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. As the bubbles carry over to the discharge side of the pump, the fluid conditions change, compressing the bubble into liquid and causing it to implode against the face of the impeller.
Understanding and avoiding pump cavitation
One of the simplest ways to prevent pump cavitation is to properly operate a pump best suited for the application. In the rental industry, for example, it is common for the end user to lack a working knowledge of pump technology. Instead of running a pump at the ideal rpm for the job at hand, some well-meaning rental customers push pumps too hard to move fluid at faster rates. If a pump works well at 1,800 rpm, the belief is that it will work even better at 2,300 rpm. This is not the case because forcing a pump’s performance too far to the right or left of its BEP will result in cavitation over time. If a pump is correctly sized and not starved, the pump will run at the intended speed while maintaining the BEP.
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Water Pump Cavitation: What Cavitation In Pumps Means
That is because these are not really bubbles you see when it comes to the cavitation in pumps — they are voids. Inside these tiny voids is super-heated vapor that can erode metal and crack plastic. Cavitation in pumps is not typically the fault of the water pump itself, it is only the victim of other problems with the coolant and other components.
Pump Cavitation Damage Control Tips
To correct discharge cavitation (operating on the far left side of the curve) may require reducing the head or increasing the flow of the pump. Changing to a higher or lower speed may help in some cases, but a system head curve must be plotted to know the correct solution before corrective action is taken. The pump must be brought back inside its operating range.
Pump Impeller Cavitation: Major Causes and Prevention
These gas bubbles occupy space inside the pump and affect the pump’s operating pressure and flow. With vapor bubbles in the low-pressure zones of the pump, the motor’s energy is wasted expanding the bubbles instead of bringing more liquid into the pump. When the vapor bubbles collapse inside the pump, the liquid strikes the metal parts at the speed of sound. The noise generated from these collisions of gas bubbles into the metal parts of the pump, it sounds like attempting to pump marbles and stones.
How to prevent pump cavitation?
It’s called “classic Cavitation”. According to Bernoulli’s Law, when velocity goes up, pressure goes down. Centrifugal pump works by acceleration and imparting velocity to the liquid in the eye of the impeller. Under the right conditions, the liquid can boil or vaporize in the eye of the impeller. When this happens we say that the pump is suffering from vaporization cavitation. This type of cavitation is also called inadequate NPSHa cavitation. To prevent this type of cavitation, the 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).