Rectangular Duct Connections

8 M2 + M3 + M4 Rectangular Flanges

16 Corner Pieces for Formed-on Flanges

METU-SYSTEM Catalog 6b 7
 Rectangular
Flanges M2 M3 M4
4-Bolt connection system with
an external bead for the easy
installation of clamps.

The METU-SYSTEM
triangular shape provides an
optimal flange stability.

Well engineered clamps allow an

easy and efficient installation.

Available in 20, 30 and 40 mm

profile heights.

Also available with injected

sealant (hd version).

The bead on the external web The angled section of the profile
of the profile section simplifies provides additional rigidity
the fitting of clamps (resistance against traction in the
corner piece areas, and against
compression generated by the
gasket between the corners)

The upturned leading edge on some The hd version of the profiles has
profiles allows the flange to easily an injected soft sealant into which
pass onto the duct wall the edge of the duct imbeds

The edge of the duct serves as a

stop when fitting the flange frame,
thus avoiding distortion or bowing of
The dished internal web presses the profile section
against the duct wall, acting
as a metallic self-sealing lip

8 METU-SYSTEM Catalog 6b
Rectangular Duct Connections M2 M3 M4

The most important aspects of a rectangular duct work connection

Air-tightness

Influences the: Prominent edge in

- energy consumption the corner area
- noise generation
- air quality Sealing lip

The METU Answer

Profile Deflection
Influences the Hollow triangular
- efficiency and integrity profile
- applications range
- appearance

The METU Answer

Corner Piece Strength

Triangular shape
Influences the for maximum
- air-tightness after installation rigidity
- required number of clamps
- required number of supports
Press-formed
corners

The METU Answer

Gaping: Lateral supporting

side increasing the
Influences the
resistance against
- air-tightness
torsion
- appearance
- required number of supports

The METU Answer

The above mentioned criteria determine the performance, quality and appearance of your ductwork.
Not all rectangular connections are created equal!

METU-SYSTEM Catalog 6b 9
Rectangular Duct Connections M2 M3 M4

Corner Pieces

The METU-SYSTEM corner pieces

are exceptionally robust, as they are 1 A-Type
made of a thick material which has The original and strongest corner
been deep press-formed to confer piece. The duct wall seam must be
them a shape making them even 1 notched out. Available for the 20, 30
sturdier. and 40 mm profiles.

Having strong corners is important

for any 4-bolt rectangular connection
system. They furthermore minimize 2 A-Type with Oval Hole
the need to install clamps, translating Same as above, but with an oval hole
in less parts and faster installation for more flexibility during the assem-
2
times. bly. The duct wall seam must be
notched out. Available for the 20 mm
Various corner piece types are suited profiles only.
to the various working habits and duct
work stability requirements.
3 A-Type with Short Legs
With shorter legs fitting small
rectangular duct sizes.
3
The duct wall seam must be
notched out. Available for the
20 mm profiles only.

4 S-Type
The duct wall seam does not need
to be notched out. Although 30%
4 weaker than the A-corners, these are
heavy-duty press-formed parts which
are stronger than most corner pieces
in the market. Available for the 20, 30
and the 40 mm profiles.

5 S-Type with Short Legs

5 Same as above but with shorter legs
fitting small rectangular duct sizes.
The duct wall seam does not need to
be notched out. Available for the
20 mm profiles only.

6 B-Type
More economical corner piece. The
6
duct wall seam does not need to be
notched out. About 40% less sturdy
than the A-corners. Available for the
20 and 30 mm profiles.

7 D-Type
7 Most economical corner piece. The duct
wall seam must be notched out.
Available for the 20 mm profiles only.

Profile and corner piece

dimensions: see additional
information ZI-501

10 METU-SYSTEM Catalog 6b
Rectangular Duct Connections M2 M3 M4

Clamps

G-Clamp Drive Clamp

This clamp is based on the proven principle which presses This clamp is ideal for situations where installation space
the profiles together using a bolt. This results in a flexible is restricted, such as ducts close to ceilings, walls, or
and easy installation. other ducts or equipment. The clamp is slightly tapered
to ease its installation. Such a clamp is therefore much
Because of its solid construction, the G-Clamp is designed easier to put in place than the C-shaped long clips.
to cope with high loads. The clamp bolt is always the
same size as the corresponding flange bolts, so that Thanks to its broad end-face, the drive clamp can be
installation can be carried out using the same wrench size. easily driven into position in confined areas using a piece
of pipe for instance.
Installation:
Hook the G-Clamp over the profile bead and tighten the
bolt. Avoid over-tightening the bolt, since this could deform
either the profile or the clamp.

Installation:
The flanges must be forced together either by tightening
the corners or by using pliers, grips or other suitable tools
before fitting the Drive Clamp.

On flanges using type S or type B corner pieces, the

clamp can be fitted after bolting the corners together.
On flanges using A type corners, the drive clamp must be
fitted before the corners are bolted together.

METU-SYSTEM Catalog 6b 11
Rectangular Duct Connections M2 M3 M4

Profile Choices According to Stability (the imperial figures are approximations)

The profiles load-bearing capacity and stability against deflection depend on the operating pressure and the width of
the duct. The recommended dimensions are maximum duct widths (DW = maximum duct width).

Max. deflection = 1/250 of the DW

DW
International norms require that a flange profile under operating pressure should not deflect more than the 250th part of the
total duct width (Example: the allowed deflection of a 1000 mm wide duct would be 4 mm).
The figures provided on the table below take this requirement into consideration. Prerequisites are sufficiently stiffened duct
walls with adequate sheet metal thickness according to DIN EN 12236, April 2002, and the recommended use of clamps
as described under Clamping Recommendations in this section of the catalog. The operating range of the rectangular
flanges can be increased through the installation of tie rods near the flanges. The reference with tie rod means that a tie
rod must be installed close to the flange (the distance from the flange must not exceed 50 mm or 1,95 in).

Max. Operating Pressures Recommended maximum duct widths in mm

(positive or negative in Pa) M2-Profile (20 mm) M3-Profile (30 mm) M4-Profile (40 mm)

M2-0,6 M2-0,7 M2-0,9 M3-0,7 M3-0,9 M3-1,2 M4-1,2 M4-1,5

500 Pa without tie rods 700 1000 1200 1300 1600 2000 2500 3000
500 Pa with tie rods - - 1400 2000 2500 3500 4000 5000
1000 Pa without tie rods 500 800 1000 1100 1400 1600 2000 2500
1000 Pa with tie rods - - 1200 1500 1800 2500 3500 4000
1500 Pa without tie rods - 700 900 1100 1300 1500 1800 2200
1500 Pa with tie rods - - 1200 1500 1800 2400 3200 3600
2000 Pa without tie rods - 600 800 1000 1200 1400 1600 1800
2000 Pa with tie rods - - 1200 1400 1700 2200 2800 3400
2500 Pa without tie rods - 600 800 900 1000 1200 1400 1600
2500 Pa with tie rods - - 1200 1400 1600 2000 2500 3000
3000 Pa without tie rods - 600 700 800 900 1100 1300 1500
3000 Pa with tie rods - - 1100 1300 1500 1900 2400 2800
3500 Pa without tie bars - - 600 700 800 1000 1200 1400
3500 Pa with tie bars - - 1000 1200 1400 1800 2200 2600
4000 Pa without tie rods - - 500 500 600 800 1000 1200
4000 Pa with tie rods - - 1000 1000 1200 1600 2000 2400

Important: The above recommendations are based on tests which have been conducted on test duct work according to the norms. Other
duct constructions, insufficiently stiffened duct walls, different sheet metal thickness, bad quality lock seams, and so on, may have nega-
tive effects on the stability of the air duct. The execution of the duct construction according to the above recommendations constitutes
therefore no guarantee for sufficient duct stability and does not take away the responsibility from the duct work manufacturer to conduct
his own tests. Special conditions such as pulsating air, sudden pressure changes, vibrations, man loads, damaged duct, etc. have not
been taken into consideration. In such cases the duct work should be manufactured and tested according to these requirements.

METU-SYSTEM Profile Flectional Strength

The following figures are indications only and do not replace the judgment and analysis of the user with respect to the
contemplated application. The stability depends on the sheet metal thickness.
Profile Type: Second Moment Section Modulus Profile Form (with A) Profile Form (without A)
(in center of area) (in center of area) y y
Ixs Iys Wxs Wys
M2-0,6-Profile (with A) 0,300 cm4 0,300 cm4 0,200 cm3 0,200 cm3
M2-0,6-Profile Small (w/o A*) 0,200 cm4 0,200 cm4 0,100 cm3 0,200 cm3 x x
M2-0,7-Profile (with A) 0,327 cm4 0,302 cm4 0,200 cm3 0,223 cm3
M2-0,7-Profile Small (w/o A*) 0,220 cm4 0,281 cm4 0,155 cm3 0,217 cm3
M3-0,7-Profile (with A) 0,623 cm4 0,893 cm4 0,311 cm3 0,482 cm3
M3-0,8-Profile (with A) 0,715 cm4 1,018 cm4 0,359 cm3 0,545 cm3
* Approximative values as they have
M4-1,2-Profile (w/o A) 2,416 cm4 3,676 cm4 0,915 cm3 1,433 cm3 been calculated for profiles with A.

12 METU-SYSTEM Catalog 6b
Rectangular Duct Connections M2 M3 M4

Profile Choice depending on the Air-tightness Requirements

Most of the METU-SYSTEM profiles are also available with injected sealant (hd). The profile choice according to the air-
tightness requirements is therefore independent from the profile choice based on stability requirements. When using hd
profiles leakage is practically eliminated, thus allowing the total duct work leakage to be reduced by 30 to 50% at very
little additional cost.

Recommendations for the Ductwork Manufacture According to DIN EN 1507

Class A
a) Flanges can be made with METU-SYSTEM profiles without injected sealant.
The corner area of the flange however has to be carried out with care.
b) Seams should also be folded precisely if no additional sealant is to be applied.
c) During assembly extra care should be brought to properly cover the exposed edge of the duct
in the corner area with gasket.
Class B
a) Flanges should be made with METU-SYSTEM profiles with injected sealant (with hd).
The corner pieces have to be sealed with mastic.
b) The seams on ducts with duct edges above 500 mm have to be of high quality. We recommend to apply
mastic on snap lock seams. The seams on ducts with duct edges below 500 mm should also be all sealed with
mastic, as their number per m2 of duct is larger. The easiest way to do this is to apply the mastic inside the ducts right
after their manufacture.
c) During assembly we recommend applying two layers of gasket in the corner piece areas.
This is especially important if you use S type corner pieces.
Class C
a) Flanges have to be made with METU-SYSTEM profiles with injected sealant (with hd).
After installing the flange onto the duct, the corner area has to be sealed with mastic.
b) All seams have to be sealed carefully with mastic. The easiest way to do this is to apply the mastic inside the ducts
right after their manufacture.
c) Two gasket layers and/or mastic should be applied in the corner piece area. You should make sure that the gasket
layers are placed adequately on the exposed edge of the duct which is not covered by the profile.
Class D
a) This air-tightness class can only be achieved through proper workmanship and careful installation practices.
b) In addition to the caulking measures required for the air-tightness class C, a mastic sealant can be applied along the
entire length of the flange without requiring an hd profile version. In this regard, we strongly suggest that you conduct
your own air-tightness tests, as this is the only way to determine precisely which sealing measures are sufficient.
This is especially important if the installation is done by a third party.
c) The assembly must be carried out with the greatest care. Mastic sealants (applied on the face of the profiles) usually
bring better results than the more common self-adhesive foam gaskets bands. Special caution is necessary in the
corner piece areas. Also very important is to select large and sturdy enough profiles and corners in order to
guarantee that enough compression is exerted on the gaskets and/or mastic at all points of the connection.
For all duct work designed for operating pressures above 1000 Pa, METU-SYSTEM hd profiles should be used.

Sealing the corner area The DE Corner Gasket provides a secure Gasket fitted flush to the inner edge of the
with mastic and very easy-to-apply seal flange, covering the ducts exposed edge

Important: The recommendations above are based upon our 30 years experience in duct work manufacturing (prior to 1987).
However, no liability is accepted for the information provided above. Please keep in mind that leakage is the sum of many smaller
leaks. In order to achieve the requirements it is therefore important to respect all the relevant points described above. A bad installation
can make an airtight ductwork leak, but a very careful installation can not make bad ductwork airtight!

METU-SYSTEM Catalog 6b 13
Rectangular Duct Connections M2 M3 M4

Installation Instructions

1. Cutting the Profiles to Length

The profile length depends on the type of corner piece used:
A and D corner piece types: inner duct length minus 4 mm
S and B corner piece types: inner duct length minus 30 mm
Most circular saws are suitable to cut the profiles. Make sure to clamp the pro-
file on both sides of the saw blade over as much surface as possible in order
to restrict any movements. This will protect the sawing blade and your ears!
If possible, clamp the profile section in the position as illustrated and note the
direction of rotation of the sawing blade. This will ensure that the burrs remain
in the inaccessible spots of the flange.

2. Frame Assembly
Assemble the frames vertically, and not horizontally.
a) Insert two corner pieces in the ends of both longer profile sections.
b) Insert the two shorter profile sections on the corners of one of the profiles.
c) Insert the second longer profile with its corners into the shorter profiles.
The corner pieces are designed to fit closely into the profile inner shape.
A rubber mallet might therefore be necessary to insert them into the
profile ends.

3. Frame Seating
Start at one of the upper corners and hammer along the line of the duct (not at
the outer edge of the profile). To enable the profile to fit more easily hold it in
a slightly inclined position. We recommend to fit the flanges with the duct in a
horizontal position. Fit the flanges to both duct ends before fixing. Work on a
table or any other flat surface allowing the duct to align itself.
To avoid distortion, particularly on small ducts, check if the flanges are aligned
on both ends before fixing. On ducts less than 1500 mm long, the flanges can
be fitted in the vertical position.

4. Fixing the Frame

It is essential that the flange is securely fixed at the corners (i.e. spot-welding,
stitching or blind rivets), where the maximum strength is required. There should
be two fixing points with a maximum distance of 20 to 30 mm from each other
and as close as possible to the ends of the profile sections. It is also very
important that the flange is fully seated against the edge of the duct before
fixing. Suitable fixing methods are spot welding, pressure jointing or blind rivet-
ing. As soon as the corners have been securely fixed, each length of profile
is fixed at a spacing between 80 mm (M2 and M3 profiles) and 120 mm (M4
profiles). For profiles exceeding 600 mm a center fixing is required. Make sure
that the flange is fully seated and check the duct alignment before fastening.

5. Sealing of the Corners

The sealing of the corners is important as they can often be a source of
leakage. Due to irregularities in the length of the duct walls (i.e. offset seams),
a gap can easily be formed which cannot be bridged by the ducts sealing
gasket. Injecting mastic sealant into the pockets of the corner can prevent this
leakage risk. The corner pocket should be filled flush with sealant to the face of
the flange and over the edge of the duct.

14 METU-SYSTEM Catalog 6b
Rectangular Duct Connections M2 M3 M4

Clamping Recommendations (only for products made of galvanized steel)

Straight duct to straight duct

connections
DW

DW: duct width

Clamps required for the following duct widths:

20 mm Profiles 30 mm Profiles 40 mm Profiles

Operating M2-0,6-Profile M2-0,7-Profile M3-0,7-Profile M3-0,8-Profile M3-0,9-Profile M4-1,2-Profile

Pressures M2-0,9-Profile M3-1,2-Profile M3-1,5-Profile
up to 1000 Pa from 1000 mm from 1200 mm from 1200 mm from 1300 mm from 1500 mm from 2000 mm
above 1000 Pa from 800 mm from 1000 mm from 1000 mm from 1100 mm from 1200 mm from 1500 mm

Explanations: straight straight

In this case an optimal flange support is reached, since duct duct
the duct walls run vertically on both sides into the profile.
Fewer clamps are required for that reason.

Straight duct to fitting connections,

Fitting to fitting connections

DW

DW: duct width

Clamps required for the following duct widths:

20 mm Profiles 30 mm Profiles 40 mm Profiles

Operating M2-0,6-Profile M2-0,7-Profile M3-0,7-Profile M3-0,8-Profile M3-0,9-Profile M4-1,2-Profile

Pressures M2-0,9-Profile M3-1,2-Profile M4-1,5-Profile
up to 1000 Pa from 800 mm from 1000 mm from 1000 mm from 1100 mm from 1200 mm from 1500 mm
above 1000 Pa from 600 mm from 800 mm from 800 mm from 900 mm from 1000 mm from 1200 mm

Explanation: Angled or bent duct walls do not provide an optimal support to the flange.
In these cases (please refer to the examples below) more clamps are required.

Straight duct Elbow (outer Straight duct Reducer

bow)

Reducer

Elbow
Straight duct Elbow
(inner bow)

Important information:
The above recommendations are not applicable to flexible joints, since support from the duct wall is lacking. The duct work manufacturer should therefore determine the number of
clamps required according to the kind of flexible joint used.

The above recommendations are based on tests which have been conducted on test duct work according to the norms DIN EN 1507. Other duct constructions, insufficiently stiff-
ened duct walls, different sheet metal thickness, bad quality locks and so on may have negative effects on the duct work stability. The execution of the duct construction according
to the above recommendations constitutes therefore no guarantee for sufficient duct stability and does not take away the responsibility from the duct work manufacturer to conduct
his own tests. Special conditions such as pulsating air, sudden pressure changes, vibrations, man loads, damaged duct, etc. have not been taken into consideration. In such cases
the duct work should be manufactured and tested according to these requirements.
The information above are only valid with the A and S type corner pieces.

METU-SYSTEM Catalog 6b 15
 Corners for
Formed-on Flanges
Two-part corner pieces
designed for ductwork with
formed-on flanges (i.e.FIRMAC
duct lines).

The patented corner design

guarantees a 90 angle and
maximum stability.

Fast and easy installation:

a hammer is all that is needed!

A special stop secures the

corners into the flange.

Shape of the corner pieces

outside the profile

Both corner pieces fit perfectly

flat together. This increases their The Flat Part Corner Piece is kept
stability into position by a large groove,
thus ensuring a 90 angle

Flat part Formed part

of the corner piece of the corner piece

Shape of the corner pieces

inside the profile

The thick material increases the

corners stability in order to resist
the bending loads generated by
the corner bolts.

Formed part Flat part

of the corner piece of the corner piece

16 METU-SYSTEM Catalog 6b
Corners for Formed-on Flanges

Installation Instructions

The M2-Z and M3-Z corner pieces

consist of a formed-part ...
... and a flat-part

Hammer the formed part

1 2
inside the profile

Then insert the flat-part in the

U-shaped groove of the formed-part

Then hammer the flat-part

3 4
all the way down.

Finally, secure the corner piece

in place by hammering
down the stop

Dimensions (mm)

A
A
B C
F B
C

D D
E E

Formed Part A B C D E F Flat Part A B C D E F

M2-Z-Corner 70,0 5,2 9,2 9,0 18,0 2,0 M2-Z-Corner 70,0 1,5 3,0 9,0 18,0 2,0
M3-Z-Corner 100,0 7,5 14,0 12,0 27,0 2,5 M3-Z-Corner 100,0 2,5 4,0 12,0 27,0 2,5

Designation

M2-Z-Corners (for 20 mm formed-on profiles) M3-Z-Corners (for 30 mm formed-on profiles)

Art. No. Description Art. No. Description
A02A-2003 M2-Z-Corner, galv., Flat Part A02A-3003 M3-Z-Corner, galv., Flat Part
A02A-2004 M2-Z-Corner, galv., Formed Part A02A-3004 M3-Z-Corner, galv., Formed Part

METU-SYSTEM Catalog 6b 17