Chemical Compatibility
The pumped fluid contacts only the inside surface of the tubing thereby negating concern for other valves, O-rings or seals that might be incompatible with fluid being pumped. Therefore, only the composition of the tubing that the pumped medium travels through is considered for chemical compatibility.
The tubing needs to be elastomeric to maintain the circular cross section after millions of cycles of squeezing in the pump. This requirement eliminates a variety of non-elastomeric polymers that have compatibility with a wide range of chemicals, such as PTFE, polyolefins, PVDF etc. from consideration as material for pump tubing. The popular elastomers for pump tubing are Nitrile (NBR), Hypalon, Viton, Silicone, PVC, EPDM, EPDM+polypropylene (as in Santoprene), Polyurethane and Natural Rubber. Of these materials, the Natural Rubber has the best fatigue resistance, and EPDM + Hypalon have the best chemical compatibility. Silicone is popular with water-based fluids, such as in Bio-pharma industry, but have limited range of chemical compatibility in other industries.
Extruded fluoropolymer tubes such as FKM (Viton, Fluorel, etc.) have good compatibility with acids, hydrocarbons, and petroleum fuels. But the material has insufficient fatigue resistance to achieve an effective tube life.
There are a couple of newer pump tubing developments that offer a broad chemical compatibility: a lined tubing approach and the use of fluoroelastomer approach.
With the lined tubing, the thin inside liner is made of a chemically resistant material such as poly-olefin and PTFE that form a barrier for the rest of the tubing wall from coming in contact with the pumped fluid. These liners are materials that are often not elastomeric, therefore the entire tube wall cannot be made with this material for peristaltic pump applications. This tubing provides adequate chemical compatibility and life to be used in chemically challenging applications. There are a few things to keep in mind when using these tubes - any pin holes in the liner during manufacturing could render the tubing vulnerable to chemical attack. In the case of stiff plastic liners like the polyolefins, with repeated flexing in the peristaltic pump they can develop cracks, rendering the bulk material again vulnerable to chemical attack. A common issue with all lined tubing is delamination of the liner with repeated flexing that signals the end of the tube's life. For those with need for chemically compatible tubing, these lined tubing offer a good solution.
With the fluoroelastomer tubing, the elastomer itself has the chemical resistance. In the case of Chem-Sure, it is made of a perfluoroelastomer, that has the broadest chemical compatibility of all elastomers. The two fluoroelastomer tubes listed above combine the chemical compatibility with a very long tube life stemming from their reinforcement technology, but come at a pretty high initial cost. One has to justify the cost with the total value derived over the long tube life, and compare with other options such as other tubing or even other pump technologies.
There are many online sites for checking the chemical compatibility of the tubing material with the pumped fluid. The manufacturers of these tubing may also have compatibility charts specific to their tubing.
While these charts cover a list of commonly encountered fluids, they may not have all the fluids. If there is a fluid whose compatibility is not listed anywhere, then a common test of compatibility is the immersion testing. A 1 to 2 inch sample of the tubing is immersed in the fluid to be pumped for anywhere from 24 to 48 hours, and the amount of weight change from before and after the immersion is measured. If the weight change is greater than 10% of the initial weight, then that tube is not compatible with the fluid, and should not be used in that application. This test is still a one way test, in the sense that there is still a remote chance that the tubing that passes this test can still be incompatible for the application since the combination of borderline compatibility and mechanical flexing can push the tube over the edge, resulting in premature tube failure.
In general, recent tubing developments have brought broad chemical compatibility to the peristaltic pump option that many chemical dosing applications can benefit over other current pump technologies.
Read more about this topic: Peristaltic Pump, Key Design Parameters
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