As shown in Figures 2 and 3, the tester has two axially-connected cylinders: the fixed-volume Sample Cylinder, and the variable-volume Vacuum Cylinder. The volume of the Vacuum Cylinder is controlled by the position of the Vacuum Piston. When the Vacuum Piston is fully extended, which is the position illustrated in Figure 2, the Vacuum Cylinder volume is zero. Conversely, when the Vacuum Piston is fully retracted, as shown in Figure 3, the volume of the Vacuum Cylinder is at its maximum.

Referring to Figure 2, with the Vacuum Piston fully extended and the Feed Valve and Overflow Valve opened, the liquid to be sampled flows through the Sample Cylinder. Closure of the Feed and Overflow Valves isolates a sample in the Sample Cylinder.

Referring to Figure 3, the Vacuum Piston is then retracted, thereby generating a high vacuum on the sample. The high vacuum causes the dissolved gas in the liquid to be released into the gas phase which then is dispersed as “entrained gas” in the liquid phase. The thin liquid layer with a high surface-to-volume ratio, illustrated in Figure 3, significantly increases the rate of release of dissolved gas when compared with older technology in the “piston and cylinder” class of testers. Additionally, a high-frequency low-amplitude pulsation of the Vacuum Piston further increases the release rate.

After the dissolved gas has been released, the Vacuum Piston is fractionally extended to establish a starting pressure. The Compression Piston, which has been fully contained within the Vacuum Piston, is then extended into the liquid sample in order to compress the entrained gas. The pressure change is measured with the Pressure Transducer and the volume change is determined by the distance travelled by the Compression Piston. The entrained gas content, calculated using a gas law, represents the amount of gas which was originally dissolved in the liquid.

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