Two-stage (lo/hi) vacuum former plumbing, with pictures

[drcrash]

(Continued from another thread)

Drcrash do you have any photos of your 2 stage system that you mention on TK560. I'm trying to plumb my tank to vacuum pump and I need a little help.

Yes. Some other people have been asking, too, and I finally got around to it. (Sorry for the wait.)

Here's a picture of the whole plumbing setup, laid out so that you can see everything. It's a little different from the diagram, and there's an extra ball valve in there that's going to come out.

I've seen the setup you drew put I still don't understand how the ball valve works.

Do you mean the ball valve, or the sump pump check valve?

The ball valve is just a regular (quarter-turn, fully ported) valve. ($5 at Harbor Freight, slightly more at Lowes or Home Depot.) When you open it, air can flow from the platen into the tank and/or the vacuum pump.

Here it is a little bigger:



It's connected on each side with hose barb fittings. The one coming from the platen is a 5/8" hose barb squeezed into 1/2" I.D. braided PVC tube. The one going to the tank and vacuum pump is a 3/4" hose barb sqeezed into 5/8" I.D. high-pressure washer hose. (Both have 1/2" pipe threads on one end, and a hose barb on the other. The smaller one is nylon, and the larger one is brass, because that's what I found.)

The sump pump check valve is the tricky bit. I drilled it and epoxied a 1/2" hose barb in it, and put a tiny eyebolt in the flapper, with a rubber band to hold it closed by default.



The white stuff around the top is just PTFE (Teflon) plumbing sealing tape. The yellow thing just below that is a gasket I made from a piece of craft foam. (Not necessary if you use enough PTFE tape and don't keep playing with the thing.) At the very top you can see an ugly piece of wire I bent into a circle with crisscrosses, to attach the rubber band to.

It screws into a 1 1/4" galvanized steel floor flange on the bottom of the platen. That's way overkill for a little machine, but will let me use mostly the same plumbing on a much bigger machine.

My little high-amp hand vac attaches to the bottom of the sump pump check valve, and sucks most of the air out from under the plastic.
The high-vac system attaches to the little hose barb, and when you open the main ball valve, it sucks the check valve shut, so that it won't just suck air backwards throught the vacuum cleaner.

Here it is in the machine, looking up. (Old picture, with the platen up on a couple of temporary 2 x 4 spacers.)



The black high-pressure washer hose goes from the other side of the ball valve to the tee, which connects it to both the vacuum tank and the vacuum pump.

In these pictures, that simple scheme is complicated in two ways. I actually use a garden-hose type fitting so that I can disconnect the tank and vacuum pump from the main valve and the platen, for moving and storage. If you don't need that flexibility, you don't need that.

I also have an extra, completely useless ball valve between the (garden-hose) disconnect fitting. It's only there because I was afraid the cheap hose fittings would leak. They work fine, so I'm going to take it out.

The female fitting is a cheap plastic "hose mender" from the garden department at a hardware store. The male fitting is another brass one with a 3/4" hose barb on one end and 1/2" pipe threads on the other. It should screw directly into the tee.

The tee is a white PVC all-thread tee that connects to the tank with a 1/2" gray PVC nipple. That screws into the 1/2" threads of the tank opening.

The other side of the tee has a nylon reducer fitting from 1/2" pipe threads to 1/4" hose barb.

From there I use 1/4" braided PVC to connect to the vacuum pump (Food Saver) and a vacuum gauge, using a 1/4" nylon hose barb tee:



Notice the little black thing between the hose barb tee and the vacuum pump. That's a check valve. (A "vacuum check valve," about $6 from mcmaster.com.) It's a one-way valve that keeps the tank from sucking air backwards through the vacuum pump when the pump is off.

That's why I don't need two ball valves as I originally had, with one isolating the tank as in the original schematic.

If I didn't have the check valve, which works automatically, I could use the extra ball valve to isolate the tank from the vacuum pump manually. I'd attach it to the PVC tee on the vacuum-pump side, rather than the platen side, and screw the 1/4" barb reducer fitting into it.

Here's the connection to the Food Saver:



I made a reducer from 1/4" hose barb to 1/8" hose barb, using a 1/4" barb with 1/4" female pipe threads and a 1/8" barb with 1/4" male pipe threads. The 1/4" female one is from the air compressor accessory section at Home Depot. (2 of them for $4); they don't have them in the plumbing department. They're teflon-taped and screwed together.

They do make one-piece reducers, which you might find in some hardware stores, or could buy online if you're ordering from someplace like Grainger or McMaster-Carr.

Here's how I set up my Food Saver II as a vacuum pump:



The Food Saver wants you to push both sides of the lid down before it will actually run. I just bungeed a board across it to squeeze the whole lid down, so that I can turn it off and on with the power switch.

The Food Saver II has a little hose connecting to a barb on the inside of the lid, which I guess connects to the accessory port. (I didn't know what that was when I bought it.) I just ran it out the slot in the back instead, and taped it in place there. It might have been better to use the accessory port, and that's likely to work with different makes and models of food vacuum sealers, but I didn't know what I was doing or have an accessory port hose.

If I haven't overexplained anything, let me know.

Paul

P.S. Some random notes for people who haven't been following all this on tk560.com, and may want to adapt this stuff to other situations:

0. One reason I like hoses is that I like to be able to reconfigure and adjust things. For example, I like to be able to raise and lower my platen so that it's as close to the oven as possible while leaving room for sag. This lets the oven keep heating the plastic to a useful degree after it's pulled down, and extends the thermoforming time.

1. Hose barbs have an inside diameter that's only about 2/3" of their nominal diameters, and can restrict the air flow. That's why I use oversized hose and oversized barbs for the hose. A 3/4" hose barb has about the same inside diameter as a 1/2" pipe. (Be careful about hose fittings. For example, some 5/8" garden hose barbs have the same inside diameter, because the walls are thin, but others don't.)

2. The quarter-inch hoses are fine for gauges and wimpy little vacuum pumps, even with hose barbs reducing the effective diameter. If I had a pump that pulled more than a couple of CFM, I'd use 3/8" I.D. hose for the vacuum-pump connections. (There are nice barbs with 1/4" pipe threads and 3/8" barbs, which preserve the I.D. of 1/4" pipe.) If it pulled more than about 5 or 6 CFM, I'd use 1/2" I.D. hose. Quarter-inch is fine for gauges in any case. (Even smaller would be okay, but quarter-inch air fittings are common and cheap.)

3. The half-inch hose barb epoxied into the sump pump check valve is a potential bottleneck. It's 3/8" inside diameter is big enough for a 12" x 18" platen, but maybey not one that's more than a couple of square feet. I only used such a little barb because that's all that would fit in the place I drilled the sump-pump check valve. You could use two or three and tee them together, but that would be ugly. Better to use some kind of nipple or elbow in between the valve and the flange, and drill that---or just use a big tee and a reducer fitting for the high-vac connection.

4. The half-inch braided PVC hose doesn't stand up well to vacuum, as the quarter-inch hose does. That seems to be okay on the platen side, where it's not under continuous vacuum, but it's lame. I should have used 1/2" compressed air hose, or 5/8" high-pressure washer hose there too. You could also try 7/8" high-pressure washer hose on 1" barbs, but I don't know if the 7/8" size can stand up to vacuum. (External pressure handling falls off rapidly with diameter.)

5. The 1/2" pipes and 3/4" hose barbs are big enough to use without the vacuum cleaner (or the sump pump check valve) in a high-vacuum-only system, for this size platen. You could just use a 1/2" floor flange and a 3/4" hose barb to directly connect 5/8" high-pressure washer hose all the way from the platen to the main (ball) valve. That would be simpler, but would require a bigger tank for the same level of performance, and a faster pump to evacuate it in reasonable time.

6. This size plumbing is also big enough for a much bigger platen, say 2 x 2 feet, in a two-stage system with a vacuum cleaner. That's what I'll probably do, eventually. I'll remove the bottleneck at the sump pump check valve, and use the 5/8" hose with 3/4" barbs all the way, and plug it all into a bigger system.

7. If you're worried about slow leaks, you may want to put hose clamps around your hose barbs, and use teflon tape on all the threaded joints. I haven't bothered; I just put teflon tape on the metal-to-metal joints and anything that seemed kinda loose. Mostly I just screw the plastic threads tight, and it's good enough. My system leaks about half of its one cubic foot in about 8 hours, but doesn't leak noticeably during a vacuum forming cycle. If it starts to leak more, I'll seal things better.

8. Some rough price info, for figuring out what this sort of thing will cost you:

7-gallon compressed air carry tank: $20 at Wal-Mart (You can usually get used 30- to 50-gallon water heater tanks free for the hauling if you look on craigslist or freecycle. That's better, if you have the room for it and a pump that can evacuate it fast enough for your tastes, and it can do a good job with a big platen. I do have a better pump now, but I don't have that much room.)

Vacuum gauge (optional, but nice) $3.50 from Noshok Direct on eBay, but shipping is $6. (If you buy two, shipping's $7.)

sump pump check valve: about $7 at Lowes

vacuum check valve w/barbs: about $6 at McMaster-Carr

1/2" full-ported ball valve (threaded): about $5 or $6 at Harbor Freight or Lowes

3/4" brass hose barbs (w/ 1/2" male pipe threads); about $2.10 at plumbing supply stores or McMaster or Grainger

5/8" high-pressure washer hose: about $1.30/ft at Lowe's
1/4" braided PVC hose: about $0.30/ft at Lowe's

Brass garden hose adapters: about $2.50

Misc nylon hose barb fittings: 50 cents to $2.00, depending on size.
Misc small brass hose barb fittings: $1 or $2 or thereabouts in the plumbing or air compressor accessory section of hardware stores.

PVC nipples: 50 cents to a dollar depending on size
PVC tee: a couple bucks(?)

These things add up to several times what I spent on my vacuum sources, but those cost almost nothing---I got the hand vac and the Food Saver for a few bucks each at thrift shops.

[drcrash]

I've been asked about the ugly wire in the picture of the sump pump check valve.

The wire is there to make a strut across the throat of the valve and hold it in place. The strut is what you attach one end of the rubber band to; the other end holds the flapper of the valve lightly shut.

(I screwed a tiny eyescrew into the center of the disc-shaped valve flapper; the valve I got from Lowe's had a dimple there, like it was meant to happen.)

The wire around the throat of the valve is just there to keep the part that crosses the throat from slipping in, in a kind of circle-with-a-slash-across it shape, where the slash is the important part and the circle holds it in place.

This is pretty much in accordance with Doug Walsh's instructions in his nice little book "Do It Yourself Vacuum Forming for the Hobbyist," which I hadn't actually read when I did it. (But now I have. Good book.)

Here's a diagram from an ad for his book, which you can get on eBay or from his site, build-stuff.com:

[drcrash]

A few of things I've learned since I wrote the original post...

I got a Thomas Wob-L oilless piston pump and hooked it up in place of the FoodSaver. (Didn't need to, but I wanted the Thomas for a larger setup.)

1. I wish I'd gone with 3/8" hose and barbs in the first place. When you upgrade to a 2.3 CFM pump, the 1/4" hose barbs restrict the flow and slow the pump down by about 25 percent. 3/8" braided PVC hose works fine and 3/8" high-pressure air hose is almost as cheap as braided PVC anyway. (Not as pretty, though. )

As it happens, 3/8" hose barbs for 1/4" pipe fittings are common and cheap, so there was no point in using 1/4" hose barbs.

You can find them in the air tools section of a hardware store, likely labeled as "hose ends." They will probably have both "3/8 inch male hose ends" and "3/8 inch female hose ends," i.e., barbs with male or female 1/4" NPT pipe thread connections. (You can find the 1/4" hose versions there as well, also with 1/4" NPT threads, but don't bother.)

If your pump pulls more than 3 or 4 CFM, you might want something bigger still.

General rule: if you use hoses and barbs, do use a larger size than your pipe thread fittings. Don't assume that the mfgr is generous about sizing the fittings and that and that you can use 1/4" hoses and barbs on a pump with 1/4" fittings. (Likewise, if you have 3/8" NPT ports, don't assume 3/8" I.D. hose is big enough; if it's a 4 CFM pump, they may not be.)

(Apparently this is true of pressure stuff as well. "3/8 inch" hoses with 1/4" pipe thread fittings are very common.)

I probably shouldn't be using a 1/8" barb to fit the 1/8" I.D. hose on the Food Saver II, either---I should be squeezing a 3/16" barb into it, to avoid narrowing the pipe much. (The barbs built in to the machine have thin walls, so they restrict flow less than the barb I used to connect it up to the vacuum forming system.) If my calculations are correct, that barb is a bottleneck.

2. The little 1/4" barbed "vacuum check valve" from McMaster-Carr is a bit of a bottleneck for a 2+ CFM pump, as well. I'm guessing that the 3/8" version wouldn't be. Hopefully they size them not to be a big pressure drop relative to the cost of the barbs you connect them with. I could be wrong about that.

3. The check valve is important if you use a piston pump and a vacuum gauge. The pulses of pressure from a piston pump can beat the hell out of a vacuum gauge, making the needle dance wildly around the gauge; the check valve reduces the slamming by over 90%.

I did some controlled vacuum pump tests, with and (mostly) without the check valve, to measure airflow, and in the process I discalibrated my vacuum gauge so that now it consistently reads about 1 1/2 inches of mercury too high. (I can still use it for judging what to do when, when vacuum forming, but it's annoying.)

So even thought the check valve is a potential restriction on airflow, it's a very good thing to have if your pump is the bangy-bangy type. Get one. if you don't have one, and your needle is bouncing madly all over the gauge, realize that you may be damaging your gauge.

[drcrash]

Another tip:

Big auto parts places like Pep Boys likely have a much better selection of hose barb fittings (tees, reducers, reducing tees, wyes, etc.) than a hardware store, sold explicitly as vacuum fittings. So if you want something like a 3/8" x 3/8" x 1/4" tee, to connect a gauge, you can probably find it locally.

[abbay]

Thanks for sharing this instrument's knowledge...you can read the more about foodsaver from here....

http://www.foodsaverblog.com/