In every industrial process, the control valve may look like a relatively small component, but its role is critical. When chosen correctly, a control valve ensures reliability, efficiency, and safety. When misapplied, however, it can become a source of unplanned downtime, dangerous conditions, and significant cost.
Industry data shows that while severe service control valves (SSCVs) represent only 3–10% of a plant’s total valve population, they often account for up to 40% of valve costs. Yet, even at this scale of investment, mis-sizing and misapplication remain common. Often, project teams choose the wrong valve during the project stage. This can cause problems during commissioning, start-up, or steady-state operations.
This guide provides a practical overview of control valve basics, the challenges of severe service conditions, and guidance on how to make informed choices for your process. For a detailed technical discussion, download the full white paper: Selecting the Correct Control Valve
For a refresher on valve fundamentals, see our Valve Basics guide.
What is a Control Valve?
A control valve is a device that regulates the flow of a fluid, like liquid, gas, or slurry, by varying the size of its passage. By doing so, it helps manage critical process variables such as flow rate, pressure, temperature, and liquid level.
At its core, a control valve regulates flow by adjusting the pressure drop between the upstream and downstream sides of the system. Proper sizing and valve selection ensure that flow is modulated safely and efficiently.
Explore our Control Valves product page to see solutions designed for both general and severe service conditions.
Types of Control Valves
Control valves come in many designs, each suited for different applications. While some are common in general service, others are built specifically for severe conditions.
Globe Valves
Known for precise throttling and flow control. Often used in severe service when paired with hardened trims or multi-stage designs.
Rotary Valves (Ball, V-Ball, and Rotary Plug)
Compact and efficient, often used where space is limited. However, they may not be suitable for extreme cavitation or flashing unless specially designed.
Butterfly Valves
Lightweight and cost-effective, ideal for large-volume flow control. They are less suitable for severe service because of vibration and noise issues under high pressure drops.
Angle Valves
Designed with an angled body to reduce erosion by keeping flow parallel to the valve surface. Common in flashing applications.
Severe Service Control Valves (SSCVs)
Engineered designs that combine features like multi-stage trims, noise attenuation, and hardened materials. One of the know manufacturer is the Nova Hydromet that produces severe service control valves designed for industries that operate under these
Major Severe Service Challenges
Control valves come in many designs, each suited for different applications. While some are common in general service, others are built specifically for severe conditions.
Cavitation in Control Valves
Cavitation happens when the pressure inside a valve drops below the liquid’s vapor pressure, creating vapor bubbles. When these bubbles collapse, they release powerful energy that damages valve internals and piping. It’s one of the most common, and most destructive problems in liquid service.
Impacts of cavitation include:
- Cavitation erosion: Collapsing bubbles create rough surfaces that accelerate wear.
- Cavitation corrosion: Cavitation strips protective layers from metals, making them prone to corrosion.
- Cavitation noise: Loud, localized noise that harms both valves and workers nearby.
- Vibration: Leads to piping fatigue, calibration drift, and valve malfunction.
- Flow instability: Reduces valve capacity and can cause choking earlier than expected.
Case Study: In a hydrogen unit boiler feedwater line, cavitation quickly eroded valve trim. Engineers solved it by using a drilled-hole retainer to shift bubble collapse away from metal surfaces. Larger, higher-pressure systems required multi-stage anti-cavitation trims for lasting performance. Detailed case studies are available in the full white paper.
Flashing in Control Valves
Flashing occurs when liquid changes to vapor inside the valve and stays vapor downstream. Unlike cavitation, the vapor bubbles don’t collapse but remain mixed with liquid. The result is a high-velocity flow that continuously wears down valve components.
Impacts of flashing include:
- Severe erosion that polishes valve surfaces smooth or leaves grooves along the flow path.
- Higher flow velocities that increase turbulence and noise.
- Continuous wear of trim and piping, especially in carbon steel valves.
Case Study: In pulp and paper black liquor service, flashing destroyed rotary valve trims within hours of startup. The issue was contained by upgrading to chrome-moly bodies, angle-body valves, and expanded outlets to manage high velocities. Read more case examples in the full white paper.
Noise in Control Valves
Control valve noise comes from pressure drops and turbulence. While often overlooked, excessive noise is more than a nuisance — it can damage equipment and endanger people.
Types of valve noise include:
- Mechanical noise: Caused by vibration of valve parts.
- Hydrodynamic noise: Turbulence in liquid service, often linked with cavitation or flashing.
- Aerodynamic noise: Generated in gas or steam service when velocities get too high.
Impacts of noise include:
- Accelerated wear of trim and valve bodies.
- Damage to downstream piping from vibration.
- Unsafe acoustic levels that can exceed hearing protection limits.
Case Study: A natural gas pressure reduction system faced extreme pressure drops of over 3,000 psi, generating damaging noise and vibration. A low-angle valve design with hardened trim allowed safe operation under these severe conditions. Additional details are included in the full white paper.
Applications Across Industries
The control valves, both general service and severe service are found across nearly every industry.
- Power Generation: Boiler feedwater and steam control often require multi-stage trims to prevent cavitation.
- Pulp & Paper: Black liquor and wash water combine flashing, cavitation, and erosion, making them among the toughest services.
- Oil & Gas: Separator feeds, flare systems, and hydrocarbon lines often involve multiphase flows and high velocities.
- Mining & Hydrometallurgy: Slurries and corrosive leaching fluids demand ceramic trims or erosion-resistant alloys.
- Chemicals & Petrochemicals: High-temperature steam and hydrocarbon mixtures pose cavitation and noise risks.
Across these industries, one principle remains: the application dictates the valve. Matching the design to the process avoids costly failures and downtime.
Control Valve Selection Considerations
When approaching control valve selection, the temptation is often to choose the least expensive option that meets minimum requirements. However, this CAPEX-focused approach usually results in higher lifecycle costs (OPEX) due to failures, downtime, and maintenance.
A practical checklist for selecting the right valve includes:
- Accurate process data: Pressures, temperatures, fluid properties, and expected operating ranges.
- Service severity: Identifying cavitation, flashing, and noise risks early.
- Valve type & trim design: Choosing between linear vs rotary, multi-stage vs single-stage, and material compatibility.
- Lifecycle cost analysis: Considering erosion resistance, maintenance schedules, and long-term reliability.
- Supplier expertise: Working with experienced partners who can match application history with proven solutions.
Ultimately, the decision is not just about sizing a flow control valve; it’s about engineering reliability into the entire system.
Common Issues & Maintenance Tips
Even with the correct selection, maintenance is critical to extending valve life.
Common problems include:
- Cavitation-induced erosion and vibration.
- Flashing damage leading to smooth, polished trim wear.
- Noise-driven failures of actuators and downstream components.
- Mis-sizing resulting in poor flow control or premature choking.
Maintenance tips:
- Schedule routine inspections of trim and body wear.
- Monitor vibration and noise levels as early indicators of problems.
- Specify hardened or ceramic materials for high-risk applications.
- Work closely with valve suppliers for predictive maintenance strategies.
By combining proper selection with proactive maintenance, plants can achieve significant cost savings and reliability gains.
Conclusion
Selecting the correct control valve is more than a sizing exercise. It requires balancing science, practical experience, and application history. Severe service conditions such as cavitation, flashing, and noise cannot be ignored and applying a general service valve in these cases can be a failure.
The takeaway is simple: the application dictates the valve. By recognizing severe service conditions early and selecting the right technology, plants can reduce downtime, improve safety, and optimize lifecycle cost.
This article highlights the practical considerations for valve selection. For complete technical data, case studies, and reference charts, see our full paper: Selecting the Correct Control Valve
At CGIS, we provide valve solutions for every industry — from general service to the most severe applications. Contact us today for a free consultation to find the right control valve for your process.
References:
- ISA S75.01 – Control Valve Sizing Equations.
- IEC 60534-8-3 – Noise Prediction Methods.
- ISA-RP75.23-1995 – Considerations for Evaluating Control Valve Cavitation.
- MSS Standards on Severe Service Valves.
- Les Driskell, Control Valve Selection and Sizing, ISA.
- Guy Borden Jr., Control Valves, Practical Guides for Measurement and Control, ISA.