Can you calculate absolute pressure using U-tube manometer?

Answer 1

Calculating absolute pressure with a U-tube manometer requires filling it with a non-volatile fluid and sealing one end. The non-sealed end is exposed to whatever fluid you wish to measure the pressure of. The difference in the height of the manometer fluid between the open arm and the sealed arm is an indication of absolute pressure. At zero absolute pressure the fluid should be at the same height in both arms with vacuum above the fluid in the sealed arm. From a practical standpoint, there are no fluids that have zero vapor pressure, but fluids are available with vapor pressures low enough to be negligible compared to the limitations of the ability of the person reading the measurements to read the height of the fluid. As an example, under most operating conditions Mercury has a negligible vapor pressure. If you start getting up to high temperatures, however, all bets are off.

Answer 2

To calculate absolute pressure using a U-tube manometer, you will need to add the difference in the fluid levels in the two arms of the manometer to the atmospheric pressure. The equation would be: Absolute pressure = Atmospheric pressure + Difference in manometer fluid levels.