Step 1: Obligatory Safety Mesage
- If you use a good vacuum pump you are dealing with very high pressure. Atmospheric pressure is over 14 psi which doesn't sound like much until you realize that 1-foot cube has just over a ton of pressure on each side. I crushed a thick metal pan (see picture) that I thought could handle the pressure.
- Keep your fingers away from the air-intake of your vacuum pump. It will tear or rip off your skin in no time. You are a complete moron if you check to see that your vacuum is working by using your fingers to feel for air. Do not ask me how I know this.
Step 2: Materials and Tools
- Vacuum pump. I bought a Robinair 15310 VacuMaster from Amazon for $106.
- 1/2" thick polycarbonate (AKA Lexan). Mine is 18"x13" for $24 at a local plastics shop. A small piece of polycarbonate for practicing is recommended.
Plumbing: 1/4 inch NPT fittings, all from Amazon
- Male nipple $7
- Female tee $7
- Inline ball valve with hose nipple. $16
- Vacuum gauge $9
- Teflon tape $1.50
- Nylon tubing to fit over ball valve nipple $8 at HomeDepot
- Nipple for attaching hose to vacuum pump $2 at HomeDepot
- Some sort of rubber mat. Mine is HomeDepot "Grip liner" for $5.
- Something strong and air-tight to use as the vacuum chamber. I've been using a frying pan.
- Some rare earth magnets (I used 1" magnets I had laying around)
- Small nylon washers
- Plastic epoxy.
- Paper clips
- Freezer-quality plastic slide-seal bags.
- Drill (preferably a drill press) and 7/16th drill bit.
- 1/4" NPT pipe tap $9 on Amazon.
- Spray bottle with soapy water.
- Scissors or razor
- Half-inch polycarbonate may be overkill but it's better to be safe than sorry. (Polycarbonate is used to make windshields for jet fighters.) Even at a half-inch thick I can see it sag a little bit when the vacuum gets near 29" inHg.
- My piece of polycarbonate is obviously a lot larger than the pan I use in the demonstrations. I made it larger because I may want to try to make a larger chamber. You can use a smaller piece.
- The vacuum chamber I bought appears to be middle-tier on Amazon (i.e. there are cheaper and more expensive). I got this one because it evacuates air at 3 CFM which is more than most (many are 1-1.5 CFM) and thus faster. It takes about 5-10 seconds to get to 29" inHg with this pump.
Step 3: Drill and Tap Polycarbonate
Drilling the hole in the polycarbonate is much easier if you have a drill press because you'll likely need to pull out the bit multiple times to clean the plastic off the bit. It will help if you practice on a scrap piece of polycarbonate so you can learn what to expect. It's not hard but polycarbonate is expensive enough that it sucks to screw up.
Figure out where you want to drill the hole. You probably don't want it directly in the center because the gauge and tubing will get in the way when you seal the bags. According to the manufacturer of Lexan you can use a general purpose bit at a low speed if you keep it lubricated (see PDF here). Keep the bit and hole wet with soapy water and you'll be fine.
Tapping the hole is just a matter of screwing your tap into it. Keep it well lubricated with the soapy water.
Step 4: Assemble the Hardware
Assembling the tubes is easy. Be sure to use Teflon tape in all the joints.
Step 5: Create Gasket
Cut up the rubber matting and put a hole in the middle to act as a gasket.
Step 6: Prepare the Bags for Sealing
To close the seal inside the chamber I needed a way to attach the slider to a magnet. What I've done so far is glue plastic washers to the slider using plastic epoxy. Leave enough of a gap so that you can thread a paperclip through the hole.
Step 7: Operating the Vacuum Chamber
- Attach the magnet to washer on the bag.
- Tape the bag to the side of the chamber (pan).
- Put the gasket in place and cover the chamber with the polycarbonate.
- Place your other magnets over the inside magnet.
- Operate the vacuum pump until you get your max chamber.
- Slide the top magnets. The inside magnet will close the slide sealer.
I keep the other magnets in the plastic film because it makes it easier to work with them.
Step 8: Effectiveness
For the most part this setup works very well. There are two areas that could use refinement and I'd love to get some ideas on how my design can be improved. Please leave comments with your thoughts!
1) The method of sealing the bags is a bit awkward. I want to keep the ability to re-use bags but I'd like a more robust method for sealing them, preferably without having to glue anything to the bags. I had some frustrating moments when the washers broke off from the slider.
I'm not against using a heat sealer if it's a supplemental method (i.e. I can either use Ziplocs or heat-seal).
2) The result of the packing is very tight if the item is dry (like in the demonstration video). When I seal wet food, though, there is a little bit of air left in the bag after sealing. I believe what's happening is that water is boiling off of the food when it gets to near-vacuum and gets trapped in the bag as water vapor. I've tried chilling the food and even freezing it before sealing but the result still isn't as good as I'd like. I believe this is more of a technique problem; perhaps I need to seal the bag and immediately release the air. How to commercial vacuum chambers deal with this?
Finalist in the
Food Science Challenge