CO₂ gas train

Safety

Put on all PPE, including cryogenic gloves, before tightening the cylinder joint. Follow the instructions included with the SodaStream adapter. Never fit a mismatched adapter to a high-pressure CO₂ joint: only full thread engagement holds it, and a partial, mismatched engagement fails suddenly. Keep the solenoid manual override closed (horizontal line pointing at 0 on the front of the solenoid). The solenoid valve must be 3-way venting (3/2). A 2-way valve traps CO₂ between the valve and the broth on closing; the CO₂ dissolves and draws liquid back up the line.

This step builds the gas train with the adapter’s pin backed off, so no gas goes in. Admit CO₂, next, opens it.

1. Thread the 1 mm-bore anodeThe positive electrode: a titanium tube coated with mixed metal oxide (IrO₂-Ta₂O₅). Oxygen forms on it, and CO₂ flows down its bore into the vial. feed tube through the MMO anode, and pull it tight at the top.

2. Trim the feed tube’s lower end with sharp scissors.

3. Push a female luerA standard medical screw fitting. A male luer (the spigot) screws into a female luer (the socket). In this build, male ends mark outlets. onto the feed tube’s top end: this is the CO₂ inlet.

4. Work in a well-ventilated room. Put the SodaStream cylinder into its holder at the rear of the raft.

5. Put on all PPE, including cryogenic gloves.

6. Back off the KegLand adapterThe cylinder-to-regulator adapter (KegLand KL15578). Back its pin off while making the joint, then screw the pin in to let gas through.’s pin (thumbscrew out and loose), and seat the o-ring on top of the cylinder.

7. Screw the adapter on, tighten it with the gas cylinder wrench, and turn the cylinder so the adapter faces the front.

8. Unscrew the John Guest push-fitA push-in tube fitting: push the tube in and it grips and seals. The regulator's outlet port comes with one, which this build unscrews and replaces with the reducer. from the regulatorDrops the cylinder's pressure (about 60 bar when full) to a working pressure, about 1 bar here. Its flathead screw fully anti-clockwise is closed. outlet port.

   

9. Insert the o-ring into the regulator outlet port. It seats against the reducerThe 1/4" BSP to 1/8" BSP hexagon nipple that joins the regulator outlet to the solenoid valve., so this joint needs no Loctite.

   

10. Screw the reducing nipple (1/4” male to 1/8” male) into the regulator outlet port, and tighten with the wrench.

11. Apply Loctite 577An anaerobic thread sealant: it cures only without air, inside a tightened thread. Fixtures in 10 to 60 minutes at 22 °C; full pressure after 24 hours. to the second thread (not the end one) of the reducer’s 1/8” male outlet, and screw the solenoid valveAn electric valve on PWM channel 4 that opens to sparge. It must be 3-way venting (3/2), so the line vents when it closes.’s left port onto it, electronics to the rear. Work up to vertical; do not pass it and turn back.

12. Holding the solenoid, screw the blanking plugA 1/8" threaded plug that seals the solenoid's unused right port. It seals on its own o-ring, so it needs no sealant. into its right port with a 5 mm hex key. Use no sealant.
13. Apply Loctite 577 to the needle valveA fine-adjustment valve on the solenoid's front port. It sets how fast CO₂ flows; turn clockwise to close.’s inlet thread (second thread), and screw it into the solenoid’s front port, stopping with it pointing straight up.
14. Close the needle valve (clockwise), and check the solenoid manual overrideThe dial on the front of the solenoid. 0 is normal (closed without power); 1 holds the valve open. is at 0.
15. Close the regulator (turn its flathead screw fully anti-clockwise), then screw it onto the adapter and tighten.
16. Wait for the Loctite 577 to fixture before admitting gas: 10 to 60 minutes at 22 °C. It reaches full pressure rating after 24 hours.

Notes

• Solenoid override: 0 is normal (closed without power); 1 is always open.
• Use an o-ring wherever the joint has a seat for one, and Loctite 577 on every other threaded joint. Loctite 577 is anaerobic thread sealant, not glue. Skipping the end thread keeps it out of the gas path. Clean the threads with ethanol first where you can.
• Do not use PTFE tape in the gas train. Applied correctly it seals, but it is fiddly and leaks too often.

Parts

• 1×Silicone feed tube, tubular anodepart
• 1×MMO anode, 100 mm long, 6 mm OD, 4 mm ID, 70 mm active lengthearlier step
• 1×CO₂ regulatorpart
• 1×O-ring, 8 mm ID, 2 mm CSpart
• 1×1/4" BSP to 1/8" BSP reducing hexagon nipplepart
• 1×Loctite 577 thread sealantconsumable
• 1×Solenoid valvepart
• 1×CO₂ needle valvepart
• 1×1/8" blanking plugpart
• 1×Cylinder-to-regulator adapterpart
• 1×SodaStream CO₂ cylinder (blue screw-in)consumable
• 1×Dovetail holder, CO₂ cylinderearlier step

Tools

• 1×28 mm gas cylinder wrenchtool
• 1×Banded oil filter wrenchtool
• 1×Cryogenic glovestool
• 1×Eye/face protectiontool
• 1×Lab coattool

Check your work

1. Before any gas goes in, where do the adapter's pin and the regulatorDrops the cylinder's pressure (about 60 bar when full) to a working pressure, about 1 bar here. Its flathead screw fully anti-clockwise is closed. stand?

   • Pin backed off; regulator screwed fully onto the adapter
   • Pin screwed in; regulator screwed fully onto the adapter
   • Pin backed off; regulator part way onto the adapter
   Show the answer

   Answer: Pin backed off; regulator screwed fully onto the adapter

   • If you see Pin screwed in; regulator screwed fully onto the adapter: Back the pin off now (thumbscrew out and loose). The pin admits the gas, and Admit CO₂ opens it once the Loctite 577An anaerobic thread sealant: it cures only without air, inside a tightened thread. Fixtures in 10 to 60 minutes at 22 °C; full pressure after 24 hours. has fixtured.
   • If you see Pin backed off; regulator part way onto the adapter: Screw the regulator fully onto the adapter and tighten it. Only full thread engagement holds a high-pressure joint. Never fit a mismatched adapter.

2. What does the solenoidAn electric valve on PWM channel 4 that opens to sparge. It must be 3-way venting (3/2), so the line vents when it closes.'s manual overrideThe dial on the front of the solenoid. 0 is normal (closed without power); 1 holds the valve open. point at?

   • 1 (horizontal line at 1)
   • 0 (horizontal line at 0)
   Show the answer

   Answer: 0 (horizontal line at 0)

   • If you see 1 (horizontal line at 1): Turn it to 0. At 1 the solenoid is always open, so CO₂ would flow all the time.

≈ 0.02 g CO₂e per view