Electronics > Projects, Designs, and Technical Stuff
silicone (PDMS) slipperyness?
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coppercone2:
add a dye to the water to test for leaks, even if it leaks for a bit, stops (i.e. a 'fart leak') and evaporates you will get a stain residue.

Your method is not great to detect a transient leak during a long run time.
coppercone2:

--- Quote from: frogg on May 16, 2019, 05:31:31 pm ---Does this have to be a rotary valve?

The schematic looks like it's possible to accomplish via some combination of check valves, 3-port 2-way valves, and some method of synchronization (mechanical linkage or electronic)

--- End quote ---

that thing is like an ASIC. Why its good for hydraulics? Because you get less 'dead space' in the circuit. Basically all the excess space in a sampling system that is continuous will accumulate previous sample and dilute it so you get a lag in your response, so you need to flush it more frequently. And if its an organic material or food it can rot in there etc. You can think about it almost like RF design. You want to make it easy to flush too.

They have 'sampling valves' that are manual, you basically turn it and it scoops some stuff up and releases it into the other section like a manual pump with a single turn. Check valves with springs and stuff are difficult to flush.
vindoline:

--- Quote from: ChristofferB on May 15, 2019, 11:54:49 pm ---Here's an image of the valve I'm trying to recreate. The commercial ones are MAD expensive.

--- End quote ---

So is precision electronics test gear . . . if you pay retail  :box:
eBay is your friend! I can't imagine why you would want to DIY one of these, there are so many solutions in the life-sciences. Valco valves are the big player. Look for derelict or broken HPLC equipment. I've bought them for under $100.

If you're thinking about amateur HPLC, I'll warn you that the cost of EVERY SINGLE PIECE will make you weep. You won't believe what a single nut, connector or piece of plastic tubing will cost. Then there's the cost (and sourcing) of high purity HPLC grade water and (typically) acetonitrile. You also can't pour the waste down the drain! Hazardous waste disposal fees!

I'm definitely NOT trying to be a wet blanket, just making sure you go in eyes wide open.
ChristofferB:

--- Quote from: vindoline on May 17, 2019, 01:13:59 pm ---
--- Quote from: ChristofferB on May 15, 2019, 11:54:49 pm ---Here's an image of the valve I'm trying to recreate. The commercial ones are MAD expensive.

--- End quote ---

So is precision electronics test gear . . . if you pay retail  :box:
eBay is your friend! I can't imagine why you would want to DIY one of these, there are so many solutions in the life-sciences. Valco valves are the big player. Look for derelict or broken HPLC equipment. I've bought them for under $100.

If you're thinking about amateur HPLC, I'll warn you that the cost of EVERY SINGLE PIECE will make you weep. You won't believe what a single nut, connector or piece of plastic tubing will cost. Then there's the cost (and sourcing) of high purity HPLC grade water and (typically) acetonitrile. You also can't pour the waste down the drain! Hazardous waste disposal fees!

I'm definitely NOT trying to be a wet blanket, just making sure you go in eyes wide open.

--- End quote ---

Haha I'm well aware that it's not on the cheap end! I'm also not really trying to do HPLC, more like LPLC//flash/FPLC? so HPLC-ish in setup, but at much lower pressures. But you're right, the sample valve might be the one place where finding one used is unbeatable.

There are a lot of truly great scientific papers on analytical standard "DIY" hplc detectors; UV absorbance detectors and fluorescence detectors made from single PEEK cross fittings with column in/out, and optical fibers in the two other ports going to a simple UV LED/photodiode system that I want to try to mess around with.

I'm also hoping to source parts from Ebay, but everything I can avoid buying is a win. For low pressures, I've designed a very cheap fluid connection system consisting of 1/16" PTFE HPLC tubing mashed over lenghts of hypodermic tubing. This gives me both ports to epoxy into things, syringe ports, fittings etc. See attached.

I'm also planning on using non-toxic solvent systems, you can get a long way with water/ethanol or water/acetone mixtures. At this stage I'm not super concerned about solvent purity either.

Thanks for the interest!



ChristofferB:
Okay so I made a quick prototype to see how the valve would behave, both elements of acrylic, and to noone's surprise, it leaks badly. It does hold at VERY slight positive pressures though, it seems, although this might just be because the leak becomes too small to notice.

I'll attempt different rotor pieces on this base, maybe LDPE or HDPE and definitely PTFE.

If nothing else the prototype looks kinda cool.

Enjoy!

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