO Multi-Fastener Flange

Seal Face

Dimensions: "'^^'*''

(mm) 1

i F -

T ."IZZ-

Seal Face

Nominal"

Flange Size

Desig-

nation

(mm)

NW63

NW80

NWlOO

NW160

NW2(X)

NW250

NW320

NW400

NW500

NW630

Suggested

Tube/Pipe

Dims.''

o.d. X Wall

(inches)

2.5 X .065

3.0 X .065

4.0

.065

6.0 X .083

8.0 X. 120

10.0 X. 125

12.75 X .165

16.0 X .188

20.0

.188

25.0

.25

ISO Multifastener

Hange (ISO-MF)

(o.d.)

3.74

(95)

4.33

(110)

5.12

(130)

7.09

(180)

9.45

(240)

11.42

(290)

14.57

(370)

17.72

(450)

21.65

(550)

27.16

(690)

(thick-

ness)

.47

(12)

.47

(12)

.47

(12)

.47

(12)

.47

(12)

.47

(12)

.67

(17)

.67

(17)

.67

(17)

.87

(22)

No.

Clamps

Required

3-4

4-8

6-12

8-12

8-16

12-16

16-20

(o.d.)

5.12

(130)

5.71

(145)

6.50

(165)

8.86

(225)

11.22

(285)

13.19

(335)

16.73

(425)

20.08

(510)

24.02

(610)

29.53

(750)

ISO Bolted

(thick-

ness)

.47

(12)

.47

(12)

.47

(12)

.63

(16)

.63

(16)

.63

(16)

.79

(20)

.79

(20)

.79

(20)

.94

(24)

(bolt

circle)

4.33

(110)

4.92

(125)

5.71

(145)

7.87

(200)

10.24

(260)

12.20

(310)

15.55

(395)

18.90

(480)

22.83

(580)

28.35

(720)

Flange

(bolt

(no.

Wren(

holes) holes) (mm

.35

(9)

.35

(9)

.35

(9)

.43

(11)

.43

(11)

.43

(11)

.55

(14)

.55

(14)

.55

(14)

.55

(14)

"NW is retained here by convention. It does not specify the flange type but is from the German

Nennweii

meaning "nominal diameter."

* Schedule 5 pipe for sizes 320 and above. .

Dimensions:

(mm)

4.2.3 Common Flange Systems

419

MF flanges. The flanges described in the ISO standards are dimensioned for

welding to metric tubing. Flanges made in the United States generally have inch-

sized stubs or tube sockets, while the flange interface dimensions are made to ISO

standards. This allows flanges from different manufacturers or countries to be

used together. As of this writing, the ISO standards do not include the KF 50 size.

This is because the 50 size is not from the "first ISO preference series" or pro-

gression. For more explanation, the reader is referred to the ISO Standard, ISO 3,

"Preferred Numbers-Series of Preferred Numbers." Two other KF sizes from the

second preference series have been made —

and 32, but these are no longer in

conmion use. PNEUROP standard 6606/1981, prepared by the European Com-

mittee of Manufacturers of Compressors, Vacuum Pumps and Pnuematic Tools,

includes the KF 50 flange. The dimensions in this standard are used by most flange

manufacturers and are under consideration for addition to the ISO standard.

Either ISO flange is available with weld stubs, weld or braze sockets, unbored

or blank for user modification, or in adaptors to other flange or fastening systems

such as pipe threads. Both types of ISO flanges are primarily designed

be 0-ring

sealed, but metal seals are available. To obtain the higher sealing forces necessary

for metal seals, special stronger clamps must be used with KF flanges, while with

MF flanges additional clamps must be used.

KF,

and smaller MF flanges, are particularly suited for forelines. They are also

convenient for building vacuum systems for short-term use, or where frequent

disassembly for maintenance or modification is required. The lower pressure limit

is usually determined by outgassing of the 0-ring seal material. KF flanges are

not very tolerant of large pressure differentials. If these flanges are exposed to

more than a 5 psig differential, over pressure rings that surround and confine the

0-ring are necessary.

4.2.3.3 Knife-Edge-Sealed Flanges

In the early 1960s Varian Associates introduced the ConFlat® series of metal

sealed flanges for UHV applications. Interchangeable flanges, often referred to as

CF flanges, are available from numerous manufacturers.

A joint with these flanges is illustrated in Figure 5. The sealing mechanism of

the CF flange is described and discussed in Section 4.6.3.4 on seal design and ma-

terials. Briefly, the seal is formed by knife edges in each flange penetrating a soft

metal gasket between them. The knife edges are slightly recessed below the flange

face for protection. Bolts hold the flange pair together and provide the seal force.

The flanges are sexless, but because of the bolts they are not infinitely rotatable.

To provide rotational alignment, a two-piece rotatable version is used. This is il-

420

Chapter 4.2: Flange and Component Systems

Fig.

Flanges and hardware for a knife-edge flange joint.

Insert, with knife edge,

to rotatable flange

Bolt ring to

rotatable

flange

Gasket

uf ff {{ if {{ (f n if^ai

• j^f ^x ^f yy yf If y/

Welds to tubing

Nonrotatable and a rotatable flange are used together to provide rotational alignment. Bolt

holes are aligned by rotating the bolt ring.

lustrated in Figure 5 and consists of an insert with the knife edge and a concentric

bolt ring. The insert is welded to the tube or component, and the bolt ring is ro-

tated to the desired alignment. Flanges with tapped holes are available for use

where nuts would be inconvenient. The threads in tapped flanges may be either

metric or

U.S.

system, depending upon origin.

The flanges are commercially available in a variety of stainless steel alloys and

aluminum. Aluminum flanges have a hard coating over the flange face and knife

edge so that the knife edge is hard enough to penetrate the gasket without dam-

age.

The bolts in a CF joint should be the same alloy as the flanges to ensure uni-

form expansion during bakeout. This helps to prevent leaks. The tensile strength

of the bolts must be adequate to withstand the necessary sealing forces. Copper is

the most common gasket material and provides the most reliable sealing, but alu-

minum and nickel alloys are also used. Nickel gaskets require higher sealing

forces, so high-tensile strength bolts must be used. Nickel or other hard materials

can damage the knife edge, limiting the number of seals that can be made with the

flange.

CF flanges are available for use with tubing from j inch to 16 inches O.D. Di-

mensions of CF flanges for up to 8-inch-diameter tubing are given in Table 5. Se-

Table 5

Typical Dimensions of Knife-Edge Flanges Manufactured in the United States. Flanges made

outside the United States may have slighdy different dimensions and metric threads. Bolt rings

for flanges larger than 3.375-inch O.D. may be thicker than the values given. (Reproduced

with the permission of HPS Division of

MKS

Instruments, Inc., Boulder, Colorado.)

Rotatable Nonrotatable

H h-G

Flange

Size

(in)

Nominal

Tube

Diameter

.75

(19.0)

1.00

(25.4)

1.50

(38.1)

2.00

(50.8)

2.50

(63.5)

3.01

(76.2)

4.00

(101.6)

6.00

(152.4)

8.00

(203.2)

Flange

Outside

Diameter

1.33

(33.8)

2.12

(53.8)

2.75

(69.8)

3.38

(85.8)

4.50

(114.3)

4.61

(117.6)

6.00

(152.4)

8.00

(203.2)

10.00

(254.0)

Bolt

Circle

Diameter

1.06

(26.9)

1.62

(41.1)

2.31

(58.7)

2.85

(72.4)

3.63

(92.2)

4.03

(102.4)

5.13

(130.3)

7.13

(181.1)

9.13

(231.9)

Thickness

.30

(7.6)

.50

(12.7)

.50

(12.7)

.69

(17.5)

.69

(17.5)

.81

(20.6)

.78

(19.8)

.88

(22.4)

.97

(24.6)

Number

Holes

inch

Dimensions:

Tapped

Holes

Thread

8-32

i-28

^-24

16 ^^

A_24

16 "^^

^-24

16 ^^

--24

16 ^^

^-24

16 ^^

--24

16 ^^

Through

Holes

Diameter

.172

(4.3)

.265

(6.7)

.265

(6.7)

.332

(8.4)

.332

(8.4)

.332

(8.4)

.332

(8.4)

.332

(8.4)

.332

(8.4)

Face to

Counter-

bore

.18

(4.6)

.17

(4.3)

.21

(5.3)

.22

(5.6)

.38

(9.6)

.28

(7.1)

.43

(10.9)

.50

(12.7)

.50

(12.7)

(mm)