Running a centrifugal pump with the discharge valve closed is a critical scenario that can lead to damage, overheating, and energy waste. Here’s what happens and how to prevent issues:
Zero Flow Condition:
No fluid exits the pump → stagnant liquid inside casing.
Pump operates at shut-off head (max pressure on the curve).
Power consumption drops (but not zero due to recirculation).
Pressure Buildup:
Discharge pressure rises to maximum shut-off head (check pump curve).
Risk of overpressure if pipes/valves aren’t rated for shut-off head.
Heat Generation:
Energy from the motor converts to heat (no flow to cool the pump).
Liquid temperature rises → risk of vaporization, seal damage, or casing deformation.
Cavitation Risk:
If fluid heats up enough, local boiling can occur → cavitation damage.
Bearing & Seal Stress:
High radial thrust on impeller → bearing wear.
Mechanical seals may overheat and fail.
Small Pumps (≤10 kW): A few minutes (≤3–5 min).
Large Pumps (>50 kW): Never run closed-valve for more than 30 seconds.
Hot Liquids (e.g., boiler feed): Never run closed-valve (instant overheating).
Rule: Always ensure minimum flow (bypass or recirculation line) if the pump must run without discharge flow.
To prevent damage when the discharge valve is accidentally closed:
| Solution | How It Works |
|---|---|
| Automatic Bypass Valve | Opens at low flow to recirculate fluid. |
| Minimum Flow Orifice | Ensures a small continuous flow. |
| Pressure Relief Valve | Vents excess pressure to a safe location. |
| Motor Trip on High Temp | Thermal sensors shut down the pump. |
| Soft Start/VFD Control | Reduces sudden pressure surges. |
Immediately shut off the pump to avoid overheating.
Check for damage:
Inspect seals, bearings, and casing temperature.
Listen for unusual noises (cavitation, rubbing).
Restart properly:
Open discharge valve before starting.
Use a bypass if the system requires closed-valve startup.
Priming: Some pumps need a closed valve briefly to build suction pressure.
Testing: Engineers may test shut-off head for short durations.
Emergency: If a downstream pipe bursts, closing the valve isolates the leak.
But: Always follow manufacturer guidelines—most centrifugal pumps are not designed for prolonged closed-valve operation.
✅ Never run a centrifugal pump with a closed valve for more than 1–2 minutes (risk of severe damage).
✅ Use bypass lines, relief valves, or minimum flow systems for safety.
✅ Always open the discharge valve before starting (unless priming).
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