Pressure Difference - Delta P

Delta P, also called pressure difference or differential pressure, typically refers to the drop of pressure in a piping system, heat exchanger, or other machine where liquid passes through. The delta symbol represents the mathematical difference between two values.

Delta P stands for the difference between two measured pressure values, which can be measured at different times to track trends, or at different positions in a system (such as comparing inlet versus outlet pressure). Measurement is accomplished using either an analog pressure gauge or electrical sensor connected to a central data system.

In piping systems or heat exchangers with moving fluid, pressure typically drops due to friction between the water and contacting surfaces like pipe walls. Higher pressure differences suggest increased fouling in the system. As incrustations accumulate, from limescale, suspended solids, biological growth, or other deposits, the pressure drop increases. The deposits build up in pipes and interfere with water flow, making Delta P useful for measuring flow resistance and calculating deposit amounts.

The equation for pressure difference is: Delta P = P2 - P1, where P2 is outlet pressure and P1 is inlet pressure. High deposit concentrations lead to high pressure drops because water cannot flow freely, resulting in much lower outlet pressure than inlet pressure. Performance monitoring applications use Delta P measurements, which should decrease to design levels following system treatment installations.