Hydrostatics: Pressure & Manometry

Hydrostatics deals with fluids at rest. The primary variable of interest is pressure.

Variation of Pressure with Depth

Pressure increases linearly with depth in a static incompressible fluid.

$P = P_{atm} + \gamma h$

• $P$ = Absolute Pressure
• $P_{gage} = \gamma h$ = Gage Pressure
• $\gamma$ = Specific Weight of fluid
• $h$ = Depth below free surface

Pressure Head ($h$): $h = \frac{P}{\gamma}$

Manometry

Manometers use columns of fluids to measure pressure differences. The fundamental equation for manometry is:

$P_A + \sum \gamma_{down} h_{down} - \sum \gamma_{up} h_{up} = P_B$

• Move from point A to B.
• Add pressure when moving down ($\gamma h$).
• Subtract pressure when moving up ($\gamma h$).

Solved Problems