sir, how about cavitation in pumps??in centrifugal pumps?

Answer 1

Cavitation is a general term used to describe the behavior of voids or bubbles in a liquid. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation and non-inertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Such cavitation often occurs in pumps, propellers, impellers, and in the vascular tissues of plants. Non-inertial cavitation is the process where a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths, and will also be observed in pumps, propellers etc.

Major places where cavitation occurs are in pumps, on propellers, or at restrictions in a flowing liquid.

As an impeller's (in a pump), or propeller's (as in the case of a ship or submarine) blades move through a fluid, low pressure areas are formed as the fluid accelerates around and moves past the blades. The faster the blades move, the lower the pressure around it can become. As it reaches vapor pressure, the fluid vaporizes and forms small bubbles of gas. This is cavitation. When the bubbles collapse later, they typically cause very strong local shockwaves in the fluid, which may be audible and may even damage the blades.

Cavitation in pumps may occur in two different forms:


Suction cavitation
Suction cavitation occurs when the pump suction is under a low pressure/high vacuum condition where the liquid turns into a vapor at the eye of the pump impeller. This vapor is carried over to the discharge side of the pump where it no longer sees vacuum and is compressed back into a liquid by the discharge pressure. This imploding action occurs violently and attacks the face of the impeller. An impeller that has been operating under a suction cavitation condition has large chunks of material removed from its face causing premature failure of the pump.


Discharge cavitation
Discharge cavitation occurs when the pump discharge pressure is extremely high, normally occurring in a pump that is running at less than 10% of its best efficiency point. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to flow out the discharge. As the liquid flows around the impeller it must pass through the small clearance between the impeller and the pump cutwater at extremely high velocity. This velocity causes a vacuum to develop at the cutwater (similar to what occurs in a venturi) which turns the liquid into a vapor. A pump that has been operating under these conditions shows premature wear of the impeller vane tips and the pump cutwater. In addition, due to the high pressure conditions, premature failure of the pump's mechanical seal and bearings can be expected. Under extreme conditions, this can break the impeller shaft.

Discharge cavitation is believed to be the cause of the cracking of joints.Serious damages are caused by cavitation.

Answer 2

First of all, cavitation is the formation of cold steam, caused by reducing the pressure on the supply side of the pump. You probably know water boils at a lower temperature at high altitudes. This is because the air pressure is lower than at sea level. Extend this thinking to water in a pump at low pressure and you get the idea. The vanes of a centrifugal pump move rapidly through the water, causing localized areas of very low pressure. This creates the cold steam bubbles. The bubbles collapse when they move to an area of higher pressure. The generation and collapse of these bubbles is what erodes the impellers.

Cavitation in pipes is likely to occur at valves, tees and elbows.

Answer 3

Regardless of whether you have a pump, a valve, a widget, cavitation is cavitation. Basically, it's when air bubbles get into the fluid you are pumping and then implode upon themselves as the pressure increases. These implosions have an enormous amount of energy, and when multiplied by the amount of bubbles present, add up to a very destructive force. Basically, if you are trying to pump more fluid that what you have available, then you have regions of low pressure, flashing occurs causing bubbles to form, and if the pressure increases downstream or in the pump, the bubbles will implode, or "cavitate".

Answer 4

Ma'am, cavitation occurs when the acceleration induced by the pump on the water causes the pressure to drop so low that the water boils. This happened at my mother's house, where the pipe feeding into the hot water circulation system was undersized, and that caused cavitation which eroded the copper pipe and flooded her entire basement. Youch!