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Keg Balancing Formula

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jaytee

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Guys, just want to check my logic and numbers before I cut the beer line

My old fridge is currently running at about 8C
I want about 2.3 volumes of co2
I have 5mm beer line
Restriction is 33kpa (not 100% sure on this)
Dispensing pressure is 13psi or .90kpa

Dispensing pressure divided by resriction gives me a hose length of 2.73 metres

For those that have done the calculations before, am I on the right track ?
 

sosman

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jaytee said:
Guys, just want to check my logic and numbers before I cut the beer line

My old fridge is currently running at about 8C
I want about 2.3 volumes of co2
I have 5mm beer line
Restriction is 33kpa (not 100% sure on this)
Dispensing pressure is 13psi or .90kpa

Dispensing pressure divided by resriction gives me a hose length of 2.73 metres
Your keg pressure is about right (I make it 80-90kPa - see CO2 table in SI units).

5mm hose is apparently around 33kPa per metre (remember this is based on a flow of 4.5 litres/min). So 90 - 2.73 * 33 is about zero. Anyway your calcs sound right but I run 4m of 4mm ID tubing and I wouldn't cut it any shorter.

There is some more stuff on this at brewiki kegging and carbonation.

So why don't you start with 5m and cut it back after you try it.

Despite maintaining a page with the maths on it - I very rarely refer to it, I go by feel.
 

jaytee

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Cheers Sosman,

I'd read - but maybe not fully digested - the links previously.
I wasn't 100% sure on the restriction of 5mm line and the LHBS wasn't any help.

I ended up 3 metres and 1kpa and great pour.

After various fridges and fittings and a misguided attempt to balance the system using restriction value for 3/16" line (assumed 3/16 and 5mm were the same) lines ended up being way too short and I wasn't getting good results

The balancing formula looked to be the way to go - but I've been known to butcher an instruction or two and miss the obvious so thought I'd better check
 

MAH

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jaytee said:
After various fridges and fittings and a misguided attempt to balance the system using restriction value for 3/16" line (assumed 3/16 and 5mm were the same) lines ended up being way too short and I wasn't getting good results
3/16" line is basically 5mm, but to be precise it's 4.7625mm. I serve most my beers at approximately 85kPa and use 2.5m of 3/16" without a problem. The system is nice and balanced.

What people forget is that the line restriction values are only approximations. the actual resrition will vary depending upon the manufacturer. A 5mm line from company X might have a completely different restriction value than 5mm line produed by company Y. One company might make their line with a smoother bore, which would give less restriction.

Also keep in mind that your regulator might not be giving an accurate reading.

But don't get too caught up in all this, jut use the aproximate values and you should be fine, and you shouldn't need to be installing lines that are 4m+.

Cheers
MAH
 

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