Using an air tank for vacuum?

The usual setup when using venturi vacuum generators (Piab is on of the large mfrs -

It's been several years since I've had occasion to use a Piab unit, but I believe some models provide for an external surge tank that kicks in when the air supply is turned on. Details might be on Piab's site.

Ned Simmons

I chopped a propane tank up to make my first vacuum chamber for coating telescope mirrors. Worked fine at 2x10-5 torr (a pretty good vacuum, at least good enough for my needs).

Take Care, James Lerch

Looks nice. 2x10-5 torr is the same as "20 microns", is that right?

The pump that I will soon pick up, is supposedly able to get 25 microns. I am aware that I do not need that for solder sucking, but it may be helpful in other instances.

SWITCH I will assume you mean't, of course you can or may need to use a contactor or relay as well.

Good ol' Mcmaster has switches for vacuum situations, but they are listed under "Pressure" switches.

The most reliable are the Bourdon Tube type with a mercury bulb, but they are not cheap.

The "Snap Switch" type are best installed on something that rattles or shakes as sometimes they will stick. Nothing a good kick doesn't take care of, but if you leave the shop for a week and forget to unplug the pump, you might find it melted down when you get back (don't ask how I know).

EBAY often has bourdon tube units for around $25.

Grummy

A few projects ago I was looking to cast some clear resin, and was looking for a vacuum chamber. I found an old 1 gal. paint pot at an auction. I changed some fittings so as to be able to use my automotive A/C gauges and vacuum pump with it. The pot turned out to be an acceptable vacuum chamber for my project.

John Normile

No.

You can't measure it anyway unless you have a thermocouple vacuum gauge.

I have two welch (1400 & 1405) two stage pumps. Getting down to under

Rule #1. Everything leaks below 1 torr Rule #2. Everything leaks even more below 50 milli-torr

For example, I hooked up a short length of 3/8 automotive hose to the 1400 pump. It could easily get to 100 milli-torr but not much lower. Dead headed either pump will get a litle under

Getting vacuum down in the 10-5 torr range is getting pretty fancy requiring a diffusion pump (or turbo pump) and maybe even a cold trap. Now you need yet another vacuum gauge to measure levels this low.

Everything you ever wanted to know can be found with a google search for sam's laser and vacuum page.

chuck

Well?

Did the air tank collapse??

We're all waiting with bated breath!

I use a Vac-u-vin coffee jar with a hand pump made from a rubber cork.

Works just fine for degassing PU and epoxy resins!

I would try to use a small glass jar as a vacuum chamber. (and a steel plate with a gasket as the cover)

Thanks Chuck. It was educational and I saved your post. Practically speaking, I doubt that I would need vacuum beyond 25 microns, and for now I would be satisfied with much lower vacuum, like 20 inches HG for desoldering. I may play with making freeze dried food, and there I likely need a vacuum that is not particularly deep.

Well wrapped with tape to control the fragments if it implodes I hope, or better enclosed in a shield as well :-)

Thanks Grummy. Looks like I won something for $12.50 or so, I'll see if this thing fits my application. If not, I will look for these bourdon tube units.

You'll probably find a pressure switch on EBay. Failing that, you can get a 0 to 100 kPa (0 to 14.7 PSIA) sensor from DigiKey for $7.88. MPXM2102AS-ND This is an absolute pressure sensor, measuring against an internal vacuum reference so you would turn on the pump when pressure in your reservoir rises above x PSIA (0 PSIA being a total vacuum) and turn it off when it goes below x - hysteresis. You could set these pressure trip points to anything you like with fixed resistors or trimpots.

Other elements needed would be an instrumentation opamp (INA126, $2.25), a 12VDC supply, a solid-state relay or a transistor and relay, maybe an LM393 comparator (42 cents) and some resistors. Maybe a 3-terminal voltage regulator for 72 cents. The whole works shouldn't cost $15 plus the relay which you probably already have.

Thanks Don. I have some parts already, such as comparator chips and an SSR and 12 vdc supplies.

I won something on ebay that is called Barksdale Pressure Switch, D1H-H18SS, 1/4 inch SS NPT, .40 - 18.00 PSI range, 1 setting, you can see it and the datasheet at

According to Ignoramus19736 :

And you *don't* want to use the same pump for food freeze drying that you use for desoldering.

The desoldering will get at least some microscopic bits of lead into the plumbing.

Bleeding back to atmospheric after freeze drying may transport those into the food.

And I really think that using the kind of pump which you have purchased (and not yet received, I believe) for de-soldering will lead to contamination of the pump oil. I would suggest a Gast rotary vane style pump for that, It runs dry, and doesn't have oil to get contaminated.

Good Luck, DoN.

That's a good point, but, I think, properly placed filters and ball valves should take care of this.

Please don't. Imploding glass containers are very dangerous. If you must, put it inside a wooden box or something to contain the fragments if it explodes. If you want a cheap bell jar, fisher scientific sells some small ones for under 50 dollars.

chuck

That should work. With that small differential your pump will probably cycle with each hit of the soldersucker valve.

A half-vacuum (7 PSIA) is plenty to suck solder.

Yes, the differential is very small indeed and not adjustable... OTOH, it would maintain accurate vacuum, not that it is important for desoldering. I checked out that digikey item, I may indeed consider going that route. It should not be difficult to decide what control system out of two is being used, by a simple DPST toggle switch.