Calibrate CO₂ flow

The FZoneThe MEP's budget CO₂ regulator. Its outlet pressure is fixed, so the needle valve alone sets the CO₂ flow. Left gauge: cylinder pressure; right gauge: pressure reaching the solenoid. 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.’s outlet pressure is fixed, so the needle valveA fine-adjustment valve on the solenoid's front port. It sets how fast CO₂ flows; turn clockwise to close. alone sets the flow. Aim for the flow of an AEP0.1.1 at 1 bar, so experiments port across. BAEP: fit the vent filtersA 0.2 µm hydrophobic membrane on luer fittings. Gas passes; microbes and liquid do not, so each gas path stays sterile. first; they change the flow.

1. Check the cylinder is open: the adapter’s pin screw is fully down.
2. Cap one of the two gas outlets with a luer lockA standard medical screw fitting. A male luer (the spigot) screws into a female luer (the socket). In this build, male ends mark outlets. cap.
3. Run 1/16” tubing from the open gas outlet into a water bath, under a measuring cylinder full of water.
4. Open 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.: turn on the relay in the Pioreactor UI, or run spargesBubbling gas through the culture. Here, CO₂ from the cylinder flows down the anode on a timer set in the electroPioreactor job. from the electroPioreactor job.
5. Sparge until the water is saturated with CO₂ (when its pH stops falling, if you can measure it), then open the solenoid for a fixed time.
6. Record the volume of CO₂ collected.
7. Calculate the flow rate, in ml of CO₂ per second of solenoid open time.
8. Adjust the needle valve, and repeat until you reach the target flow rate.
9. Record the needle valve setting, in turns from fully closed.

Shutting the gas off after a session

1. Close the cylinder: unscrew the adapter’s pin screw.
2. Turn the solenoid overrideThe dial on the front of the solenoid. 0 is normal (closed without power); 1 holds the valve open. to 1 to vent the line to zero, then back to 0.

Parts

• 1×Luer lock cappart
• 1×Silicone tubing, 50 cmearlier step

Check your work

1. As you adjust the needle valveA fine-adjustment valve on the solenoid's front port. It sets how fast CO₂ flows; turn clockwise to close. and re-measure, how does the flow behave?

   • It reaches the target and holds there on re-measuring
   • It reaches the target, then drifts over later sparges
   • It stays low, whatever the needle valve setting
   Show the answer

   Answer: It reaches the target and holds there on re-measuring

   • If you see It reaches the target, then drifts over later sparges: Needle valve creep: re-measure after a few spargesBubbling gas through the culture. Here, CO₂ from the cylinder flows down the anode on a timer set in the electroPioreactor job. and adjust.
   • If you see It stays low, whatever the needle valve setting: Look for a kinked line, then a leak at a 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. joint: pipette washing-up liquid in water onto each joint and watch for bubbles.

≈ 0.02 g CO₂e per view