When looking at vacuum pumps, how can you tell if they have enough vacuum to do the job? I've seen a few advertised that say 25 microns or 75 microns. Are those strong enough?
full vacuum would be the equivalent of reducing the bag pressure by 1 atmosphere = 14.7psi = 30 in Hg = 760 mm Hg.
resulting in an absolute pressure = 0 mm
i believe they are refering to very low absolute pressures ( good vacuum)
1 millitorr = 1 micron Hg = .001 mm Hg
25 micron Hg is the result of removing all but a few molecules of air out of the bag
pretty much 99.997% full vacuum...yikes
zfennell is correct.
It's quite likely those pumps you are looking at theones used by the refrigeration industry, to evacuate refrigerant lines before they gas them up.
Just be careful, as those types of pumps don't like running at only medium levels of vac, they are happiest at full vacuum.
The vacuum bags we use leak too much, and it will kill one of those pumps - they don't like air flowing through them much.
But if it's cheap, give it a go and it might last for a while!
what type of pump would you suggest? are the ones on fiberglasssupply.com good for the purpose?
GAST makes really good pumps look at he the CFM's 3.0 or higher.
If your barnyarding a handful of boards then perhaps a fridgepump conversion will be sufficient and cost effective. Alternatly you can can find good Gast, Rietschle-Thomas or other brands of membrane vacuum pumps. Compsands don't require really deep vacuum force so that is also a consideration.
for a cool project:
To be honest, i'd reccommend a good 'ol fridge pump.
As long as you don't have problems wiring the thing up!
Vac pumps are expensive here, so fridge pumps are amazing value, basically free.
The quietest pump you'll find, and so reliable.
Sure, you feel like an amateur using one, but the results are far from that! They are a truely valid way of building. I've built almost 50 boards with one fridge pump, and possibly more than 150 test panels as well. I have 2 other pumps, one high vacuum infusion pump, and another low vacuum bagging pump.
But the fridge pump has pride of place for bagging skins on, no doubt about it.
I've now gone through the joewoodworker website a bit and now I'm wondering whether to go w/ a Continuous Run system or an Auto Cycling system??? I'm looking at a Thomas pump that pulls 24" Hg. I plan on using 2# Marko EPS in my projects. Could you Continuous Run this pump at full boogie on 2# EPS?
I appreciate all the info you're offering up.
If you have the money or motivation, i'd buy or make a vac switch. You will get far superior results that way.
It sounds like that pump you are looking at is perfect, and will probably be perfectly happy running constantly - all the good quality ones can.
But running constantly requires a bleed valve, and bleed valves don't adjust themselves to changes in your bag pressure! If your bag springs a leak, the pressure will drop, and there is nothing in the system that compensates for it. Believe me, this does happen! It's even possible that the bag gets a better seal as you go along, which means the pressure can dramatically increase = disaster. Of course, there are plenty of people who use bleed valves and get along fine, but the best solution is a vac switch.
Have a search for instructions on how to make one using the vacuum advance diaphragm from a car, there's a couple of websites that have info. See if that is something within your capabilities, as they are not too difficult, and work fantastic.
At a guess, pressing veneer onto 2# EPS might be ok at 24" Hg. Don't quote me on that though, as I don't use 2#, and I have a vac switch and bag around 10". Try a scrap of foam and veneer and see if it sqashes it. If it doesn't, then you can run the pump constantly, as 24" is the max anyway. I predict you'll want to try lighter EPS at some stage though. :) Thats how you get light boards....
OK, so how about the venturi vac "pump" that I see from time to time? I have a big-ass compressor to drive one or two..
Will they work OK?
I would go for the venturi system!