It is an innovative sealing gasket manufactured by spongy extrusion of the material commonly called “rubber“, specifically named “EPDM” (composed of Ethylene, Propylene, Diene and Monomer), it is internationally approved and is used in countless industrial applications, construction, automotive, air conditioning, ventilation, etc …

The purpose of this gasket is to obtain a correct operation of the installation according to its project design, optimizing energy savings as a result of its maximum tightness.

It is a patented rubber gasket that, thanks to its T-shaped design, makes it possible to externally control its correct positioning, which is hidden around the union contour.

The unions of the ducts that use this gasket allow them to be quickly disassembled and reassembled, as many times as it’s convenient without any problem derived from the external seals that are usually used to achieve these maximum levels of tightness and that make the duct so ugly, also making it  “non-removable”.

By making a fitting in each corner and due to its characteristics of sponginess and elasticity, it allows it to adapt perfectly between the planes of the flanges to be joined, as well as in the corner projections as the spots with more difficulty in sealing.

This rubber gasket, assembled with the corresponding recommendations, makes it possible to easily and safely obtain the most demanding level of tightness contained in the current European standard UNE-EN 1507: 2006:

  • In overpressure CLASS D3 at +2000 Pa
  • In depression CLASS D at -750 Pa
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Detail of the corner of the joint made with the RAMI-SYSTEM® EPDM Sealing Gasket

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Our test bench for testing of joints and access doors, with a 400 x 400 mm section duct, 7 joints and a total surface area of ​​12.20 m²


Test 1 passed 2000 D 3
Test 2 passed 750 nivel D

Rapport of an overpressure test in Class D-3 at +2000 Pa with a leak value of 1.13 l / s over a limit of 1.71 l / s, which represents a 34% better result

Rapport of a Class D depression test at -750 Pa with a leakage value of 0.48 l / s over a limit of 0.90 l / s, which represents a 47% better result



The D-3 airtightness level is the highest of the European Standard EN 1507: 2006, which is the one that currently regulates the airtightness levels in the different types of rectangular ducts. This requirement is very severe and involves the highest quality rigor in the manufacture of the ducts, as well as in the subsequent assembly in the installation.

In this section we are going to detail a series of tips to carry out in these processes to be able to achieve, without problem, the maximum level of airtightness that can be required in rectangular ducts.

It must be borne in mind that each and every one of the operations carried out in the ducts is very important and that all of them must have that high level of quality since, if only one of them fails, the result will not be the desired one.

Obviously the cost of the ducts, with this high level of airtightness, is higher than normal and it must be stated this way when contracting the installation.

For this reason we want to emphasize that the objective of achieving the CLASS D-3 sealing level will not be fulfilled if a careful work pattern is not followed, from the beginning to the end, of the entire process.


First of all, the cut of the metal sheet to form the sides of the duct has to have the exact measurements. Next, the conformation of the longitudinal closures (female “Pittsburgh” seam and the 7 mm male flange) and the bending have to be perfect, because it will depend on this that each duct section has exactly the same section. In this section it is very important to have the shears, folding machines, beading machines, etc… in good condition, well adjusted and be operated by professional and efficient personnel.

The closing of the sections of the ducts (either manually or by machine) must also be carried out carefully, checking the measurements of the section in each end to properly adjust the correct measurement requested because, otherwise, then it will no longer be able to match the frames of each union well and the joint sealing function will not perform properly.

Next, the RAMI Corners will be placed in each end. To do this, the flanges should have been previously cut to their exact size and this will depend on the type of corner used:

    • For corners type A: Nominal length -3 mm
    • For corners type B: Nominal length -25 mm

As a rule to follow: the outer projections of the bracket always have to touch the ends of their contiguous flanges.

Then the measurements of the ends of the ducts will be verified to adjust them manually (with the hammer and the tas) if necessary.

Pre-sealing in workshop

Once here, the ducts must be sealed internally with caulk at all seams: Pittsburgh, flanges with the duct, and corners. In the corners you have to pay close attention so that this area is at the same level as the joining flanges (here it is good to use a spatula). We recommend a type of putty that is not very elastic so that it does not give way when tightening the screws. Our EPDM gasket has to be compressed on firm surfaces. If a type of water-based leveling paste is used to improve the finish, excellent results are achieved because it allows to sand those areas that will later determine the ability to easily achieve the proposed objectives. It is recommended to let the duct putty dry until the next day before proceeding with the assembly.


Detailed view of the putty with subsequent sanding in the corner.

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Placement of the double-sided adhesive tape to fix the EPDM gasket and be able to make the splice easily.

Duct preparation on site

First of all, and to correctly apply the EPDM gasket in the end of a duct of each union, the frames must be cleaned of dust and impurities. Then, to apply the EPDM gasket in the end of a duct of each union and so that it does not move from the correct position, we can help ourselves with a double-sided adhesive tape that, first sticking it on each frame, will allow us to fix the rubber gasket precisely without moving when splicing. The position of the gasket will always be with the small ends of the “T” on the outside of the duct and abutting the top of the flange (where the intermediate clamping clip is placed).

For proper gasket placement in the corners, we recommend the following assembling method:

  • Place each side separately and adjust it by head with its adjoining perpendicular. It will be necessary to make a die at one end to pass the screw. We recommend cutting the end of the joint adjacent to the die about 2 mm longer so that it can then be accommodated by exerting head pressure on the adjacent die-cut section
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Method of placing the EPDM gasket on the double-sided adhesive tape

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Detail of the finished assembly of the EPDM gasket in the corner area

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Another method for the assembly of the EPDM Gasket maintaining its continuity in the corners

Installation of the duct on site

Next, it is necessary to perfectly face the two sections to be joined and proceed to the simultaneous and progressive tightening of the screws while maintaining the correct position of the rubber gasket. It is not necessary to tighten too hard to avoid deforming the brackets. It is simply necessary to observe that the EPDM gasket is compressed at half its thickness (for this, the tightening torque of the screwdriver machine will be properly adjusted).

Depending on the width of the side of the duct, it is recommended to place bolt clamps every 500 mm and using the same tightening torque as the one used in the corners.