CO2 Cylinder Pressures

thegrantickle · Thursday at 8:54 PM

Howdy,

For the past couple of years I have been using Sodastream co2 canisters to run my beer lines. However I love have 3 lines and am doing closed transfer from fermenter which was getting very expensive.

So today I finally made the switch over to a 6.4kg co2 tank I got from BOC.

My question is this:
What would you expect the high pressure gauge to read out on a 6.4kg? I am getting about 400psi from the cylinder I just picked up, but I seem to remember getting a couple thousand psi from a sodastream canister? I am wondering if I picked up a dud or underfilled cylinder from Boc?

Cheers

Larse · Thursday at 9:07 PM

thegrantickle said:
Howdy,

For the past couple of years I have been using Sodastream co2 canisters to run my beer lines. However I love have 3 lines and am doing closed transfer from fermenter which was getting very expensive.

So today I finally made the switch over to a 6.4kg co2 tank I got from BOC.

My question is this:
What would you expect the high pressure gauge to read out on a 6.4kg? I am getting about 400psi from the cylinder I just picked up, but I seem to remember getting a couple thousand psi from a sodastream canister? I am wondering if I picked up a dud or underfilled cylinder from Boc?

Cheers

Yeah, my 2Kg ones usually go well over 500psi.

Can you weigh your cylinder? The tare weight should be stamped on the top, so your total weight should be that plus 6.4Kg (if it's full).

thegrantickle · Thursday at 9:22 PM

Larse said:
Yeah, my 2Kg ones usually go well over 500psi.

Can you weigh your cylinder? The tare weight should be stamped on the top, so your total weight should be that plus 6.4Kg (if it's full).

That’s a good shout. I’ll do that in the morning

Rodcx500z · Thursday at 9:33 PM

Mine are normally in the 6-700 psi range

Caramel Ox · Friday at 4:26 AM

Weight is a good shout - the pressure varies by temperature I think mine is under 500 right now so maybe not far off.

thegrantickle · Friday at 7:46 AM

Caramel Ox said:
Weight is a good shout - the pressure varies by temperature I think mine is under 500 right now so maybe not far off.

I think this explains it. Thanks - I didn’t think of that. It was -1 in Glasgow when I collected it and the temperature had dropped to -3 overnight before.

peebee · Friday at 10:38 AM

Interestimg? Why are we having this conversation? @thegrantickle should have had his answer in the first couple of posts!

The variation in pressure of CO2 cylinders, as indicated by the "high-pressure" gauge should be down to the temperature. But in reality, it's because the gauges are CWAP! No need for further analysis ... ah, okay you can go for an analogy if you like; something about silk purses and sows' ears?

The cylinders contain liquid CO2. Liquids don't have "pressure" as such, but in the cases of liquids that boil at below ambient temperature, the gas above the liquid has to be a certain pressure to stop the liquid boiling away. I think that pressure is about 860PSI for CO2 (at ambient temperature). Apart from small variations due to temperature, that pressure is fixed (sorry @Caramel Ox ): For pure CO2 it won't ever be higher, the size of container is immaterial.

Don't put the cylinder on a fire or the pressure may get a bit high! Don't fill a cylinder so there is no vapour space, if the liquid starts expanding due to temperature, it starts applying hydraulic pressure on the cylinder (which will burst) ... I don't know if it's possible to do that? But I don't think I'll try.

There is one situation where there might be notably dropping pressure. The cylinder is empty and running on fumes! Get a new one quick.

CO2 Cylinder Pressures

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