How does hose diameter affect friction loss at a given flow rate?

• A. Smaller diameter hoses have lower friction loss
• B. Smaller diameter hoses have higher friction loss
• C. Friction loss is independent of hose diameter
• D. Larger hoses increase friction loss

Answer: (B)

Water moves through a hose, and friction loss comes from the water rubbing against the hose walls. For a fixed flow rate, a smaller inner diameter means the same amount of water must pass through a smaller space, so the velocity inside the hose increases. That higher velocity increases the shear and resistance along the inner surface, converting more energy into friction losses. So, at the same flow, a smaller diameter hose produces more friction loss than a larger diameter hose. Conversely, a larger hose lets the water flow more slowly for the same volume, reducing velocity and the friction losses. Diameter thus directly impacts friction loss: smaller diameter means higher friction loss, larger diameter means lower friction loss.