Cavitation in pumps
Cavitation is a critical phenomenon in fluid dynamics that can significantly affect the performance and longevity
of pumps. It occurs when the pressure within a liquid drops below its vapor pressure, leading to the formation of
vapor bubbles. As these bubbles collapse, they generate intense shockwaves that can cause severe damage to
the pump’s components, including the impeller and casing.
Understanding cavitation is essential for maintaining pump efficiency, preventing costly damage, and optimizing
operational conditions.
Cause of Cavitation
Cavitation in pumps occurs when the pressure at the pump's inlet drops below the liquid's vapor pressure, causing
vapor bubbles to form. This typically happens near the impeller, where fluid velocity increases, leading to a pressure
drop. These vapor bubbles travel into higher-pressure regions inside the pump and collapse violently, releasing
shockwaves. This bubble collapse can damage pump components, causing pitting, erosion, vibration, and noise.
Cavitation also disrupts fluid flow, reducing pump efficiency and performance. Over time, it can lead to premature
wear and even pump failure if not addressed properly.
Types Of Cavitation
1) Suction Cavitation :
Suction cavitation occurs when the pressure at the pump's inlet
(suction side) drops below the vapor pressure of the liquid, causing
the liquid to vaporize and form bubbles.
These vapor bubbles collapse violently as they enter regions of higher
pressure within the pump, leading to damaging shockwaves.
2) Discharge Cavitation :
Discharge cavitation occurs when the pressure on the discharge side of
the pump is too high, which causes the fluid to remain at higher pressure
in the pump. This high pressure prevents the fluid from flowing out
properly, leading to the formation of vapor bubbles.
These bubbles collapse when they move to regions of higher pressure,
causing destructive forces inside the pump.
Preventions
1) Proper Pump Selection :
• Ensure the pump is correctly sized for the application.
• Match the pump’s operating conditions (flow rate, pressure) to its design specifications
• Avoid operating the pump far from its Best Efficiency Point (BEP)
2) Maintain Sufficient Net Positive Suction Head (NPSH) :
• Elevate the suction tank.
• Reduce suction pipe length and minimize friction losses.
• Select pumps with lower NPSH values, especially for high suction lift conditions
3) Avoid Excessive Pump Speed :
• High rotational speeds increase the risk of cavitation.
• Operate pumps at recommended speeds to reduce pressure drops and turbulence in the suction line
4) Regular Maintenance and Monitoring :
• Check and clean filters, suction lines, and pump components regularly.
• Monitor pump performance to detect early signs of cavitation (noise, vibrations, drop in performance).
