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Making the Cut

Dr Laurențiu Pestrițu takes the readers through the paces of installing insulation in Part 2 of the series on insulation.

| | Mar 13, 2012 | 12:53 am
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Proper insulation work in refrigeration and air conditioning applications ensures a longer lifespan of the units and minimises problems occurring later on. Dr Laurențiu Pestrițu takes the readers through the paces of installing insulation in Part 2 of the series on insulation.


Faulty installation practices while fitting of insulation material in an air conditiong system could prove to be expensive in the long run. It is, therefore, essential that professional insulators are properly equipped to do the job before they begin the insulating work. This could avoid false starts in installing elastomeric insulation materials. An installer with the right set of tools and a professionally set up workplace will do a better and a quicker job, and will enjoy the results of a project done well, to his and the customer’s satisfaction. In this regard, adequate preparation before getting started with the job is a necessary prerequisite, and will prove to be cost-effective, as time and material saved are two important factors, not to mention the durability of the unit.


Unfortunately, setting up a professional workplace on the building site is not yet a matter of normal practice that all installers follow. In this regard, a folding table or a formwork panel laid across two trestles can be used for the purpose as a quick arrangement. This kind of setup provides a more comfortable working condition for the fabrication of the insulation material into the right shapes. Also, this way, the insulation material stays clean. Since the dust on the tubes and sheets increases the risk of faulty adhesion, care needs to be exercised, as dust is the worst enemy of good contact or pressure-sensitive adhesion.

The following are the important factors that need attention when equipping a workplace before getting the job started:

  • Good lighting
  • Sharp knives
  • Suitable brushes (and/or rollers)
  • Appropriate contact adhesive
  • Cleaner (thinner)
  • Paper or cloth for drying brushes

In addition, if pieces are to be cut from insulation sheet material, the workplace should have a surface area of at least one square metre. One essential preparatory task is to stir the contact adhesive thoroughly. The heavy components (solids) from these adhesive systems, which settle at the bottom of the tin, must be mixed well with the lighter components (activating the adhesive) before work begins. If bubbles form as a result of stirring, then an evacuation period should be allowed for the air bubbles to rise to the surface and be emitted.


Before pieces of sheet material are mounted or elastomeric tubes are sleeved over, the surfaces of pipes must be cleaned carefully with a cloth. This is an important step, particularly when self-adhesive sheets or rolls are to be installed. A suitable cleaner should be used to remove grease and persistent dirt. Only then should the seam be glued.

It is essential to clean the surfaces thoroughly when insulating vessels and air ducts on which there is often a film of grease. During the cleaning process, any incompatibility between the adhesive system and the paint or corrosion protection coatings on the components can be recognised. The cleaner and the adhesive are harmonised with each other and contain the same solvents. Any incompatibility that might arise during the cleaning process – that is, if stripping effects occur – should be seen as a warning sign.


At the points where the insulation ends, preparatory work should be particularly thorough. For example, a tap usually forms the end of the insulation at the end of a valve stem. Here, self-adhesive Aerofoam NBR tape should be applied to the cleaned metal surface with great pressure, but should not be stretched. The adhesion can always be improved by applying a thin coat of glue, which should have been dried hard before the self-adhesive tape is applied. The tape will form an elastomeric substrate, an excellent basis for adhesive bonds.


In order to ensure that taps butt against the insulation of the main pipe optimally, the pieces must be bevelled, especially in the case of 90°, 60° and 45° branches. This also applies to the typical valve tap for insulating valve stems. If the material is bevelled at the wrong angle or poorly cut, faulty adhesion often occurs here. As a result, the insulation thickness calculated to prevent condensation may not be achieved at these critical points.

The insulation material is often bevelled after the shaped piece has been cut out. It is essential to ensure, in this case, that it is only carried out where the tap will actually butt against the main pipe insulation later. Experience shows that pieces are often over-bevelled here.

If bevelling is carried out whilst the parts for the shaped piece are being cut out, then the best result is achieved. A gentle transition from the bevelled to the unbevelled section can be achieved this way.


A cavity is formed under the cap, when insulating valves, strainers and other installations. This can be reduced by packing with remnants of insulation material. At the same time, this gives shape to the cap and increases its stability. The benefit lies less in the additional insulation effect, rather than in the fact that a strictly geometrical shape can be achieved.

However, a sheet of metal is even more suitable as reinforcement. The dimensions of the piece are determined by:

  • n The height (flange to flange)
  • n The length (approx. ¾ of the circumference) of the flange

If the metal reinforcement is bent slightly, it can easily be wedged onto the flange and then attached with mounting tape.

In order to protect the surface against corrosion, the self-adhesive insulation tape should be applied to the flange before the metal reinforcement is mounted. This prevents any negative impact due to the reaction of different metals with different electrical potentials. The advantage of a stable reinforcement is that the longitudinal seam of the cap (which should be located on the side wherever possible) can now be closed under pressure, working from the inside out. This procedure eliminates any risk of the seam gaping open inwards. In the case of smaller valves, it is sufficient to reinforce using a PVC foil jacket.


From the procedure shown above, it is evident that stress needs to be laid on appropriate working conditions and the preparatory work for the professional installation of closed cell insulation materials. The reliability of the insulation can be safeguarded by investing a little time and material on the process. These measures will not only help the long-term functionality of the low-temperature insulation work, but will also reduce potential problems.

The writer is Product Manager Insulation – Middle East, India and Africa, at Hira Industries. He can be contacted at laurentiu@rhira.com

References: Helms, Hubert und Weber, Michael (1999): Richtige Verarbeitung von Elastomeren Dämmstoffen. (The correct installation of elastomeric insulation materials). In: Isoliertechnik 3/1999, p. 18-27. Weber, Michael (2004): Die Dämmung von Kältepumpen. (Insulating refrigeration pumps) In: Isoliertechnik 6/2004, p. 6-14. perspective

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