You say you make skateboards where you pull the vacuum then once the vacuum is reached you turn off the system? What kind of skateboards are you making? Are they composite with a foam core or are you talking about plys of wood? I personally don't see how you could do this without a perfect seal if your not continuously running the pump. And it is very hard to get a perfect seal with a vacuum bag. If you want a perfect seal you've got to use the best bagging material and an ultra sonic leak detector to find the little leaks. And if you bag direct to a mold it has to be leak free too if you don't want to loose vacuum pressure.
I haven't tried foam yet. I have foam core skateboards for slalom and bamboo and carbon fiber and all sorts of wacky boards but I'm not aware of anyone who has tried anything but wood with the system I was talking about. Maple veneer ply, two or three sheets at a time (finished boards usually 7 to 9 ply), with a contour mat type mold set up that you put into the bag to shape concave and camber in.
Here is a consumer level set up: http://roarockit.com/us/tap.php?id=37
Gets about 15psi from the hand pump after pumping for a minute (would take forever for a bag the size of a surfboard though!). The bag is 20mil vinyl, sealed with reusable butyl sealing cord. Maybe I'll try to make a foam and fiberglass or carbon fiber board and see if it works out.
i can have the most perfect seal , as soon as the vacumn is turned off , just the connections , will make it lose vac in a matter of minutes ...
an oil vaned pump will run for years 24/7 , connected to a tank and it has no load . it works harder the more air its moving , in a vacumn the pump idles with no load .
so with your tank pressure right up , you can run any number of jobs at different pressures off your tank and your pump is doing it easy ...
mine sometimes runs for 6 weeks straight ,in the past its run for years at a time, there could be 3 or 4 jobs being done , when one comes out another goes in , so the pump keeps on running ...
sometimes ive pulled all my jobs out , then a day later i hear the pump running and i think hey hang on , theres no jobs being done , im so used of it running all the time ...
i really doubt a hand operated pump will do an adequate job , without having to keep an eye on it ...
15psi from a hand pump? Wow that is damn good. That is better than 30"Hg which is 14.7psi or so. Most inexpensive oil rotary vane pumps that are used by the airconditioning industry like the Robinair or J/B get down to around 15 microns which is roughly 29.91"Hg. And in the vacuum industry this level of vacuum is still considered a "roughing pump". To take the vacuum beyond those .91 digits you'll need to use High Vacuum and Ultra High Vacuum equipment. That stuff is pretty pricey.
I can see a 20mil vinyl bag as being pretty bullet proof, since most vacuum bag material that you get is like 1.5 to 3 mil. But is that guy serious when he says that he gets 15psi from that hand pump?
I don't know. No way to measure. All I know is that it works as advertised...
The pump gets about 24 HG at 500 feet above sea level. Thats way too much pressure for pressing surfboards. The hand pump (which comes from the wine industry) takes about 1 minute to evacuate the air from a bag that is 14 x 48. On larger bags I have seen people pull most of the air out with a regular vacuum first then use the hand pump to pull it the rest.
The system was originally designed as a kit that let people laminate their own decks from scratch. In the last 6 months most of the major woodworking tool supply companies have picked up on a simplified non skateboard version as an inexpensive way for woodworkers to laminate veneers into bent shapes.
The system only works if you have an airtight bag and a way of completely sealing it. I have done large projects with the hand pump but they have not been composite projects. The closest is the longboard deck that is below. The material costs are so high with a surfboard that unless you were very careful with the hand pump system it may become a nightmare. I think an electric pump is the way to go. You guys ever thought of a miniature low volume/high HG pump that can run continuous and put a vacuum regulator between the pump and bag. If you do a search for miniature vacuum pump there are lots of suppliers. I used to sell a kit with one of these pumps but my supply dried up. I still use them in my classes I teach at an art college. The ones I have pull 26 HG and take about 3 minutes to pull the air from a 14 X 47" bag. If you are using slow set epoxy you have lots of time to pull the air out. The advantage of these pumps is that they are small, take up no room, quiet and can run nonstop for hundreds of hours under load. You don't need the tank, piping and shutoff switch with this type of system.
Roarockit Skateboard Company
I am not sure the picture will get posted...you can see them here http://www.roarockit.com/ragged/index.html
26"Hg will not give you 15 pounds of pressure per square inch; http://roarockit.com/faq_full.php?id=5 . Even with expensive High Vacuum equipment you'd be hard pressed (no pun intended of course) to get yourself 14.7psi.
26" is more like 12psi. And the 8Hg or so used in composite surfboard making, so as to not crush the EPS, is roughly 4psi on the surfboard.
Cool thing your doing with the kids there on Maui. I lived there from 80-93, surfing regularly Pier One and Sprecks in the 8 to 10ft range Hawaiian with just one or two out, pre jet ski. Does anyone paddle into those spots anymore? Last time I was on Maui in 2002 for a couple of weeks of surfing Pier One had a great looking swell but was overrun with jet skis. Luckily an old secret spot just west of there was going off and I surfed it alone, which still amazes me.
You are right. We wrote that description a long time ago and it is incorrect. I will change it as the pump we use, hooked up to the bag produces only 24HG.
Maui is still magical. My friends surf early in the morning, either at lowers Kanaha or Hookipa. There is a great spot that locals go called Laperouse on the south shore. I am not a big surfer so am probably not the best one to talk about secret Maui spots. I do know they are still around. The jet skies are banned fron the North Shore so they are not a problem. My interest and what keeps drawing me back to Maui is the summer slalom windsurfing race series that happens every second week at Kanaha. There are around 70 locals that compete in this event and it is just a lot of fun.
We really are having a great time with the classes we teach, especially on Maui. It is my wife Norah and my way of giving something back to the island when we visit. We did a class at a place called Seabury Hall during winterim in February and it was really a great experience.
I remember last year making the mistake of trying to fix a delamed windsurf board by drilling holes in the bottom, squeezing epoxy in then putting it in a vacuum bag and pulling it down to about 24HG. That was the end of that board. Sucked it in so much it looked like a leaf.
For what its worth, I've been using an old WWII-era aspirator vacuum pump to do my bagging, with just the original needle valve to regulate pressure. No problem at all. $25 on ebay.
Why is there a need for the pump to come on and off? Is it because of the massive size of the bag making it really hard to get a totally air tight bag that won't leak?
Sorry for such a silly question.
There really is no need for the pump to turn on and off. I have been using a Gast diaphram pump for the past few years. No need for a vacuum switch or reservoir. I regulate the vacuum using a fifty cent brass aquarium air valve, along with an automotive vacuum guage to measure the vacuum. The pump runs all the time but the one I have is not too noisy.
The vacuum systems I have seen posted on this forum recently are super keen from a tech-head point of veiw, but from a purely utilitarian point of view they are very fancy and overly-complicated. Simple works.