Question:
If net positive suction head (NPSH) = ______ the liquid can vaporize causing pump cavitation and failure of components.
If net positive suction head (NPSH) = ______ the liquid can vaporize causing pump cavitation and failure of components.
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To prevent pump cavitation in dairy plants:
- Keep the pump inlet pressure high and fluid temperatures low.
- Ensure the available NPSH (\(\text{NPSH}_A\)) is always greater than the required NPSH (\(\text{NPSH}_R\)) by maintaining a short, straight suction line.
- Keep the pump inlet pressure high and fluid temperatures low.
- Ensure the available NPSH (\(\text{NPSH}_A\)) is always greater than the required NPSH (\(\text{NPSH}_R\)) by maintaining a short, straight suction line.
Updated On: Jul 23, 2026
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Cavitation is a fluid mechanics phenomenon that occurs inside pumps when the local static pressure of a liquid drops below its vapor pressure at the operating temperature.
This pressure drop causes the liquid to boil locally, forming vapor bubbles that subsequently collapse violently when they enter higher-pressure zones, causing severe mechanical damage.
Key Formula or Approach:
The Net Positive Suction Head Available (\(\text{NPSH}_A\)) is defined as:
\[ \text{NPSH}_A = H_s - H_{vp} \]
where \(H_s\) is the total absolute suction head at the pump impeller inlet, and \(H_{vp}\) is the vapor pressure head of the liquid.
To prevent cavitation, the available NPSH must always exceed the Net Positive Suction Head Required (\(\text{NPSH}_R\)) specified by the pump manufacturer:
\[ \text{NPSH}_A > \text{NPSH}_R \]
Step 2: Detailed Explanation:
Let us analyze what happens when the available NPSH approaches zero:
- When \(\text{NPSH} = 0\), the total absolute suction head at the pump inlet equals the vapor pressure head of the liquid (\(H_s = H_{vp}\)).
- At this point, the local pressure of the liquid drops to its boiling point at the operating temperature.
- The liquid begins to vaporize rapidly, forming vapor bubbles within the eye of the impeller.
- As these vapor bubbles travel into the higher-pressure regions of the impeller, they collapse instantly.
- The implosion of these bubbles generates localized micro-jets of liquid with extremely high velocities and pressures (up to thousands of atmospheres).
- These micro-jets strike the metal surfaces of the impeller, causing pitting, severe erosion, noise, vibration, and eventual mechanical failure of the pump.
Step 3: Final Answer:
If the net positive suction head (NPSH) drops to 0, the liquid can vaporize, causing cavitation and component failure.
Cavitation is a fluid mechanics phenomenon that occurs inside pumps when the local static pressure of a liquid drops below its vapor pressure at the operating temperature.
This pressure drop causes the liquid to boil locally, forming vapor bubbles that subsequently collapse violently when they enter higher-pressure zones, causing severe mechanical damage.
Key Formula or Approach:
The Net Positive Suction Head Available (\(\text{NPSH}_A\)) is defined as:
\[ \text{NPSH}_A = H_s - H_{vp} \]
where \(H_s\) is the total absolute suction head at the pump impeller inlet, and \(H_{vp}\) is the vapor pressure head of the liquid.
To prevent cavitation, the available NPSH must always exceed the Net Positive Suction Head Required (\(\text{NPSH}_R\)) specified by the pump manufacturer:
\[ \text{NPSH}_A > \text{NPSH}_R \]
Step 2: Detailed Explanation:
Let us analyze what happens when the available NPSH approaches zero:
- When \(\text{NPSH} = 0\), the total absolute suction head at the pump inlet equals the vapor pressure head of the liquid (\(H_s = H_{vp}\)).
- At this point, the local pressure of the liquid drops to its boiling point at the operating temperature.
- The liquid begins to vaporize rapidly, forming vapor bubbles within the eye of the impeller.
- As these vapor bubbles travel into the higher-pressure regions of the impeller, they collapse instantly.
- The implosion of these bubbles generates localized micro-jets of liquid with extremely high velocities and pressures (up to thousands of atmospheres).
- These micro-jets strike the metal surfaces of the impeller, causing pitting, severe erosion, noise, vibration, and eventual mechanical failure of the pump.
Step 3: Final Answer:
If the net positive suction head (NPSH) drops to 0, the liquid can vaporize, causing cavitation and component failure.
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