Abstract: A device for monitoring the leakage of cooling gas into the stator water cooling system is disclosed. The vent from the water cooling reservoir tank is connected to the inlet of a U-shaped passageway and the outlet of the passageway is connected to an atmospheric vent. A liquid is provided in the passageway so as to prevent the passage of cooling gas from the inlet to the outlet without a desired pressure differential. At the specified pressure differential however, gas bubbles from one side of the passageway to the other and is trapped by a measuring cup in one position. When a sufficient quantity of gas is passed under the cup, the buoyancy of the cup becomes positive allowing it to rise to a second position where at least a portion of the gas is discharged. Because the amount of gas discharged can be determined and a number of cycles of operation of the cup can be measured, the flowrate can be precisely measured.