Understanding Pump Cavitation and Prevention Measures

What is Pump Cavitation and Why Does it Occur?

Pump cavitation is a destructive phenomenon that occurs in fluid pumps when the local pressure in a liquid drops below the fluid’s vapor pressure, causing the liquid to vaporize, i.e. form vapor bubbles. When these bubbles move to higher-pressure regions, the pressure causes them to collapse violently, releasing energy which erodes pump surfaces, generates noise, and causes vibrations. Over time, this leads to performance loss, increased maintenance costs, and even complete pump failure.

Understanding why pump cavitation occurs requires a basic grasp of fluid dynamics. Pumps work by creating areas of low pressure to draw fluid into the pump. Each liquid has its own vapor pressure, i.e. the point at which a fluid changes into a gas, or vaporizes. When the pressure at any point within a pump drops below a fluid’s vapor pressure, this leads to the formation of vapor bubbles in that area. Vapor pressure is dependent of temperature. For example, at room temperature, water has a vapor pressure of 0.0313 bar—almost a perfect vacuum. If the pump inlet or internal components experience a pressure drop below this threshold, water coming into the pump interior passages will form vapor bubbles.

Why is Cavitation Harmful?

The problem with vapor bubbles inside a pump escalates when they collapse as the fluid moves into areas of higher pressure within the pump. This implosion generates shockwaves that impact nearby surfaces, causing pitting, cracking, and eventual material fatigue. While the process might start subtly, the damage can accumulate rapidly, especially in high-speed or high-demand applications.

Cavitation is often considered a pump’s worst enemy due to its destructive potential. It can cause:

• Erosion of internal surfaces.
• Noisy and inefficient operation.
• Premature wear and tear of pump components.
• Unwanted changes in the consistency of the fluid being pumped.

The negative effects of pump cavitation are especially harmful in industries where precise fluid management is critical, like chemical processing, analytical and medical applications, food and beverage processing, and more.

In inkjet printer pumps, for example, cavitation and gas bubbles can disrupt the smooth flow of ink through the nozzles, resulting in streaks, incomplete prints, or blurred colors on paper or packaging. Even small inconsistencies in ink delivery can lead to costly reprints or customer dissatisfaction, especially in high-quality printing where precise color and detail are crucial.

Example of damage from cavitation on a gear tip

Signs of Pump Cavitation

Although cavitation might not be immediately noticeable, it gradually damages internal pump components. The most apparent is visible damage like pitting or erosion on pump surfaces. Fluctuations in performance like inconsistent flow or cloudy output fluid can also indicate pump cavitation.

Another sign of possible pump cavitation is when the pump emits unusual noises, like a gurgling sound. A quick confirmation is to lower the pump speed and determine whether the noise dissipates.

The simplest way to check for the potential for pump cavitation is to place a pressure transducer at the pump’s inlet and to measure the vacuum at the worst operating conditions (high temperature, high speed). If the vacuum is too close to the fluid’s vapor pressure, the operator should implement some precautionary measures.

Common Causes of Pump Cavitation

Understanding the onset of cavitation is complex and depends on several factors: fluid viscosity, vapor pressure point, density, temperature, hydraulic lift, atmospheric pressure, pump type, and pump speed. Several key factors that contribute to pump cavitation are:

• Inadequate Inlet Pressure: Long or narrow inlet tubing, clogged filters, or other obstructions at the inlet increase pressure drops, pushing the fluid closer to its vapor pressure.
• High Pump Operation Speeds: Rapid movement of pump components creates localized low-pressure zones, particularly near moving elements such as impellers or gear tips.
• Fluid Properties: The vapor pressure of a fluid varies with temperature. For instance, as water heats up, its vapor pressure increases, making it more prone to cavitation.
• System Design: Poorly designed hydraulic systems with sharp bends, sudden expansions, or multiple restrictive components can create pressure imbalances that lead to pump cavitation.

Graphic rapresentation of the process of cavitation: formation and imposion of air bubbles inside a pump.

Best Practices to Avoid Pump Cavitation

Fluid pump manufacturers and pump operators have a number of measures at disposal to minimise the risk of pump cavitation and ensure longer pump life by applying smart pump design and various operational precautions.

In pump engineering and manufacturing:

• Sizing the inlet tubing to the largest diameter possible to minimize pressure drop between the reservoir and the pump inlet.
• Minimizing the number of hydraulic components on the inlet—each has a pressure drop and will add to the negative pressure at the inlet.
• Avoid using filters upstream of the pump inlet. As the filters get dirty, the pressure drop increases and can “starve” the pump of fluid.
• If quick-disconnect or tube fittings are used, make sure the inside diameter is large enough to prevent localized pressure drops.
• Design smarter systems: Optimizing internal flow paths and configurations, such as helical gears in Diener’s precision gear pumps, to minimize cavitation-prone zones.

For pump operators / OEM manufacturers:

• Control pump speed: Operate within recommended limits to reduce pressure fluctuations.
• Monitor inlet conditions: Use a pressure transducer to ensure inlet pressure stays above the fluid’s vapor pressure, even under worst-case conditions.

Working with Pump Engineers

Collaborating with experienced pump manufacturers during system design can help address potential cavitation risks. At Diener Precision Pumps USA our expert pump engineers can tailor pump designs to our clients’ specific applications, ensuring efficient, reliable performance while prolonging the pump’s life.

By proactively addressing cavitation, you can protect your systems, lower maintenance costs, and ensure consistent operation in demanding industrial environments.