Question

Gage pressure represents the difference between the absolute pressure and the local atmospheric pressure while vacuum represents the difference between the absolute pressure and the gage pressure оо

Answer 1

Gage pressure is the measurement of pressure above atmospheric pressure. Hence, gage pressure considers the atmospheric pressure as reference pressure. The atmospheric pressure is 1 atm which in bar is 1.013 which is set to be zero for gage pressure. Below image depicts the relation between gage pressure, absolute pressure and vaccum.

Gauge pressure Vaccum pressure Local atmosphere Pressure Absolute pressure Absolute Pressure Grauge pressure - Absolute pressure- local utmospheric Pressure Vaccum pressure : utmospheric pressure - absolute pressure

The gage pressure is given by following equation

P_​g = P_{​​​​​s} - P_{​​​​​​atm}

Where, P_{​​​​​​g} = gage pressure, P_{​​​​​​s} = system pressure, and P_{​​​​​​atm} = atmospheric pressure.

Here the system pressure is absolute pressure. Hence, the first part of the statement that gage pressure is the difference between absolute pressure and local atmospheric pressure.

The gage pressure can be zero, positive or negative.

The negative gage pressure is called as Vaccum pressure. It is the difference between atmospheric pressure and absolute pressure. Anything below atmospheric pressure (1 atm) is vaccum pressure. Hence, the second part of the statement is not correct (False) as the difference between absolute pressure and gage pressure is Atmospheric pressure and not the Vaccum pressure.

Hance, the statement is False.