Pumps, Motors, and Process Equipment
What you must understand
Know the pump families: centrifugal (radial, mixed, axial flow), positive displacement (diaphragm, piston, progressing cavity), and submersible and vertical turbine pumps. Understand pump curves (head vs. flow), system curves, and the operating point where they intersect. Know NPSH and cavitation (noise, vibration, pitting, flow loss), and how suction lift and temperature cause it. Understand affinity laws: flow varies with speed, head with speed squared, power with speed cubed.
For motors, know horsepower, efficiency, power factor, service factor, and motor protection (overloads, thermal, phase loss). Understand variable frequency drives and why they save energy (power ∝ speed³). Know basic valves (gate, globe, butterfly, check, air release) and their roles, plus seals, bearings, and lubrication.
Traps
Common confusion: head (energy per weight, in feet) vs. pressure (psi); convert with psi ≈ feet × 0.433 (for water). Another trap: thinking a throttled valve reduces energy-it reduces flow but wastes energy; VFDs save energy. Watch for shutoff head vs. runout and for assuming pumps can run dry.
Rule of thumb
For water, 1 psi ≈ 2.31 ft of head. A worked check: a pump delivering 500 gpm at 100 ft head moves 500 × 8.34 ≈ 4,170 lb/min; hydraulic power ≈ (gpm × head × 8.34) ÷ 33,000 hp ≈ (500 × 100 × 8.34) ÷ 33,000 ≈ 12.6 hp; divide by efficiency (say 0.7) for brake horsepower ≈ 18 hp.