Equipment, Maintenance, Pumps and Safety
What you must know
Pumps: centrifugal, positive displacement, submersible, vertical turbine and airlift; pump curve versus system curve and the operating point; best efficiency point; cavitation and NPSH margin; affinity laws; valves (gate, globe, butterfly, plug, check, altitude, pressure-reducing, air and vacuum relief); motors, VFDs, shaft alignment, bearings, seals, packing and lubrication; blowers, compressors, chemical metering pumps and their calibration.
Maintenance: preventive versus predictive versus reactive, work orders and a CMMS, vibration analysis, thermography, oil analysis, and critical spare parts.
Safety: confined space entry (atmospheric testing, ventilation, attendant, retrieval, permit), lockout/tagout, PPE, trenching and shoring, chlorine and ammonia hazards, electrical and arc-flash, HazCom and SDS, hearing protection, and calling 811 before digging.
Traps
- Treating power in the affinity laws as linear - it follows the cube of speed.
- Thinking a check valve isolates a line, or that a pressure-reducing valve prevents backflow.
- Attempting an unplanned confined-space rescue; most confined-space fatalities are would-be rescuers.
Worked example - affinity laws
A pump delivers 500 gpm at 1,750 rpm. Reduce speed to 1,450 rpm: ratio = 0.829. Flow becomes 500 x 0.829, about 414 gpm; head becomes 0.829 squared, about 69 percent; power becomes 0.829 cubed, about 57 percent. Common entry limits are oxygen 19.5 to 23.5 percent, flammable gas below 10 percent LEL, and hydrogen sulfide around 10 ppm - always follow your permit and meter.