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The sketch shows a gage connected to a tank. The gage has "vacuum" written on its face and its reading (GR) is 5.8 psi. Also attached to the tank is a manometer containing oil with a specific gravity (S.G.) of 0.9. The ambient pressure is known to be 14.5 psi. The schematic also shows a mercury barometer and a water barometer beside the tank.
Being a little careful, note that the ambient pressure of air is said to be 14.5 psi. Low atmospheric pressures generally mean inclement weather, storms and such, that is the surrounding condition of the tank and the devices.
What is the pressure of the air in the tank.
♦ The ambient pressure is 14.5 psi. We assume the gage attached to the tank was "properly" installed. The notation on the gage, "vacuum," means the pressure inside the tank is less that that outside. Consequently:
Does the barometer indicate that atmospheric pressure is 14.5 psi?
♦ The pressure of the mercury vapor above the column of liquid mercury is (~ 16Pa) very small.
Does the column of oil with SG = 0.9 indicate that the pressure in the tank is 8.7 psi?
♦ We start at