What happens to the residual pressure when there is a high flow demand from a supply line?

When there is a high flow demand from a supply line, the residual pressure decreases. This occurs because as water is drawn from the system at a higher rate, the available pressure in the supply system becomes lower due to the increased flow rate.

Residual pressure refers to the pressure available in the system after accounting for the water flow; when the demand increases significantly, the pressure drop results from factors such as friction loss in the pipes and fittings, as well as the volume of water being used at any given moment. As more water is extracted, particularly in firefighting scenarios where significant amounts are needed quickly, the flow restricts the ability of the supply system to maintain pressure levels, thus leading to a decrease.

Understanding this principle is crucial for fire officers because it influences how they manage water supply during operations and ensures that adequate pressure is available for effective firefighting.