Table of Contents
Where does cavitation occur in a centrifugal pump?
In a centrifugal pump, ‘classic’ cavitation occurs at the eye of the impeller as it imparts velocity on the liquid (see Figure 1). In a positive displacement pump, it can happen in an expanding piston, plunger or suction-side chamber in a gear pump.
What is cavitation in centrifugal pumps and how can it be avoided?
1. Pump selection. The best way to prevent cavitation is to select the right pump for the application. Cavitation increases as pump head falls or as capacity increases, so selecting the correct pump to maintain a positive margin of NPSHa above NPSHr is the best first move.
What are the effects of cavitation in centrifugal pump?
Cavitation in a centrifugal pump has a significant effect on pump performance. Cavitation degrades the performance of a pump, resulting in a fluctuating flow rate and discharge pressure. Cavitation can also be destructive to pumps internal components.
How can we prevent cavitation in centrifugal pump?
Some tips to prevent cavitation due to vaporization include:
- NPSHa > NPSHr + 3 ft or more safety margin.
- Lower temperature.
- Raise liquid level in suction vessel.
- Change out pump type.
- Reduce motor RPM.
- Use impeller inducer.
- Increase diameter of the eye of impeller.
What is cavitation and what is the effect into the pumps?
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 is the cause of cavitation?
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.
What causes cavitation in centrifugal pumps?
In addition to the above, operating a centrifugal pump to the far right of the BEP (or off the end of curve) can cause cavitation. When the flow increases, Net Positive Suction Head required (NPSHr) also increases and when the NPSHr exceeds the Net Positive Suction Head available (NPSHa), cavitation occurs.
What is suction cavitation in hydraulic pumps?
Suction Cavitation. When a pump is under low pressure or high vacuum conditions, suction cavitation occurs. The pump is being “starved” or is not receiving enough flow. When this happens, bubbles or cavities will form at the eye of the impeller.
What are the effects of cavitation on an impeller?
As with suction cavitation, the implosion of those bubbles trigger intense shockwaves, causing premature wear of the impeller tips and pump housing. In extreme, discharge cavitation can cause the impeller shaft to break.
What is cavitation and how can you prevent it?
Cavitation is a common problem in pumping systems, but with proper pump sizing, pipe design, and care of filters and strainers, damage to pumps and their impellers can be largely avoided. Gorman Rupp Pumps uses a glass faced demo pump to train groups on cavitation.