Dispelling the Myths of Teflon Hose

Teflon hoses are seldom specified in typical industrial hydraulic or pneumatic systems, yet they dominate in aerospace and tough industrial applications. Teflon (PTFE) hoses will simply outperform standard hoses in virtually any application, even in severe applications. That’s why they’re found in the Space Shuttle, landing gear and braking systems, and self-contained breathing units firefighters depend on for their survival. Teflon hoses are ideal choices for applications where the following are desired:

• Heat and cold resistance
• Corrosion resistance
• Non-toxicity
• Extremely low permeability
• Light weight
• Flex and fatigue resistance
• Ease of cleaning and sanitizing
• UV or ozone resistance

Just  as there are differences between materials used in standard hoses, so too are there differences between hoses using Teflon as the base material. Some basic considerations to bear in mind when selecting a Teflon hose for an application are:

Smooth or convoluted bore?
The primary difference is found in the bore size and bend radius of the hose. Smooth bores are typically available only in bore sizes of one inch or less, and will have a minimum bend radius of about 12 inches; convoluted bores will have a minimum bend radius of about 3 inches.

Conductivity
The characteristics of the conveyed or process fluid must be taken into account when specifying whether a hose should be conductive. Fuel line hoses, for instance (or hoses carrying other low-viscosity hydrocarbons), tend to carry the fluid at a high flow rate. This tends to build up a potential difference within the fluid due to static charge, which can arc out through the hose to the braid, creating a pinhole in the hose and potentially leading to future leak or fire concerns. Specifying conductivity will allow the static charge to arc out harmlessly to the fitting.

Wall thickness
Thicker walls tend to be better for applications where the hose is flexed severely, as the increased wall thickness will make them more resistant to buckling. Thicker walls also make the hose less permeable to gasses. Thin-walled hoses tend to cost less, because they contain less material.

Braid material
The standard braid material for Teflon hoses is 304 stainless steel. However, 316 stainless is recommended for marine applications. Monel is recommended for extremely corrosive environments, and bronze is ideal for applications where the hose may rub against other equipment.

Fittings
Crimp, swage, or reusable fittings may be used with Teflon hoses. There are no significant performance difference between the three.

Interior or exterior application
Hoses exposed to severe environmental conditions can befitted with several forms of external protection, such as extruded thermoplastic and silicone sleeves, fire-resistant sleeves, and various types of metallic protective enclosures. Hoses used within a vacuum can be fitted with internal coils or sleeves to prevent collapse.


The Myths of Teflon Hoses

To avoid specification errors in the design of processes using Teflon hoses, the following misunderstandings should be kept in mind.

1.    Teflon hoses are expensive
Teflon hoses made from PTFE is typically more expensive than rubber or other material, howver when the hose’s total lifecycle costs are considered, Teflon hoses are the more economical choice. A Teflon hose will outlast a rubber or thermoplastic hose in virtually any operating condition; the advantages of Teflon are most notable under severe conditions, but are always present. Some things to keep in mind when analyzing a hose’s total lifecycle cost are:

• What is the cost of scheduled downtime for a hose change, not only in terms of man-hours and equipment cost, but in terms of lost production as well? How does a scheduled hose change impact other processes?
• How much does unscheduled downtime due to hose failure cost?
• How much does the hose contaminating of products or process fluids cost annually?
• How much does it cost to replace expensive boiler additives lost to effusion?
• How much could be saved if rubber or thermoplastic hose jackets were as corrosion-resistant as the stainless steel brain used on Teflon hoses?

2.    Teflon hoses kink and crush easily
The truth is that ALL hoses will kink and crush, especially when improperly specified for an application or improperly installed. Teflon hoses are no better or worse at resisting kinking or crushing as standard hoses. If kinking or crushing is a concern, it is often a simple matter to add spring guards to reinforce the hose at critical points. A hose with a thicker wall will also minimize kinking and crushing.

3.    All Teflon hoses are the same
Nothing could be further from the truth! “Teflon” is a trade name that applies to a wide variety of hoses made from fluoropolymer materials. The main types of Teflon hoses are either a melt-extrudable form (such as PFA, FEP, or EFTE) and a paste-extrudable form (PTFE). Melt-extrudable hoses by necessity have a lower melting point than paste-extruded hoses, and thus exhibit lower fatigue resistance. These reduced physical properties are not limited to a specific manufacturer, but are endemic of all melt-extruded Teflon hoses. PTFE, which is not a thermoplastic, cannot be continuously extruded; thus, the length of a PTFE hose has typically been limited. The latest generation of PTFE hoses can be made to much longer lengths – a 1” ID hose at 400 continuous feet is now perfectly possible.

http://www.eaton.com