Introduction: Stock Pot Vacuum Chamber!

G'day! This is my first instructable and I hope to make many more! My interests are welding, woodworking, moldmaking and metal casting.

Today, I'll show you how I made this fairly cheap vacuum chamber. I plan to use it to degass silicones and investment powder. I might also use it for vacuum bagging and vacuum forming down the line. The gasket I used is surprisingly effective and durable and the whole system was very easy to make air tight!

Step 1: Materials

Steel stock pot: $10 from the thrift store. Mine is 9 liters. To ensure that its suitable, it must have little to no flex when you press against the walls with your fingers. My one flexed very very slightly, which worried my initially, but it did not collapse under the pressure. Do not use thin aluminum. Thick aluminum should be fine. If you just want something that's guaranteed to work, then use a pressure cooking pot, but this will raise the price significantly, unless you find something from the thrift store.

Glass/Acrylic (plexiglass)/Polycarbonate (lexan) lid: This is the part that goes on-top of the chamber, allowing you to look at what you are vacuuming. At the present moment, I am using a Casserole dish lid, which fits my chamber perfectly. It is quite a hefty piece of glass and I have tested it under vacuum. However, this is a risk I'm willing to take for now. If you want something that's guaranteed to not shatter then you need to use either;

  • Clear Acrylic (plexiglass) sheet: at least 20mm in thickness, with dimensions that fit your pot. you can buy it off a plastic supplier
  • Clear Polycarbonate (lexan): No less than 12.5mm in thickness. This is more expensive, but it's stronger than acrylic. I will eventually use this material

Pet silicone feeding mat: $5 from the big-box store, but here is a link if you cant find it: This is used as the gasket that seals the lid to the pot, so air cannot leak inside. Unlike other DIY chambers I've seen, that require a gentle push onto the lid to close the seal, this gasket creates a seal without any effort!

Water Tank fitting/Bulkhead fitting $2.20 AU from ali express: The thread size 1/2 inch BSPP or 15mm. If you are in the USA, you will likely be looking for 1/2 inch "NPT". NTP and BSP do not connect, so make sure you're using 1 or the other. For the rest of the project I will be linking you to BSP fittings.

  • You can also use a weldless keg bulkhead fitting, but these were 3x more expensive and I found it was harder to make a seal.

1/2" to 1/4" female reducer fitting:

1/4" quick connect couplers. This is optional, but allows the system to be easily stored away!

1/4" BSP 4 Way Female Cross Pipe Adapter.

2x 1/4" mini ball valves (Male to female): Any ball valve can be used, but these mini ones turn a lot more freely than other ones.

1/4 SAE Refrigaration charging hose:

One of the most frustrating parts of this build, was finding a way to connect the output port of the vacuum pump, which was a 1/4 SAE male thread to my 1/4 bsp components. I ended up cutting the hose and removing the 1/4 SAE to 4mm Barb that it contained.

4mm ID vacuum line, with 10mm OD. $2. This is optional as you can just use the refrigeration hose I supplied above. The advantage of the silicone hose is that it is very flexible and attaches to the barbed fitting effortlessly.

1/4" Vacuum gauge $5: Optional: they are not very accurate and mine has not arrived yet, which is why it is not shown. Most of them are sold with NTP threads, and I accidently bought an NTP, instead of BSP, so I will need to buy a BSP to NTP converter eventually.

Compressor Water trap 1/4" bsp: (optional) $4.50: prevents solid debris from getting sucked into your pump and also SOME of the water vapor from getting into the system, which prevents the oil from getting dirty:

  • A desiccant air filter would be more effective

1/4" x 6mm male barb fitting $3: 4mm barb can also be used and is just as effective.

Teflon tape: must be used to ensure the threads are air tight

Rotary vane single stage vacuum pump: ~$75. Most of the cheap rotary vane ones can pull 29+ inches of vacuum. This is the optimal pressure for degassing silicone. Other types of vacuum chambers, like piston ones and the ones you can salvage from refrigerators pull a little less of a vacuum. I am no expert however and you should consult other sources.

Vacuum pump oil: It is important to fill your pump with oil before using it to achieve the required vacuum. Specialty vacuum oil is recommended. I am using compressor oil however, which may be hindering performance, but I'm not sure as information is scarce. Drop me a comment if you have more information about this.

Step 2: Assembly

  • Drill a hole into the pot so it can fit the tank fitting. I made a small pilot hose in my drill press first, as stainless steel is quite tough. Then use a step-bit to gradually make the hole big enough so it can be fit through. The gasket must be placed on the inside of the pot and the nut is on the outside. tighten it reasonably well and blow into it, with your finger blocking the other end, to ensure a good seal.
  • thread the 1/2 to 1/4 adaptor into the tank fitting and remember to use teflon tape with around 6 wraps around the pipe.
  • Then thread in a 1/4 quick connect fitting
  • Attach the other end of the quick connect to one of the ports of the 4 way connector. Then on the direct opposite port attach the other ball valve, then thread in the male end of the moisture trap. Attach the barbed fitting into the female end of the moisture trap, and push the vacuum hose into the barbed fitting
  • attach a ball valve to one of the remaining ports of the 4 way connector and then a vacuum gauge to the opposite end (as I do not have the vacuum gauge yet, I have to use another ball valve for now)
  • On the other end of the vacuum hose, attach the barbed end of the 1/4 SAE female fitting, that was removed from the refrigeration hose, onto the vacuum hose.
  • draw a circle that's less than the diameter of your pot in the silicone mat. Then cut that circle out to a size that allows you enough of a view into the chamber

Step 3: Operation

connect the 1/4 SAE fitting to the vacuum pump. place the gasket on top of the pot, and then the lid on top of the gasket.

Connect the quick connect fittings together and turn on the pump!

Check out the video for a demonstration

After turning off the pump and closing the valve, the vacuum pressure was maintained overnight. Therefore this system is virtually leak-free!

Dont forget to add check your oil level

Step 4: Disassembly

you can disconnect the fittings and remove the gasket, and conveniently store all the parts inside!