Transfering specific volume from one vessel to another

[peterdan]

Hi,
I sometime need to transfer partially finished or finished beer from a large pressurized fermenter to another and I have trouble knowing exactly how much I transfer. I’ve tried with a simple, cheap flow meter but it isn’t accurate enough. I can’t open the target vessel to see the level inside. The most accurate way I’ve found is to transfer little by little going through an intermediate vessel that I keep on a scale, but this is very time consuming.

I’m thinking that there must be possible to infer the volume transferred by measuring the pressure in the target vessel. If the target vessel is purged with CO2 and have a known total volume there should be a way of calculating the volume of remaining CO2 at a given pressure (and temperature).

It’s probably a really stupid idea but does anyone have a handle on this kind of calculation? For example what is the difference in volume of CO2 at 0 PSI vs 20 PSI ?

Peter

[dick murton]

(P1*V1) / T1 = (P2*V2) / T2

where P1 & 2 are the initial and final pressures
where V1 & 2 are the initial and final volume, and
where T1 & 2 are the initial and final temperatures expressed in degrees Kelvin, accurate enough to use degrees C + 273

If you assume the temperature of the start volume and pressure is the same as the final volume and pressure then the T1 & 2 values can be ignored, so you simply use

(P1*V1) = (P2*V2)

[peterdan]

Is it really that simple? I picked the right forum then... Will test this in practice shortly.
Many thanks.