Small Pressure / vacuum setup

**Old-Biker-UK** · 28th March 2013, 02:52 AM

Picked up an old pressure cooker at a boot sale, cut an 8mm perspex lid for it so I can see what's going on inside. Turned up the bits for inlet & release from brass stock.
vacuum-tank.jpg
I'm sure the fridge pump will pull enough vacuum for my needs, previous experience impregnating fragile archaeological materials showed me that you don't need to lower the pressure by much to get the air out or the solvent boiling!
I'm thinking of making a seal from either rubber pond liner or thin closed cell foam. Won't need any clips to hold it in place, once the pump starts pulling, atmospheric pressure will hold it down.
If I want to use the setup as a pressure tank I can use the original lid although I will probably need to connect it up to the shop compressor (after doing a hydraulic pressure test on the tank of course.....

)

These old fridge compressors are great so long as you remember to squirt a drop of oil in from time to time. They originally worked on a closed system & the lube went around with the gas. Used as a small shop compressor they loose oil and will die. DAMHIK.

Mark

**salty72** · 10th June 2013, 03:27 AM

remember that a fridge compressor is not designed for constant use and will over heat / die very quickly

here is a basic link on how to make this system more user friendly ( I would also add a resivoir - the larger the volume the longer a leak will take to effect the overall pressure/vacuum)

Building your own Vacuum pump

**Old-Biker-UK** · 10th June 2013, 05:14 AM

Thanks for the link Salty , looks like one could make a decent bit of kit that way, certainly a reservoir would be a good idea, i've got a small airbrush tank I must dig out.
For consolidating I just want to pull a small vacuum for a very short time otherwise the solvent will evaporate sharpish.
I have used old fridge compressors in the workshop & at exhibitions to run models without any problems, just need to remember that in a fridge the lubricant goes around with the gas in a closed circuit but needs a squirt of oil down the inlet from time to time with an open circuit.

Mark

**salty72** · 10th June 2013, 06:27 PM

that link I sent used a vacuum diaphram- off this comes a lever and this is connected to the arm of a micro switch adjusting the length of the are adjusts the pressure and thus the on/off point of the compressor ..

Also if you extend the oil tube and place a ping- pong ball (with hole) over the end of the tube it can be filled with oil and used as a resevior so each on / off cycle will re oil the compressor

(if you don't need a huge vac you can also try a venturi..

Image taken from CNC Zone (Made my own Venturi... - Page 2)

venturi%20drawing.jpg

I have built one of these and can easily get 22"Hg from 60psi

**QC Inspector** · 12th June 2013, 09:18 PM

Nice little vacuum setup Mark. I have an old cast aluminium pressure cooker that a buddy scrounged up for me that I'll play with for vacuuming someday

. It's nice and big, perhaps 10 litre. It has a gauge on it that has a working pressure of 10 psi along with the relief valves and such. I am not sure how much more pressure one could take before getting your attention by popping, so I personally will avoid using it for that. I have an steel spray paint pot that works well for pressure so I'm covered in any case.

Pete

**Old-Biker-UK** · 13th June 2013, 08:02 AM

Found a couple of those lovely old cast iron P/Cs in an antique shop - they wanted £50 each for them so I went for the £1.50 boot sale 1960s Prestige job instead.

Mark

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