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Old 20-03-2017, 09:20 AM   #1
Sorade
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Default Minimum headspace in pressure barrel

Hi all,

I found a lot of information on having too much headspace in barrels but nothing on the minimum. I barrelled a 10 L barrel a couple of days ago and left about a half inch no more. The pressure release valve is releasing CO2 so I guess I have excess pressure in there. Did I leave enough headspace ? I assume the only thing that can go wrong is I wont be able to draw full pints at the beginning, am I correct ?

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Old 20-03-2017, 09:38 AM   #2
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I never brew enough to worry about headspace ...

... but in line with other CO2 saturated liquids (e.g. beer, soft drinks, sparkling water etc) the headspace is mainly there to prevent thermal expansion from rupturing the vessel, as opposed to over-pressure due to the CO2 coming out of solution.

It's all down to "Dalton's Law of Partial Pressures". Personally, I would always leave a headspace of at least 75mm on a standard Wilco or King Keg pressure barrel and 25mm on a Mini-Keg.

I know absolutely nothing about Corny Kegs but the problems of thermal expansion and the Laws of Partial Pressure still apply.

PS

The 75mm includes the depth of the cap which is about 30mm.


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Last edited by Dutto; 20-03-2017 at 09:40 AM. Reason: Add PS
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Old 20-03-2017, 11:59 AM   #3
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Thanks for the reply. What kind of thermal expansion ? I thought that the density of liquids was rather unaffected by temperatures (unless it freezes).
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Old 20-03-2017, 06:06 PM   #4
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Quote:
Originally Posted by Sorade View Post
Thanks for the reply. What kind of thermal expansion ? I thought that the density of liquids was rather unaffected by temperatures (unless it freezes).
The density of liquids decreases as the temperature increases. Water is a wonderful exception to this rule after the temperature falls below 4 degrees; at which point it starts to expand until it become ice which will float on water.

As a result, the bottom of the world's oceans are at about 4 degrees and if ice didn't float the astronomers reckon that the earth's oceans would be about four feet deep, the rest being ice!

However, this is only of marginal interest when discussing the effects of Thermal Expansion in an enclosed space!

Liquid is generally regarded as being "incompressible". (There are some exceptions and they can all be compressed when subjected to pressure at the centre of a nuclear explosion but let's just assume that water and beer are incompressible.)

So, in an enclosed space such as a keg, vessel or a pipeline there has to be some method by which the pressure caused by the expansion of a liquid contained within the vessel is allowed to escape. In most cases this is covered by including a "head space" which is larger than any expected expansion of the liquid.

In pipelines and other industrial systems it is accomplished by the installation of Thermal Expansion Pressure Relief Valves which are installed around every potential blockage. e.g. pipeline valves.

Hope this helps.

Have to go because SWMBO has just come in from the garage to report "That thingy is bubbling and there is something all over the bench!"
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Old 20-03-2017, 10:19 PM   #5
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Luckily, caught it in time and replaced the 330ml bottle with a nice big bowl.

Beginning to wish I had only sprinkled in one of the two packets of yeast!

I'm also glad that I didn't just pass the blow-off tube back into the water in the trug! It had passed my mind that it would be easy to do!


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Living more in hope than expectation; and seldom disappointed.

Drinking/Conditioning
AG Bitter (03/02/17)
AG Light Ale (21/02/17)
AG Mild Ale (02/03/17)
SMASH with Citra (13/03/17)
SMASH with Cascade (19/03/17)

Fermenting
Vienna Lager Batch One
Coopers Stout Kit + Grain

Note:
(**/**/**) = Date in bottle/keg
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