List typical sources of minor losses and give example K-values for common components.

• A. Fittings and devices such as 90° elbows, tees, gate valves, globe valves, sudden contractions/expansions; typical K-values: 90° elbow ~0.9–1.5, gate valve throttling ~2–10 depending on opening, sudden enlargement K = (1 − A1/A2)^2
• B. Only large pumps have minor losses.
• C. Friction factor alone accounts for all losses.
• D. There are no minor losses in piping.

Answer: (A)

Local losses in a pipe system come from places where the flow is disturbed by changes in area, direction, or by obstructions. These disturbances create energy losses that aren’t just the result of friction along a straight run; they are captured by a loss coefficient, K, so the head loss is h = K times (v^2/2g). The big idea is that fittings and components have their own characteristic K-values showing how much energy is lost for a given flow velocity.

Typical sources include fittings and devices that bend or split flow, such as 90° elbows and tees, valves (especially when throttled), and sudden changes in cross-sectional area like expansions and contractions. Each of these adds turbulence and separation, converting some of the flow’s kinetic energy into heat and mixing energy, which is why you see specific K-values assigned to them.

For example, a 90° elbow usually has a K-range around 0.9 to 1.5, reflecting the energy lost when the flow changes direction sharply. A gate valve that is throttled (not fully open) tends to produce more turbulence and has a larger K, typically in the range of about 2 to 10 depending on how open the valve is. For sudden area changes, the loss is given by K = (1 − A1/A2)^2, where A1 is the smaller area and A2 is the larger area, capturing the extra losses from the abrupt change in cross section.

Context helps here: major losses come from friction along straight pipe sections and are described by the Darcy-Weisbach factor, while these local or minor losses are captured separately with their K-values because they depend strongly on geometry and flow regime. That’s why it’s important to know typical sources of minor losses and their K-values for predicting overall head loss in a system.

The other statements aren’t consistent with how piping losses are treated. Minor losses aren’t limited to pumps, since pumps themselves aren’t sources of local energy dissipation in the same sense; they’re energy-adding devices, while the losses of interest are the local disturbances in the piping. Friction factor alone doesn’t account for all losses, because the friction factor describes only major, straight-pipe losses; local elements add their own losses that the K-values quantify. And minor losses do exist in piping, so they shouldn’t be ruled out.