Your country is not included? Please visit our global website Language How To Detect and Prevent Liquid Pump Cavitation? Almost all liquid systems can be affected by cavitation. It is therefore important to understand the causes and formation of cavitation and to know how to prevent it. Pump cavitation occurs in a pump or system when there are localized low pressure regions in the liquid, causing vapor bubbles to form and implode. This causes erosion, vibration, and noise and can lead to significant damage to the pump, other parts of the fluidic, and the pumped medium. This affects all positive displacement pumps, including diaphragm, reciprocating, and gear pumps. Cavitation can be successfully prevented by using an optimized pump solution with integrated pulsation dampers in and and by taking appropriate measures to optimize the fluidic system as a whole. What Is Cavitation and What Causes It? If the pressure in any region of the system falls below the vapor pressure of the liquid, it begins to vaporize, causing cavitation bubbles to form. These bubbles typically occur at the points in a pump where the pressure is lowest, especially where the flow is strongly accelerated or deflected. Cavitation bubbles are then transported further with the fluid flow and thus pass from the low-pressure area into zones with higher pressure. As soon as the local pressure rises above the vapor pressure again, the cavitation bubbles collapse abruptly. These implosions release highly concentrated energy and generate so-called microjets, which can cause strong pressure spikes and extreme temperature peaks. This can lead to considerable damage to the pump housing, the material used, and even the pumped media itself. What Influences Cavitation? The individual vapor pressure of the pumped fluid also has an influence on cavitation behavior. A high vapor pressure, as is the case with ethanol, for example, increases cavitation compared to fluids with a lower vapor pressure, such as water. Furthermore, the vapor pressure depends heavily on the temperature of the medium. The higher the temperature, the higher the vapor pressure of the medium, which promotes cavitation. Higher viscosity also increases pressure losses in the suction lines, which further increases the risk of cavitation. How To Detect Pump Cavitation Cavitation can sometimes be detected visually by the formation of bubbles in the liquid. The cavitation bubbles (liquid vapor bubbles) usually form and implode in the pump, meaning that they will not be visible even when transparent tubing is used. However, especially in liquids containing surfactants, the agitation caused by cavitation can often result in foaming as dissolved gases in the liquid are released and form bubbles. Acoustically, cavitation can be recognized by a very characteristic crunching noise produced by the imploding vapor bubbles. This can be a clearer indicator, particularly when the cavitation is very pronounced and is not masked by other noises. Pump Cavitation Affects Pump Performance and Accuracy Cavitation has negative effects on the entire system, the pump, and the fluid. It reduces the performance of the pump because the higher the proportion of vapor in the liquid, the less liquid the pump can transfer. The pumps in the KNF FP series, for example, have a linear performance curve. This means that doubling the rotational speed also doubles the flow rate. With other pumps, if cavitation occurs, the linear characteristic curve flattens sharply until an increase in the rotational speed no longer causes any change in the volume flow. The occurrence of pump cavitation is particularly problematic in dosing and metering applications, as the accuracy decreases significantly. What Are the Signs of Cavitation Damage? Sensitive liquids such as cell culture suspensions or inkjet inks can also be damaged by these implosions. In the case of UV inks, this can even lead to a change in the chemical composition, which impairs quality and function. This phenomenon is known as dark curing. Cavitation and Outgassing – What Is the Difference? In addition to cavitation, a phenomenon known as degassing can also occur. When liquids come into contact with gases like atmospheric air, these gases become dissolved in the liquid. At room temperature (approx. 20 °C, 68 °F) and normal atmospheric pressure, one liter of water contains approx. 15-20 ml of dissolved air, according to Henry's law. As soon as this liquid is exposed to negative pressure, air bubbles form spontaneously and very quickly. Unlike cavitation bubbles, these air bubbles do not dissolve back into the liquid when they flow back into areas of higher pressure. These detached air bubbles can significantly reduce the accuracy of pumps like dosing or metering pumps. They can also cause serious issues in applications like inkjet printing or analytical systems. Cavitation in Centrifugal Pumps In centrifugal pumps, the greatest risk of pump cavitation typically occurs at the leading edge of the impeller blades, because the fluid is accelerated rapidly there and must flow around the leading edge. Cavitation bubbles can severely damage the blades of the impeller near the leading edge as well as many other areas within the pump, which can lead to pump failure. Severe cavitation also significantly reduces the efficiency and performance of the pump. Cavitation in Gear Pumps Gear pumps transfer the fluid through the spaces between the gear teeth from the pump inlet to the pump outlet. On the return stroke, the teeth of the two gears mesh with each other, preventing the fluid from flowing back. When the cavity between the two gears opens, it is quickly refilled with fluid. This creates a deep vacuum, where the pressure is typically below the vapor pressure of the fluid, which can lead to significant cavitation problems, outgassing, or damage to the fluid. In gear pumps, the cavity between the gears opens abruptly and fills quickly with liquid. The resulting deep vacuum can lead to pump cavitation and outgassing. Cavitation in Diaphragm Pumps and Reciprocating Pumps In oscillating pumps such as diaphragm and reciprocating piston pumps, the suction and discharge strokes occur cyclically one after the other. Diaphragm pumps transfer fluids in a periodic suction and discharge cycle. This causes a start-stop movement in the suction and pressure lines, which leads to pressure pulsation and pump cavitation. This cyclic operation causes the fluid in both the suction line and the discharge line to undergo a stop-and-go motion. Due to the inertia of the fluid, this results in pressure pulsations in the pump and the connected lines. During the suction stroke, fluid is drawn from the suction line into the pump. This creates a vacuum, sufficient to overcome all resistance in the suction line and accelerate the fluid to the inlet velocity. During fast suction strokes, the resulting pressure can fall below the vapor pressure of the fluid and cause cavitation. In large pumps, these dynamic effects can be mitigated using pulsation dampers or “air chambers”. The diagram shows the pulsating flow of a diaphragm or reciprocating pump. The y-axis (1) describes the pressure that transfers the fluid cyclically and causes pulsation at the pump outlet (2) and inlet (3). The dashed lines indicate the pressure of KNF pumps with Smooth Flow technology. How To Effectively Prevent Pulsation and Cavitation To prevent pulsation and cavitation in diaphragm pumps without Smooth Flow technology, separate pulsation dampers can be installed directly upstream and downstream of the pump. In addition, operating a larger pump at a lower speed and selecting a smaller eccentric can help prevent cavitation. Systemic Measures to Prevent Pump Cavitation To prevent cavitation, it is particularly important to ensure that the pressure loss in the suction line remains low. This can be achieved by taking the following measures: Use a suction line with a larger inner diameter. Position the pump as close as possible to the supply tank on the inlet side and, if possible, below it. The positive pressure at the inlet reduces the risk of cavitation. In plant engineering, tanks are therefore often placed one floor above the pumps. In systems where the supply tank must be located below the pump, the suction should be minimized. Select larger suction-side fittings and valves that are suitable for the application requirements to minimize additional pressure drops. Furthermore, the suction line should have as few bends, valves, and fittings as possible with a sufficiently large internal diameter. From Initial Requirements to the Optimal Pump Configuration When designing pump systems, KNF's experts ensure that the solution is precisely tailored to the specific requirements of the application. All relevant parameters, such as flow rate, pressure conditions, fluid characteristics, and system geometry, are carefully analyzed together with the customer. The modular design of the diaphragm pumps allows flexible adaptation to minimize pulsation and cavitation. With the help of a powerful and user-friendly simulation environment, fluid lines can be modeled during the consultation phase. This allows critical operating conditions such as the risk of pump cavitation to be identified at an early stage, suitable pump configurations to be identified, and the overall system to be optimized efficiently. Contact us today for technical consultation on low-cavitation diaphragm pumps! Contact Us Do you want to find out more about our customized pump solutions and service opportunities? Get in touch with our local sales representatives.