What is a typical pressure for a pressure barrel

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paulgill

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Hi,

People who have connected up pressure gauges to their barrels often talk about liking to serve their beer at 3-5 PSI. Similarly, I understand that most pressure barrels will vent at about 10 PSI.

This doesn't make any sense to me as it implies that the headspace in the pressure barrel is *less* than atmospheric pressure (~14 PSI). How does this work? I thought one of the main reasons for topping up pressure in a barrel was to keep the beer pouring well. If the headspace pressure in a barrel is being kept below atmospheric pressure surely it provides less downwards pressure on the beer than the upwards pressure from the outside air at the tap.

Is this true? Is the pressure inside the barrel less than atmospheric pressure?

Note: I'm talking about cheap plastic pressure barrels (maybe with an S30 valve) here. Not corny kegs or similar.
 
Hi,

People who have connected up pressure gauges to their barrels often talk about liking to serve their beer at 3-5 PSI. Similarly, I understand that most pressure barrels will vent at about 10 PSI.

This doesn't make any sense to me as it implies that the headspace in the pressure barrel is *less* than atmospheric pressure (~14 PSI).


Is the gauge not measuring the difference in pressure between the inside and outside?

Ie the absolute pressure internally is ~24 PSI?
 
Here's my Rotokeg gassing up over 5 days, eventually gets to 6.5PSI

pressurising-1_zpsqhoxew1l.jpg
 
There are usually two ways of correctly stating positive pressure. Using 'psi' as an example, psig (pounds per square inch gauge) and psia (pounds per square inch absolute). Zero psia is a full vacuum. Zero psig is no pressure at sea level but is about 14.7psia. When people say psi they really mean psig.
So although my pb says OK up to 15psi it really means OK up to 15psig (or in new money about 1 bar gauge), which of course is a positive pressure.
 

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