This instructable was created in fulfillment of the project requirement of the Makecourse at the University of South Florida (www.makecourse.com). This Instructable leads you to create a pressure vessel used to make supercritical CO2 for the extraction of aromatics from edible ingredients.
- 7 Inches of 6.5 inch diameter 304 stainless steel round stock
- High Pressure Needle Valve (McMaster Carr Cat. No. 4999K17)
- Pressure Relief Valve 4,000 psi (McMaster Carr Cat. No. 5825T21)
- 5,000 psi Pressure Gauge (McMaster Carr Cat. No. 1798T11)
- 8x Alloy-Steel (Grade 9) 12-Point Screws 1/4"-20, partial threaded 2" (McMaster Carr Cat. No.91271A550)
- PTFE Thread Tape
- Micro Servo
- Red LED
- Multiple Black Viton 245 90 Durometer seals (4.359" I.D. X. 0.139" C.S.)
- Food-Grade Dimethypolysiloxane O-Ring Lubricant
- Arduino Uno
- IR Remote
- IR Receiver
- Small Breadboard
- Arduino Power Cable (USB-B to USB-A)
- 7.5"L x 4.5"W x 2.5"H Plastic Box with Detachable Lid(for housing electronics)
- 5v Li-ion rechargeable battery
- 220 Ohm Resistor
- Wires to Connect Electronics
- Hot Glue
- Sandpapers of approx. 200 grit, 300 grit, 400 grit, and 600 grit
Step 1: CAD and Technical Drawings
The CAD files were drawn on both Inventor and Fusion360. The files are included for possible modification/fabrication purposes. The technical drawings were made on Autodesk Inventor and were formatted to fit 8.5" x 11" paper on Powerpoint. Only a title block need be added.
If you choose to make modifications to these designs, be sure to simulate the internal pressure load with an FEM computer simulation program to ensure structural soundness. The current design handles the load exceptionally well.
Step 2: Machining
Time to turn that billet into a pressure vessel. I submitted a work order along with the technical drawings and 304 stainless steel round stock to the USF Engineering Machine Shop. They had it ready in about a week.
If similar resources aren't available to you, reach out to your nearest fabrication shop and discuss the build with the machinists there to get your metal cut to specs.
Step 3: Sanding
Since supercritical CO2 is under very high pressure and has no surface tension, the metal in contact with the O-ring must be very smooth to mitigate leaking. A surface roughness of about 10-12 rms is recommended. This takes a few hours of sanding.
The bottom side of the lid must be well polished to a satin-like finish with no visible scratches traversing the path of the seal. 600 grit sandpaper to finish works well.
Inside the gland is more difficult to sand, but goes faster. Focus your sanding on the bottom of the gland and the outer diameter; the inner diameter is non-critical for the seal since the pressure is positive internal.
Step 4: Assembling Lid
Be sure to clean the lid well to degrease it from the machine shop as this tool will be used to prepare edible substances.
After cleaning, the three fixture of the lid much be affixed. Wrap the male threads of each piece with teflon tape, about five turns each. Then carefully and fully screw them into the three prepared holes in the lid. The pressure relief valve comes with special instructions to hand tighten fully, then use a wrench for one full additional rotation.
Do not make the mistake of incomplete installation. My needle valve ended up facing an awkward direction, but awkward aesthetics greatly outweigh unsafe installation.
Step 5: Creating the Pressurized Hazard Flag
In Powerpoint, I made a little triangular flag that can be printed out. These can be cut out and folded in half around the tip of a chopstick which serves as a flagpole. Use cellotape to hold it in place and give it a laminated look. Opposite the paper are mounted two female leads for the LED to be inserted into. These are set with hot glue. Finally the base of the flag is mounted to the arm of a micro servo with hot glue, and the micro servo is mounted to the backside of the pressure gauge with a Command Strip.
Step 6: Assembling the Circuit
This is a very simple circuit as shown by the block diagram.
First connect the positive power bar to the 5v power supply on the Arduino and the ground line to the ground pin.
Starting with the LED atop the flag, connect the positive lead to your bread board and feed it 5v power through a 22 Ohm resistor. Connect the negative lead to digital pin #2.
Next, feed the micro servo 5v power and connect it to ground. Connect its data lead to digital pin #9 on the Arduino.
Now connect the IR receiver to 5v power and ground and wire its data pin to digital pin #10 on the Arduino. I have mine mounted directly to the breadboard, but it can be connected by leads and placed wherever you please.
I affixed all my electrical connections with hot glue which makes it look messy, but they are all hidden behind the box.
Last, it is time to connect the Arduino board to your 5v battery.
Step 7: Programming the Arduino
The code is quite straightforward. Make sure that you have the library for the servo and IR downloaded and set up properly.
Servo.h is a standard library that should come with the arduino IDE, but IRremote.h came from an external source.I included the .zip file for this library as I find these the easiest to add into Arduino's finicky library system.
My sketch sets up the digital circuit first, then works with an if statement that reads if the on or off button has been pressed on the remote which will toggle the variable lightOn which is used to blink the LED and sweep the Servo continuously.
Step 8: Putting It All Together
To keep continuity In my design, I modified the plastic box to fit the base of the pressure vessel, then packed the electronics in the spare space on the long ends of the box.
The arduino and breadboard are on one side while the battery is on the other. The power cord sneaks out along the base of the pressure vessel to connect the two sides.
First I cut the box to fit the base of the pressure vessel with a hacksaw. To get the nice curve in the halves of the lid, I wrapped the base of the pressure vessel with course sandpaper and rotated it around until it fit.
The final fit should be tight but not destructive. Because of the weight of the pressure vessel, it is important to take care not to crush your electronics.
Once all those were fitted, I cut small nocks in the lid to allow the servo and LED wires comfortable space and one for the IR receiver.
Step 9: Extraction
Now that everything is set up, the extractor is ready to extract.
The video Walks you through a typical extraction.
First, ensure that the device is thoroughly clean. I typically wipe out any dusts from the o-ring gland too.
Next, lubricate a new o-ring with the silicone lubricant until it is just wet all over and place it in the gland.
Load you ingredient(s) of choice.
Pack the vessel with dry ice, the more the merrier.
After ensuring that the needle valve is fully open, set the lid on top and finger tighten the bolts down to the metal.
Next, you can tighten the bolts evenly by turning them a quarter turn with a wrench using equal torque while alternating across the lid to the opposite bolt each time. For example I typically tighten bolts in the following order: 6 o'clock, 12 o'clock, 3 o'clock, 9 o'clock, 5 o'clock, 11 o'clock, 2 o'clock, then 7 o'clock. I repeat quarter turns in this fashion until all bolts are fully fastened. This ensures that the seal is evenly compressed and will withstand the full pressure of its design.
Only after the bolts are completely fattened can you then close the needle valve. As soon as it is closed, the system will begin to pressurize. Make sure you turn on the flag and light.
Now you wait for pressure to build and temperature to level. CO2 goes supercritical around 1,100 psi and 85 degrees F. Higher pressure helps as does gentle heating. Perhaps a Peltier module could provide the heating assist but I have just been using ambient temperature and sometimes a clothes steamer.
After being super critical for a while, the system is ready to be depressurized. Just crack open the needle valve a little bit and it will degas in about five minutes. Since CO2 is toxic around concentrations of 3%, it is best to do this out doors or in a well ventilated area.
After degassing, the bolts can be removed and the seal can be disposed of. The bottom of the pressure vessel should be lined with the oily aromatics. A small rubber spatula is handy for collecting it and it is ready to be used for any number of culinary applications.