Pumps, Motors, and Mechanical Equipment
What to know
Pumps move water; operators must know pump types (centrifugal, positive displacement, submersible, vertical turbine) and their best applications. Understand pump curves and system curves - the operating point is where they intersect - and how NPSH (net positive suction head) prevents cavitation, which sounds like gravel and damages impellers. Know the difference between head (energy per unit weight) and pressure, and the relationship pressure = head × 0.433 psi/ft for water. Learn affinity laws: flow varies with speed, head with speed squared, power with speed cubed. Understand motor basics - voltage, current, power factor, efficiency, overload protection, and VFDs for speed control. Know preventive maintenance: lubrication, vibration monitoring, seal and bearing inspection, alignment, and valve checks.
Traps
Questions often confuse head and pressure units, or assume a larger pump always increases flow - the system curve limits it. Another trap: cavitation blamed on discharge side when it is a suction-side NPSH problem. Watch for power calculations that ignore efficiency.
Worked example / rule of thumb
A pump delivers 100 gpm at 1200 rpm. Doubling speed to 2400 rpm gives 200 gpm (flow ×2), 4× head, and 8× power by the affinity laws. Rule of thumb: cavitation is a suction problem - check NPSH available versus required.
Study tip
Memorize the affinity law exponents (1, 2, 3) and the 0.433 conversion; both appear in calculations.