1. Overview of the Incident

A 25 MW unit’s circulating cooling system uses two  பிளவு உறை குழாய்கள். Each pump's nameplate data:

Flow (Q): 3,240 m³/h

Design head (H): 32 m

Speed (n): 960 rpm

Power (Pa): 317.5 kW

NPSH required (Hs): 2.9 m (≈ 7.4 m NPSHr)

Within just two months, one pump impeller became perforated due to cavitation erosion.

2. Field Investigation & Diagnostics

Pressure readout on discharge gauge: ~0.1 MPa (versus expected ~0.3 MPa for 32 m head)

Symptoms observed: violent needle fluctuations and cavitation “popping” sounds

Analysis: The pump was operating far to the right of its Best Efficiency Point (BEP), delivering only ~10 m head rather than 32 m.

3. On-site Testing & Root Cause Confirmation

Operators slowly throttled the pump discharge valve:

Discharge pressure increased from 0.1 MPa to 0.28 MPa.

Cavitation noise ceased.

Condenser vacuum improved (650 → 700 mmHg).

Temperature differential across the condenser dropped from ~33 °C to <11 °C, confirming restored flow rate.

Conclusion: Cavitation was caused by consistent low-head/low-flow operation, not by air leaks or mechanical failure.

4. Why Closing the Valve Works

Throttling the discharge increases overall system resistance, shifting the pump’s operational point left toward its BEP—restoring sufficient head and flow. However:

Valve must remain only ~10% open—poses wear and inefficiency.

Running continuously under these throttled conditions is uneconomical and could cause valve damage.

5. Management Strategy & Solution

Given the original pump specs (32 m head) and actual need (~12 m), trimming the impeller wasn’t viable. The recommended solution:

Reduce motor speed: from 960 rpm → 740 rpm.

Redesign impeller geometry for optimal performance at lower speed.

Result: Cavitation eliminated and energy use significantly reduced—confirmed in follow-up testing.

6. கற்றுக்கொண்ட பாடங்கள்

Always size பிளவு உறை pumps near their BEP to avoid cavitation damage

Monitor NPSH—NPSHa must exceed NPSHr; throttle control is a band-aid, not a fix

Main remedies:

Adjust impeller size or rotational speed (e.g., VFD, belt drive),

Re-pipe system to boost discharge head,

Ensure valves are sized correctly and avoid running pumps permanently throttled

Implement performance monitoring to detect low-head, low-flow operation early.

7. தீர்மானம்

This case highlights the necessity of aligning pump operation with its design specifications. A split casing pump forced to operate far off its BEP will cavitate—even if valves or seals appear fine. Correctives like speed reduction and impeller redesign not only cure cavitation but improve overall energy efficiency.