Pumps, Motors, Valves, and Mechanical Equipment
Learn pump families: centrifugal (flow varies with head, common for water), positive displacement (fixed volume per stroke, used for chemical feed), submersible, turbine, and booster pumps. Understand the pump curve and system curve, operating point, NPSH and cavitation, affinity laws (flow ∝ speed, head ∝ speed², power ∝ speed³), efficiency, and brake horsepower. Motors: horsepower, voltage/phase, service factor, overload protection, and power factor in concept.
Valves: gate (isolation), globe (throttling), butterfly, check (prevent backflow), pressure-reducing, altitude, air release/vacuum, and blowoff. Know priming, air binding, water hammer, and surge causes and controls.
Traps: using a discharge valve to control flow on a positive displacement pump (dangerous-use a relief valve); confusing head (feet) with pressure (psi); forgetting 1 psi ≈ 2.31 ft of head; and assuming a bigger motor fixes cavitation (it does not-fix suction conditions).
Rule of thumb: pump power (hp) = (flow, gpm × head, ft) ÷ (3960 × efficiency). Worked example: 500 gpm at 100 ft with 70% efficiency = (500 × 100) ÷ (3960 × 0.70) ≈ 18 hp; select the next standard motor size with margin.