To prevent damage to centrifugal pumps caused by water hammer effects during rapid closure of outlet valves, the following specific precautions can be taken:

1. Extend Valve Closing Time

· Measure: Adjust the control program of the valve actuator (e.g., electric or pneumatic actuator) to extend the valve closing time to exceed the round-trip time of the water hammer pressure wave in the pipeline (T > 2L/a, where L = pipeline length, a = water hammer wave speed).

· Principle: Gradual valve closure reduces sudden pressure surges, avoiding direct hydraulic 冲击 (shock).

2. Use Multi-Stage Closing Valves

· Measure: Employ two-stage or three-stage closing valves (e.g., slow-closing check valves):

i. First stage: Close rapidly (e.g., 70–80% opening) to reduce flow rate.

ii. Second stage: Close slowly (remaining opening) to balance pressure gradually.

· Application: Long-distance water transmission or high-pressure pipeline systems.

3. Install Water Hammer Mitigation Devices

· Measures:

i. Accumulators/Pressure Vessels: Absorb pressure fluctuations and cushion water hammer impacts.

ii. Relief Valves: Automatically open to release pressure when exceeding set thresholds.

iii. Water Hammer Arrestors: New-type devices that absorb water hammer 冲击力 (impact force) via hydraulic principles, converting it into low-level energy.

· Selection Criteria: Match device capacity to system pressure, flow rate, and pipeline size.

4. Add Check Valves and Bypass Systems

· Measures:

i. Slow-Closing Check Valves: Delay closure to prevent instantaneous backflow.

ii. Bypass Pipelines: Divert flow through bypass during valve closure to reduce pressure peaks in the main pipeline.

5. Optimize Pipeline Design

· Measures:

i. Increase Pipe Diameter: Reduce fluid velocity to minimize conversion of kinetic energy to pressure energy.

ii. Avoid Sharp Bends/Steep Slopes: Reduce sudden changes in local resistance.

iii. Strengthen Pipeline: Use higher-pressure-resistant materials for high-pressure sections.

6. Control Systems and Monitoring

· Measures:

i. PLC Control: Program linear or curved valve closure, 联动 (interlock) with pump shutdown.

ii. Pressure Sensors: Real-time monitoring of pressure fluctuations to trigger protective actions (e.g., emergency relief valve activation).

7. Pump Start-Stop Protection

· Measures:

i. Soft Start/VFD Control: Gradually adjust pump speed to avoid sudden flow changes.

ii. Shutdown Sequence: Reduce speed slowly before closing the valve (especially for long pipelines).

8. Hydraulic Analysis and Simulation

· Measure: Use software (e.g., HAMMER, AFT Impulse) to simulate water hammer scenarios and optimize valve characteristics and system design.

9. Example Combinations

· Long Pipeline Systems: Slow-closing check valve + water hammer arrestor + extended closing time (PLC control).

· High-Pressure Systems: Relief valve + accumulator + two-stage valve closure.

By implementing these measures, the risk of water hammer-induced damage to centrifugal pumps can be significantly mitigated, ensuring safe and stable system operation.