| Electronics > Projects, Designs, and Technical Stuff |
| silicone (PDMS) slipperyness? |
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| LukeW:
I would just consider finding a commercial HPLC valve (Rheodyne or similar) on eBay. https://www.ebay.com/itm/Thermo-Scientific-Rheodyne-6-port-injection-valve-MHP9900-601-1/283169374615?hash=item41ee35c197:g:TnYAAOSw0c9booSW Or maybe you can use real spare parts / rebuild kits - e.g. the packing, the seal etc, and partially build your own? I wouldn't use acrylic. What happens if you want to run DCM as a solvent? I don't think the epoxy will be very solvent resistant either. Maybe PEEK would be a good choice? PTFE is probably the best choice - for slipperiness as well as chemical resistance. PDMS seems like a bad choice, unless you're trying to make microfluidics. |
| kony:
OP, the PMMA prototype design you showed is absolutely unsuitable for purposes of liquid chromatoraphy or anything that operates with larger than negligible overpressure to ambient as you already discovered. Had you ever repaired HPLC injector valve? The lapped ceramic surfaces with massive support stainless plates and thrust bearing with a very substantial preload are there for a very good reason. Sourcing scavenged parts ex Ebay is really your best (and cheapest) option. Not even PEEK will be good choice if you try to replicate it with correct setup due to long term creep under the preload (teflon and PE being absolutely out of question due to this). Ceramics and glass-ceramic composites are used for such purposes, lapping of the sealing surfaces not being optional but rather a must (at least one of the surfaces if you do get bit clever in the design). Has this project expected commercial output? |
| ChristofferB:
--- Quote from: LukeW on May 19, 2019, 08:43:56 am ---I would just consider finding a commercial HPLC valve (Rheodyne or similar) on eBay. https://www.ebay.com/itm/Thermo-Scientific-Rheodyne-6-port-injection-valve-MHP9900-601-1/283169374615?hash=item41ee35c197:g:TnYAAOSw0c9booSW Or maybe you can use real spare parts / rebuild kits - e.g. the packing, the seal etc, and partially build your own? I wouldn't use acrylic. What happens if you want to run DCM as a solvent? I don't think the epoxy will be very solvent resistant either. Maybe PEEK would be a good choice? PTFE is probably the best choice - for slipperiness as well as chemical resistance. PDMS seems like a bad choice, unless you're trying to make microfluidics. --- End quote --- I'll probably end up doing that. Just aquiring the high performance polymers might reach a price where getting a second hand rheodyne valve is better. --- Quote from: kony on May 19, 2019, 10:43:57 am ---OP, the PMMA prototype design you showed is absolutely unsuitable for purposes of liquid chromatoraphy or anything that operates with larger than negligible overpressure to ambient as you already discovered. Had you ever repaired HPLC injector valve? The lapped ceramic surfaces with massive support stainless plates and thrust bearing with a very substantial preload are there for a very good reason. Sourcing scavenged parts ex Ebay is really your best (and cheapest) option. Not even PEEK will be good choice if you try to replicate it with correct setup due to long term creep under the preload (teflon and PE being absolutely out of question due to this). Ceramics and glass-ceramic composites are used for such purposes, lapping of the sealing surfaces not being optional but rather a must (at least one of the surfaces if you do get bit clever in the design). Has this project expected commercial output? --- End quote --- I completely agree, it was more or less made to see if i could fabricate the channels and ports with the tools i had on hand, intending to do the entire "real" valve in another polymer. I never intended the valve to function at higher pressures, the desired working pressure was something like "very slight push on syringe". and no, in no way at all does this project has any commercial output, it's purely for personal amusement. Thanks for the interest! I think I'll just look for a 2nd hand 6-port valve. It was an interesting excercise nonetheless. |
| coppercone2:
I found your post interesting because I was not sure what would happen. Its too messy of an experiment to deal with for me. |
| ChristofferB:
Thanks! Doing "wet" projects like this is always an issue in a home shop setting, but keeping it in the realm of microfluidics, having tiny volumes of fairly benign liquid, and having a closed waste liquid receptacle helps a lot. My ealier gas chromatography project was more pleasant that way, only waste was helium and a tiny amount of analyte. I was wondering however if it would be possible to implement a sample valve such as described on a microfluidic chip, using air or liquid pressure ports that compress a PDMS membrane and block flow.. Would be neat. --Chris |
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