Rick, What model Robinair do you have? Are they oil-less?
15500 (5 CFM) nope not oiless.
http://robinair.com/product-new/detail.php?id=1060&catid=11
Got mine off of e-Bay from a supplier called “Climate Doctors” IIRC. I don’t think they sell on e-Bay anymore. Good price under $200 but they took forever to ship it.
well robinair pumps pull 50 microns for the non cooltech pumps, cooltech robinair pumps pull 20 microns, yellowjacket pulls 15 microns
0 microns is like pulling 30hg (perfect vacuum) so the lower the micron number the better
also the cfm (cubic feet per minute) i guess if i were you i would look for something around 5-6cfm unless you have more $$ to spend… thats just how much air it will move per minute…higher the cfm faster it wil suck all the air out
Just go and find yourself a fridge vac pump. You can find them for sale for cheap or free at your local dump. I have been using one for a while and it works great. Pulls about 28" at 3000ft elevation.
Thanks for the info KnottyBuoyz. Like I mention though, in terms of size and complexity of shapes a car bonnet would probably be the biggest thing that I will make or attempt to make.
With that in mind, what kind of cfm rated pump would I be needing? 5, 10cfm??
As for a refrigerator pump, I have read up on this and there seems to be a few people running that set up on this board. My question however, what kind of mould size limit would be present on this? Im guess it wont be powerful enough to infuse a car bonnet???
look for a 5cfm robinair like me and knotty have. pulls 50 microns and i got mine for $190 off craigslist
The size of the pump (volume) isn’t the most critical factor. What’s important is that it can pull a deep vacuum. A car hood with a 5 cfm pump would probably take less than a minute to pull down and with a 2 cfm pump it’d take 2-3 minutes. It’s only a measure of volume of air the pump can move per minute. Once the bag with your part is pulled down to maximum vacuum it won’t be moving great volumes of air, it ain’t like a shop vac!!! 
As long as you’re not in a hurry a low volume pump is fine. A good all round pump is something in the 3-5 cfm range. Anything larger means bigger motors, more cost, more heat, more noise, etc. and aren’t any more efficient than the refer compressor.
There’s a fella who recently posted on one of my threads, Fram, who’s building a tri-hull catamaran using resin infusion.
http://www.fram.nl/workshop/controlled_vacuum_infusion/cvi.htm
He’s using a small lab pump and it works fine. You can probably imagine that it takes awhile to pull the bag down but after you achieve a good vacuum you don’t need volume.
the fridge pump works great. It pulls down medium size molds fairly quick. If you build yourself a small pressure vessel/pressure pot, the additional volume will pull the bag down real quick.
well i was pulling 22-23hg with the other vaccum generator i had, i always got some kind of bridging somewhere…i hated it…now i pull 28hg and that pretty much solved all the bridging i had
+1
I have been using my fridge pump for some time now, works great, absolutely silent, and works well. it gets my about 27-28" Hg (I’m at a high altitude).
only cost me $40…
+2 Fridge pump winner lol
Love my fridge pump. I run a double reservoir now made from 4" PVC piping. Each about 3ft long. Once the tanks are charged/evacuated I can pull out a hood or trunk mold in about 3mins or so.
I;m still wanting to get a setup with a mac valve and vacuum switch so I dont have to leave the pump running until the resin gels. With that setup the pump will kick on when the vac falls to a set limit. genius! 
Looks like fridge compressor pump its gonna be then lol!
Just thought someone can give me some extra feedback though, for this pump to work though which would be the right one to use?
Are we talking about the pump out of a normal kitchen fridge/freezer or would something like just a small garage/bar fridge work just as well too?
Also whats the deal with these pressure pots/reservoirs? How do they make the process faster? Are you guys just closing the line that runs from the mold to these pressure pots till it reach full vacuum then releasing them or something?
the reservoir acts just like a reservoir, but in this case as a reservoir for a vacuum, when you open up the valve it would equalize the pressure between the mold and the reservoir, jsut a way of speeding up the evacuation of the mold. I don’t have anything like this, I find it more then quick enough to evacuate my molds.
Just call around to 2nd hand appliance shops or those repair apliance shops, chances are they keep old fridge compressors. ask to buy one, just make sure they have removed all the freon in the propper manner…
the ones that I have come with a built in mech to automatically start up, some might need one put on, ask around for one that has on on it, that much easier and less hassle.
I just run the line form the compressor to the mold and clamp off the lines from the mold etc as I need.
The best place to get all the info you will need regarding setting up a fridge pump and tanks is www.joewoodworker.com
I bought 3 units when I first went with this setup (only used 1) for $25 bucks from a used appliance place. Just normal fridge pumps are fine, I doubt the smaller pumps would be as good though.
FYI- don’t know if they say this on the JW site but remember to ask the place you buy from that the pump doesn’t have a thermal shut down switch.
Thanks for the info, Im definitely going to go to some used appliance stores and be asking them for some pumps next week.
The reason I asked about the smaller bar fridge type is because there is a few going on for sale on my local auction sites. Starting at $1 reserve as well so if they work, they’ll be a steal for the price 
Examples;
to be real honest i wouldnt waste my time…or money for that matter…the extra vacuum you get from a real pump makes a world of difference i promise you that…ask anyone that makes semi/complex parts on here they will tell you that a “real” pump is indeed alot better in the long run
what sort of extra vacuum do you get form a real pump? pulling 29" with a fridge pump is the same as pulling 29" with any other pump.
well my fridge pump pulls 27-28" every day with no worries.
complexity of the part has no bearing on the amount of vacuum the pump pulls.
I’ll say without hesitation I wouldn’t use the fridge pump to infuse a boat hull or anything larger than a auto hood. But it works JUST fine for everything I need it for.
i may or may not be wrong but i highly doubt you are going to pull 29hg from a fridge pump…i have a robinair and i dont even pull 29hg, nor did the yellowjacket my father had and it was quoted by the company to pull 15microns, my robinair is supposed to pull 50 microns
of course it depends on your relative height in to sea level…but im sure i am correct in saying that a fridge compressor most likely wont pull anywhere near 29hg…there is a reason why the “real” pumps cost more than fridge pumps…its not just some magical number someone just thought about for robinair/yellow jacket…etc…there is a reason they cost more just like there is a reason ferrari’s cost more than toyota’s…do your own investigation on google like i did and you will get the answers you seek about fridge pumps vs heating/ac, medical, other types of vacuum pumps or generators
google has lots and lots of information out there so just peek around
I measured just the other day (I’m at pretty high altitude Edmonton Alberta) but I was registering 25-26"…