I know that topic was already extensively discussed but I can not find on our forum.

Question is : What is the vacuum level required for fiber glassing bag ( to avoid squashing polystyrene core ) ?

I did my vacuum pump from old fridge and now trying to attempt first fiberglass.

Still few more questions: how to regulate the vacuum? Maybe by creating water level in vertical pipe 1 m or 2 meter?
How to connect hose to the bag and where to buy fitting ?

Macroscien said..
I know that topic was already extensively discussed but I can not find on our forum.

Question is : What is the vacuum level required for fiber glassing bag ( to avoid squashing polystyrene core ) ?

I did my vacuum pump from old fridge and now trying to attempt first fiberglass.

Still few more questions: how to regulate the vacuum? Maybe by creating water level in vertical pipe 1 m or 2 meter?
How to connect hose to the bag and where to buy fitting ?

here you go, all you could possibly need. Cut and paste this into google and away you go:

vacuum bagging site:seabreeze.com.au

I ended up using a car vacuum gauge, just because it was easy to source, and it was a decent size and price. The vacuum gauge that came with my pump is meant for vacuuming down air conditioning lines, so it was not really a good range for vacuum bagging.

Vacuum pumps on ebay are a decent price, so that's what I ended up with after trying a few fridge compressors. The guy I bought it from also gave me a fitting that I tapped into some PVC, so that I could use the air-con vacuum hoses. I also tapped an airline fitting, plus a ball valve to dump the moisture, into the same high pressure PVC pipe.

I should really check, but I think I have my setup set for 15 to 20 inches of mercury. Without a reservoir, it will cycle quickly, with some decent reservoirs it cycles much less frequently. This is important as if you run it at night, it only cuts in for a minute or so every 30 minutes or better, and it doesn't matter. If it cycles every minute, it gets annoying.

Surprisingly, normal air-line fittings work fine with vacuum and to my surprise seem to seal themselves under vacuum. I can plug in two reservoirs, a few pickups, as well as the pump and gauge. Its a nice way to be able to connect everything together.

What sort of negative pressure we could expect for the standard board vacuum bagging ?
If "0" is our atmospheric pressure and 10 is the max negative (10 meters of water equalize our atmospheric pressure).
Alternatively we could express in pulling water in meters.
If that will be 1 or 2 meters or rather 5 to 8 meters ?

I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?

Just a thought.

FormulaNova said..

Mark _australia said..
I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?

Just a thought.

I can see the same, although I can't criticize. I often have a go at re-inventing the wheel. Sometimes the results are better than something you can buy, but often its not. I enjoy the making of things as much as anything else.

That could be the easiest if you could just find complete vacuum pump with pressure switch on eBay. But we can not.
Beside now I know now thank to decrepit that we need negative pressure 2.5 meters on average.

One more: How do to seal the hose entering bag ?

FormulaNova said..
I ended up using a car vacuum gauge, just because it was easy to source, and it was a decent size and price. The vacuum gauge that came with my pump is meant for vacuuming down air conditioning lines, so it was not really a good range for vacuum bagging.

Vacuum pumps on ebay are a decent price, so that's what I ended up with after trying a few fridge compressors. The guy I bought it from also gave me a fitting that I tapped into some PVC, so that I could use the air-con vacuum hoses. I also tapped an airline fitting, plus a ball valve to dump the moisture, into the same high pressure PVC pipe.

I should really check, but I think I have my setup set for 15 to 20 inches of mercury. Without a reservoir, it will cycle quickly, with some decent reservoirs it cycles much less frequently. This is important as if you run it at night, it only cuts in for a minute or so every 30 minutes or better, and it doesn't matter. If it cycles every minute, it gets annoying.

Surprisingly, normal air-line fittings work fine with vacuum and to my surprise seem to seal themselves under vacuum. I can plug in two reservoirs, a few pickups, as well as the pump and gauge. Its a nice way to be able to connect everything together.

I know of others who have used old fire extinguishers as a reservoir. They are made so cheaply in China that it is more economical to replace them rather than pressure test them (at 5 years old), hence your local fire service company may be able to give you an old one.

Macroscien said..

FormulaNova said..

Mark _australia said..
I am finding this a bit like Macto's half built catamaran with honeycomb carbon space age laminate thread.
Macro - perhaps research first then build...?

Just a thought.

I can see the same, although I can't criticize. I often have a go at re-inventing the wheel. Sometimes the results are better than something you can buy, but often its not. I enjoy the making of things as much as anything else.

That could be the easiest if you could just find complete vacuum pump with pressure switch on eBay. But we can not.
Beside now I know now thank to decrepit that we need negative pressure 2.5 meters on average.
One more: How do to seal the hose entering bag ?

Like I said all the fittings required are at the place you buy the carbon etc from.
There is a thing like 2x 20c pieces that screw together each side of the bag film, with a hose barb on one side. Many different designs to achieve same purpose.
Here is one example
www.fibreglast.com/product/vacuum-connector-891/Vacuum_Fittings