Amano New Year Build!

@Jakes , while sitting here I noticed the cylinder lever has two holes, one for the closed position and another for the open. Bargain, I'm now using the pin to keep it open instead of your cable tie trick. Check yours, maybe you'll get lucky as well.

It kinda makes sense because you'd want some way to keep the valve open while refilling.

 

Interesting, will check tomorrow.

 

I dunno about this fire extinguisher business, fellers. I've been sitting watching the bubbles, and the effect on the bubble checker. It's clearly working (checker is a nice grassy green and current pH at 6.5 is an order of magnitude less than normal, which is kinda lekka), but it's also obvious that the gas being dispensed contains other gases - probably air.

I can watch a bigger bubble being produced, and it rapidly diminishes in size as the CO2 dissolves - but what is left is a pinprick and the pinpricks never disappear except by eventually scumming at the surface. None of the bubbles, no matter how small initially, ever disappear. I can only conclude that it is some other residual gas(es).

This doesn't bother me in principle, but it does bother me aesthetically, because my tank is a haze of tiny dots and I'd like to keep the diffuser towards the front to monitor its operation - but my flow arrangement to keep the bubbles in suspension creates a wall of bubbles towards the front of the tank. And the setup for the inlet and outlet is kinda set in stone unless I make major changes that ruin the neat hiding away of the tubes.

I first figured it just needs some time - CO2 is heavier than the other stuff so it will eventually push out all the other gas at the top of the cylinder first, right? Turns out it doesn't work that way, some schtuff called Dalton's and Graham's laws ensure that brownian diffusion happens at a faster rate than settling due to density. The mix will always be homogenous and the only way to get a haze-free water column is to use pure CO2.

 

co2 fire extinguishers only contain liquid co2 and the bit of gas that fills up the rest of the bottle. as the gas leaves the bottle, it is replaced by more gas from the liquid co2, there should not be other gas, especially air, otherwise it would not make a very good fire extinguisher..

 

Well lemme do some sums.

The cross section of the cylinder is 130mm, and its height is roughly 600mm. Not accounting for the wall thickness and the curvy bottom and top, that gives an internal volume of roughly 8Lt.

The volume of liquid CO2 is approx. 1.3dm3/kg. Times that by five gives 6.5Lt of volume - there is no way there is any liquid in this cylinder, the physics doesn't allow it. I also turned it upside down and there was no bubbling or evaporation going on in the bubble counter.

 

this is not correct:


The volume of liquid CO₂ in a 5 kg fire extinguisher depends on its density.

Density of Liquid CO₂

• At 20°C, the density of liquid CO₂ is ~0.770 kg/L.
  
  
• This means the volume of 5 kg of liquid CO₂ can be calculated as:
  

Volume=Mass / Density

Volume=5 kg / 0.770kg

≈6.49 liters approx

• A 5 kg CO₂ extinguisher contains ~6.5 liters of liquid CO₂ at 20°C.
  
  
• The total cylinder volume is larger because there's also CO₂ gas above the liquid to maintain pressure.
  
  
• If temperature increases, liquid density decreases slightly, increasing the volume.

The pressure in a CO₂ extinguisher is mainly dependent on temperature, not on the amount of CO₂ inside (as long as there's liquid CO₂ present). At room temperature (around 20°C), the pressure inside is approximately:

CO₂ Cylinder Pressure≈55 bar(5500 kPa or 800psi)

If the temperature increases, the pressure rises. For example:

• At 0°C → ~35 bar
  
  
• At 20°C → ~55 bar (Inside the cylinder, CO₂ is mostly liquid due to high pressure (~55 bar at 20°C))
  
  
• At 30°C → ~72 bar
  
  
• At 50°C → ~125 bar (dangerously high!)
  

When you discharge the extinguisher:

• The liquid CO₂ rapidly expands into a gas.
  
  
• The temperature drops sharply (Joule-Thomson effect), which is why CO₂ extinguishers produce dry ice "snow" at the nozzle.
  
  
• The pressure in the cylinder will remain nearly constant until all the liquid CO₂ is used up—then it drops rapidly.
  

Since 1 kg of liquid CO₂ expands to about 509 liters of gas at atmospheric pressure, a 5 kg extinguisher releases approximately:

5×509=2545 liters of CO₂ gas

 

I'm sorry, but this is basic Boyle's law stuff. The claim of two separate volumes of gas, with one being liquid, is outright false because the overall pressure in the system would need to be high enough to force the gas past its condensation point - which would apply to the supposed volume of gaseous gas to begin with. You can't expect the "gas above the liquid" to exert pressure on the liquid without condensing itself. It just doesn't work that way, and your AI is full of it.

If a compound is a gas at STP, and the available volume is greater than that the liquid volume, then the entire lot will boil off into gas. Boyle's law.

 

Boyle’s Law states that for a fixed amount of gas at a constant temperature, the pressure (P) and volume (V) are inversely proportional:

P1V1=P2V2

However, in a CO₂ fire extinguisher, Boyle’s Law applies only to the gaseous portion of CO₂, not the liquid. The reason is that liquid CO₂ does not behave as an ideal gas, and its volume does not change significantly with pressure like a gas would.

• Inside the extinguisher, liquid CO₂ and gaseous CO₂ exist in equilibrium under high pressure.
• Boyle’s Law governs the gas portion—as pressure decreases, the gas expands.
• Liquid CO₂ does not follow Boyle’s Law directly but evaporates to maintain equilibrium.
• The rapid expansion of CO₂ gas upon release leads to cooling and pressure drop, which is why the extinguisher gets very cold.

 

THERE IS NO LIQUID - it's begging the question.

 

• The pressure in the cylinder will remain nearly constant until all the liquid CO₂ is used up—then it drops rapidly.

it's the same principal as butane in a lighter, you can see the liquid in those cheap plastic lighters even though it's a gas at STP, gas comes out of the lighter, not liquid. there is gas and liquid in the lighter at the same time.

are you saying there is no liquid gas in lighters as well?

 

I concede, and I learned a couple of things now.

To wit:

To determine the pressure at which 5 kg of CO₂ will condense into a liquid at 20 °C in a volume of 8.33 L, we need to consider the vapor pressure of CO₂ at that temperature. The condensation of a gas into a liquid occurs when the pressure exceeds the vapor pressure at a given temperature.

Vapor Pressure of CO₂
At 20 °C, the vapor pressure of CO₂ is approximately 5.2 atm. This means that if the pressure in the cylinder exceeds this value, CO₂ will condense into a liquid.

Step 1: Calculate Moles of CO₂
First, we need to calculate the number of moles of CO₂ from the given mass:

• Molar Mass of CO₂:
  
  12.01 g/mol (C)+2×16.00 g/mol (O)=44.01 g/mol12.01 \, \text{g/mol (C)} + 2 \times 16.00 \, \text{g/mol (O)} = 44.01 \, \text{g/mol}12.01g/mol (C)+2×16.00g/mol (O)=44.01g/mol
• Convert 5 kg to grams:
  
  5 kg=5000 g5 \, \text{kg} = 5000 \, \text{g}5kg=5000g
• Calculate Moles:
  
  n=5000 g44.01 g/mol≈113.63 moln = \frac{5000 \, \text{g}}{44.01 \, \text{g/mol}} \approx 113.63 \, \text{mol}n=44.01g/mol5000g≈113.63mol

Step 2: Use the Ideal Gas Law
We can check the conditions to determine if CO₂ will condense at the given volume.

Using the Ideal Gas Law:

PV=nRTPV = nRTPV=nRT
Step 3: Calculate Pressure Required for Condensation
To find the pressure (PPP) where CO₂ would condense:

Rearranging the Ideal Gas Law:

P=nRTVP = \frac{nRT}{V}P=VnRT
Substituting values:

• n≈113.63 moln \approx 113.63 \, \text{mol}n≈113.63mol
• R=0.0821 L⋅atm/K⋅molR = 0.0821 \, \text{L} \cdot \text{atm} / \text{K} \cdot \text{mol}R=0.0821L⋅atm/K⋅mol
• T=293.15 KT = 293.15 \, \text{K}T=293.15K (20 °C in Kelvin)
• V=8.33 LV = 8.33 \, \text{L}V=8.33L

Now substitute these into the equation:

P=(113.63 mol)⋅(0.0821 L⋅atm/K⋅mol)⋅(293.15 K)8.33 LP = \frac{(113.63 \, \text{mol}) \cdot (0.0821 \, \text{L} \cdot \text{atm} / \text{K} \cdot \text{mol}) \cdot (293.15 \, \text{K})}{8.33 \, \text{L}}P=8.33L(113.63mol)⋅(0.0821L⋅atm/K⋅mol)⋅(293.15K)
Step 4: Calculate Pressure
Calculating:

1. Calculate the numerator:
   
   P≈113.63⋅0.0821⋅293.158.33P \approx \frac{113.63 \cdot 0.0821 \cdot 293.15}{8.33}P≈8.33113.63⋅0.0821⋅293.15
2. Calculate:
   
   P≈2748.168.33≈329.51 atmP \approx \frac{2748.16}{8.33} \approx 329.51 \, \text{atm}P≈8.332748.16≈329.51atm

Conclusion
The calculated pressure for 5 kg of CO₂ in an 8.33 L cylinder at 20 °C is approximately 329.51 atm. Since this is well above the vapor pressure of 5.2 atm, CO₂ will indeed condense into a liquid under these conditions. If the pressure is maintained above 5.2 atm, the CO₂ will remain in liquid form.

"Well above" it says. The formatting didn't transfer well but it's unimportant. The high-side pressure gauge on my regulator only reads 35psi (instead of the theoretical > 4800psi if it was all gas) - so some of it HAS to be in the liquid phase.

Namaste!

 

i love learning new things, and this sometimes means being corrected when i am wrong about something, and i just assume most people are like this, please don't take it personally or as an attack

it's always a good day, when i can say i learned something new today

 

I was ready to rumble, hay! I was so convinced I was right but I confused a number of things. Doh!

Turns out Boyle's law has nothing to do with it either.

 

Very interesting! I enjoyed the read too, thanks for sharing

 

In a previous life I worked on the Isle of grain LNG gas expansion project, 3no. 190 000m³ unpressurised liquid gas storage tanks. Very interesting how gas can be stored as liquid without pressure at scale.

 

Guten moaning.

My drop checker took practically the whole day yesterday to turn lime green, and I'd modified the schedule to turn off at 4pm which it did. This morning it was still lime green. What gives? The CO2 turned on at 6AM as per schedule but I'm tempted to turn it off.

The checker solution is only a few days old. I have no idea of my KH/GH so can only speculate about any potential buffering or whatever else is going on. Any ideas? pH is about 7. The water surface is clear and there's a fair bit of flow. And the drop checker is right next to the outlet so it's not sitting in stagnant water.

 

Check this out! This is a small fragment of Parrot's Foot I nabbed from the pond outside and experimentally threw in among the floaters. The brown leaves at the bottom is emmersed growth that died off. It eventually started pushing out fresh immersed growth and so I shoved it in at the front of the tank.

Yesterday afternoon I noticed that it was surprisingly tall - I could have sworn it was flat on the substrate, but couldn't be sure so took a pic (I enabled timestamps on my phone for exactly this).



This is how much it grew overnight, in the space of 12-13 hours, most of it darkness. I'll be keeping a close eye on this guy because it's bloody amazing to see despite this being precisely what makes it such a pest.

And yes, I know PF is blacklisted so it's not for sale. Sorry

Also, notice the weird blue stains on the substrate against the glass? I have this consistently around the tank and have no idea what it could be - perhaps some sort of fert added to the soil I used as a substrate? I think I need to invest in a copper test....

 

the blue stains might be the start of cyano (blue green algae), you can squirt some excel or peroxide in there with a syringe if it really bothers you..

 

It's too blue to be cyano imo. All the stains spread downwards under gravity in a cone shape as if there was a particle of blue dye dissolving.

 

Here's a nice pic to illustrate. This is the left bottom of the tank, I have the outflow + a small USB pump at the left rear to help push the CO2 bubbles downwards, so the flow against the glass in front is from the upper left and you can see how the stains spread in the flow direction - perhaps not under gravity. The stains were there before I added CO2, but only mention it now because I took a pic of the PF with a stain in the frame.