Piping, Valves, and Fluid Handling
Core concepts
This domain covers pipe sizing, pressure drop, fittings, supports, expansion, and valve selection. Understand the Darcy-Weisbach and Hazen-Williams approaches conceptually, and how velocity, diameter, and friction factor affect pressure loss. Know valve types: gate, globe, ball, butterfly, plug, check, and control valves, plus their flow characteristics and where each is used. Study valve actuators, positioners, and the meaning of Cv. Piping topics include thermal expansion, hangers and anchors, water hammer, air binding, and code-required testing and identification.
Traps to watch
Questions often confuse a gate valve, intended for isolation, with a globe valve, intended for throttling. Check valves prevent backflow but are not isolation devices. A common trap is selecting a valve by size alone without considering Cv or cavitation limits. Water hammer questions may hide the cause as rapid valve closure rather than pump failure. Watch for items on expansion loops versus slip joints and which requires maintenance.
Worked example
To estimate pressure drop, use the Darcy-Weisbach relation: ΔP = f (L/D)(ρv²/2). If velocity doubles in a fixed pipe, friction loss roughly quadruples because loss rises with velocity squared. Rule of thumb: keep liquid line velocities around 1–3 m/s to limit erosion and noise, and size control valves so normal flow occurs at 60–80 percent of travel for good controllability.