Pump Operation, Startup, and Shutdown

Pump Operation, Startup, and Shutdown

Why This Skill Matters

Centrifugal pumps move treated water through distribution systems and raw or treated wastewater through collection and treatment systems. An operator who starts or stops a pump incorrectly can cause water hammer, seal failure, motor burnout, or a loss of system pressure that threatens public health. Licensing exams for Class I and Class II water and wastewater operators test pump knowledge directly, and every licensed facility requires operators to follow a written Standard Operating Procedure (SOP) for pump work.

How a Centrifugal Pump Works

A centrifugal pump uses a rotating impeller to add velocity to liquid. That velocity converts to pressure as the liquid slows in the volute casing. The pump draws liquid in through the suction port and discharges it under pressure through the discharge port. Key performance points are:

• Flow rate – how many gallons per minute (gpm) the pump delivers
• Total Dynamic Head (TDH) – the total pressure the pump works against, measured in feet of head or pounds per square inch (psi)
• Efficiency – the ratio of hydraulic power output to motor power input
• Best Efficiency Point (BEP) – the design flow at which the pump operates most efficiently and with the least mechanical stress

Operating far from the BEP increases vibration, heat, and wear.

Safety First

Before touching any pump or motor, identify all energy sources and apply your facility's lockout/tagout (LOTO) program whenever you are performing maintenance. For this lab, the instructor controls energy isolation. During operation:

• Wear safety glasses at all times in the pump room.
• Wear hearing protection when noise levels are elevated; rotating equipment can exceed safe exposure limits.
• Keep hands and clothing away from rotating shafts and coupling guards. Never remove a coupling guard while the pump is running.
• Be aware of slipping hazards from water on the floor.
• Know the location of the emergency stop before startup.

Pre-Operation Walkthrough

A written pre-start checklist prevents the most common startup mistakes. Complete every item before requesting instructor authorization:

1. Packing or mechanical seal – Inspect for leaks or damage. A small controlled drip from packing glands is normal; mechanical seals should show no visible leakage.

2. Lubrication – Check oil level or grease fittings per the manufacturer's specification.

3. Suction valve – Confirm it is fully open. Starting with a closed suction valve causes cavitation or no flow.

4. Discharge valve position – For most centrifugal pumps, start with the discharge valve partially closed to reduce startup load on the motor, then open slowly after startup. Follow your SOP; some systems differ.

5. Coupling guard – Verify the guard is in place and secured.

6. Prime – Confirm the pump casing and suction line are filled with liquid. A centrifugal pump cannot self-prime in most configurations; running dry damages the seal and impeller rapidly.

Supervised Startup Sequence

1. Confirm pre-start checklist is signed off.

2. Start the motor. Listen for abnormal noise immediately.

3. Slowly open the discharge valve while watching the discharge pressure gauge rise steadily.

4. Check suction pressure gauge. Suction pressure should remain positive (above atmospheric) or within the expected range for your system.

5. Check for unusual vibration by touch or with a vibration tester.

6. Measure motor amperage with a clamp meter on one phase lead. Compare to the nameplate full-load amperage (FLA).

7. Record all readings on your operations log at 0 minutes (just after valve is open), 5 minutes, and 15 minutes.

Data fields to record each interval: time, suction pressure (psi), discharge pressure (psi), flow rate (gpm), motor amperage (A), and vibration level or observation.

Reading the Pump Curve

The pump curve is a graph published by the manufacturer. The x-axis shows flow (gpm) and the y-axis shows head (feet or psi). As flow increases, head decreases along the curve. A separate efficiency curve peaks at the BEP. When you compare your recorded data to the pump curve:

• Plot your measured flow and calculated head on the curve.
• If your point falls far to the left (low flow, high head), the discharge valve may be too closed or there is a blockage.
• If your point falls far to the right (high flow, low head), the system resistance is lower than expected, and the motor may be overloaded.

Controlled Shutdown Sequence

1. Slowly close the discharge valve before stopping the motor to prevent water hammer in most centrifugal pump installations.

2. Stop the motor.

3. Close the suction isolation valve if required by the SOP.

4. Record final readings.

5. Inspect the pump for any leaks or unusual conditions before leaving the area.

Post-Run Log Review

After shutdown, compare each recorded parameter to the nameplate ratings and pump curve. For any reading outside the acceptable range, write a brief corrective note explaining the likely cause and recommended action. This habit is required practice for licensed operators and reflects what exam questions call "troubleshooting" or "operational analysis."

Connecting to the License Exam

State Class I and Class II operator exams include questions on pump operation, reading gauges, interpreting pump curves, identifying cavitation, and calculating flow and pressure. Accurate log-keeping also demonstrates the professional standard regulators expect from licensed operators.