Question

Consider the following statements:
Cavitation generally results from a combination of several influences

Which of these statements are correct?

• A. 1, 2 and 3
• B. 1 and 2 only
• C. 2 and 3 only
• D. 3 and 4

Answer 1

The correct option is B 1 and 2 only

When the pressure in any part of the flow passage reaches the vapour pressure (limiting value) of the flowing liquid, its starts vapourizing and small bubbles of vapour form in large numbers. The bubbles when reach to the high pressure zones, suddenly collapse as the vapour condenses to liquid again. Due to sudden collapsing of the bubbles or cavities the surrounding liquid rushes in to fill them. The liquid moving from all directions collides at the centre of the cavity, thus giving rise to very high local pressures. Any solid surface in the vicinity is also subjected to these intense pressures. The alternate formation and collapse of vapour bubbles may cause severe damage to the surface which ultimately fails by fatigue and the surface becomes badly scoured and pitted. This phenomenon is known as cavitation which if found to occur in turbines and pumps as well as in various hydraulic structures such as penstocks, gates valves, spillways etc. Since the total energy remains constant in the system thus if the pressure is reduced to limiting value, the velocity or elevation might have been increased and vice-versa.