Teflon® tubing for beverages and other pure media » a simple solution with many advantages.
In the beverage filling industry, thick-walled molded PTFE hoses have become the standard for connecting product distributors and valves over the past several years. Previously, it was common practice in process engineering to use stainless steel-jacketed hoses with polytetrafluoroethylene liners . However, the beverage technology industry relies on pure Teflon® tubing without an additional pressure-resistant outer layer, such as stainless steel braiding. What is the reason for this? I’d like to explain that here.
Why not use stainless steel-clad “PTFE tubing”?
Stainless-steel-braided hose assemblies have the disadvantage that, in the event of a rupture of the so-called liner—that is, the inner layer of plastics—a visible leak to the outside does not occur immediately. This creates a risk of contamination from bacterial colonies that cannot be detected immediately. Aseptic processing experts do not accept this. The highest standards of hygiene and protection against contamination are absolute requirements in the food industry.
Advantages of “PTFE Hoses”
PTFE is chemically resistant to virtually all substances and can therefore be used in a wide range of applications within the chemical industry. This material’s temperature resistance ranges from approximately -200 to +200°C. Furthermore, its non-stick properties and physiological safety are highly valued in the food and pharmaceutical sectors. The purity of this fluoroplastic also makes it attractive for semiconductor applications.
It therefore stands to reason that plastics could be used to manufacture tubing that flexibly connects rigid product lines. Two tasks have always been—or at least have been until now—challenging:
- Compressive strength requirements.
- The Design of the Connector
Flexible “Custom-Made PTFE Molded Tubing”
Re 1: If the wall thickness of the hose is selected to be sufficiently large, it is entirely possible to achieve the required burst strength even under pressure surges and in steam applications. The resulting loss of flexibility can be compensated for by precisely preforming the hoses to fit the installation space. This results in pre-assembled polytetrafluoroethylene(PTFE) tubing that does not require additional reinforcement with braided stainless steel or other textiles. In the (unlikely) event of a leak, it is immediately detected.
And what about the screw connection?
Re 2: The now thick-walled Teflon® tube can be machined as desired. This allows it to be combined with stainless steel half-shells, corresponding cap nuts, or flange connectors. For repeated assemblies, O-rings are often used as well to compensate for the minor drawback of the delicate sealing surfaces. The only limit to the creativity involved in designing these custom plastic lines is the machining process itself.
Another option is to flare the ends. This method is often used for small nominal diameters up to about 10 mm. For this, it is recommended to slide the flange connector onto the hose beforehand so that you can later install a ready-to-install assembly later on.
What has been your experience with lines, hoses, or pipes used for critical media? I look forward to receiving your feedback and comments!
Stefan Bock
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