Why Consulting a Valve Expert Is Essential for Process Control Success

Designing process control systems that require industrial control valves demands a high level of expertise and precision. Industrial control valves play a pivotal role in regulating flow, pressure, temperature, and fluid levels within various industrial processes. Any misstep in their selection or implementation can lead to inefficient operations, safety hazards, and increased costs. Therefore, consulting with an experienced process control valve expert becomes not just beneficial but critical in ensuring the success and safety of these systems.

Industrial control valves come in an array of types, materials, sizes, and specifications. Each valve must meet the specific demands of the process conditions it will encounter, such as temperature extremes, corrosive substances, or high-pressure environments. An experienced valve expert possesses in-depth knowledge of these variables and understands how they interact within a complex system. They can navigate the intricate details a general engineer might overlook, ensuring that the selected valves align perfectly with the system's requirements.

Moreover, valve experts stay abreast of the latest technological advancements and industry standards. They bring insights into new materials, designs, and control technologies that can enhance system performance. By leveraging their expertise, they can recommend valves that meet current needs and offer scalability and adaptability for future process changes. This forward-thinking approach can save time and resources in the long run, preventing the need for costly overhauls or replacements down the line.

The financial implications of improper valve selection or implementation are significant. Incorrect valves can lead to leaks, equipment damage, or system failures, resulting in unplanned downtime and repair costs. An experienced valve expert can mitigate these risks by ensuring that every valve is suited to its specific function and environment. They can conduct thorough assessments and simulations to predict how valves will perform under various conditions, thereby preventing potential issues before they arise.

Safety is another paramount concern in industrial processes. Valves not appropriately selected or maintained can pose serious safety risks, including explosions, fires, or exposure to hazardous substances. Valve experts understand the critical safety standards and regulations that govern industrial operations. They ensure that all valves comply with these standards, providing peace of mind that the system operates safely and efficiently. Their expertise can also contribute to a safer work environment by reducing the likelihood of accidents caused by valve failures.

In addition, collaborating with a valve expert fosters better communication and understanding among the engineering team. These experts can bridge gaps between disciplines, ensuring that mechanical, electrical, and control systems work harmoniously. They can provide valuable training and support to the team, enhancing overall competency and confidence in managing the control system.

Time efficiency is yet another benefit of involving a valve expert. Designing and implementing control systems is a time-sensitive endeavor, and any delays can have cascading effects on project timelines and budgets. Valve experts streamline the selection and implementation process, making informed decisions quickly and accurately. Their experience allows them to anticipate and address challenges proactively, keeping the project on schedule.

The complexity and critical nature of industrial control valves necessitate the involvement of an experienced process control valve expert in the design of process control systems. Their specialized knowledge ensures optimal valve selection, enhances system performance, reduces financial risks, and upholds safety standards. Engineers and project managers can achieve a more efficient, reliable, and safe control system by consulting with these experts. It is an investment that pays dividends in operational excellence and peace of mind, underscoring the indispensable role that valve experts play in industrial process control.

CTi Controltech
https://cti-ct.com
925-208-4250

Techniques to Reduce Flashing and Cavitation in Control Valves

Industrial control valves are pivotal in managing fluid flow in numerous applications across various industries, including oil and gas, chemical, and power generation. A common challenge in the operation of these valves is the phenomena of flashing and cavitation, which can severely damage valve components, reduce operational efficiency, and increase maintenance costs. Manufacturers have developed several port modification techniques to mitigate these issues, enhancing the longevity and reliability of control valves. One notable solution in this area is Flowserve Valtek's CavControl technology.

Flashing occurs when the pressure of a liquid drops below its vapor pressure, causing it to vaporize as it flows through the valve, leading to erosion and wear on valve components. Conversely, cavitation happens when vapor bubbles formed from flashing collapse downstream of the valve seat in a liquid phase, causing shock waves that can damage valve parts and connected piping systems. To address these challenges, engineers have devised various port modification techniques focused on controlling the flow within the valve to manage pressure drops more effectively and reduce the likelihood of flashing and cavitation.

One such technique involves the use of multi-stage trim designs. These designs distribute the pressure drop across several more miniature stages or steps within the valve, thereby preventing the pressure at any point from falling below the liquid's vapor pressure. This staged pressure reduction minimizes the energy available for vapor formation as the fluid progresses through the valve, effectively mitigating flashing and reducing the potential for cavitation.

Another port modification approach is incorporating specially designed flow paths that smooth fluid transition from high to low pressure. By carefully shaping these paths, engineers can ensure a more gradual pressure decrease, which helps maintain the liquid state of the fluid and reduces vapor bubble formation. This method not only combats cavitation but also optimizes the flow profile within the valve, enhancing performance and efficiency.

Flowserve Valtek's CavControl technology exemplifies applying advanced port modification techniques to combat cavitation. Cavcontrol utilizes a unique trim design that manages the pressure drop across the valve in a controlled manner, effectively mitigating the conditions that lead to cavitation. The technology incorporates a series of specially engineered notches or grooves in the valve's trim that create a series of pressure-reducing stages. As the fluid passes through these stages, the pressure decreases incrementally, preventing any sudden drop below the vapor pressure and thus avoiding the formation of vapor bubbles.

Furthermore, CavControl's design also focuses on energy dissipation. Controlling the flow path and dissipating the fluid's kinetic energy throughout the valve reduces the fluid's velocity and the impact of any vapor bubbles that may form, minimizing the potential for damage. This approach extends the valve's life and ensures smoother operation and improved control accuracy.

The challenge of flashing and cavitation in industrial control valves requires sophisticated engineering solutions. Port modification techniques, including multi-stage trim designs and controlled flow paths, effectively mitigate these issues. Flowserve Valtek's CavControl technology stands out in this field, demonstrating how advanced design and engineering can enhance the performance and reliability of control valves, ensuring their safe and efficient operation in industrial processes.

CTi Controltech
https://cti-ct.com
925-208-4250

Control Valve Application Notes

Using an incorrectly applied or sized control valve may have significant ramifications for operation, productivity, and, most importantly, safety. Here is a brief list of fundamentals to consider: 

Control valves are not isolation valves: 

Control valves do not isolate a process and do not offer a bubble-tight seal, and utilization in a shutoff capacity is unwise. 

Choose the suitable materials for the job: 

The valve body, seat, and wetted materials must all be compatible with the process under control. Before selecting a valve, evaluate the pressure ratings, operating temperatures, and material compatibility. 

Sensor placement: 

Place the flow sensor upstream of the control valve when configuring the control loop. When the flow sensor placement is downstream of the control valve, exposure to an unstable fluid (bubbles) created by the flashing and turbulence of the flow in the valve cavity is possible.

Control precision and mechanical constraints: 

Consider the degree of controllability you need and the inherent Deadband produced by your valve and associated components. Deadband is the built-in movement that occurs in a control valve between the signal change and the direction of the valve, which exacerbates by worn or poorly designed couplings between valve and actuator, mechanical sensor tolerances, friction in the valve stems and seats, or an undersized actuator. Due to opening/closing oscillations, too much deadband leads to poor controllability (hunting). 

Stiction: 

Stiction is the "stickiness" in valve action induced by packing gland, seat, or force against the disk friction. It may happen if the valve sticks in one position for a prolonged time or is constantly traveling in a minimal range for an extended period. The actuator must apply more force to break the disk free, resulting in overshoot and poor control. 

Tuning the loop controller and/or positioner: 

A poorly configured loop controller or positioner is often the source of poor control and loop instability. Advanced auto-tuning capabilities in PI (proportional with integral), PD (proportional with derivative), and PID (proportional with integral and derivative) controllers have replaced human (often trial and error) loop tuning. 

Valve sizing should be correct: 

Control valves are often oversized, permitting maximum flow at just a tiny percentage of total travel. Minor adjustments in valve position have a significant impact on flow. A high valve-position-to-flow ratio promotes continual "hunting," which leads to excessive valve wear. A decent rule of thumb is to size a control valve at around 70% to 90% of its travel. 

What sort of flow characteristics does your valve produce: 

The flow characteristic of a control valve is the connection between the position of the valve disk, gate, or globe and the change in flow rate through the valve under normal circumstances. A linear flow characteristic is desirable. However, different valve designs have varying flow characteristics, some of which are linear and others that are not. Globe control valves have linear flow properties, while butterfly and gate valves have non-linear flow characteristics. Manufacturers will often create specifically shaped disks or orifices to "characterize" the valve's flow to improve linearity.

The above is a brief list of the most common things to consider when applying control valves. There are many other criteria to consider. It is suggested in the strongest terms to consult with an experienced application expert before selecting or using a control valve.

Linear and Quarter-turn Industrial Valves

Various valves are designed and used for multiple roles in process control. Linear and quarter-turn valves are two types of valves used to regulate and control fluid flow in the industry. Their design and construction reflect the intended use of the valves, with each suited to a different class of service. 

All valves work by controlling the position of an internal structure that obstructs fluid passage to some extent. In general, fluid flow at the valve classifies as unrestricted (valve fully open), stopped (valve fully closed), or throttled (valve partially open). The operational requirements of the process will determine whether only two of those conditions (fully open and fully closed) or all three are required. When choosing an appropriate valve, the fluid, the process, and the surrounding environment must be considered. It is not always a simple task. 

Linear valves distinguish themselves using straight-line motion to position the valve plug, disc, diaphragm, or other flow controlling elements. The linear valve trim's shape, size, and arrangement provide the operator with a flow range through the valve. The linear valve's positioning allows it to regulate fluid flow slower but more accurately. Linear motion valves include gate and fixed cone valves—linear valves best suit flow control.

Quarter turn valves move from fully open to closed by rotating a shaft connected to the controlling element 90 degrees. Their relatively simple operation allows for a rugged and compact design. The ability of quarter-turn valves to quickly reposition from open to closed positions is one of their distinguishing features. The torque required to operate the valves is typically low to moderate. Quarter turn valves include ball and butterfly valves. 

Depending on the situation, linear valves and quarter-turn valves are the best choices for specific process environments. The linear valve's accuracy and ability to move in a linear fashion rather than a quarter-turn come with easy maintenance and a lower likelihood of cavitation. Both valve types are widely used and are not competing for the same application. Each excels in a specific set of applications.

https://cti-ct.com
925-208-4250

The Flowserve Valtek FlowTop GS Control Valve

The Valtek FlowTop GS control valve (types V746 and V748) improves the reliability and uptime of production processes while minimizing operating and maintenance costs. Designed for general service applications, the FlowTop GS globe valve is a competitively priced, fully integrated valve-actuator-instrumentation package for continuous process flow loop control throughout the plant.

For more infomration about Flowserve Valtek products in Northern California and Western Nevada, contact CTi Controltech. Call them at 925-208-4250 or visit their website at https://cti-ct.com.

Reversing the Fail Action and Air Action on the Flowserve Valtek VL Actuator

The Flowserve Valtek VL series spring cylinder linear actuators are powerful, compact, high-performance pneumatic actuators that provide solid throttling or on-off operation for automatic control valves. The positioner supplies air to both sides of the piston, providing stiff, precise movement and high-frequency response and quick stroke speeds.

The VL series is the standard set of actuators for Valtek control valves, providing precise control and reliable performance. Providing maximum thrust from a compact lightweight package, the VL cylinder has set the industry standard for two generations.

For more information about Flowserve Valtek products, contact CTi Controltech by calling 925-208-4250 of by visiting https://cti-ct.com.

Control Valves by CTi Controltech

CTi Controltech handles a complete portfolio of control valves. From linear control valves to rotary control valves, CTi can handle the most severe services, including cryogenic, superheated steam, volatile, erosive, and corrosive fluids, high pressure drops, vibration, cavitation, flashing, and high noise levels. CTi's applications engineers can select and size the best choice for your application, and counsel you on the best practices for safety, accuracy, and long operating life.

https://cti-ct.com

925-208-4250

Master-Martyr Valve Arrangements

Electric actuator for industrial valves.
Image courtesy Rotork

Some industrial fluid flow applications are best served with what is known as a master-martyr valve set. Let's look at this arrangement and how it is used.

Valves are used to regulate flow. They are also applied to isolate portions of a fluid system by providing positive leak free shutoff. A master-martyr valve set utilizes two valves, with the performance of each targeted at differing performance goals. By coordinating the operation of the two valves, operational benefits accrue.

The master valve serves as the isolating valve. It will be located upstream of the martyr valve. The master valve provides fully open or fully closed operation and is commonly selected to accommodate the most severe operating condition anticipated in the system. Usually, this valve is normally open and is designed to contribute little to no pressure drop to the fluid flow. A good example is a full port metal seated ball valve. It offers very low pressure drop, substantial resistance to system pressure or heat, and can be driven from fully open to closed positions quickly.

The martyr valve provides flow regulation or throttling and is not intended to be the positive means of shutoff for the fluid flow. This valve will experience a range of pressure drop, possibly some flashing, or other conditions that, along with the frequent repositioning applied to the valve, will serve to produce wear and tear on the mechanism. Generally, the martyr valve is expected to wear out from normal operation and need servicing or replacement. The master valve, located upstream, serves as a point of isolation that allows the martyr valve to be easily serviced.

The overall goal is to operate the master valve as little as possible and expose it to the lowest possible pressure drop. Generally, this will call for the master valve to be opened first and closed last.

There are numerous potential applications for this valve arrangement. Smart actuators can function within the control system by delivering information about valve position and service level, as well as responding accurately to system commands. Share your fluid flow control challenges and applications with valve automation specialists. Leverage and effective solution by combining your own knowledge and experience with their product application expertise.

Eccentric Rotary Plug Control Valve

The MaxFlo 4 eccentric rotary plug control valve
Image courtesy of Flowserve Valtek

There is an extensive array of valves from which to select for a process control operation. Each candidate valve is targeted by its designers for a range of fluid applications, fortified with construction materials and design features specifically suited for meeting the challenges of that application range.

Flowserve, under their Valtek brand, developed a control valve that combines a number of useful design features. The MaxFlo 4 is an eccentric rotary plug valve intended for fluid control operations. The valve has some attractive design features.

• There is no shaft extending through the flow path, leaving flow unobstructed when the valve is fully open (see the illustration in the document included below).
• Valve trim provides tight bi-directional shutoff.
• Metal or soft seat construction is available to accommodate a wide range of applications.
• A variant provides flange to flange dimensions that allow the MaxFlo 4 to drop in as a replacement for standard size globe valves.
• High Cv rating may enable use of a smaller valve, when compared to other designs.
• Precise position control is delivered by the shaft form and plug mounting.
• Double offset eccentric plug eliminates sliding of plug across sealing surfaces, reducing wear and required seal maintenance.

More detailed information is provided in the document provided below. There is a revealing cutaway illustration showing the mounting and movement path of the plug. Share your industrial process control valve requirements and challenges with a valve selection and automation specialist to get the best match of control valve to application.

Eccentric Rotary Plug Control Valve from CTi Controltech

Electric Actuator for Linear and Quarter Turn Control Valves

Many process control valve installations present the option of selecting either electric or pneumatic actuators as part of the control component train. Pneumatic actuators have been in use for many years, but advances in electric motor design that delivered greater torque and more precise operation have brought electric valve actuators into a prominent market position.

Electric actuators are compact and comparatively self contained, requiring only cable connections and none of the additional devices sometimes needed for a pneumatic installation. There are some points of advantage to consider with electric actuators. Rotork introduced their CVA line of electric actuators almost ten years ago, making it something of a mature product now. Here are some advantageous points about the CVA actuators that likely apply generically as well.

• Setup is accomplished with a Bluetooth enabled device which provides quick calibration of open and closed positions, as well as establishment of valve setup parameters.
• A separately sealed electrical connection compartment keeps motor and mechanical compartment isolated from the environment while electrical connection section cover is removed.
• An on board datalogger records thrust and position data over time for use in asset management and service functions. Data can be downloaded by Bluetooth or transmitted by common protocol to another station.
• Change in setpoint produces a rapid and precise change in valve position with high resolution accuracy and repeatability.
• Actuator can be programmed to move to a preset condition in the event of a loss of electric power. The energy to achieve the failsafe position is stored in the actuator.
• Force balance positioning used in pneumatic valves, with spring force vs. air pressure, has resilience that can result in a change in position of the valve trim in response to a bump in system pressure. Resistance from the gear train on electric drives prevents this movement.
• Static friction of the valve packing and other parts increases the amount of force to intially get the valve moving toward a new position. The additional time required to build air pressure and force to overcome static friction results in delayed valve response, then overshoot of the new setpoint. A combination of a sensor system and the mechanical drive section of an electric actuator eliminates overshoot and delayed response.

Electric actuators can be had in quarter turn and linear versions, with torque ranges suitable for a broad range of process control applications. The datasheet below, from Rotork, provides useful illustrations of the actuator interior, along with additional detail about electric actuators. Share your process control valve requirements and challenges with product application specialists, combining your own process knowledge and experience with their product application expertise to develop the best solutions.

Application of Limit Switches on Automated Industrial Valves

Employed in a wide range of industrial applications,

limit switches are known for ease of installation,

simple design, ruggedness, and reliability.

Courtesy Flowserve Automax

Limit switches are devices which respond to the occurrence of a process condition by changing their contact state. In the industrial control field, their applications and product variations are almost countless. Essentially, the purpose of a limit switch is to serve as a trigger, indicating that some design condition has been achieved. The device provides only an indication of the transition from one condition to another, with no additional information. For example, a limit switch triggered by the opening of a window can only deliver an indication that the window is open, not the degree to which it is open. Most often, the device will have an actuator that is positively activated only by the design condition and mechanically linked to a set of electrical contacts. It is uncommon, but not unknown, for limit switches to be electronic. Some are magnetically actuated, though most are electromechanical. This article will focus on limit switch designs and variants used in the control and actuation of industrial process valves.

Valves, devices used for controlling flow, are motion based. The movable portions of valve trim create some degree of obstruction to media flow, providing regulation of the passage of the media through the valve. It is the movement of critical valve trim elements that limit switches are used to indicate or control. The movable valve trim elements commonly connect to a shaft or other linkage extending to the exterior of the valve body. Mounting electric, hydraulic, or pneumatic actuators to the shaft or linkage provides the operator a means to drive the mechanical connection, changing the orientation or position of the valve trim and regulating the media flow. Because of its positive connection to the valve trim, the position of the shaft or linkage is analogous to the trim position and can be used to indicate what is commonly referred to as “valve position”. Limit switches are easily applied to the valve shaft or linkage in a manner that can provide information or direct functional response to certain changes in valve position.

In industrial valve terms, a limit switch is a device containing one or more magnetic or electrical switches, operated by the rotational or linear movement of the valve.

What are basic informational elements that can be relayed to the control system by limit switches? Operators of an industrial process, for reasons of efficiency, safety, or coordination with other process steps, may need answers to the following basic questions about a process control valve:

• Is the valve open? 
• Is the valve closed? 
• Is the valve opening position greater than “X”? 
• Has the valve actuator properly positioned the valve at or beyond a certain position? 
• Has the valve actuator driven the valve mechanism beyond its normal travel limits? 
• Is the actuator functioning or failing? 

Partial or complete answers to these and other questions, in the form of electrical signals relayed by the limit switch, can serve as confirmation that a control system command has been executed. Such a confirmation signal can be used to trigger the start of the next action in a sequence of process steps or any of countless other useful monitoring and control operations.

Applying limit switches to industrial valve applications should include consideration of:

• Information Points – Determine what indications are necessary or useful for the effective control and monitoring of valve operation. What, as an actual or virtual operator, do you want to know about the real time operational status of a valve that is remotely located. Schedule the information points in operational terms, not electrical switch terms. 
• Contacts – Plan and layout a schedule of logical switches that will provide the information the operator needs. You may not need a separate switch for each information point. In some cases, it may be possible to derive needed information by using logical combinations of switches utilized for other discrete functions. 
• Environment – Accommodate the local conditions and hazards where the switch is installed with a properly rated enclosure. 
• Signal – The switch rating for current and voltage must meet or exceed those of the signal being transmitted. 
• Duty Cycle – The cycling frequency must be considered when specifying the type of switch employed. Every switch design has a limited cycle life. Make sure your selection matches the intended operating frequency for the process. 
• Auxiliary Outputs – These are additional contact sets that share the actuation of the primary switch. They are used to transmit additional signals with specifications differing from the primary signal. 
• Other Actuator Accessories – Limit switches are often integrated into an accessory unit with other actuator accessories, most of which are related to valve position. A visual local indication of valve position is a common example. 

Switches and indicators of valve position can usually be provided as part of a complete valve actuation package, provided by the valve manufacturer or a third party. It is recommended that spare contacts be put in place for future use, as incorporating additional contacts as part of the original actuation package incurs comparatively little additional cost.

Employing a properly configured valve automation package, with limit switches delivering valve status or position information to your control system, can yield operational and safety benefits for the life of the unit. Good advice is to consult with a valve automation specialist for effective recommendations on configuring your valve automation accessories to maximize the level of information and control.

Valtek Mark One Valve Build - Piece by Piece

Here is a video produced by Flowserve that gives an inside look at the Valtek Mark One globe control valve. The Mark One is suitable for gaseous and liquid service, and the animation illustrates the ease with which the valve can be disassembled in place for easy maintenance.

Contact a product specialist for more information and share your fluid process control challenges with them. Combining your process knowledge with their product application expertise will yield an effective solution.

Process Control Solution for Dosing and Discharging of Bulk Goods - Demonstration Video

EBRO Amaturen Cycle Lock System

Industrial processing applications can sometimes require controlled dosing or dispensing of bulk dry material. Transfers may be injected into an ongoing continuous process, or may be coordinated with a filling operation. There are many possibilities.

One manufacturer has developed a system for controlling the dispensing and flow of bulk solids and powders, combining the necessary valves, sensors, and controllers into a pre-engineered package that can be easily integrated into a new or existing process. The EBRO Armaturen Cycle Lock is compatible with a wide range of communication protocols and can operate as a standalone unit or part of a larger system. The Cycle Lock accommodates all of the manufacturer's extensive line of control valves. The bulk material chamber can be customized in shape, size, material, and coatings to meet customer requirements.

The demonstration video illustrates the operating modes of the Cycle Lock. More information and assistance with all your process control challenges is available from product application specialists. A product data sheet is available.

Control Valve Cavitation - A Demonstration and Some Considerations

Cavitation can be damaging to process components.

Consider a generic industrial fluid process control operation. There are pumps, valves, and other components installed in the process lines that, due to their interior shape or their function, cause changes in the fluid motion. Let's look specifically at control valves and how their throttling operation can create conditions able to greatly impact the valve itself, as well as the overall process.

Fluid traversing a control valve can undergo an increase in velocity when passing the constriction presented by the valve trim. Exiting the trim, fluid then enters the widening area of the valve body immediately downstream with a decrease in velocity. This change in velocity corresponds to a change in the kinetic energy of the fluid molecules. In order that energy be conserved in a moving fluid stream, any increase in kinetic energy due to increased velocity will be accompanied by a complementary decrease in potential energy, usually in the form of fluid pressure. This means the fluid pressure will fall at the point of maximum constriction in the valve (the vena contracta, at the point where the trim throttles the flow) and rise again (or recover) downstream of the trim.

This is where cavitation begins.

If the fluid being throttled is a liquid, and the pressure at the vena contracta is less than the vapor pressure of the liquid at the flowing temperature, portions of the liquid will spontaneously vaporize. This is the phenomenon of flashing. If, subsequently, the pressure of the fluid recovers to a level greater than the vapor pressure of the liquid, any flashed vapor will rapidly condense, returning to liquid. This collapse of entrained vapor is called cavitation.

Flashing, the generation of vapor bubbles within the liquid, will precede and set the stage for cavitation. When the flashed vapor bubbles condense to liquid they often do so asymmetrically, with one side of the bubble collapsing before the rest of the bubble. This has the effect of translating the kinetic energy of the bubble’s collapse into a high-speed “jet” of liquid in the direction of the asymmetrical collapse. These liquid “microjets” have been experimentally measured at speeds up to 100 meters per second (over 320 feet per second). What is more, the pressure applied to the surface of control valve components in the path of these microjets can be intense. An individual microjet can impact the valve interior surfaces in a very focused manner, delivering a theoretical pressure pulse of up to 1500 newtons per square millimeter (1.5 giga-pascals, or about 220000 PSI) in water. In an operating fluid system, this process can be continuous, and is known to be a significant cause of erosive wear on metallic surfaces in process piping, valves, pumps and instruments. As the rapid change in pressure takes place, the bubbles (voids in the liquid) collapse (implode), and the surrounding metal surfaces are repeatedly stressed by these implosions and their subsequent shock waves.

Consequences for control valves, as well as for the entire control process, vary and are often destructive. They may include:

• Loud noise
• Strong vibrations in the affected sections of the fluid system
• Choked flow caused by vapor formation
• Change of fluid properties
• Erosion of valve components
• Premature destruction or failure of the control valve 
• Plant shutdown

The video provides a visual demonstration, through clear piping, of what happens inside the piping system when a valve is operated in a manner that causes substantial cavitation.

The solution lies in minimizing the potential for cavitation to occur through proper valve selection and sizing, along with coordinating operating characteristics of pressure drop inducing components with the total system performance. One valve manufacturer's recommendations are summed up in four basic approaches.

• Avoidance of cavitation through proper valve selection. Use a valve with a rated liquid pressure recovery factor greater than that required for the application. Some applications may be suitable for the use of an orifice plate downstream of the valve.
• Cavitation Tolerant Components capable of withstanding limited amounts of cavitation without excessive wear. Increased flow noise is likely to accompany this route.
• Prevention of cavitation through the use of valve trim design that reduces pressure in several steps, avoiding excessive flashing. These valves can be expensive, but their effectiveness makes them an alternative worth considering.
• Containment of the harmful effects of limited to moderate cavitation through trim designs that eliminate contact of the fluid with metal surfaces which are more susceptible to damage.

Share your requirements and application challenges with a valve specialist and gain insight through their recommendations. Combining your process knowledge with their product application expertise will yield a great solution.

Industrial Valves - When Butterfly Valve Is The Best Choice

Butterfly Valve
Courtesy Durco - Flowserve

Industrial process control valves are available in uncountable combinations of materials, types, and configurations. An initial step of the selection procedure for a valve application should be choosing the valve type, thus narrowing the selection field to a more manageable level. Valve "types" can generally be classified by the closing mechanism of the valve.

A butterfly valve has a disc that is positioned in the fluid flow path. It rotates around a central axis, the stem, through a 90 degree arc from a position parallel to the flow direction (open) to perpendicular (closed). A variety of materials are used in the valve body construction, and it is common to line the valve with another material to provide special properties accommodating particular process media.

What attributes might make a butterfly valve a beneficial selection over another valve type?

Manually Operated Butterfly Valve
Courtesy Ebro Armaturen

• The closure arrangement allows for a comparatively small size and weight. This can reduce the cost, space, and support requirements for the valve assembly.
• Generally low torque requirements for valve operation allow for manual operation, or automation with an array of electric, pneumatic, or hydraulic actuators.
• Low pressure drop associated with the closure mechanism. The disc in the flow path is generally thin. In the fully open position, the disc presents its narrow edge to the direction of flow.
• Quarter turn operation allows for fast valve operation.
• Some throttling capability is provided at partially open positions.
• Small parts count, low maintenance requirements.

What may be some reasons to consider other valve types?

• Butterfly valve throttling capability is generally limited to low pressure drop applications
• Cavitation can be a concern.
• Some sources mention the possibility of choked flow as a concern under certain conditions.

Butterfly valves, like other valve types, have applications where they outperform. Careful consideration and consultation with a valveexpert is a first step toward making a good selection. Combine your process know-how with the product application expertise of a professional sales engineer to produce the best solutions to your process control challenges.

Severe Service Valves - More Than Just Heavy Duty

Severe Service Industrial Control Valves
Courtesy Flowserve - Kammer

Industrial process control applications can be associated with some very stringent and challenging performance requirements for the physical equipment and components that are part of the process chain. In fluid based operations, the control valves can be a point of significant impact of extreme fluid conditions, requiring careful design and selection consideration to assure proper performance and safety levels are maintained in a predictable way.

Industrial valves that are intended for application at the extremes are generally referred to as severe service valves. While there are plenty of published and accepted standards for industrial valves, one does not exist to precisely define a severe service valve.

So, how do you know when to focus valve selection activities on severe service valves, as opposed to general purpose valves?

There are a number of basic criteria that might point you in that direction:

• Very extreme media or environmental temperature
• High pressure drop operation that may cause cavitation
• Rapid and extreme changes to inlet pressure
• Certain types or amounts of solids contained in the fluid

Certainly, any of these criteria might be found in an application serviceable by a general purpose valve, but their presence should be an indicator that a closer assessment of the fluid conditions and commensurate valve requirements is in order. The key element for a process stakeholder is to recognize when conditions are in evidence that might overrun the capabilities of a general purpose valve, leading to premature failure in control performance or catastrophic failure that produces an unsafe condition. Once the possibility of a severe service condition is identified, a careful analysis of the possible operating conditions will reveal the performance requirements for the valve.

There are numerous manufacturers of severe service valves, each seeming to concentrate on a particular niche. Kammer, a brand in the Flowserve family, has an interesting approach to accommodating the highly varied requirements of severe service applications. Their product line consists of a number of standard configurations, but also includes semi-modular components that can be combined to meet the many custom requirements of severe service applications.

I have included a technical bulletin (you know it's technical when it's not in color) that describes and nicely illustrates how the company employs various interchangeable body styles and packings with their multi-stage plug to meet a wide range of severe service challenges. Browse the bulletin, as it has some good cutaway views of valve interiors. 

You can always get more information, or discuss your special requirements, with a product application specialist. They have access to technical resources that can help with selecting the right valve components to meet your severe service applications.

Kammer Severe Service Valves For Industry from CTi Controltech

Benefits of an Intelligent Control Valve System

Intelligent Control
Valve and Loop System

An intelligent control valve system, the Flowserve StarPac can stand alone or be integrated into a system, and is available for a variety of applications including oil and gas, chemical, paper, mining, industrial gases and power generation.

Advantages for using this type of device are the following:

Process Diagnostics – Evaluation of process equipment is possible with the StarPac intelligent control system. By generating an initial signature of the process and then identifying a standard process signature, a pump, compressor, heat exchanger, reactor, etc., can be discovered to be defective and in need of servicing. Process diagnostics can be per- formed with a personal computer or DCS connected to the unit via its serial data port.

Logging / Tuner Operation – The StarPac will take a 'snapshot' of process conditions at user-specified intervals (1 to 9999 seconds) and store them in its memory for later retrieval to aid in diagnosing process upsets. The personal computer operator interface will trend process variable, set point, and stem position to aid in tuning the control loop. This data is in a form that can be read by loop auto-tuning software to calculate the optimum PID constants.

Process Transmitters – The StarPac has sensors in the valve body to measure process conditions including upstream and downstream pressure, temperature, and flow. Flow is indicated both as the current value and a totalized amount. For gases, flow is reported in mass units, such as pounds per hour (since gas flow is always compensated for changes in pressure and temperature). Other sensors measure stem position and pressures in the top and bottom chambers of the cylinder actuator. All of these values are available over the serial link to a computer or DCS.

Connections to Operator Interface – The StarPac can be connected to an operator interface (personal computer, DCS console or hand station and recorder) through its analog, discrete and digital channels. The StarPac houses two analog inputs and one analog output. Up to six analog outputs are available using an external converter module. Two discrete inputs and two discrete outputs are also available at the StarPac. The user can define how these channels will be defined. Normally one analog input is a command signal, one discrete input sets the control mode, and the discrete outputs signal alarm conditions. The digital channel can be connected to computers and most DCSs through gateways or Modbus ports. All of the process and configuration information is available through the digital channels.

High Interchangeability – Since the Valtek Mark OneTM, MaxFloTM and ShearStreamTM control valves are the basis of the StarPac system, most valve parts are interchangeable with other Valtek valves, reducing parts inventory.

Local Display – Eight variables (P1, P2, temperature, gas flow, liquid flow, total flow, setpoint, stem position) can be displayed on a liquid crystal display in the electronics module. Each variable can be set to display continuously, or the StarPac can be set to scroll through the chosen variables at ten-second intervals. An error indicator will show if the StarPac system should fail any internal diagnostic or if the process is out of range.

Multiple Failure Modes – StarPac technology allows multiple failure modes to be set, including: power, air supply, command signal, or process failure. This results in greater reliability and consistency of the process during emergency shutdowns, protecting the process and people.

Valve Diagnostics – A maintenance feedback package allows StarPac intelligent systems to display the condition of the valve packing, seat, actuator, and O-rings with only a brief process interruption without removing the valve from the line. PC software displays the actuator or process signature for analysis. Optional valve diagnostic software can determine specific valve failures.

User Friendly Software – When the user is not connecting the StarPac unit to a DCS, StarTalk software can configure, operate, and diagnose the StarPac unit through a personal computer. The software has a graphical user interface, allowing most users to operate their StarPac systems with minimal training.

Environmental Considerations – Locating pressure and temperature sensors in the valve body eliminates several process connections. All pressure sensors have at least two seals to reduce the possibility of leaks to the atmosphere. Remote-mounted pressure sensors can be fitted with isola- tion and/or purge valves to aid maintenance of the sensors.

Check out this video for further explanation:

CTi Controltech
22 Beta Ct.
San Ramon, CA 94583
Phone: 925-208-4250
Fax: 925-208-4251
Email: contactus@cti-ct.com
www.cti-ct.com

Large Control Valves for Higher Pressures and Bubble-tight Shutoff

High performance
rotary control valve
(courtesy of Valtek)

High performance control valves, providing a bubble-tight seal along with a wide range of sizes and pressure classifications are used in many industrial applications. Examples are:

• Fire protection
• Gas service
• Condenser cooling
• Gas scrubbing
• Mine dewatering
• Pipeline service,
• Cooling water

This type of control valve should achieve bi-directional, bubble-tight shutoff while maintaining low breakout torque - at both high and low pressure drops.

Often, these valves are available in carbon steel, 316 stainless steel and other alloys and is available in ANSI Classes 150 through 2500, sizes 2 through 30-inch. 

Rotary disc, high performance control valves offer a double offset designed into the disc that lifts the disc out of the seat immediately upon actuation. This avoids wear on the seat and disc, reducing leakage and parts replacement. It also improves throttling by eliminating friction.

For more information, review the tech manual below:

Valtek Valdisk Control Valves from CTi Controltech

Reducing Cavitation Damage in Control Valves

Here is a document that describes how cavitation occurs in control valves and what can be done to mitigate its adverse effects:

Cavitation Reduction in Industrial Process Control Valves from CTi Controltech

Excellent Control Valve Actuator White Paper from Rotork

Here is a white paper from electric actuator manufacturer Rotork pointing out the benefits of electric actuators over pneumatic.

Electric control valve actuators provide excellent performance and are ideal for oil and gas wells in remote production fields. Instrument air supply systems are costly and require significant energy to run. If mains power isn’t available, an instrument air supply isn’t practical, especially when only a few control valves are in use at a location. Solar powered DC electric actuators are ideal for such an application.

Control Valve Actuators: Their Impact on Control and Variability from ctict