El-Cheepo Vacuum pump set up. A sealed unit, compressor, from a small fridge. The plastic jar receives the out air from the unit and catches the oil, can't be seen there clearly but there is a small vent hole in the lid. A short squirt of oil into the intake line before use is all that is needed for lubrication.
With no volume to evacuate the gauge needle went fairly quickly around to hit the stop pin at about 28 inches mercury. I switched the unit off and let it sit for about 24 hours and the reading was still the same so I know that the valves in the sealed unit are good.
I decided to see how long it would take to vacuum this compressor tank. The test started at 20 minutes past 5. The tank looks crappy but it is in good condition, I will be hydrostatically testing it in the near future so I can clean it up, paint it and put in my air system.
At 10 minutes the vacuum is at about 18 inches mercury.
At about 20 minutes it read about 22 inches but then it took a long while to get around to the stop pin, as you can see almost 40 minutes. I have another smaller tank I'm thinking of using as a vacuum resavoir for my final set up.
I hacksawed some scrap 150mm plastic pipe, rough sanded the end then filed the high spots and finally sanded the end smooth and flat by clamping sanding sheet down and pushing the tube back and forth, turning it 1/4 of a turn regularly. You can see the pencil mark around top end yet to be done.
Both ends of tube done and with 6mm clear plastic sheet sitting on top. I still have to make a base board with soft rubber sheet glued to it and sort something for the top. The top gasket may be a sheet of something clear and softish or I may lay a thin bead of Silastic on the top edge of the pipe and set the perspex(greased) on top until Silastic sets. I also have to fit a brass hose tail into the plastic pipe to connect to the vacuum source.
Uses for such a vacuum chamber; degassing RTV (Room Temperature Vulcanising) product when making moulds for wax patterns which are used in the lost wax casting process. I would like to try lost wax casting someday. Drying of degassing granules prior to plunging them into molten Aluminium.
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