Calibrating low pressure gauge

[peteru]

Is there a simple DIY method for ball-park sanity check/calibration of low pressure gas gauges?

Something along the thermometer 0/100C, icebath/boiling water trick.

I only have one regulator with high and low pressure gauges. I am starting to suspect the value shown by the low pressure side. Most people talk about using 10-20psi in their setups. I find that I get my optimal results in the 20-30 range. I have no issues with how my beers pour, but it would be nice to know whether the actual CO2 pressure is anywhere near what the gauge is actually reporting.

 

[malt junkie]

That seriously sounds like your LP gauge is stuffed. 8-12 Psi is normal for ales, lagers, 15-20Psi for stouts if you have a stout tap. I don't know what reg your currently using, but it will either need the LP gauge replacing or fully re-kiting or both or new reg entirely.

 

[bevan]

For the cost of getting it checked (unless you know someone who will do it for nicks or beer) it would be cheaper to get another one I'd say.
eg http://kegking.com.au/co2-cylinders/low-pressure-gauge-0-80psi.html

 

[Lyrebird_Cycles]

Is there a simple DIY method for ball-park sanity check/calibration of low pressure gas gauges?

First one uses a smallish pressurisable vessel like a growler or minikeg.You'll also need a delivery line, a graduated jug larger than the vessel and a bucket larger than the jug.

Weigh the vessel, tare, fill vessel with water, net weight = vessel volume.

Empty the vessel, pressurise it to 1 Bar gauge as indicated by the gauge in question.

Fill the bucket with water*, submerge the jug and turn it upside down whilst submerged.

Vent the vessel into the jug until gauge reads zero. Pull the jug up so the water line inside is level with outside.

Note the gas volume. If the gauge is reading correctly and you haven't lost anything it should equal the vessel volume.



*For max accuracy, throw some citric acid into the water to get the pH down around 3 but you probably won't need this.

 

[Lyrebird_Cycles]

Second one relies on having an accurate set of scales that will weigh a medium size pressure vessel (eg a corny) to better than 1 g.

Determine vessel volume as above.

Push the water out with CO2, weigh the keg.

Pressurise to 1 Bar gauge as indicated by gauge to be calibrated, weigh keg again.

Repeat at pressures up to max pressure.

Draw a calibration curve of weight vs pressure. The slope should be ~2 g/l/Bar and the intercept at zero.

 

[Lyrebird_Cycles]

Third one uses a pneumatic cylinder and a force transducer ( a set of scales will do).

Set up the cylinder so that when it extends it pushes on the force transducer / scales.

Pressurise the cylinder to a series of pressures per the gauge to be calibrated, noting the force for each pressure.

Go from zero up to max pressure and then back down again.

Draw a calibration curve from these figures and compare it to the operation curve given by the cylinder manufacturer.

 

[MHB]

Bit of clear, hose run it up a ladder or up the side of a 2 story house... connect to a keg full of water
from P=Ro*g*h
Ro is density, for water that is 1
g is acceleration due to gravity 9.81
h is head height in meters.
At 20kPa 20=1*9.81*h > 20/9.91= 2m of head (well 2.0387m)

Just measure from the top of the water in the keg, run the line down to the ground then back up, use the gas to pump some water up the line, turn off the gas vent the keg and let the water fall back, mark the water level on the line and measure from there.

There is a small error as the water in the keg goes down, if you lay the keg on its side that would be minimal, or you could spend a lot of time working out the movement but I doubt it would matter.
Mark

 

[TheWiggman]

Never seen ρ written as Ro before, fell like I haven't lived. There's a minor error in it though -
ρ is in kg/m3 which is approx. 1000 for water at room temp
P is in Pascals (Pa)

On that principle though, I think it could be done simpler but would be a 2 person job

1. Pressurise a litre of water in a keg to 30 kPa. Keep gas connected
2. On the second story / roof of the house, dangle a 4m length of beer line with a liquid disconnect on it
3. Connect line to keg, and measure distance between the ground and liquid level in the beer line

Plug the height into the equation -

P = 1000 * 9.8 * measured height (in metres)
Divide by 1000 to get kilopascals (kPa)

That should be identical to your gauge, 30 kPa. If it's off by much, that's your error.

 

[MHB]

Same thing, Ro is the name of the density symbol ρ, like using Pi ,Alpha, Beta or even Omega rather than the Greek symbol.
I just simplified the equation by putting density over Kilo (1000/1000=1)

If the high of water is 2M, gauge pressure would be 20kPa, 3M-30kPa...
But you should be measuring the difference between the two surfaces, not to the ground, just a big manometer really.
Mark

Well Rho is probably more common.
M

 

[TheWiggman]

Was going to say Rho but withheld my OCD with great strength. Spent 4 years studying density amongst other things
Between the surfaces is correct hence why I said a litre of water. Base of a corny and 1 litre is probably 70mm? Not much over 3m. I reckon there'd be more error reading the gauge.

 

[Lyrebird_Cycles]

I reckon there'd be more error reading the gauge.

Particularly when you are trying to read 20 to 30 kPa on a gauge with FSD of 500 to 600. Half the smallest scale division is 5 kPa, that's an error of up to 25%.