To avoid having a vacuum pump running continuously for hours, a vacuum plenum (reservoir) can be used. I made one using a big polyethylene tube I had with plywood end caps. I coated the ply with epoxy the eliminate the porosity and used "dum-dum" (vacuum bag sealant, aka monkey shit) to seal it to the tube. I also added 3 fittings, one for a gauge and 2 for ball valves. With this thing I can get a 27"HG vacuum in a couple minutes and keep it for a long time. This proved also very usefull to listen for vacuum leaks in my vacuum bag. Once I have a good vacuum, I just turn the pump off and easily spot any leaks. I also turn the radio off so it is very silent! Now I want to buy a vacuum triggered switch to have the pump start automatically at a preset vacuum value.I estimate that my pump will run about 30 seconds every hour during the cure of the epoxy to keep a vacuum of 25"HG.
I decided to make a 4' x 8' panel as a first try, instead of a full 24' panel, in order to check everything. I am using a small Robinair pump for now but it emits an oil mist so it will not stay here long... I am bidding on a GAST pump on EBAY, fingers crossed!
I used 2.4 litres of 2:1 epoxy to laminate both sides of the foam. Judging from the excess that the breather fabric is absorbing, I think I used too much. The peel ply, the perforated foam and polyethylene film all seem to work fine. It is amazing to watch a vacuum bagged panel. It becomes so flat and compacted it is very encouraging. No more "contact" laminating for me... I will de-bag tomorrow morning, my epoxy is very slow curing.