What Is Valve Cavitation? Symptoms, Causes, and Prevention Methods

In industrial facilities, valve selection is not simply a matter of determining the correct diameter, pressure class, or material. Especially in systems where liquid fluids are controlled under high differential pressure, cavitation is a significant problem that can reduce valve performance and, over time, lead to serious equipment damage.

Valve cavitation occurs when the pressure inside the valve drops below the fluid’s vapor pressure, causing vapor bubbles to form and then suddenly collapse as they enter a higher-pressure region. This phenomenon can cause erosion, vibration, and noise in the valve body, internal components, and even the downstream piping.

Therefore, proper valve selection and accurate pressure control are critical to reducing the risk of valve cavitation.

What Is Valve Cavitation?

Valve cavitation is a physical phenomenon that begins when the local pressure drops below the fluid’s vapor pressure due to the high pressure drop experienced by the liquid as it passes through the valve.

In the valve’s constricted flow passage, the flow velocity increases, causing the local static pressure to decrease. When the pressure falls below the fluid’s vapor pressure, small vapor bubbles begin to form.

As the fluid moves through the valve and reaches a higher-pressure region, these bubbles rapidly collapse. During the collapse of the bubbles, extremely high local pressures can develop. This can cause erosion, pitting, and surface damage, particularly on metal surfaces.

In brief, the process occurs as follows:

High pressure → passage through the valve → high flow velocity → local pressure drop → vapor bubbles → bubble collapse → noise, vibration, and erosion

What Causes Cavitation?

The primary cause of valve cavitation is the high pressure difference (ΔP) between the valve inlet and outlet. However, pressure differential alone is not sufficient; the fluid temperature, vapor pressure, flow rate, and valve design also affect the risk of cavitation.

The main causes are as follows:

1. High pressure drop

As the pressure drop across a valve increases, the flow velocities and local pressure variations within the valve can also increase.

Especially in control valves, applications involving high ΔP are more susceptible to cavitation.

2.High fluid temperature

As the temperature increases, the liquid’s vapor pressure also rises. Therefore, cavitation can occur more easily in hot fluids.

3.Low outlet pressure

When the pressure downstream of the valve approaches the fluid’s vapor pressure, the risk of cavitation increases.

4. Incorrect valve sizing

If the valve is undersized for the application or an unsuitable model is selected for the operating conditions, it can increase flow velocities and pressure losses within the valve.

UNOX’s valve sizing guide also states that incorrect valve sizing can lead to cavitation, noise, vibration, premature wear, and high maintenance costs.

5. Incorrect pressure reduction method

Especially in pressure-reducing systems, reducing the pressure by a very high ratio across a single valve can increase the risk of valve cavitation.

UNOX’s pressure-reducing control valve operating instructions also recommend properly adjusting the outlet pressure to mitigate the risk of cavitation and, when necessary, reducing the pressure gradually in stages.

What Are the Symptoms of Valve Cavitation?

Valve cavitation often produces various warning signs before the valve fails completely. Detecting these symptoms early can help prevent unplanned downtime and high maintenance costs.

1. Unusual noise

One of the most noticeable symptoms of valve cavitation is an unusual noise coming from the valve.

Due to the continuous formation and collapse of vapor bubbles, a noise resembling gravel or metal particles moving around the valve may be heard.

2. Vibration

As cavitation progresses, vibration may occur in the valve and the connected piping.

Continuous vibration;

• valve connections,
• the piping,
• the actuator,
• the connection components

can be adversely affected.

3. Wear on the valve’s internal surfaces

The collapse of vapor bubbles near metal surfaces can create small pits on the surface. As the damage progresses, the surface may develop a rough, porous, or sponge-like appearance.

4. Reduced flow rate and control performance

As cavitation progresses, the valve may no longer provide the expected flow control. This can make it difficult for the process to operate at the desired pressure or flow rate.

5. Premature valve failure

Prolonged cavitation that is left unchecked can cause damage to the valve’s internal components and body.

As a result, the issue can lead not only to valve replacement but also to unplanned production downtime and additional maintenance costs.

What Is the Difference Between Cavitation and Flashing?

Cavitation and flashing are two similar phenomena, but they are not the same.

In cavitation, the fluid vaporizes in the low-pressure region inside the valve, and the resulting vapor bubbles collapse when they reach a higher-pressure region.

In flashing, however, the pressure downstream of the valve remains below the fluid’s vapor pressure. As a result, the vapor bubbles continue to flow downstream with the fluid after leaving the valve.

This distinction is important for selecting the correct valve and flow control solution.

How Can Cavitation Be Prevented?

Eliminating cavitation completely may not be possible in every application. However, the risk can be significantly reduced through the right engineering approach.

Determine the Correct Valve Size

When selecting a valve, it is not sufficient to consider only the existing pipe diameter.

The following parameters should be evaluated together:

• Fluid type
• Debi
• Operating Pressure
• Outlet pressure
• Pressure differential (ΔP)
• Operating temperature
• Fluid vapor pressure
• Valve type
• Valve Kv value
• Operating conditions

Therefore, performing engineering calculations is essential for professional valve selection.

Reduce Pressure Gradually in Stages

Instead of applying a very high pressure differential across a single valve, gradually reducing the pressure in stages, where appropriate, can help reduce the risk of cavitation.

UNOX’s pressure-reducing control valve documentation also recommends reducing the pressure in stages using two pressure-reducing control valves when a low outlet pressure is required.

Consider Cavitation-Resistant Valve Designs

In applications where high pressure drops are unavoidable, specialized designs such as anti-cavitation trim can be considered instead of standard valves.

In these types of designs, the pressure drop is divided into multiple stages to maintain the minimum pressure inside the valve in a more controlled manner.

Consider the Kv Value When Selecting a Valve

The Kv value is an important selection parameter that indicates how much flow a valve can provide at a given pressure differential.

A valve with an incorrect Kv value may not provide the control range required by the system. Therefore, flow rate, pressure differential, and Kv value should be evaluated together when selecting a valve.

In Which Systems Is Cavitation More Common?

The risk of cavitation becomes particularly important in systems where liquid fluids are controlled under high pressure differentials.

For example:

• Water treatment plants
• Pump systems
• Pressure reduction stations
• HVAC systems
• Energy facilities
• Chemical Plants
• Process lines
• Industrial water systems
• High-pressure liquid pipelines

The potential for cavitation should be considered when selecting valves for applications such as these.

How Does Cavitation Affect Valve Life?

Cavitation should not be regarded merely as a temporary noise problem.

The repeated formation and collapse of bubbles can cause microscopic damage to the metal surfaces inside the valve. Over time, this damage can worsen and develop into surface erosion.

As a result:

Cavitation → surface erosion → sealing problems → performance loss → maintenance → valve replacement

This can result in a cost chain that progresses as follows.

Therefore, detecting cavitation at an early stage is important not only for valve life but also for overall plant operating costs.

Proper Valve Selection Reduces the Risk of Cavitation

One of the most effective ways to prevent cavitation is to select the valve based not only on its DN and PN ratings, but also on the system’s actual operating conditions.

Particularly in applications with high pressure differentials;

Flow rate + pressure + temperature + fluid + Kv + valve type + operating range

should be evaluated together.

UNOX’s valve selection guidelines also emphasize that flow rate, flow velocity, pressure loss, fluid properties, and the Kv value should be considered together when determining the valve size.

At this point, conducting an application-specific technical evaluation to determine the right product is a safer approach than relying on a standard valve selection.

Conclusion: Prevent Cavitation Before It Causes Valve Failure, Not After

Valve cavitation is a problem that should not be overlooked, especially in liquid systems operating under high pressure differentials.

A process that begins with noise and vibration can, over time, lead to erosion of the valve’s internal surfaces, reduced control performance, and even severe equipment damage.

To reduce the risk of cavitation:

• The correct valve size should be determined,
• Flow rate and pressure differential should be calculated,
• Operating temperature should be taken into account,
• The valve’s Kv value should be selected correctly,
• If necessary, the pressure should be reduced gradually,
• For high ΔP applications, cavitation-resistant valve solutions should be considered.

If you are unsure which valve type would reduce the risk of cavitation in your project or which Kv value is appropriate, it is important to seek professional technical support and provide details about your application, including operating pressure, flow rate, temperature, and fluid properties.

UNOX’s pressure-reducing control valve documentation also clearly states that the risk of cavitation should be evaluated, particularly in relation to pressure settings.