A Better Vacuum

qc · Post by qc » Wed Jul 23, 2008 9:14 am

So I've set up a vacuum (and pressure) pot/chamber...but have yet to really use it (since I'm still working on a master).

But after Sparky's and Valk's talks at the wonderfest seminars I thought I'd pull my equipment back out and fine tune it. My original first set up was only pulling about 27.5" (Hg). I'm hoping to get more out of it.

I have yet to play with any RTV, but sit a glass of water in my pot and got zero bubbles. Should I be concerned? I was think'g of mixing up some old RTV tonite and just run a test. I understand 28" is a minimum....is this a hard line in the sand kind of number...or can you get a soft boil off 27" for example.

I'm hoping to get some help "overclocking" my setup. Below is a list of potential areas I feel I may be loosing some vacuum. Please add any help you can on these or other areas:

VP in question:
[/url]http://www.amazon.com/gp/product/B000OUX9EU[url]

1) The vacuum pump itself has a main line hook up but also a release? smaller valve off the main neck...kinda looks like 1/8 valve...but has a plastic cap over it (ends up looking like an old bike valve, without the inside "valve needle"). I teflon taped this up (with the cap on), but i fear its still letting air in. The thread/size is weird and can't find a fitting to fit it correctly. I'm considering filling the hole up totally...maybe some epoxy or something.

2) I set up my vacuum AND pressure rig to go from pump/compressor into a 10 gallon aux. tank (for build up and quick release) then into the pot. The fittings/valves/gauges all seem tight there. I was really surprised how fast the vacuum pump works (and I don't need to get a quick vacuum when vac'g RTV...maybe resin later). I may reroute the lines to bypass the tank...and go from vac.pump to pot directly (with the gauge sitting at a T). This may bypass some of the potential little leaks around the aux. tank.

3) My pot is the starter 2.5 gal pot from Harbor freight with a 3/4" plexi lid. I tapped a hole in the plexi in the lid and epoxied a female 1/4" npt UNIVERSAL fitting. The universal fitting is tight for pressure applications, but not for vacuum. Both industrial and automotive fittings in a universal have some "give" (in and out ...not side to side). I can manually press the male fitting into the universal female and get some extra inches on my gauge...but this is not ideal way of operating. I've been told that acetone can undo epoxy. I ran a little trial and letting it sit, the acetone was eating the epoxy, but I fear this may take forever and not provide a very "welcoming" open IF i do manage to get the fitting out and replace it with the non-universal fitting. Should I just cap/epoxy that one and redrill another hole? Get another piece of plexi (was lucky...after much searching found a vendor and gave $25? for it) and start over?

4) My gasket. I went to my local rubber/plastic fabricator and gave me some sheet rubber. Looks to be similar to what bicycle tubes are made of. Has that slightly chalky dry feel to it..and is soft. But is fairly thin (think bicycle tube again...I'm guessing 1/16" max? I cut a nice donut shape and 3M spray adhesive'd that to the plexi top. I am able to clamp down (using the pots built-in clamps) the plexi to the pot...and I can see the the chalky grey rubber gasket make a black line (due to the pressure of the plexi against it) when the clamps are cranked down. I wonder if I'm loosing a little there. Umi mentioned that ACE hardware has 1/8" sheet rubber...maybe the extra thickness would "wrap around" the pot lid better..and provide a form fit? Maybe I can put some kind of liquid around the lid/pot junction and look for bubbles (air escaping)?

Anybody got any ideas?

Much Thanks

Joseph Osborn · Post by **Joseph Osborn** » Wed Jul 23, 2008 10:34 am

Depending on your altitude and the viscosity of your rubber, 28" is usually when the magic starts to happen. It sounds like you know what you're doing as far as tracking down any leaks, so go ahead and isolate different parts of the plumbing to test the suckability. I'd suggest NOT using the pot's clamps on the plexi lid-- the vacuum should pull that lid down tighter than the clamps. A thin coat of vaseline on the rubber may help a little. Your weirdo fittings on the pump are A/C fittings. There are probably some brass caps available somewhere but I don't have any source handy. Drilling holes in the plexiglas is usually not recommended, so drilling another hole is probably not a good idea. Can you slip a good reinforced hose over the universal fitting that's in your lid and clamp it tight, then put a disconnect at the other end of the hose? Oops, just re-read your post and saw you put a female fitting there-- you may be SOL on this lid

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Wed Jul 23, 2008 3:08 pm

At the chamber, you can spray some windex, soapy cleaner, or just soapy water, and look for bubbles.

At your vacuum resivoir you might apply 10-15 psi and spray the connections and look for bubbles.

At your quick release valve, Spend $8-$12 bucks for a nice
ball valve at ACE. I don't think a small vinyl cap would seal too well.

treker2557 · Post by **treker2557** » Sat May 22, 2010 10:48 am

1) The vacuum pump itself has a main line hook up but also a release? smaller valve off the main neck...kinda looks like 1/8 valve...but has a plastic cap over it (ends up looking like an old bike valve, without the inside "valve needle"). I teflon taped this up (with the cap on), but i fear its still letting air in. The thread/size is weird and can't find a fitting to fit it correctly. I'm considering filling the hole up totally...maybe some epoxy or something.

Ok, the valve off the neck of the pump probably the handle you are referring to? That is a vent for the pump. Make sure you read the instructions for the pump and follow the directions on how to vent it each time you use it. Also, you need to keep the pump level.

Next is your setup. All you need is a compressor and since you are using a a 2.5 gallon pot any size compressor will work fine. Just place a quick connect on the compressor and the pot and get a cheap curly compressor hose. They are like $10 at harbor freight and quick connects are cheap as well.

Next lid setup. Normally don't use Plexiglas since it will deflect. You have a 3/4 sheet and only a 2.5 gallon pot so you might be ok but you might be getting deflection around the edges and around the hole drilled causing the vacuum pressure to not reach 29.5. I would purchase a 1/2 sheet of lexan that will overlap by 1 inch around. Next you should be using at least 1/8 in neoprene gasket that I would adhere with 3M spray. Spray both the lexan and the neoprene with a hole precut out in the middle. Let it get tacky then lay and use a roller to create a good seal and remove any air bubbles. Then drill and tap a hole and wrap fitting with teflon. You won't have any air leaks. Then make a tee setup so you can have a shutoff valve, a gauge, and hose attachment. Get a thick hose and fittings that grip the hose to create a good seal.