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Triclamp PRV <15 PSI Stainless & PTFE


iskiebaedistillery

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Hi HedgeBird, I am looking to mount this at the top of the pot above the fill level so it will not be submerged. It will be exposed to ethanol vapor, and of course the fores/heads vapor as well. I really only trust PTFE for the most part in these conditions. Rubber compounds do not mix well with ethanol vapors and could result in them becoming brittle/cracking.

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Just so you guys know. Those valves are not UL listed. If you are interested. I have US made, UL listed Apollo pressure relief valves with a NPT to tri clamp adapter and the PTFE gaskets for a better price than the non UL listed Chinese made valves. Here is the page with the valves http://www.distillery-equipment.com/oshop/index.php?main_page=index&cPath=23_76 If you want stainless ones just let me know paul@distillery-equipment.com Here is a link to the NPT to Tri Clamp Adapters http://www.distillery-equipment.com/oshop/index.php?main_page=index&cPath=26_75'>http://www.distillery-equipment.com/oshop/index.php?main_page=index&cPath=26_75 Here is a link to our tri clamp parts in general http://www.distillery-equipment.com/oshop/index.php?main_page=index&cPath=26 here is a link to our gaskets http://www.distillery-equipment.com/oshop/index.php?main_page=index&cPath=10 Teflon and PTFE are the same of course. The Viton gaskets serve a different purpose. They will not work with ethanol.

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Hi Bluestar.

The TFE seats in the valves are good for 250°F The PTFE gaskets are good for at least that.

OK, yes, I guess it depends on the valve design. PTFE is not a good gasket at higher temps with applied pressure, unless the gasket capture design restricts flow. That is because PTFE (and Teflon) are thermoplastics that will start to flow as you get above 200°F (actually, the glass transition temperature of PTFE is above 220°F, so it will remain solid, but the transition is a gradual affair, with increasing creep under pressure as you approach from below). There can actually be an advantage for an appropriately designed seal or valve to cycle close to the glass transition temperature: the PTFE gasket will creep each cycle, and further conform to the shape and defects in the seats. This tends to work better in well-captured seals than in valves. And valves that shear at the gasket are prone to fail.

But I still feel the need to caution readers about general use of PTFE as a gasket material exposed to temperatures in the 200°F region, like gaskets in tri-clamp joints: under pressure, the polymer can flow (how much depends on temperature, time, and pressure), and the seal may fail. Regular retightening can reseal, but eventually may deform the gasket enough that it won't perform. For tri-clamps, we use PTFE everywhere in our spirit path where temperatures are below 150°F, and silicone above. We don't put EDPM in the spirit path, but we do use it for mash/wash.

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Bluestar,

You are correct, but the data shows that you will not have any issues at 15psi or less or at temps. of 250°F or less. Which is why you will find Teflon Gaskets and Teflon seats in valves that are rated for 250°F and less at pressures of 15 psi and less, but you will not normally see it in gaskets and teflon valve seats rated at higher temps and pressures.. Also, some people choose Teflon over silicone because silicone is not an A rated with ethanol and Teflon is. However the type of silicone used in these gaskets leaches such a small amount that it does not matter. Personally I like the silicone gaskets better because they are softer and give a better seal and are therefore less likely to leak, in my opinion. However, the first 4 large pro series stills that we built have Teflon gaskets between the 12" column flanges and none have failed or leaked after 3 years of use.

Please read the below especially about elastic memory and recovery of Teflon. This pretty much explains why you don't have any issues at 212°F but there are issues at 350°F

*Quinn et al., J. Applied Phys. 22, 1085 (1951)

Low Temperature Properties Parts fabricated of Teflon® PTFE resins exhibit high strength, toughness, and self-lubrication at low temperatures. Teflon® PTFE resins are useful from –268°C (–450°F) and are highly flexible from –79°C (–110°F). Thermal Conductivity and Specific Heat The average thermal conductivity of Teflon® PTFE is 1.7 ± 0.3 Btu⋅in/h⋅ft2 ⋅°F. The average heat capacity is 0.3 Btu/lb⋅°F for Teflon® PTFE. These data were obtained at temperatures ranging from 20–260°C (68–500°F). Heat Distortion Temperatures obtained for heat distortion of Teflon® PTFE are (ASTM D648) 122°C (252°F) for a stress of 66 psi and 56°C (132°F) for a stress of 264 psi. Elastic Memory Parts made from Teflon® PTFE resins tend to return to their original dimensions after a deformation, but the process of recovery may require a long time. A fabricated part that creeps or deforms over a period of time under stress will recover its original shape when stress is removed and the part is raised to sintering temperature. However, partial recovery will occur at lower temperatures. At any given temperature, recovery to be expected at that temperature is substantially complete in 15 min or less, but extent of recovery increases with increased temperature. For example, a filament of Teflon® PTFE 4 in long, stretched to a length of 12 in and heated at 100°C (212°F), recovers to approximately 11 in within 15 min and then remains substantially unchanged. A similar piece heated to 200°C (392°F) recovers to 10 in. The first piece, after additional heating to 200°C (392°F), undergoes further recovery until it is 10 in long. When heated to 350°C (662°F), both pieces return to their original length of 4 in.

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Oooh, SH, I could talk plastic/elastic stress/strain of PTFE and Teflon with you for hours! Having used it in designing scientific instrumentation applications for about 40 years now. But I think we are agreeing, it is all in the design of the device for that behavior. And staying below the glass transition temperature. The elastic properties of Teflon (often somewhat better than pure PTFE) co-exist with its plasticity, and so it is always a competition between plastic flow and elastic strain, which depends on time, temperature, and force (pressure). And, of course, Teflon can refer to other derivatives of pure PTFE that have slightly better mechanical properties, particularly, the deformation recovery you refer to in the passage. But full recovery depends upon the right annealing sequence.

But with general PTFE gaskets (as opposed to use in a valve the manufacturer rates for continuous operation at 250°F), even low pressures at long times and higher temperatures can cause failure. That's why I caution against using them for tri-clamp gaskets that will be sealed for longer times, are often not tightened optimally or carry load, and operate in the vapor path. True, some silicones can leach, but the highest food-quality should not (absence of plasticizers), and certainly nothing compared to EPDM (yuck).

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