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Plastic grade and carbon micron information

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Hi guys.

A couple of questions today...

1: Could you advise what grade of plastic we need in our pump that can handle 40% vodka, the gaskets will also need to be up to the job?

2: We have been asked by our filter supplier to find out what micron size activated carbon is so they can provide the correct grade filter.

As usual any advice will be greatly appreciated.

Many thanks.

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1. Don't us plastic, plastic will degrade over time and even faster when it comes in contact with alcohol. You want brass or stainless steel and explosion proof for the best pumps. Though this is a matter of some debate among distillers.

2. As for filters we use Norit Rox 0.8 for our activated carbon water filter (http://www.bulkreefsupply.com/bulk-premium-rox-0-8-aquarium-carbon.html). Then we'll be using a .45 micron filtration system from EMD Millipore for filtering our final product. (http://www.millipore.com/catalogue/item/kvhla10tt1)

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There seems to be a lot of fear concerning plastics and elastomers when it comes to pumping alcohol. If you plan to pump up to pure ethanol, your best seal/gasket/part materials are Teflon, HDPE, EPDM, Viton, and Silicon...in that order. Each has it's own characteristics that need to be taken into account. I've used all of them in pumps, and apart from the product monographs, here's what I've found. Teflon is pricey, and works great. It takes greater pressure to seal properly, and rebuilds poorly, so you either need to mark your gaskets during an overhaul, or replace everything every time. But it lasts well. HDPE materials are great, but also expensive...they seal better than teflon, but nick relatively easily. I find HDPE diaphragms fail where they contact harder materials. EPDM is my favorite...it will degrade in pure ethanol, especially at elevated temperatures (180F) but holds up as long as my pumps go between rebuilds. It is significantly cheaper than HDPE...it will degrade at elevated temps in water as well, BTW. Viton is great because it's usually color coded, and stands up extremely well. It's pricey, and diaphragms and dynamic parts tend to flake a bit over time in any liquid environment. It's totally inert, though, and will be caught by any coarse paper filter. Silicon stands up very well, and seals very well. However, it's got a very low durometer and can be overtightened in gasket and diaphragm situations, which can pinch it and put a hole in it or push it into the liquid path...potentially causing bacterial harbors (not an issue in ethanol). The biggest problem with silicone gaskets is that they tend to "creep" which can lead to join failure in triclamp or other unsupported joins if left for an extended period. I like that creep in areas with vibration, as silicone can help damp that out. Cast silicone only, not RTV. Also, with 40% ABV max, you will probably be just fine using good old Buna-N neoprene parts. Just don't go over 160 proof with it.

As far as pump bodies go, you are best with stainless steel, 316 alloys being a bit better than 304, but any austenitic (non-magnetic) stainless steel is fine. Brass is also good, but often has trace amounts of lead to improve machinability. Some plastic pump bodies are good, with Polypropylene being the best (and often the cheapest.) I don't recommend PE (polyethylene) bodies, but HDPE is ok. Acetal is not recommended for pure ethanol, but ok for 40%...which will have no effect on it for a very very long time. Nylons are a complete no-no, as is pentacryl (sometimes you find these for pumping certain solvents, but they suck for alcohol)

The big problem with plastic pump bodies is that most of them have female NPT inlets and outlets, and we tend to put stainless triclamp fittings into them...when you overtighten the fitting trying to get it to stop leaking, the plastic cracks. I recommend putting a stainless Oetiker or other ear-type clamp over the outside of the pump fitting before tightening your MNPT fittings. Especially with acetal! Also, if your pump is white plastic, it's probably not groundable. If it's gray or black, it probably will conduct enough to dissipate static charges. Of course, metal is great.

Aluminum pumps sometimes hit the market, and they work well...the issue with aluminum is that if anything is out of alignment, it will shave the aluminum off rather than deforming a groove. Aluminum has very interesting properties with it's ductility.

Hope that helps. If in doubt, google the material monograph, and you can find lists of solvents (ethanol included) and compatible plastics. Any thing at "good" or "excellent" is usually fine for a craft distiller.

Hope some of that helps!

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I missed the carbon part...

most of us use granulated activated carbon (GAC) rather than pressed block carbon (common in small filters) You want a mesopore carbon, no matter what you use. The mesh size of the carbon varies greatly...I know of some places using 2"x2" bricks, and others using 20x40 mesh. The numbers refer to the screen sizes...a 8x30 means that 85% of the carbon goes through a #8 mesh screen, but is 95% retained by the 30 mesh screen. 12 x20, 8x30, and 12 x40 are popular sizes in water filtration, but there are many grades. You can look up the screen sizes easily.

If you use carbon block media (extruded activated carbon) be aware that it's held together with a binder, and you need to know that the binder is compatible with your alcohol. If it's an impregnated carbon filter (carbon pressed into a fiber binder) then you need to decide what size you want to filter out. I'd go no larger than 5 micron, personally. We filter at 1.2 micron for polishing.

Fun stuff!

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