How do we prevent cavitation in PUMPS?

Pump cavitation

1. Vaporization cavitation, To prevent this type of cavitation, the NPSHa in the system must be higher than the NPSHr of the pump.
2. Internal re-circulation cavitation, you need to open the restricted discharge valve on the pump...
3. Vane passing syndrome cavitation, To prevent damage due to such cavitation, free space between the impeller blade tips and the cutwater should be at least4% of the impeller diameter.
4. Air aspiration cavitation, Tighten all joints such as flanges....
5. Turbulence cavitation.Design the pump suction piping and routig to avoid excess turbulence.

Prevention or Action measures to be taken

The dynamic process formation of bubbles inside the liquid, their growth and subsequent collapse is called cavitation. 

The pump always need to have a sufficient amount of suction head present to prevent vaporization at lowest pressure point in the pump. So NPSH is important.

NPSH (Net positive suction head) is the total head at suction flange of the pump less than the vapor pressure converted to fluid column height of the liquid.

Cavitation can be avoided by increasing the NPSHa (Net positive suction head) available greater than the NPSH required.

NPSH available= Pressure head in suction reservoir + Static suction head + velocity Head at pump suction flange - friction head in suction line - vapor pressure of liquid at that temperature.

So as you see in the equation to increase the NPSHa you will have to

1. Increase the height of the tank
2. Pressurize the tank
3. Increase flow of the liquid
4. Reduce friction by increasing the diameter of the pipe
5. Reduce temperature of liquid to decrease the vapor pressure

1-MAKE SURE THAT THE PUMP WORK IN ITS WORKING RANGE

• 2-  MAKE SURE THAT THE IMPELLER  IS SUBMERGED WITH WATER 

1. NPSH Available should be greater than NPSH Required means available suction head must be greater than required suction head.

2. Proper priming of the pump should be done so that no air is left inside the casing.

3.  Discharge of pump should be uninterrupted to prevent recirculation inside casing.

Pump cavitation is the formation of bubbles or cavities in the liquid, developed in areas of relatively low pressure around the eye of an impeller. As the bubbles/cavities travel to the discharge side of the pump, moving to a high pressure area, the cavities implode. The imploding or collapsing of these bubbles triggers intense shockwaves inside the pump, causing damage to the impeller, vibration, and excess noise. 

1. Internal re-circulation cavitation, you need to open the restricted discharge valve on the pump...

1. Lower the temperature.
2. Raise the liquid level in the suction vessel.
3. Change the pump.
4. Reduce motor RPM if possible.
5. Increase the diameter of the eye of the impeller.
6. Use an impeller inducer.
7. Use two lower capacity pumps in parallel.
8. Use a booster pump to feed the principal pump.
9. You need to open the restricted discharge valve on the pump.
10. The problem could be a clogged downstream filter.
11. A closed discharge valve.
12. An over-pressurized header.
13. Check valve installed backwards
14. Operating the pump at or close to shut-off head.
15. Tighten all flange faces and gaskets.
16. Tighten all pump packing rings and all valve stem packing on suction piping.
17. Keep the velocity of the fluid in the suction piping at less than 8 ft per second. It may be necessary to increase the diameter of the pipe.
18. Consider using dual mechanical seals with a forced circulation barrier fluid.
19. Design the pump suction piping and routig to avoid excess turbulence
20. Take precaution while fixing the pump suction line size to avoid turbulence and have sufficient NPSHa
21. Respect the maximum allowable flow limit of the pumps.

base should be good bearings  must be in good condition 

A. NPSHa in the system (the available energy in the system), must be higher than the NPSHr of the pump (the pump’s minimum energy requirement).

B. If Caviation Due To Internal Circulation.

This condition cannot be corrected on pumps with an enclosed impeller.

1. You need to open the restricted discharge valve on the pump.
2. The problem could be a clogged downstream filter.
3. A closed discharge valve.
4. An over-pressurized header.
5. Check valve installed backwards
6. Operating the pump at or close to shut-off head                                                                                                        C.Cavitation Due To Vane Passing Syndrome -To prevent damage due to such cavitation, free space between the impeller blade tips and the cutwater should be at least 4% of the impeller diameter. For example, for a 10” impeller, the free space should be 4% of the impeller diameter between the blade tips and the cutwater. 10” x 0.04 = 0.4”.                                                                                                                                                                            D.Cavitation Due To Air Aspiration-Tighten all flange faces and gaskets,Tighten all pump packing rings and all valve stem packing on suction piping,Keep the velocity of the fluid in the suction piping at less than 8 ft per second. It may be necessary to increase the diameter of the pipe,Consider using dual mechanical seals with a forced circulation barrier fluid.                                                                                                                                                                    E. Cavitation Due To Turbulances -Take precaution while fixing the pump suction line size to avoid turbulence and have sufficient NPSHa,Respect the maximum allowable flow limit of the pumps.

by eliminating any loses or obstruction could be exist in the suction line

1.REDUCING MOTOR SPEED

2.INSTALL AN IMPELLER INDUCER

3.INCORPORATE A BOOSTER PUMP INTO YOUR PUMP SYSTEM

4.REDUCE THE TEMPERATURE OF THE PUMP