1 atm = 760 mmHg = 14.6 psi =33.8 ft H2O , yes ??
I’m rebuilding the whole vac setup and the only valve I can easily find (joewoodworker.com) only goes down to -30 mmHg.
I dunno if this is enough pressure for boards as Ive never used a valve before but just eye-balled it.
Can anyone help with a range of functional pressures ?
Thanks guys, SF.
You sure that isn’t 30 inches of vacuum (or -30 inchesHg from atmospeheric)? 760mmHg converts to 29.92 inHg, almost 30. A ‘full vacuum’ is usually known as 30 inHg of vacuum in most circles, like air conditioning and such…
JSS
McMasters-Carr item #3941K53 $9.37. Check it out, by the way the one you were looking at is in inches of Hg, and 30 inches of Hg is outerspace, and I have pumped for 24 hours to get down even close to that with more then just a little vacuum pump. Either one of these gages will work just fine believe me.
I use that gauge, it’s perfect for your purpose. I don’t think you’ll ever need to pull anywhere near 30"Hg for a surfboard…
the inside of your dial reads in bar…
you wont be going near 30 inhg unless you like pancakes, really flat ones… 
I have the same gauge at the pump.
For #1lbEPS I go 9-7HG max and have the pump turn on at 5hg.
With #2lb EPS you can go to 10-13HG.
My pump maxes out at 24HG.
Get the auto shutoff switch too and your golden.
surf foils,
30 hg is way too much for bagging onto foam (try 6-10 i think). might be ok for doing the prefabbed skins.
I found a place near me here that sells gauges for $20 + gst. I am going to get one next time i go past them.
I can get an extra one and mail it down to you if you want. might be cheaper than from jww.
PM me if your keen.
or maybe try some process control companies around you.
the one i’m looking at is from www.anzcontrols.com.au
specs
63mm, bottom entry, stainless steel case, brass/bronze internals, ¼”BSPt, -100/0 kPa/ 30”Hg $ 20.00 + gst
scot
That is phenomenal guys !!
You all gave me great clarification, tips, offers to help. Thank you. ( I’ll let you know Scot.)
Just as a second question,
And here the theory that I am working from…
Vaccing works by applying a uniform pressure to the board while the resin cures. The vacuum decreases the pressure within the bag so that the atmospheric pressure ‘appears’ /is greater. Please correct me if I’m mistaken here.
Now heres the second question. Do you think theres an opportunity to use immersion as a bagging technique ? A board could be immersed to a depth thats equal to a vacuum pressure.
It would require zero electricity and produce no noise ( brownie points for the environmentally focused)
No monitoring for variation ( less labour hours)
Have a universally replicable set of standards (no confusion due to metric/imperial/language/component availability or effifiency)
The required number of mechanical components required would be less and less wasteage.
The only problem I can forsee would be leaks, but if this was totally solved, why would immersion not be suitable ??
Third question. What depth of H2O would be equal to the recommended 6~10 hg. ??
For the groovy~minded, its kinda like a water birth, duuude… ! 
Thanks again for your helpful replies, SF.
Surffoils,
If the vac process is just about uniform clamping then there are probably quite a few methods (i thought about using a blow up mattress with some kind of backing, sort of reverse bagging).
But i think that the removal of air is also a major component. Probably in regards to replacing the air with resin.
I’m not sure about all this tho cause i’m still settign up for number 1, so its all theory at the moment. maybe some more practically experienced baggers can comment.
scot
You’ll ahve to fight buoyancy and will still need to use some kind of power source to (a) pump water or (b) sink/retrieve the structure.
But you can probably achieve pressure greater than vacuum.
Only thing is the low pressure in vac bagging can be used for other cool tricks.
Scot, I am rebuilding my whole setup so I was keen to try something new if the ‘Sway-Brains’ thought it was worth a go. I dont know about the ‘air replacing the resin’, but I try to keep the resin minimal so it cant go too far.
Doug, I thought about the water filling technique but it depends on how much water depth is required, Ive done some rough figures and think it might require a depth of only 2 feet to mimic 6~10 Hg.
That puts the volume of water at around 720 litres for boards under 2 metres or 6’7", similar to the same amount in a household bath. With a 240v 2000 l/m pump, thatd take 21 secs to drain.
For the sink/retrieve structure I figure immersing the board upside down on a solid rocker bed using the boards own bouyancy to keep the board firmly in place and using a set of pulleys similar to a yachts boom system so theres no hydraulics or heavy weights.
I’m ready to make the leap into immersion or start buying components for a standard system.
Can anyone work out the depth required to achieve the right pressure??
Thanks, SF.
From my scuba experience 10 metres depth underwater is 1 bar of pressure, so 10 metres of water would give you 30 inches of mercury, and you’d need 2 to 3 metres for 6-10 inches Hg.
Does that sound reasonable? Is Mercury 14 times as heavy as water?
This is very interesting! I really hope you give us a blow-by-blow of how it goes…
But don’t you dare let that water go down the drain 
Muhleder, thanks for the info on pressure, I dunno where to go the make absolutely sure of the numbers, do you have a www so I could see how you worked it out please?
Doug, I never even thought of pulling the plug, water restrictions being what they are in this country !
With Mulleders figures it doesnt make it impossible , just in need of redesign. I initially was going to make/buy a 3 foot high box
just slightly oversized for the boards I want to make,but if I need 2 metres of depth, maybe a tall oval water tank would do?
I could buy it to connect to the house, collect the government rebate and then make boards in it ! Government funded surfboard design ?
SF.
edit: Muhleder, www.digitaldutch.com/unitconverter/ backs your figures but does it in Hg mm. Thanks.
Ah, it’s hard to tell. You having a gmail account, not setting your location, etc. Some countries aren’t on water restrictions.
Keep us posted bud!
just watch out for pinholes in your vac bag…
McMasters-Carr item #3941K53 $9.37. Check it out, by the way the one you were looking at is in inches of Hg, and 30 inches of Hg is outerspace, and I have pumped for 24 hours to get down even close to that with more then just a little vacuum pump. Either one of these gages will work just fine believe me.
Did a product search at MM-C for Item # 3941K53 and no such item found. Closest guage (0->30 in vacuum, glycerin-filled) would appear to be Item # 384645K11 at a little over $17.00 (+shipping). As I recall, there was another vacuum guage for around $11 (+shipping), but was not glycerin-filled.
mtb
Muhleder, thanks for the info on pressure, I dunno where to go the make absolutely sure of the numbers, do you have a www so I could see how you worked it out please?
Doug, I never even thought of pulling the plug, water restrictions being what they are in this country !
With Mulleders figures it doesnt make it impossible , just in need of redesign. I initially was going to make/buy a 3 foot high box
just slightly oversized for the boards I want to make,but if I need 2 metres of depth, maybe a tall oval water tank would do?
I could buy it to connect to the house, collect the government rebate and then make boards in it ! Government funded surfboard design ?
SF.
edit: Muhleder, www.digitaldutch.com/unitconverter/ backs your figures but does it in Hg mm. Thanks.
It’s a simple proportionality relationship between the height of a column of mercury and the equivalent depth of water:
Hw(water depth-in feet) = (32.8 ft) x Hm(mercury column height in inches)/29.92 = 1.096 x Hm(inches)
Hence for the equivalent of 6" of Hg, you’d need a depth of 1.096 x 6 = 6.68 ft (or approx. 6’ 7" of water)
For the equivalent of 10" of Hg, you’d need 1.096 x 10 = 10.96 ft (or approx. 10’ 11-1/2" of water)
I would definitely be inclined to not use water immersion (e.g. you’ll really have a mess if your enclosing bag develops a leak).
mtb
LOL!
At least you can detect the leaks easily!
seriously though, it strikes me as being a real hasslle to lay it all up, fix it all together skins, glass , core, held in place, bagged and then sink it two meters down, I mean that’s a lot of weight to hold down a board, a rocker table and the residual are in the bag. It’s pretty tough to hold a soccer ball one meter under water, let alone the whole setup.
But, good luck nonetheless and I eagerly await pictures!
The idea of pulling a vacuum it to remove as much air as you can and replace it with epoxy/resin, your bag under water idea will work as long as you can get the air out and keep the water out, so you are going to need a check valve, as well as a way to get the air to go to the check valve which to me says you will need to stand the board on end. Or another way of doing it is to pull a vacuum on the bag before you put it under the water but then you are right back where you were trying to get away from.