Look for different pump or impeller options that require less NPSH. It is not uncommon for a manufacturer to have different impellers for the same pump with different NPSH requirements. Some manufacturers will offer an inducer that works in conjunction with the impeller to reduce the NPSHr.

CHANGES THAT AFFECT NPSH Source Liquid Level – Changes in the liquid level feeding to the pump will affect NPSH. A raised liquid level in the tank will increase NPSHA, while a lower than expected liquid level will cause NPSHA issues.

The NPSHr can be reduced through the following methods:

1. Throttle the pump discharge using a throttling valve or a restriction orifice. This will increase the pump head by reducing the flow rate and operate the pump in a lower NPSHr region.
2. Use an oversized pump.
3. Use an impeller with a larger diameter eye.

Some tips to prevent cavitation due to vaporization include:

1. NPSHa > NPSHr + 3 ft or more safety margin.
2. Lower temperature.
3. Raise liquid level in suction vessel.
4. Change out pump type.
5. Reduce motor RPM.
6. Use impeller inducer.
7. Increase diameter of the eye of impeller.

NPSHa is a value that expresses the absolute pressure acting on a liquid as it enters the pump. NPSHr is a value that expresses the minimum absolute pressure that must be acting on a liquid as it enters the pump impeller to avoid excessive cavitation and degradation of pump performance.

When the pump is running, the reading from this gauge will be equal to your NPSHA, less vapor pressure. If after subtracting vapor pressure this value is less than the pump’s NPSHR, you have confirmed that this is a cavitation problem.

The net positive suction head is the most critical factor in a pumping system. A sufficient NPSH is essential, whether working with centrifugal, rotary, or reciprocating pumps. Marginal or inadequate NPSH will cause cavitation, which is the formation and rapid collapse of vapor bubbles in a fluid system.

3. When the casing in a centrifugal pump decelerates the flow, what increases? Explanation: When the casing in a centrifugal pump decelerates the flow, pressure in the turbine increases. The diffuser helps this happen.

How to Prevent Cavitation

1. Reduce motor speed (RPMs).
2. Install an impeller inducer.
3. Incorporate a booster pump into your pump system.
4. If possible, reduce the temperature of your pump, liquid, and/or other components.
5. Increase liquid level around the suction area.

Cavitation causes pump performance deterioration, mechanical damage, noise and vibration which can ultimately lead to pump failure. Vibration is a common symptom of cavitation, and many times the first sign of an issue. Vibration causes problems for many pump components, including the shaft, bearings and seals.

Cavitation happens when bubbles, or voids, form within a fluid because the pressure quickly drops below the vapor pressure. When the bubbles experience higher pressures they collapse, creating small shockwaves that, over time, damage parts. When these pressure waves punch tiny holes into parts, it’s called pitting.

Simply defined, cavitation is the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller. The imploding or collapsing of these bubbles trigger intense shockwaves inside the pump, causing significant damage to the impeller and/or the pump housing.

What are the symptoms of cavitation? The obvious symptoms of cavitation are noise and vibration. When bubbles of vapour implode they can make a series of bubbling, crackling, sounds as if gravel is rattling around the pump housing or pipework.

approximately 9 MPa

The effects of cavitation are hydraulic (low efficiency due to flow instability) and mechanical (surface damage, noise and vibration). In addition, it may also lead to surface erosion[3]. It is difficult to avoid cavitation in hydro turbines which cannot be avoided completely but can be reduced.

Cavitation bubbles grow from smaller bubbles containing dissolved gas and vaporized water that are expelled from crevices on the surface of suspended solid particles (such solid heterogeneities are always present in a liquid).

Positive displacement pumps can cavitate…but because of the difference in operation between positive displacement pumps and centrifugal pumps, they don’t normally see as great a reduction in fluid pressure while drawings fluid into the pump, and so are less likely to have the fluid pressure drop below the vapor …

Cavitation occurs when the fluid pressure in the flow drops to the equilibrium vapor pressure at the prevailing temperature. The equilibrium vapor pressure increases with temperature. So, with increasing temperature, cavitation occurs at a higher pressure. So high temperature facilitates cavitation.

No. Temperature of fluid will not increase due to pumping. Because pump will not squeeze the liquid. Pump imparts some energy to liquid so it can be lifted to higher level.

As temperature increases, so does the vapor pressure, but not at the same rate. As you work your way up from 32°F (just above freezing at sea level), the vapor pressure rises very slowly. However, as you approach and surpass temperatures of 100°F, the vapor pressure begins to exponentially increase.

The effect of water temperature on performance and cavitation inception of a centrifugal pump has been studied experimentally. The results showed that the pump head and pump efficiency increase with the decrease of water temperature. The results showed that increasing water temperature speeds up cavitation.