The Entrained Gas Tester (EGT) is a 2 inch (5 cm) diameter, 1/4 inch (0.6 cm) wall, clear cast acrylic tube that has a sample volume of approximately 1 1/2 pints (700 ml). The EGT basically uses Boyles' Law for gases (P1*V1=P2*V2) to determine the amount of air in a sample. One atmosphere of pressure (about 15 psi) is applied to the sample by turning a knob on the EGT. The pressure is indicated by a trapped air bubble in the Pressure Indicator and one atmosphere is reached when the bubble is reduced in size by one half. At this time, it is compressing the volume of all of the air in the sample by one half. Since the total volume of the sample chamber is a known constant, there is just a simple percentage of air factor for each full revolution of the knob. Simply stated, after the one atmosphere pressure is applied, all one has to do is count the number of revolutions it takes to get the knob all the way back out. Then subtract a Correction Factor and multiply by the Percentage of Air Factor to get the final answer in percent air.
EGT - Tester
Entrained Gas Tester Manufactured by G.B. Machining