Tubing Buying Tip #12: Moisture
Does your application involve water, condensation, or humidity? Tubing and reinforced hose materials react to moisture differently, and their reactions can vary depending on temperature, contact time, and the amount of moisture.
Some materials absorb water and other liquids, which in most cases, you don’t want. Absorption can cause the tubing to swell. If the application involves dispensing measured amounts of fluid, you may actually be getting less than the desired amount. Swelling can also affect tubing properties such as elasticity and tensile strength.
Tubing that absorbs fluids can leach those fluids back into the stream and cause contamination in critical applications. Problems with fitting connections can also occur, jeopardizing applications involving a tight fit.
Another issue involving moisture and liquids is adsorption. This is where molecules from a liquid or gas collect on the surface of another substance, like a solid. In other words, bits of something starts to stick to the tubing walls. Adsorption differs from absorption in that the molecules are attracted to the surface but do not enter the tubing’s minute spaces as in absorption. Materials such as PVC and fluoropolymer have smooth, slick surfaces, leaving limited possibilities for fluid adsorption.
Other materials vary regarding their moisture resistance. Ether-based materials polyurethane naturally resist moisture and inhibit mold growth. Polyethylene provides moisture protection, as does polypropylene, although other factors, such as chlorine and oxidation, can greatly affect polypropylene’s moisture resistance. Many nylon formulations absorb water, and this helps prevent the material from becoming brittle.
Be sure to check tubing and hose descriptions for information regarding moisture resistance when you believe it could affect your application. Test tubing candidates before committing to a material.
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