Pressure Gauge differences keg vs regulator

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Pressure Gauge differences keg vs regulator

Postby craigev » 28 May 2009, 16:25

I have just been doing a spot of recalibration re fridge temps, carbonation levels and psi levels.

I notice a weird difference between the readings on my pressure gauges attached to the gas cylinder regulator versus a hand-held gauge attached to a corny valve adaptor thingy. Anyone experience this before ? if so, did you find a reason and did you find out which one was more accurate a measurement ?

So, eg. hand held gauge reads 10 psi, regulator reads 13psi. and they are consistently 2 to 3 psi up versus the handheld. I only have one hand held gauge, but four regulator gauges, all the regulator gauges match each other to within 1 psi for the same keg which i pressurised to varying levels for the tests from 5psi upto 20psi. One of the regulators is attached to a cylinder inside a fridge, so the cold could perhaps account for some difference there, but my other dual regulators are attached to a cylinder outside a fridge.

based on carbonation levels i THINK im getting judging for the beer i pour, i would tend towards trusting the hand-held gauge.

im wondering if it is that simply having three gauges on a single regulator causes each one to offset its reading slightly ?

I have also tested the hand-held on a keg full and half full each time represurising to the same level, and i still get the same readings. could it be the poppet valves on the keg not opening fully perhaps.

anyone know, care to take a guess?
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Re: Pressure Gauge differences keg vs regulator

Postby keat » 28 May 2009, 21:44

co2 tanks in the fridge has a lower pressure due to the lower temp. However, that is not the reason for 2 gauges to read differently. My guess is that you are measuring the pressure of gas coming out from the tank vs the pressure of the keg. Another guess would be a small leak in your handheld.
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Re: Pressure Gauge differences keg vs regulator

Postby Hunty » 29 May 2009, 07:12

looks like a simple systematic error to me... i'd check the regulator in the fridge and compare it to the other one at the same temp and in the same keg... if all four are the same I'd guess the handheld was inaccurate, just my 2c.
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Re: Pressure Gauge differences keg vs regulator

Postby craigev » 29 May 2009, 13:05

keat - your suggesting that it is reasonable for there to be a difference between the pressure coming from the tank versus the pressure coming from the keg - why ? do you also have a difference ? if so whats the diff.

Actually, to reword my question your spot on - why is there a difference between the pressure of gas coming out from the tank vs the pressure of the keg ?

did you guys ever try comparing the two pressures ?

Hunty - yes - four tank pressures gauges read the same as each other, the handheld reading the keg is 2-3psi lower. All using the same keg at the same temperature. maybe i will try swapping the gauge from the handheld with one from the tank.
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Re: Pressure Gauge differences keg vs regulator

Postby Hunty » 29 May 2009, 13:27

Actually, to reword my question your spot on - why is there a difference between the pressure of gas coming out from the tank vs the pressure of the keg ?


i sense confusion here. as soon as you connect the regulator to the keg, you will get pressure equalisation between the regulator valve and the keg. they cannot be different otherwise you would have a dynamic situation with gas flowing one way or the other. if the gas is not flowing then by definition the pressures must be equal for all connected gas spaces that are not separated by a valve. so, if you have two different pressure guages attached to the same gas space and they read differently, then one of them must be wrong or faulty. does this make sense ?
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Re: Pressure Gauge differences keg vs regulator

Postby keat » 30 May 2009, 16:36

Hunty wrote:i sense confusion here. as soon as you connect the regulator to the keg, you will get pressure equalisation between the regulator valve and the keg. they cannot be different otherwise you would have a dynamic situation with gas flowing one way or the other. if the gas is not flowing then by definition the pressures must be equal for all connected gas spaces that are not separated by a valve. so, if you have two different pressure guages attached to the same gas space and they read differently, then one of them must be wrong or faulty. does this make sense ?


Hunty's explanation sounds more plausible than mine...mine was a wild guess :D
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