When the discharge valve of a centrifugal pump is closed while the pump is running, several critical issues arise due to the lack of fluid flow. Here’s what happens and why it’s dangerous:
The pump recirculates the same liquid inside the casing.
Since no fluid exits, useful work (flow) is zero, but the motor still consumes energy.
Energy from the motor converts into heat instead of fluid movement.
Liquid temperature rises quickly, which can:
Cause cavitation (if near boiling point).
Damage seals, O-rings, or mechanical seals (thermal shock).
Vaporize the liquid, leading to pump dry-running.
The pump generates maximum shut-off head pressure (highest pressure at zero flow).
Risks include:
Pipe or seal bursts if pressure exceeds design limits.
Gasket or flange failures in the discharge line.
High radial loads on the impeller (if running near shut-off).
Bearing & shaft damage due to vibration and heat.
Impeller & wear ring damage from recirculation erosion.
Seal Failure – Overheating destroys mechanical seals or packing.
Bearing Failure – Lack of cooling flow increases friction.
Cavitation Damage – If liquid vaporizes, bubbles collapse on impeller surfaces.
Motor Overload – Some pumps may trip on thermal overload; others may burn out.
✅ Very Short Durations (e.g., during startup or testing).
✅ If the Pump Has a Bypass or Recirculation Line (to prevent overheating).
✅ With a Pressure Relief Valve (to avoid overpressure damage).
❌ Never run a centrifugal pump against a closed valve for more than a few minutes!
✔ Install a Minimum Flow Bypass (Recirculation Line) – Diverts excess flow back to the suction tank.
✔ Use an Automatic Recirculation Valve (ARC Valve) – Opens when flow drops too low.
✔ Pressure Relief Valve – Protects against overpressure.
✔ Motor Protection (Overload Trips) – Stops the pump before overheating.
✔ Avoid Manual Valve Closure While Running – Always ensure flow path is open.
Running a centrifugal pump with a closed discharge valve leads to overheating, pressure surges, and mechanical damage. While brief operation (e.g., during startup) may be acceptable, prolonged operation must be avoided unless protective systems (bypass, relief valves) are in place.
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