Cavitation Avoidance in Centrifugal Pumps — Suction Conditions To mitigate cavitation risk in a centrifugal pump, which inlet-side condition should be ensured for reliable operation at the design flow rate?

Introduction:
Cavitation occurs when local static pressure in a pump falls to or below the liquid vapor pressure, forming vapor bubbles that collapse and damage components. This item checks understanding of inlet (suction) conditions required to avoid cavitation in centrifugal pumps.

Given Data / Assumptions:

• Radial-flow centrifugal pump, steady operation.
• Liquid with known vapor pressure at operating temperature.
• Concept of Net Positive Suction Head (NPSH) is applicable.

Concept / Approach:
To avoid cavitation, the available NPSH at the pump suction must exceed the required NPSH of the pump by a safe margin. Practically, this means keeping the absolute suction pressure sufficiently high above the vapor pressure (reduce suction lift, minimize losses, lower temperature, or raise static head).

Step-by-Step Solution:
Define NPSH_available = (p_suction_absolute - p_vapor) / (rho * g) + V_suction^2 / (2 * g).For a given pump at a given flow, NPSH_required is specified by the manufacturer.Ensure NPSH_available ≥ NPSH_required + margin by raising suction head, reducing inlet losses, or lowering fluid temperature.Therefore, a “high” suction pressure (in absolute terms) is beneficial and required to suppress bubble formation.

Verification / Alternative check:
Field practices include placing pumps below supply tanks (flooded suction), using larger suction pipes, and avoiding throttling on the suction side—all aimed at maintaining higher inlet absolute pressure.

Why Other Options Are Wrong:

• High delivery pressure/low delivery pressure: Discharge-side pressure does not directly fix inlet absolute pressure.
• Low suction pressure: Increases cavitation risk by reducing NPSH_available.

Common Pitfalls:
Confusing gauge and absolute pressures; cavitation depends on absolute pressure relative to vapor pressure, not on discharge head alone.

Final Answer:
the suction pressure should be high (sufficient NPSH available)