Hose selection requires attention to application variables such as temperature, pressure and flow, as well as requirements ranging from chemical compatibility to drainability. Hoses “cost” more than their purchase price. Be sure to consider hose longevity, maintenance and replacement costs and other cost-of-ownership factors.
A hose has four main parts: core tube material and construction; reinforcement layers; covers; and end connections.
When selecting a hose, start with the core tube, the hose’s innermost layer that comes into contact with the system media.
Is the material chemically compatible with the system media? Will it
corrode or deteriorate over time?
Can it tolerate the temperature range of the system media?
Will the material prevent or limit permeation and absorption? All materials, even metals, are subject to such, so this question is one of degree. Permeation occurs when media passes through a material, whereas absorption is when media absorbs into and becomes part of a material. Neither is necessarily an issue.
Will the core material stand up to the cleaning practices for your system, both in terms of temperature, pressure and material compatibility with any solvents and cleaning agents employed?
First, let’s review the materials that core tubes are made of; then, we will review some choices for core tube wall construction.
Metal cores (commonly 316L stainless steel) are good for general needs. They are usually rated for temperatures between -325 F and 850 F, which makes them an especially good choice — sometimes the only choice — for system media at extreme temperatures. A metal core is also good when there is little allowance for permeation or absorption. With the advent of fluoropolymers, metal is usually not chosen for highly caustic or acidic media because of issues with corrosion.
Sanitary, high temperatures
Historically, silicone has been a common choice for sanitary applications. A typical temperature range for silicone is from -65 F to 500 F. Silicone became the material of choice for sanitary applications because of its flexibility. However, that advantage has disappeared with advancements in fluoropolymer hose construction.
Silicone, which is incompatible with common solvents, has limited chemical compatibility overall. In addition, it is absorptive, which can lead to contamination. If a fluid is absorbed into the walls of the core tube, it may remain there for a period of time before leaching out, at which point it may contaminate media then in the system.
With silicone, removing the absorbed fluid is usually not possible. Steam cleaning, one of the most common sterilization methods for silicone, may not remove it, and high temperatures may cause premature failure. The hose will become brittle and break down.
In place of silicone, fluoropolymer cores are becoming the material of choice for sanitary applications. PTFE, PFA, and FEP are three common fluoropolymers, with a typical temperature range from -65 F to 450 F. Fluoropolymer cores are the most chemically inert available. They are non-aging, nonstick, easy to clean, and can withstand repetitive steam cleaning. Like metal, fluoropolymers also have a low absorption rate.
In addition, reinforcement layer advances allow fluoropolymer cores to overcome their stiffness and gain flexibility comparable to that of silicone. Bonding technology allows a fiberglass braid to be added as a layer for increased flexibility. The glue-free process means it isn’t present to be absorbed into the core walls. PTFE cores comply with FDA regulation 21CFR Part 177.1550, USP <88> Class VI and 3-A.
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