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Pump Cavitation And Prevention.

Pump Cavitation And Prevention.

 

Preventing cavitation of a pump is a significant operation for the smooth and efficient operation of a pump. Failure to prevent sin cavitation can result in complete damage to the pump impeller or pump. Which prevents any process from running smoothly. The term pump cavitation refers to conditions within the pump that where the actual suction pressure drop below the vapor pressure of the liquids, at the corresponding temperature. Abnormal sound, vibration occur in the pump during cavitation, and delivery pressure and flow rate decrease.

 

# The suction pressure drop May be produced by one of the following reasons:

  • An increase in the static lift of the centrifugal pump.

  • A decrease in the atmospheric pressure with a rise in the altitude.

  • A decrease in the absolute pressure in the system.

  • As in the case of pumping from closed vessels.

  • An increase in the temperature of the pumping liquid and

  • Increase in velocity by speeding up the pump.

  • The Net Positive Suction Head or NPSH is less than the liquid vapor pressure.

  • Over speed of the driver.

  • Section pipe not sufficiently submerged.

  • Pump fluid passage has obstructed.

  • Excess air and gases in the fluid.

  • Please also check the article: Centrifugal Pump & Troubleshooting.

 

# Pump Cavitation may affect in operation as:

  • Create noise and vibration.

  • The impeller can be damaged by vane pitting, corrosion, erosion fatigue failure of metals.

  • Drop-in head vs capacity and efficiency curves.

  • Batch processes or continuous processes may be discontinued.

  • Organizations can face huge losses.

 

# Prevention of centrifugal pump cavitation:

  • In this case, adjust the Suction lift.

  • In this case, the line from the suction to the pump should be filled with liquid to expel the air and the casing vent of the pump should be opened and purged until the air is free.

  • Consult with the manufacturer.

  • In case, the suction pipe or flange leaks, then rectify the leak.

  • You need to check if the discharge of the pump is open enough.

  • Increase the diameter of the suction pipe.

  • Reduce the length of the suction pipe.

  • Install a suction stabilizer.

  • Sub-cool the liquid to decrease the suction temperature.

  • Please also check the article: Centrifugal Pump & Troubleshooting.

 

# NPSH:

To avoid Pump cavitation, the pleasure at the Pump Inlet must exceed the vapor pressure (Pv) of the liquid, at the corresponding temperature by a certain value, the called net positive suction head or NPSH.

The net positive suction head or NPSH is the total suction head less than the vapor pressure (Pv) of the liquid, expressed in feet (Meters).

 

The NPSH can be shown by the following equation and figure:

NPSH ≥ ( Hts - Pv)

Where;   Hts= ( Patm  +  Pgs  +  Hvs  -  Hfs ± Z )

Hts = Total suction head, 

Patm = Atmospheric pressure,

Pgs = Gage   pressure,

Hvs = Suction velocity head,

Hfs = Suction line friction loss,

 Z = Suction elevation head,

Pv = Vapor pressure of the liquid at corresponding Temperature,

 

# Increase the NPSH the following attempt can be taken;

  • Increase the diameter of the suction pipe.

  • Reduce the length of the suction pipe.

  • Install a suction stabilizer.

  • Elevate the suction liquid level.

  • Sub-cool the liquid.

 

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