Differential pressure is typically measured by what arrangement?

• A. The sum of two pressures
• B. The product of two pressures
• C. The difference between two pressures
• D. The ratio of two pressures

Answer: (C)

Differential pressure is measured as the difference between two pressures taken at two points in the fluid path. Typically, two pressure taps are placed (one upstream and one downstream of the element whose flow or restriction you’re monitoring) and feed a differential pressure sensor or manometer. The sensor outputs the value of P_upstream minus P_downstream, giving a pressure drop that reflects how much the flow is being impeded. This arrangement makes sense because the pressure drop across a component is what changes with flow and obstruction, and it provides a direct, meaningful quantity in units of pressure. Using a sum would not represent the drop across the element, and a ratio would be a dimensionless quantity that doesn’t directly convey the drop or the flow condition.