# Centrifugal Pump Issue: Identification and Solution ## Step 1: Identifying the Phenomenon **Observation:** - Significant drop in discharge pressure - Unusual noise like "marbles rattling" inside the casing **Most Likely Phenomenon:** **Cavitation** **Explanation:** Cavitation occurs when the pressure at the pump inlet drops below the vapor pressure of the liquid, causing vapor bubbles to form. These bubbles collapse violently as they move to higher pressure zones, causing noise and possible damage. --- ### Graph: Pressure Profile in a Pump Showing Cavitation  *Fig: Pressure vs. Pump Location. Cavitation occurs where the pressure dips below vapor pressure.* --- ## Step 2: Causes and Prevention ### Primary Cause: NPSH - **NPSH (Net Positive Suction Head):** - **NPSHa (Available):** Pressure available at the pump suction. - **NPSHr (Required):** Minimum pressure required to avoid cavitation. - **Cavitation occurs if:** \[ \text{NPSHa} < \text{NPSHr} \] **Example:** If the NPSHa is 2 m and the NPSHr is 3 m, then \[ 2\,\text{m} < 3\,\text{m} \] Cavitation will occur. --- ### Two Ways to Prevent Cavitation 1. **Increase NPSHa (Available):** - **Example:** Raise the supply tank or reduce suction pipe losses (use shorter/wider pipes). 2. **Decrease NPSHr (Required):** - **Example:** Operate the pump at a lower speed or select a pump with a lower NPSHr requirement. --- ## Final Answer - **Phenomenon:** Cavitation - **Primary Cause:** NPSHa is less than NPSHr (insufficient inlet pressure) - **Prevention:** 1. Increase available NPSH (e.g., raise liquid level, reduce pipe losses) 2. Decrease required NPSH (e.g., lower pump speed, select a different pump)