What is the most common diameter of LDH supply line?

The most common diameter of large diameter hose (LDH) supply line is typically 4 or 5 inches. This size is widely used because it strikes a balance between flow capacity and maneuverability, making it effective for supplying large volumes of water from hydrants or other water sources to fire apparatus. The larger diameter allows for reduced friction loss, which is crucial in maintaining adequate water pressure over long distances, particularly in firefighting situations where rapid water delivery is essential.

In contrast, smaller diameters, such as 2 or 3 inches, while useful for various applications and smaller volume needs, do not provide the same flow rates or efficiency that larger lines do. Similarly, 6 inches is less common and often used in specific applications that require extremely high volumes, such as industrial firefighting or in specialized contexts, rather than standard fireground operations. Thus, 4 or 5 inches represents the standard practice in most fire service scenarios for LDH.