Yet another vacuum press question

Tahooda · Post by **Tahooda** » Tue Nov 10, 2009 8:42 pm

Hi, I have read just about every thread on this site on vacuum presses and have also read the information on http://www.joewoodworker.com/veneering/welcome.htm. I was originally going to use a clamp style press with a water filled fire hose between the ski and top mold to equalize the pressure such as in this thread viewtopic.php?t=1628. I began constructing this last year and then due to school I was unable to complete the skis before winter was over and didn't do anything over summer, I did build some skateboards though. Now I'm trying to finish these and do one more pair before the start of the season and am thinking I may want to scrap my top mold and just use the bottom with a vacuum bag. I have a 80 gal., 27 CFM compressor in my garage so the V2 kit from veneersupplies.com seemed like a good idea but now I'm seeing electric vacuum pumps on Ebay for around 40 bucks, so that is enticing as well. So would a vacuum pump such as this http://cgi.ebay.com/Gast-Vacuum-Pump-Ex ... 19b79dc47a or this http://cgi.ebay.com/Gast-Vacuum-Pump-Ex ... 19b79dc1fd work for a pair of skis? It says they pull 28" hg, I'm just not sure how to tell if it's suitable for continuous use and all that jazz.

Thanks!

twizzstyle · Post by **twizzstyle** » Tue Nov 10, 2009 9:28 pm

I would defintely recommend a vacuum pump, over a vacuum generator (compressor driven). They can run for days with no issues, and Gast is a big name in vacuum pumps.

Tahooda · Post by **Tahooda** » Tue Nov 10, 2009 9:39 pm

Ok so to make sure I have this correct, I would just need to run a line from the pump to the bag correct? It's not necessary to have the vacuum control and mac valve to make it turn on and off depending on the pressure? And how loud is a pump like that gast one on eBay since it will be running for a few hours and may anger my neighbors?

krp8128 · Post by **krp8128** » Wed Nov 11, 2009 5:28 am

I have a very similar pump, it is quiet enough to run continuously.

You don't need the mac valve, but you should build a reserve tank and use the vacuum switch. The reserve tank gives you a little extra vacuum (you WILL have bag leaks). Combined with the switch, it keeps the pump from cycling on and off every few minutes.

Use the switch so the pump can shut off. No reason for it to run once full vacuum is achieved.

twizzstyle · Post by **twizzstyle** » Wed Nov 11, 2009 6:41 am

Yeah these things are very quiet. I don't vacuum bag my skis, but do lots of other random projects with molded parts (carbon fiber, etc).

I've never used a switch either, I just leave my pump running continuously. I've left a pump running overnight many times, as he said its hard to have a completely leak proof seal, and even if you do have it leak proof when you first get it all sealed up... leave it alone for a couple hours, and there's always the chance of a leak forming, you coming back to check, and finding the bag totally loose.

Tahooda · Post by **Tahooda** » Wed Nov 11, 2009 8:15 am

Thanks for the replies, unfortunately I am still a little confused. On joewoodworker.com it says you have to have a mac valve to direct it to a sub reservoir that acts as an exhaust or else it won't start back up under pressure. Is this necessary becasuse if I buy a vacuum pump and then have to buy the evs kit off veneersupplies.com I'm spending more money than if I bought the V2 kit since I already have a compressor more than up to the job. So are there any huge disadvantages to a venturi type vacuum?

krp8128 · Post by **krp8128** » Wed Nov 11, 2009 8:44 am

Tahooda wrote:Thanks for the replies, unfortunately I am still a little confused. On joewoodworker.com it says you have to have a mac valve to direct it to a sub reservoir that acts as an exhaust or else it won't start back up under pressure. Is this necessary becasuse if I buy a vacuum pump and then have to buy the evs kit off veneersupplies.com I'm spending more money than if I bought the V2 kit since I already have a compressor more than up to the job. So are there any huge disadvantages to a venturi type vacuum?

I don't know why he has all that shit hooked up. Here's what i do, and i have yet to kill the pump.

Vac pump>check valve>reserve tank>outlet to pressure gauge/switch>outlet to bag.

Once the pump shuts off, any residual vacuum (in my setup at least) bleeds off through the pump. Vacuum is maintained on the bag side by the check valve.

I suppose you don't need the switch, but it is nice when you get your system tweaked to have the pump run for a minute every 2 hours to maintain 24" mercury.

Venturi systems use A LOT of air to generate the vacuum. They are also loud, plus the compressor will run almost constantly.

twizzstyle · Post by **twizzstyle** » Wed Nov 11, 2009 9:53 am

krp8128 wrote: Venturi systems use A LOT of air to generate the vacuum. They are also loud, plus the compressor will run almost constantly.

Yep, thats why I don't like them. Even with that large 80 gal compressor, you will use that up pretty quick.

And again, having the switch/valve setup is nice, but you don't need it. You can run a vacuum pump non-stop for days without any overheating or problems at all.

thefreshpimpofbigair · Wed Nov 11, 2009 10:21 am

I use the joe wood worker set up w/ mac valve, switch, reservoirs, etc., but only because I used a refrigerant compressor. Because it draws so slowly, the res. is crucial in aiding the initial suck down. I also used the kit because I did not trust the compressor and didnt want it running endlessly. It seems though if you have a good pump this wont matter.
Maybe if you simply added a timer....

Tahooda · Post by **Tahooda** » Wed Nov 11, 2009 11:16 am

Okay thanks for all the help. What I think I'll do is just buy one of those pumps on eBay and just run it continously for this first pair, depending on how loud it is. I'll probably gather together the parts needed for the switch and other stuff before I press another pair, looks like it should be less than the V2 unit which is another plus.

Thanks again!

Tahooda · Post by **Tahooda** » Mon Nov 16, 2009 4:41 pm

So I have been looking for a vacuum pump and haven't been able to find one for under like 80 dollars so with that along with a vacuum controller and reservoirs and what not it is probably going to be more expensive than a venturi setup plus I have to worry about whether a used vacuum pump will be in good condition.

So I think I'm leaning towards the venturi setup up again since I understand how that works and it makes sense, so if I get the kit with the reservoirs and the vacuum controller and everything else will it really use that much air? It seems like it shouldn't cycle very often unless i get a really horrible seal.

CAFactory · Post by **CAFactory** » Mon Nov 16, 2009 7:26 pm

I have used the venturi system with a fairly large construction grade compressor and my tests turned out well. Held 24.5'' Hg of vacuum for 24 hours and lost around 1'' HG every 8 hours. The harbor freight cheapo Venturi has worked well so far. Just be sure your compressor is large enough, or else problems will arise. A refrigerator pump, If available, is indeed the best choice for your application.

My setup goes: Compressor---Venturi---1/4'' to 1/2'' fitting (On Vacuum outlet) ---1/2'' pipe---Ball Valve---"T" which uses one outlet to run vacuum gauge--- 1/2'' pipe to 1/4'' barb fitting---1/4 in tubing-bag inlet

Cost around $20 bucks at home depot total

Tahooda · Post by **Tahooda** » Tue Nov 17, 2009 11:28 pm

So with the harbor freight venturi does your compressor have to run constantly? Because I thought that was the reason for having the vacuum controller and mac valve - to shut off the air flow when once the vacuum has been achieved. If the harbor freight one has some kind of vacuum controller built in then I'll just try that.

Thanks

CAFactory · Post by **CAFactory** » Wed Nov 18, 2009 1:02 pm

There is no vacuum controller inside of the venturi from harbor freight. How my setup works is that once I achieve full vacuum I turn the ball valve to closed, then turn off the compressor, and thus ending the vacuum on the venturi side of the valve, but the vacuum on the bag side of the valve
remains.

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Yet another vacuum press question

Yet another vacuum press question