DIY Vacuum Chamber, What Could Go Wrong

For some time I have wanted to build a vacuum pump and chamber.

The options for uses of these are endless. Vacuum Bagging of composites, Vacuum Impregnation of wood, boiling point experiments, plaster investing for casting to name a selection.

Looking on the internet you will find numerous references to the reuse of a fridge compressor as a compressor, or as a vacuum pump.

Don't expect to win any prizes on the speed of these but my goodness the pressure they can pump and the vacuum they can suck.

Being an environmentally responsible citizen you should first ensure that your compressor is drained of all of the ozone depleting CFC's before 'hacking' into it.

Releasing CFC refrigerant to atmosphere is rather illegal so do heed this warning.

I have read also that heating of these gases with a blowtorch can result in some rather nasty compounds being created.

To prepare my compressor I bought it from an appliance repair man and had him degas it first, it was removed from the fridge already so I had to do little from here.

Be careful that you keep the applicable wiring, you will need the starter circuit. This will often be in a junction box of sorts on the motor.

The oil in a fridge motor is also not meant to be 'nice' therefore I drained it out and replaced it with ordinary compressor oil.

It was then for me as simple as applying a plug to it and powering it up, One tube sucks and one tube blows.

Doesn't win any prizes for speed but you can see how effective it is very quickly when you use it to apply vacuum to a soft drink bottle and suck it right down.

Step 1: The Fail(s)

Wanting the setup to be useful I then went about constructing a vacuum chamber.

I went and purchased some brass fittings, reinforced rubber fuel hose, a vacuum gauge and an aluminium pot to use as a chamber.

Using some brass compression fittings I was quickly, easily and relatively cheaply able to plumb onto the copper pipes coming out of the compressor. I then used a threaded to barbed adaptor to fit the hose on.

Very early on I was able to 'bottom out' my vacuum gauge by shutting off the end of the pipe.

While reinforced fuel line is designed for pressure it is super effective for vacuum also.

Many of you tinkerers will be able to identify, we work with pressure so often and say 100psi seems so familiar to us, we can almost feel the pressure. To this very moment while I have seen the vacuum gauge it does not seem something one can identify with.

You expect vacuum to behave like pressure but surprise surprise it does not. Where pressure will try and find any place it can to escape, vacuum try's to do the same but as it sucks it often seals the leak.

Using a brass fitting I plumbed the rubber hose to the lid of the pot. I purchased a silicone pressure cooker seal to go around the lid to assist with the sealing.

I smeared the seal faces with petroleum jelly then flicked the switch, watching eagerly on the vacuum gauge as the vacuum climbed. Probably I should have been watching the pot instead. I heard a slight creak (should have stopped here but I carried on) then there was a noise that sounded like the cross between a bang and a gulp as the pot imploded.

I should have been disappointed at the failure of this chamber but I understood why it had happened immediately.

Step 2: Version 2, Another Fail.

Back to the drawing board...
A week or 2 later I was back with revision 2, a sturdy 10 litre stainless steel bucket and a 10mm thick piece of Perspex for a lid.
Once again I used a brass fitting to plumb the hose to the Perspex lid.
I had purchased another silicone seal but it did not fit so I applied lots of petroleum jelly as a seal. Firmly pressing on the lid I was able to achieve an airtight seal.
Proudly I yelled to my Wife to come and look at my success. With me in the garage and her in the house she got to the back door before an almighty bang was once again heard and this much more sturdy bucket was imploded.
I appeared at the door of the garage with a crumpled bucket and a grin from ear to ear. (no photo sorry, has already gone in the trash I think)
Once again a fail but once again a learning experience.
I have to be honest, something rather fulfilling about imploding a bucket and a pot.
This project is on the backburner for now and the compressor pump sits on the bench and I have a few ideas as to how to make version 3 work.
It will probably involve the use of a valve in the system to allow me to evacuate a partial vacuum then isolate it. Also the use of a vacuum relief safety device.
Surely some of you out there have had some similar experiences.

Comments

[ascardina]

as for the safety warning about torching on a system that still has refrigerant in it: you're absolutely right. anything with chlorine in it (CFC and HCFC refrigerants) will produce phosgene gas which is extremely poisonous and often deadly.

[clayton.cowgill]

I've been using an old Harbor Freight paint pressure pot (used to be about $50, but I see now that they only have the larger sized $99 one now [#66839]-- they do go on sale frequently though, or use one of the ubiquitous 20% off coupons) and a HF vacuum pump [#61245]. Remove the pressure regulator from the paint pot and replace it with a vacuum pressure gauge and connect the pump to the pot with rigid air hose (again, I just used HF hose). It will pull down to full vacuum, but it is a little slow if you're using fast curing resins. (To speed things up, you can do a two-stage setup with some ball valves-- add an empty/inert propane tank to the system with anothe valve and vacuum it out first and close it off with the valve, then once your casting is in the pot, open the valve to the propane tank and let it quickly pull 'most' of the air from the system and close it off at the valve and close it again. Then, open a valve to the vacuum pump and let it run-- that way the small vacuum pump only has to pull the relatively small remaining air volume and hold it down if there are any small leaks.)

[Bverysharp]

I use an empty propane tank to hold the vacuum. - 1 side to the pump, 1 side to the propane tank, the T to the vacuum chamber via a ball valve. The great advantage of an old propane tank is that it has a gate valve on it which can be closed off to keep the vacuum for next time. For the vacuum chamber, A fully enclosed metal container is not great, because you often need to be able to see the thing you are vacuuming. (you can watch your RTV silicone overflow its container when the vacuum is turned on......) At the moment I use a glass jar (which had chutney in it) as the vacuum chamber. - I figured that it had already had vacuum sealed chutney in it, so it should be able to withstand a vacuum, and it does. It was easy to put a screw fitting into the metal lid, too. It's not big enough. I will use a pipe for the next vacuum chamber.

[Bruce_T_NZ]

Nice one, so the propane tank forms a sort of vacuum accumulator. A glass jar, this obviously works to hold the vacuum for you (a bit scared of imploding it too). Having not been successful in creating the chamber just yet I don't have a feel for just how much (or how little) vacuum it takes to achieve degassing. Thanks for sharing your experiences, this will certainly help with my next attempt.

[LaurJ]

As a tip: I've worked with laboratory vacuum bell jars. An integral part of the rig is a 1mm steel safety shroud around the bell, used during evacuation, in case the jar has had a ding while not in use, and decides to implode.

[TXcat22]

Nice work. May just incorporate this into the airbrush compressor I built using a fridge compressor and portable tank. The compressor ( actually four of them), I came across at my local City Recycle Center. They had already been degassed and were ready to remove with simple tools. The best part:....they were Free.

[Bruce_T_NZ]

Free is always great, all the best with your project

[XTL]

Pressure cooker is good. Tap a T junction with Ball valve on one side, midway up ( so accidental spills don't come out). At the rim, cut an old inner tube into a ring and fold it over the brim (for airtight seal). For the clear top - add a 10mm (minimum) thick piece of polycarbonate to see through. This will enable you to see your degassing fluids (in a tiptop :) container) and know when to release pressure with the ball valve. If you need a bigger vac chamber than a pressure cooker can provide, then cut an old propane tank near the top and do the same.

[Bruce_T_NZ]

Nice, I think I'll give it a try

[bpatton6]

Perhaps cutting open a canister designed to handle at least 14.7 psi. The pressure cooker below would be a good choice, because it is already designed with a lid. If you have the means, an empty propane tank could be modified for your purposes. You could also cap the ends on a large diameter pipe. I think this will be cool when you get it finished.

[Bruce_T_NZ]

Hi pbatton6, I like the idea of the propane cylinder because of the shape of it. Still might have to limit the vacuum though because wow can those compressors suck.

I will return to the chamber eventually but a number of projects on and rather low on the priority list.

[Lectric Wizard]

I'm building a similar vac chamber. I plan on using a pressure cooker for the chamber replacing the relief valve with the vac fittings. Might work for you too.

[Bruce_T_NZ]

Hi, I certainly did think of a pressure cooker but haven't tried one just yet.

Pretty keen to have a viewing window too so need to keep the perspex lid, still this may work with a pressure cooker though

[BeachsideHank]

Tthese are a popular choice for home shed woodworkers doing vacuum veneering of woodworking projects.