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2 vac pumps = more CFM?

 
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Boxjoint
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Joined: 09 May 2007
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PostPosted: Mon Jun 04, 2007 11:49 am    Post subject: 2 vac pumps = more CFM? Reply with quote

I have a very very quick and dirty thermoforming machine (IE- now that I tried out thermoforming vs. fiberglass I will be doing thermoforming)

I used a 4 cfm pump from e-bay with2 11 gallon tanks. Worked well enough but would like to build a 30 gallon tank and instead of laying out the bucks for a 10+ cfm vac pump was looking at buying another 4-6 cfm unit. I was thinking if I link them togeather with a ball valve at either pump I could bypass one if an issue arises with it. Also, I figured that if I have two 4 cfm pumps that pull down to 26" linked, I would have 7-8 cfm's now but it would still just pull to the rated vac (still at 26")

Is this correct?
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drcrash
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PostPosted: Mon Jun 04, 2007 12:54 pm    Post subject: Re: 2 vac pumps = more CFM? Reply with quote

Boxjoint wrote:
I have a very very quick and dirty thermoforming machine (IE- now that I tried out thermoforming vs. fiberglass I will be doing thermoforming)


Cool. Pictures?

Quote:

I used a 4 cfm pump from e-bay with2 11 gallon tanks. Worked well enough but would like to build a 30 gallon tank and instead of laying out the bucks for a 10+ cfm vac pump was looking at buying another 4-6 cfm unit. I was thinking if I link them togeather with a ball valve at either pump I could bypass one if an issue arises with it.


That will work. Check valves (one-way valves) would be better than ball valves, though. They'll keep either pump (or your tank) from sucking air backwards through the other pump, whether the pumps are on or off. Once they're installed, you don't have to do anything; they just work.

Quote:

Also, I figured that if I have two 4 cfm pumps that pull down to 26" linked, I would have 7-8 cfm's now but it would still just pull to the rated vac (still at 26")

Is this correct?


Yes. Putting similarly-rated pumps in parallel works fine. Just make sure your tee & the pipe from there is big enough to handle the combined flow. (Maybe plus a bit if they're piston pumps, so that the momentary pulses from each pump don't interfere with the other. Just the tubing to each pump is probably enough of a reservoir for that, though.)

Using your 2 11-gallon tanks for two-stage two-tank (no vacuum cleaner) plumbing may work better than a 30-gallon tank. 30 gallons isn't much bigger than 22, and 2-stage uses your tank space more efficiently. (And saves wear on your pump(s).)

Or you could tee the 2 11-gallon tanks together to make a 22-gallon second-stage tank, and buy a $20 Wal-Mart 7-gallon "air carry" tank to use for the first stage. That'd give you almost 30 gallons total and suck harder than a 30-gallon one-stage scheme.

Check it out:

http://www.cnczone.com/forums/showthread.php?t=38493
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Boxjoint
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PostPosted: Mon Jun 04, 2007 10:26 pm    Post subject: Reply with quote

I'm almost embaressed to post pics of my setup because it is soo rough
BUT
Here is how I have it set up:
I have a large PVC check valve going to my shop vac with a hole drilled and tapped for the hi-vac line after the check valve and before the platten.

I did not even have a hinged or guided frame. I lifted it from the oven (2 standard oven coils in an aluminum pan I riveted togeather) and dropped it on the platten. The shop vac was on before the drop and I hit the hi vac ball valve and turned off the shop vac.

Again, I did just make the setup to see if vacuum forming is what I wanted.


What I was thinking of doing is kindof similar (but refined) to my current 2 stage.

Getting a large PVC ball valve and drilling it in the closed position and plastic welding a fitting to the new hole. Have the shop vac running for the initial drop and hit the ball valve which will go right to high vac.

____/ \________
to high vac tank
___ _________
\__--------/
I I
I I
I I <----- to shop vac


_______



I thought of the check valve thing but the only metal housed check valves that I have seen small enough are for gas welders for flash back prevention.

With the above setup the ball valve in open to the shop vac would have the new drilled hole to the platten, closed to the tank and the origonal hole to the shop vac.

Flip the lever and it will be open to the tank, to the platten and closed to the shop vac.
That would give me a true 2 stage unit but I would have to be careful with the drilling and plastic welding, and make sure that the new hole is de-burred so I don't tear up the gasket in the ball valve.

____________
________________/ \_________________
I I
I I
--- I
To platten I
(Drilled hole) ---- I To high vac tank
I I
I I
_______________ ____________________
\___ __/
\ /
I I
I I
To shop vac (Plastic welded Tube to new hole in ball valve)


A simple contact switch could be rigged up so that when you switch from shop vac to high vac it'll kill the power to the shop vac. If you can picture it in the above diagram a clockwise rotation of the ball valve will block the shop vac and switch to high vac.[img][/img]
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Boxjoint
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PostPosted: Mon Jun 04, 2007 10:30 pm    Post subject: Reply with quote

Ohh well, the diagrams did not work but you get the idea!
Surprised
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Boxjoint
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PostPosted: Mon Jun 04, 2007 10:53 pm    Post subject: Reply with quote

Here is a pic that might help:
http://home.comcast.net/~swilliams620/vac1.bmp

http://home.comcast.net/~swilliams620/vac2.bmp
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drcrash
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PostPosted: Thu Jun 07, 2007 8:15 am    Post subject: Reply with quote

Boxjoint wrote:
Ohh well, the diagrams did not work but you get the idea!
Surprised


You need to put them between CODE and /CODE tags. (With square brackets around each tag.) That tells the software to use a fixed-width font and preserve spaces. (It's for program code, so that you can see the indenting of the code that shows nested structure, but it works for ASCII pictures too.)

Also it looks like your IMG tags weren't quite right. If you put the URL of a picture between IMG and /IMG tags (in square brackets), it should work to display your pictures in the post rather than just the URL. (It looks like your URL wasn't between the tags, or something)

You can go back and edit your posts (click on the EDIT button at the top of the post, on the right) to fix the formatting.
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Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com
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drcrash
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PostPosted: Thu Jun 07, 2007 8:36 am    Post subject: Reply with quote

I've thought about drilling a new hole in a big plastic ball valve, too...

One thing to be careful about is that the hole through a full-ported ball valve is really big (relative to the size of the ball). If you drill a hole at right angles to that, and it's that big, you may have a problem with one path through the ball still being partly open when the other starts to open, letting air flow a different way than you meant to. (From the low-vac system into the high-vac system, so that your tank sucks air backwards through your vacuum cleaner.)

For a two-stage system with a vacuum cleaner and a high vac, though, the hole that connects the high vac doesn't need to be nearly as big as the hole that connects the shop vac, so that may work out OK. Or if you use a small hole for the high vac, you may be able to drill it at a funny angle so that it doesn't move across your new port until a bit later. I need to think about that.

If that works, it may also work with a high-vac-only two-stage system with a small first-stage tank instead of a vacuum cleaner. (The hole for the second-stage tank doesn't need to be as big as the one for the first-stage tank.) I need to think about that, too.
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Boxjoint
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PostPosted: Thu Jun 07, 2007 9:02 am    Post subject: Reply with quote

drcrash wrote:
I've thought about drilling a new hole in a big plastic ball valve, too...

One thing to be careful about is that the hole through a full-ported ball valve is really big (relative to the size of the ball). If you drill a hole at right angles to that, and it's that big, you may have a problem with one path through the ball still being partly open when the other starts to open, letting air flow a different way than you meant to. (From the low-vac system into the high-vac system, so that your tank sucks air backwards through your vacuum cleaner.)

.


oe way around that is to use a PVC check valve in line withthe shop vac. Once the vacuum is higher on the outher side of the vac the the check valve will close within a milisecond so vacuum loss in the hivac side is minimal.
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Boxjoint
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PostPosted: Thu Jun 07, 2007 9:03 am    Post subject: Reply with quote

drcrash wrote:
Boxjoint wrote:
Ohh well, the diagrams did not work but you get the idea!
Surprised


You need to put them between CODE and /CODE tags. (With square brackets around each tag.) That tells the software to use a fixed-width font and preserve spaces. (It's for program code, so that you can see the indenting of the code that shows nested structure, but it works for ASCII pictures too.)

Also it looks like your IMG tags weren't quite right. If you put the URL of a picture between IMG and /IMG tags (in square brackets), it should work to display your pictures in the post rather than just the URL. (It looks like your URL wasn't between the tags, or something)

You can go back and edit your posts (click on the EDIT button at the top of the post, on the right) to fix the formatting.


For some reason the img tags did not work with my server so I just put the link.
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drcrash
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PostPosted: Thu Jun 07, 2007 9:13 am    Post subject: Reply with quote

Boxjoint wrote:

oe way around that is to use a PVC check valve in line withthe shop vac. Once the vacuum is higher on the outher side of the vac the the check valve will close within a milisecond so vacuum loss in the hivac side is minimal.


I have a setup like that, only using a sump pump check valve with a rubber band to help it close, like in Walsh's book. It leaks a noticeable amount of air before it shuts, and I don't like having a rubber band in there because it'll eventually break, but it basically works.

I also have a PVC check valve from Lowe's sitting here, that I've been meaning to replace it with, but I haven't gotten around to that.

I've been wondering how much the PVC check valve will restrict the air flow. Blowing through it (with my mouth) it seems like it has a substantial amount of drag. (More than the sump pump valve.) I suspect it will be fine for a small vacuum former, but I'm not so sure about a big one. It might slow down the initial pull-down. I wonder if the spring-loaded thingamajig in there will keep the valve from ever fully opening with just a vacuum cleaner sucking on it.

The nice thing about a big three-ported valve (and no check valve) is that it wouldn't restrict airflow when it was fully open.

How big is your former that you've got the PVC valve on?
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Boxjoint
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PostPosted: Thu Jun 07, 2007 12:13 pm    Post subject: Reply with quote

24x36
The sping in the check valve worked well with my 5hp shop vac. Don't forget, I would use this in conjunction with the two stage ball valve so even if it leaks a tad it will only be between switching the ball valve from stage 1 to stage 2.
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drcrash
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PostPosted: Wed Jun 20, 2007 11:44 am    Post subject: Reply with quote

Boxjoint wrote:
24x36
The sping in the check valve worked well with my 5hp shop vac. Don't forget, I would use this in conjunction with the two stage ball valve so even if it leaks a tad it will only be between switching the ball valve from stage 1 to stage 2.


I'd be interested in hearing more about this.

I've been figuring that with a spring-loaded check valve, the problem likely wouldn't be leaking when it's shut, but slow airflow when it's open, with only a couple of PSI from a vacuum cleaner to open it.

That might not be noticeable most of the time---only with tall or hollow molds, or several medium-tall molds that act like tent poles to trap a bunch of air under the plastic, between them.

Could you give more detail on what shapes you were forming, and how long it took to pull the plastic down? (I'm aiming for 1 second max in fairly bad cases. If you can do that in bad cases with a spring-loaded PVC check valve in the way, that'd be VERY interesting.)

I'd also be interested in hearing more about drilling out housings and balls to make 3-port valves.

Another option would be to use a big tee-ported three-port PVC valve, which isn't terribly expensive, and close off one branch of the T-shaped hole through it, and make it into an L-ported valve. That wouldn't require drilling the housing & the ball neatly.
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Boxjoint
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PostPosted: Wed Jun 20, 2007 5:40 pm    Post subject: Reply with quote

I was working on a saddle bag for my motorcycle. Approx 13" high x 24.5" long x 6" tall. Solid mold. It took about a second to three seconds total. Again, I was using a very very rough forming machine. My next will be 24" x 32" (less wasted plastic from a 4x8 sheet. I would get 6 squares from a sheet)
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drcrash
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PostPosted: Wed Jun 20, 2007 8:12 pm    Post subject: Reply with quote

Boxjoint wrote:
I was working on a saddle bag for my motorcycle. Approx 13" high x 24.5" long x 6" tall. Solid mold. It took about a second to three seconds total. Again, I was using a very very rough forming machine. My next will be 24" x 32" (less wasted plastic from a 4x8 sheet. I would get 6 squares from a sheet)


Thanks. That's useful information for me.
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