This Comprehensive Control Valve Technical Information Page covers Selection and Design, Cavitation and Flashing in Control Valves, Control Valve Actuators, Butterfly Control Valves, Control Valve Sizing, Split Range Control Valves, Control Valve Applications, Control Valve Noise Calculation and Prediction, Control Valve Maintenance, Control Valve Positioners and Self Operated Regulators.
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Go to Specific Subject: Control Valve Selection and Design | Control Valve Handbooks and Design Guidelines | Cavitation and Flashing in Control Valves | Control Valve Characteristics | Control Valve Emission Control | Control Valve Fail Safe Position | Control Valve Leak Class | Control Valve Noise Calculation and Prediction | Control Valve Performance | Control Valve Rangeability | Control Valve Sizing | Control Valve Styles | Control Valve Trim Materials | Control Valve Material Selection, Corrosion and NACE Applications | Control Valve Maintenance | Control Valve for Safety Instrumented Systems Applications | Split Range Control Valves | Control Valve Actuators | Butterfly Control Valves | Control Valve Applications | Control Valve Positioners and Accessories | Control Valve Education | Self Operated Regulators | Emergency Shutdown and Blowdown Valves | Composite Valves | Specialist Power Plant Valves | HVAC Control Valves
Control Valve Selection and Design
The following information is from Powerflo Solutions Pty Ltd and Masoneilan.
Selecting a Control Valve - Fluid velocity in a control valve is a key parameter that must be considered when sizing and selecting a control valve. High fluid velocities can lead to erosion damage, trim wear, trim component failure, vibration and high noise levels. Therefore, it is vital to design for valve velocities within acceptable limits so that these problems are avoided. This paper addresses these issues.
Looking Inside the Valve - Asher Glaun - Modern control valves can monitor pressure and flow control in a full range of specialist process industries. Now, even better prediction of a valve's performance can be calculated and it is possible to find out what is really going on inside a valve.
Fluid Velocity Considerations - by Jospeh Shahda, Senior Applications Engineer, Masoneilan Operations.
Control Valve Handbooks and Design Guidelines
Control Valve Sizing Handbook - This handbook on control valve sizing is based on the use of nomenclature and sizing equations from ANSI/ISA Standard S75.01.01 and IEC Standard 60534-2-1. Additional explanations and supportive information are provided beyond the content of the standards. This document contains information on Flow Coefficient CV, Operating Conditions, Specific Gravity, Pressure Drop across the Valve, Flowing Quantity, Liquid Flow Equations, Liquid Pressure Recovery Factor, Combined Liquid Pressure Recovery Factor, Cavitation in Control Valves, Effect of Pipe Reducers, Equations for Non-turbulent Flow, Gas and Vapor Flow Equations, Multistage Valve Gas and Vapor Flow Equations, Ratio of Specific Heats Factor, Expansion Factor, Two-Phase Flow Equations , Choked Flow. Supercritical Fluids, Compressibility and Thermodynamic Critical Constants - From Powerflo Solutions Pty Ltd, Masoneilan and Instrumentation and Control Net.
Top 10 Masoneilan Control Valve Sizing Handbook Documents for the Instrumentation Technician - from Instrumentation and Control Net.
The Fisher Control Valve Handbook - This superb 295-page PDF whitepaper is a control valve resource that has been consistently updated for 30 years. It contains vital information on control valve performance and latest technologies. Thanks to Emerson Process Management.
Practical Control Valve Sizing, Selection and Maintenance - Dave Macdonald BSc(Eng) - This manual is intended to provide an understanding of the key issues involved in the selection of control valves for typical process industry applications. This chapter looks at the fundamental principles involved in the control of fluid flow and it describes how the adjustment of flow capacity is typically used to control pressure, flow, level and temperature in processes - thanks to IDC.
Control Valve Selection and Sizing Engineering Design Guideline - There are many available guidelines developed to aid engineers in selecting and sizing the valves, but mostly these guidelines are developed by certain companies and might only be suitable for the application of the valves provided by their own companies. Hence, it is important to get the general understanding about control valve sizing and selection first. Later, whenever changes are needed in a process system, this basic knowledge is still applicable. This guideline is made to provide that fundamental knowledge and a step by step guideline; which is applicable to properly select and size control valves in a correct manner. Control valve supports the other devices and work together resulting and ideal process condition. Hence, it is crucial to make some considerations before deciding the correct control valve sizing and selection. The selected valve has to be reasonable in cost, require minimum maintenance, use less energy, and be compatible with the control loop. Malfunction in control valve might cause process system does not work properly - from kolmetz.com.
Ease Control Valve Selection - Trevor Bishop, Meredith Chapeaux, Liyakat Jaffer, Kiran Nair and Sheetal Patel - With so many types and options available, choosing the right control valve can seem daunting. Selection can be simplified by considering the process fluid, the service requirements, and how the various valves function - from CEP Magazine.
Valve Sizing & Selection Technical Reference - This is an excellent resource! -A Control Valve performs a special task, controlling the flow of fluids so a process variable such as fluid pressure, fluid level or temperature can be controlled. In addition to controlling the flow, a control valve may be used to shut off flow. A control valve may be defined as a valve with a powered actuator that responds to an external signal. The signal usually comes from a controller. The controller and valve together form a basic control loop. The control valve is seldom full open or closed but in an intermediate position controlling the flow of fluid through the valve. In this dynamic service condition, the valve must withstand the erosive effects of the flowing fluid while maintaining an accurate position to maintain the process variable. A Control Valve will perform these tasks satisfactorily if it is sized correctly for the flowing and shut-off conditions. The valve sizing process determines the required CV, the required FL, Flow Velocities, Flow Noise and the appropriate Actuator Size - from Warren Controls.
Commonly Asked Questions about Control Valves - This list of questions will be very useful to Graduate Instrument Engineers - from Mitech.
Fluid Kinetic Energy as a Selection Criteria for Control Valves - by Herbert L. Miller and Laurence R. Stratton - Reproduced with the permission of CCI Sulzer Valves.
Your Best Bet in Control Valves - Hans Bauman - Control valves may be the most important, but sometimes the most neglected, part of a control loop. The reason is usually the instrument engineer’s unfamiliarity with the facets, terminologies, and areas of engineering disciplines, such as fluid mechanics, metallurgy, noise control, and piping and vessel design that can be involved depending on the severity of service conditions - From ISA and InTech.
Plant Design and Control Valve Selection under Increasing Cost and Time Pressure, Part 1 - Holger Siemers - Following a career spanning three decades, Mr Siemers is well aware of the pitfalls to be avoided when specifying control valves for a range of demanding applications. In his latest paper for Valve World, he looks further into plant design and control valve selection when working under increased time and cost pressure. This article is split into two parts: broadly speaking, part one looks at control valve operating points and provides a case history involving a mismatch. The author then introduces better valve sizing practices and uses this theory to resolve the problems introduced in the case history - from Conval and Valve World.
Plant Design and Control Valve Selection under Increasing Cost and Time Pressure, Part 2 - Holger Siemers - Part two starts by explaining the trends and definitions of inherent valve characteristics before focusing on "quick and dirty“ sizing. The paper then addresses cavitation before concluding with the expert software available to help select the optimum valve characteristic form - from Conval and Valve World.
The Plant Maintenance Resource Center has some very useful links on Control Valves including;
- Control Valve Concepts - Control Valves Do What They Are Told!
- Control Valve Terminology - A comprehensive terminology list
- Control Valve Tips & Tricks - An excellent list of useful tips and tricks for the control valve user
- Control Valves - Flow Recovery Coefficient
- Control Valves - Pressure Recovery Factor
Cavitation and Flashing in Control Valves
Control Valve Cavitation, Damage Control - James A. Stares - This paper outlines the application methods used by leading control valve manufacturers to avoid the damaging effect of cavitation on control valve performance and reliability - from Masoneilan.
Cavitation Guide for Control Valves - J. Paul Tullis - This guide teaches the basic fundamentals of cavitation to provide the reader with an understanding of what causes cavitation, when it occurs, and the potential problems cavitation can cause to a valve and piping system. The document provides guidelines for understanding how to reduce the cavitation and/or select control valves for a cavitating system. The guide provides a method for predicting the cavitation intensity of control valves, and how the effect of cavitation on a system will vary with valve type, valve function, valve size, operating pressure, duration of operation and details of the piping installation. The guide defines six cavitation, limits identifying cavitation intensities ranging from inception to the maximum intensity possible. The intensity of the cavitation at each limit is described, including a brief discussion of how each level of cavitation influences the valve and system. Examples are included to demonstrate how to apply the method, including making both size and pressure scale effects corrections. Methods of controlling cavitation are discussed providing information on various techniques which can be used to design a new system or modify an existing one so it can operate at a desired level of cavitation - from the Office of Scientific and Technical Information.
Control Valve Shutoff Classification and Allowable Leakage Rates - Jerry Butz - Sometimes when commissioning or troubleshooting automatic control valves, it is discovered that the control valve, even though fully closed, doesn’t fully shut off the flow of process fluid through the plug and seat. Although closed, there is an “allowable leakage rate” as part of each control valve’s specification. This article aims to clear up some confusion about control valve shutoff - from Flow Control.
Liquid Flow in Control Valves - Choked flow, Cavitation and Flashing - Jon Monsen - This blog gives details on Choked flow, Cavitation, Flashing and how to prevent Cavitation and Cavitation damage - from Valim.
Cavitation in Valves - Cavitation can occur in valves when used in throttling or modulating service. Cavitation is the sudden vaporization and condensation of a liquid downstream of the valve due to localized low pressure zones. When flow passes through a throttled valve, a localized low pressure zone forms immediately downstream of the valve. If the localized pressure falls below the vapor pressure of the fluid, the liquid vaporizes (boils) and forms a vapor pocket. As the vapor bubbles flow downstream, the pressure recovers, and the bubbles violently implode causing a popping or rumbling sound similar to tumbling rocks in a pipe. The sound of cavitation in a pipeline is unmistakable. The condensation of the bubbles not only produces a ringing sound, but also creates localized stresses in the pipe walls and valve body that can cause severe pitting - from Valmatic.
Video - What's Cavitation in Control Valves? - from Fisher.
Video - Fundamentals of Cavitation and Flashing Video - An explanation of cavitation, how it differs from flashing, the damage that it can cause, and methods of controlling it - from Fisher.
The following links are from Samson Controls:
Cavitation in Control Valves - Cavitation can arise in hydrodynamic flows when the pressure drops. This effect is regarded to be a destructive phenomenon for the most part. In addition to pump rotors, control valves are particularly exposed to this problem since the static pressure at the vena contracta even at moderate operating conditions can reach levels sufficient for cavitation to start occurring in liquids. The consequences for a control valve as well as for the entire control process vary and are often destructive causing: Loud noise, Strong vibrations in the affected sections of the plant, Choked flow caused by vapour formation, Change of fluid properties, Erosion of valve components, Destruction of the control valve and Plant shutdown.
Cavitation - Of the greatest importance in connection with valves has to be “cavitation”. Cavitation develops if liquids - due to high velocity - evaporate temporarily in the interior of the valve. The bubbles filled with vapor proceed through the liquid flow in the direction of the valve outlet. Due to an inevitable pressure recovery behind the throttling area the bubbles reach a zone of higher pressure and this leads to a sudden implosion of these bubbles. The implosion effect forms micro jets with velocities of up to 500 m/s. During the impact of such micro jets on a firm body (e.g. valve body wall or trim), extremely high local pressure peaks occur which can destroy almost any material very quickly.
Control Valves for Critical Applications - Know the Causes of Cavitation and Flashing and How to Prevent Them - J. Kiesbauer - In refineries, the process media flowing through valves are primarily liquids. With liquids, critical operating conditions caused by cavitation or flashing may occur. Symptoms are, for instance, increased noise emission, valve and pipe component erosion or low-frequency mechanical vibration in the valve and the connected pipeline. Under these conditions, in particular, neglecting details can result in negative influences on plant performance and costs of ownership. Unfortunately, common practice today is to select control valves in a “quick and dirty” fashion, because the phases of planning, bidding and order processing are connected with significant pressures of cost and time. This article presents the basic principles underlying these problems and shows how to eliminate them based on practical examples from refineries. Moreover, a new throttling element is introduced, that is especially suited to reducing noise emission produced by cavitation. This new throttling element is being implemented in refineries with increasing success.
Taking the Mystery out of Cavitation Pilot-Operated Automatic Control Valves - Brad Clarke and Kari Oksanen - Cavitation can be an extremely damaging force as related to the application of pilot-operated automatic control valves. The consequences of cavitation are numerous and can include: loud noise, extreme vibrations, choked flow, destruction or erosion of control valves and their components resulting in disruption of water distribution or plant shutdown. This white paper deals with cavitation solutions as they relate to valves and specifically pilot-operated automatic control valves. A high level description of what causes cavitation and the associated impacts is covered. Typical occurrences of cavitation and consequences are also discussed in some detail - from Singer Valve.
Vibration of Valves and Piping - What Would Cause Vibration in a Gas Service, and What Protection Can Be Applied If It Occurs? - A question and answer article from Control Global.
Control Valve Characteristics
Guidelines for Selecting the Proper Valve Characteristic - “The tank is overflowing!” Not a nice thought, but that could be a result of a system out of control due to a poor choice of the valve characteristic. Selecting the proper valve characteristic is the easiest way to ensure process stability at all loads. So what valve characteristic to use? This article makes recommendations for the four basic process controlling variables: liquid level, pressure, flow, and temperature. These recommendations are based on a complete dynamic analysis of the process and serve as “rules of thumb” to be used as part of valve selection. The “valve characteristic” refers to the relationship between the position of its flow-controlling element (e.g. valve plug) and its resulting flow. Graphically, this is normally plotted with the valve’s resulting flow on the vertical axis vs. the valve plug’s travel on the horizontal axis. The shape of the resulting output vs. input curve describes the type of valve characteristic - from Emerson Process Management.
Best Control Valve Flow Characteristic Tips - Greg McMillan - Often arguments as to whether a linear or equal percentage trim is best are based on the theoretical inherent flow characteristics. Valve rangeability is often stated as simply a deviation of the catalogue flow characteristic from the theoretical characteristic. Here we will see how the consideration of the changes in process dynamics, available valve pressure drop, and control valve dynamics can alter what you consider as the best flow characteristic - from Control Global.
Control Valve - What you need to Learn? - An interesting paper on Control Valves which includes information on Characteristics, Capacity Sizing and Rangeability - From the School of Chemical Engineering Malaysia.
Determine the Characteristic Curve of an Installed Control Valve - Jeff Sines - The performance of a control valve is defined by its inherent and installed characteristic curves. The inherent characteristic curve is a plot of the percent of valve opening vs. the percent of maximum flow coefficient (CV). The inherent characteristic curve is determined by measuring the flow rate at various positions of valve travel with a fixed differential pressure across the valve (typically 1 psid) and calculating the CV at each position using a form of the generalized Control Valve CV equation - From Engineered Software.
Control Valve Flow Characteristics - Trim design will affect how the valve capacity changes as the valve moves through its complete travel. Because of the variation in trim design, many valves are not linear in nature. The relationship between valve capacity and valve travel is known as the flow characteristic of the valve. Valve trims are specially designed, or characterized, in order to meet the large variety of control application needs. This is necessary because most control loops have some inherent nonlinearities, which you can compensate for when selecting control valve trim - from The Plant Maintenance Resource Center.
Control Valve Emission Control
How Stem Finish Affects Friction and Fugitive Emissions with Graphite Based Control Valve Packing - Mark Richardson - In previous papers we have discussed how graphite based valve stem packing can be used in control valve applications. Benefits of using a graphite based packing include improved thermal stability, compared to traditional PTFE chevron seals though, there is a minor penalty of increased friction. However, whilst the PTFE seals have been widely used for many years, achieving reliable performance with graphite packing sets in high cycle duties requires a different approach to the boundary tribology between the packing and stem. Further research into the effect this has on sealing performance and friction characteristics was required, as these were not well documented nor the effects well understood. The optimisation of the stem condition is required in order to achieve a desired high level of tightness, whilst minimising friction. A greater understanding of these factors, specifically in relation to control valve packing, would allow specification of a valve stem finish based on the sealing material and required performance. This paper discusses the equipment, test methods and results generated using the James Walker methane test facility that simulates a rising stem valve. Tests will be carried out on test stems with surface finishes ranging from polished chrome to a rough ground 2.6µm Ra. Effects of increased packing load and thermal cycling on leakage and friction will be investigated including the hypothesis that there is an optimum surface finish specific to a packing, which maximises performance of these two parameters - from James Walker.
The Development of Effective Fugitive Emissions Control for Valves - Dave Cornelsen - This article discusses development and testing work carried out to help reduce fugitive emissions of VOCs through valves. As restrictions tightened, the scope of the programme was widened to include the development of a new stem packing design. This packing was subsequently evaluated in the laboratory and during field trials - from ValveWorld.
Metal Bellows Seal - Stem sealing constructions utilizing a metal bellows seal, guarantee, unlike conventional stuffing boxes, a maintenance-free service and the retention of the specified tightness. However to ensure a life time of approx. 200,000 full stroke cycles - which corresponds normally to a non-interrupted service of several years - most control valves have to be improved in important details. As a rule of thumb, the length of a bellows seal should be approximately ten times the nominal stroke of the control valve. Only such a design ensures an adequate service life - from Samson Controls.
Packing and Gaskets - The chemical industry has carried environmental surveys for many years. These surveys provide valuable information regarding environmental pollution which is usually related to leaking packings and gaskets. Packings are, in principle, gaskets too, they are, however, in addition exposed to dynamic strain. For the reliability of packings or gaskets there are primarily two factors, Suitable selection of type and material, and regular maintenance, in order to avoid wear and tear and a compression of the sealing element - from Samson Controls.
Fugitive Emissions Philosophies for Control Valves - Holger Siemers - It is interesting to compare the use of the bellows seal design versus low emission packing material. The bellows seal design seems to have been forgotten in international discussions and published papers, but it is still unbeatable as regards its life cycle and 'quality of tightness'. In the 'world of valves' under the requirements of fugitive emissions approximately 5% are control valves - thanks to SA Instrumentation and Control.
Fugitive Emissions and Control Valves - This paper describes the history of the development of the fugitive emissions requests, the standards committees and manufactures reactions to them. How do these standards differ? How do they compare? The paper also describes the approach and issues a control valves manufacturer has to deal with to meet the various requirements on fugitive emissions. It is recognised also that control valves by their function of continuous movement have more tendency to wear out than on/off valves and are therefore more easily subject to packing leakage - from www.valve-world.net.
Video - Sliding-Stem Control Valve Packing - This video gives an excellent description on how spring loaded packing works - from BTC Instrumentation.
Control Valve Packing - Packing is a sealing system which normally consists of a deformable material such as TFE, graphite, asbestos, Kalrez, etc. Usually the material is in the form of solid or split rings contained in a packing box. Packing material is compressed to provide an effective pressure seal between the fluid in the valve body and the outside atmosphere - from The Plant Maintenance Resource Center.
Control Valve Fail Safe Position
Fail-safe Control Valves in Case of Fire - W. Schneider - An essential part of equipment safety is the fail-safe position to be maintained when a fire breaks out. In case of pneumatic linear actuators, the fail-safe position must be assumed and maintained when air supply fails or the diaphragm ruptures - from SA Instrument & Control.
Valve Fail Action - Frederick Meier and Clifford Meier - Control valves may fail in various positions -open, closed, locked, or indeterminate. The position of a failed valve can have a significant impact on associated equipment, and therefore, it is of interest to operations personnel - from the ISA and InTech.
Control Valve Actuator Operating Modes - Details on fail safe conditions, fail closed and fail open - from The Plant Maintenance Resource Center.
Control Valve Leak Class
FCI 70-2-2013 - Control Valve Seat Leakage - You will have to pay to download this document - This standard establishes six classes of seat leakage for control valves. Also defined are specific test procedures to determine the appropriate class. Included are classes commonly associated with double-port, double-seat or balanced single-port control valves with a piston ring seal or metal-to-metal seats; commercial unbalanced single-port, single-seat and balanced single-port valves with extra tight piston rings or other sealing means and metal-to-metal seats; valves for critical applications where the control valve may be required to be closed, without a blocking valve, for long period of time; and resilient seating control valves with "O" rings or similar gapless seals, among others.
ANSI Valve Leakage Standards - There are six different seat leakage classifications as defined by y ANSI FCI 70-2. These are detailed here - from GEMCO Valve.
Leak Testing of Valves - Standards for Acceptable Rates of Valve Leakage - Covers API standard 598, MSS standard MSS-SP-61, ANSI standard FCI 70-2 and ISO standard 5208 - from wermac.org.
Control Valve Seat Leakage - D Sanders - Tolerance of leakage can vary widely from application to application; tight enough in one case can be overkill in another and insufficient in a third. And to top it off, the various industry standards that classify seat leakage in industrial valves fail to address some of the practical issues that confront valve manufacturers, specifiers and end users. In fact, it is quite possible to successfully specify, manufacture and test a valve according to a well-established industry standard, yet still experience less-than-satisfactory results in the field. This article helps address the technical and practical issues related to seat leakage, discussing the fundamentals behind the governing industry standards and offering guidance that users can apply to enhance initial seat leakage performance and help extend the life of their valve assets - from Hydrocarbon Processing.
Leakage Classifications of Control Valves - Classification of seat leakage through control valves - Control valves are designed to throttle and not necessary to close 100%. A control valve's ability to shut off has to do with many factors as the type of valves for instance. A double seated control valve has a very poor shut off capability. The guiding, seat material, actuator thrust, pressure drop, and the type of fluid can all play a part in how well a particular control valve shuts off - from SVF.
Standards for Control Valve Seat Leakage - This document details the various leakage classes - from Mitech.
Control Valve Seat Leakage Classifications - There are actually six different seat leakage classifications as defined by ANSI/FCI 70-2-1976. But for the most part you will be concerned with just two of them: CLASS IV and CLASS VI. CLASS IV is also known as METAL TO METAL. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat. CLASS VI is known as a SOFT SEAT classification. SOFT SEAT VALVES are those where either the plug or seat or both are made from some kind of composition material such as Teflon - from The Plant Maintenance Resource Center.
Control Valve Noise Calculation and Prediction
Valve Noise Prediction verses Velocity Head Limitations in Gas Applications - Joseph Shahda - Principal Engineer Masoneilan - from Masoneilan.
In recent years, the control valve industry has seen an important debate about the validity of limiting the valve trim exit velocity head to a maximum of 480 kPa in gas and steam applications. This velocity limitation is assumed to provide an acceptable noise level and avoid problems that arise in control valve gas and steam applications. However, in a very large number of applications, adopting a velocity limiting approach may require the use of expensive multi-stage or multi-turn trim designs. This article demonstrates that low noise levels can be achieved without following this overly conservative and expensive trim exit velocity head limitation. It also highlights that having a trim exit velocity head lower than 480 kPa will still generate a very high valve noise level if the valve outlet Mach number is high.
Masoneilan Noise Control Manual - from Masoneilan - This 24 page manual provides comprehensive informative material regarding noise in general and control valve noise in particular. It covers Control Valve Noise, Aerodynamic Noise Prediction, Aerodynamic Control Valve Noise Reduction, Atmospheric Vent Systems, Hydrodynamic Noise and Installation Considerations.
Improving Prediction of Control Valve Noise - from Masoneilan.
Control Valve Exit Noise and its use to Determine Minimum Acceptable Valve Size - Alan H. Glenn - This paper describes general aerodynamic noise generation and prediction and, in more detail, the IEC 60534-8-3 exit noise prediction. It will describe noise generation inside the valve and at its exit, its propagation down the pipeline, and its transmission through the pipe wall and into the outside environment. Several sample cases are included. A simple computer program that could be used to facilitate the calculation of the control valve exit noise for control valves is also briefly explained - from Flowserve and Valve World.
Understanding IEC Aerodynamic Noise Prediction for Control Valves - from Emerson Process Management.
Valves: Noise Calculation, Prediction, and Reduction - Béla Lipták - This section begins with an overview of general noise principles, followed by a description of the types of noise produced by ?uid ?ow through control valves. The discussion of control valve noise mitigation includes both the treatment of the noise source (modifying the valve) and the treatment of the noise path (providing downstream insulation or silencers). Other options include protection of the receiver (by personal protective equipment such as earplugs or earmuffs) or the removal of the receiver (by placing a barrier or distance between the noise source and personnel). The section ends with a discussion about recent improvements in predicting and calculating probable noise levels. Because most valve noise calculation standards avoid excessive detail, only the SI system of units will be used in this section. Users of U.S. Customary units should refer to Appendix A.1 and A.2 for the proper conversion factors, including gravitational units conversions (i.e., gc) when necessary - from Unicauca.
Control Valve Noise - Without meaningful standards being adopted in environmental control (to which also the prevention of valve noise appertains), chemical or petrochemical plants would today not be approved. For this reason, “acoustic planning” for the dominating noise sources is categorically required. This applies particularly for compressors, process ovens, cooling fans and not least for control valves and pipelines. In order to keep the emitted sound power within limits quite extensive corrective measures are required. Since noise attenuation measures within a severe costs/benefit analysis must also make sense, one will only implement noise reducing precautions where it is absolutely necessary. As a result, the competitiveness of the whole enterprise, who wants to construct their plant near a residential area, may be questioned if the permissible sound power level near the plant boundaries has to be especially low - from Samson Controls.
Control Valve Performance
A Simple Method to Determine Control Valve Performance and Its Impacts on Control Loop Performance - Michel Rue - A control loop consists of the process, measurement, controller, and a final control element (valve, damper, etc. and its associated equipment such as positioner, I/P). Optimal process control depends on all of these components working properly. Hence, before tuning a loop, one must verify that each component is operating properly and that the design is appropriate. Choosing the optimal PID tuning should be done after making sure all of the other components are working properly. Our experience in the field has shown us that the impact of good tuning is more important than equipment performance itself. We will discuss a method to determine if the valve is performing well and this is done while the process is running. We will demonstrate how a poorly performing valve will have a minimal effect on control loop performance if the tuning parameters are not optimal. However, if a control loop is tuned to achieve performance, the control valve behavior will have a major impact on performance.
How to Achieve Optimal Control Valve Performance - Shawn Anderson and Neal Rineharts - ince control valves are the only devices in the process loop that actually “move” to adjust the process, their performance is critical. The best way to achieve excellent performance is to initially select the most appropriate final control valve for the application and then to maintain its performance over time - from Emerson Process Management.
Evaluation of Control Valve Performance is Necessary in Plant Betterment Programs - Sanjay V. Sherikar - Reproduced with the permission of CCI Sulzer Valves.
Control Valve Rangeability
What is Turndown and Rangeability? - A short definition - from Eng Tips.
Control Valve Rangeability - Greg McMillan - There are a lot of ways of looking at rangeability. Nearly all of them lead to the wrong conclusion as to what type of valve is best for process control. Some of the absolute worse valves for control (e.g. on-off piping valves) have the highest stated rangeability. Valve rangeability is particularly important for pH control, batch control, startup, and plant turndown - from Modeling and Control.
Inherent Rangeability - Ideally the open-loop gain remains constant independent of the position of the valve in a closed-loop control system. Unfortunately, this condition is only achieved in rare cases. Every user has already experienced a situation where a control valve at higher travel positions is completely stable, yet permanent oscillations occur at small travel positions. This is caused by a higher gain of the valve and a steeper slope of the valve characteristic. In order to simplify the application and the selection of control valves for the control specialist, certain boundary values for the slope of the inherent characteristic have been set. In this way, the permissible slope tolerance is exceeded if the inclination of the straight line which connects two neighboring measured values (e.g. points 5 % and 10 %), is more than 2:1 or less than 0.5:1. This rule applies for valve characteristics which the control valve manufacturer has specified for the same travel positions in its literature-from Samson Controls.
Limits of Rangeability - The term rangeability was, for a long time, not clearly defined so that it was interpreted in various ways. Even today “rangeability” is often confused with the term „turn-down ratio“ which means the ratio of maximum to minimum flow through a control valve without regarding any tolerances of the inherent flow characteristic, but usually considering flow repeatability. Using this definition and assuming the application of a control valve positioner which guarantees a travel repeatability of 0.5 %, a turn-down ratio of 100:1 and higher can be achieved, while the rangeability, as defined in standard IEC 60534 is not much greater than 15:1. With most trim types, the plug immerses into the seat ring, which requires a minimum gap width, in order to avoid sticking caused by thermal influences or even seizing of seat ring and plug. As a result, an unintentional flow occurs through the gap. This determines the minimum controllable flow and sets natural rangeability limits for any control valve - from Samson Controls.
Control Valve Sizing
It is very important that if you are contemplating sizing control valves that you source the latest sizing handbooks and/or software from the manufacturers that you are considering,
Masoneilan Control Valve Sizing Handbook - from Masoneilan - Masoneilan have been taken over by GE and thus the Handbook here may not be the latest edition.
Sizing Control Valves - This article defines a more standard procedure for sizing a valve as well as helping to select the appropriate type - From cheresources.com.
Valve Sizing and Selection - Sizing flow valves is a science with many rules of thumb that few people agree on. This article covers a more standard procedure for sizing a valve as well as helping to select the appropriate type of valve. From cheresources.com.
Nelprof Control Valve Sizing and Selection Software - Apply for the CD from Metso Automation.
Valve Sizing Information from Samson Controls.
Sizing Actuated Control Valves - Do you Really Understand your Application Requirements? - Jody Malo - There are many options and several conditions that need to be considered when purchasing a valve. The more information from the field, the better the choice will be. The ultimate goal is to identify the best valve for the job required at the most economical price. While it’s not rocket science to do this, there is some fundamental information that needs to be taken into account - from Flow Control.
Control Valve Styles
Introduction to Valves - By definition, valves are mechanical devices specifically designed to direct, start, stop, mix, or regulate the flow, pressure, or temperature of a process fluid. Valves can be designed to handle either liquid or gas applications. By nature of their design, function, and application, valves come in a wide variety of styles, sizes, and pressure classes. The smallest industrial valves can weigh as little as 1 lb (0.45 kg) and fit comfortably in the human hand, while the largest can weigh up to 10 tons (9070 kg) and extend in height to over 24 ft (6.1 m). Industrial process valves can be used in pipeline sizes from 0.5 in [nominal diameter (DN) 15] to beyond 48 in (DN 1200), although over 90 percent of the valves used in process systems are installed in piping that is 4 in (DN 100) and smaller in size. Valves can be used in pressures from vacuum to over 13,000 psi (897 bar). An example of how process valves can vary in size is shown in Fig. 1.1. Today’s spectrum of available valves extends from simple water faucets to control valves equipped with microprocessors, which provide single-loop control of the process. The most common types in use today are gate, plug, ball, butterfly, check, pressure-relief, and globe valves. Valves can be manufactured from a number of materials, with most valves made from steel, iron, plastic, brass, bronze, or a number of special alloys - from mhprofessional.com.
The following Technical Information is from Samson Controls.
Control Valve Styles - Control valves exist in innumerable styles and options. The most common constructions used in process industries today are discussed. To reach a certain systematic in the description of the various styles, a distinction is made regarding essential criteria and functionalities. A rough overview of the control valves most frequently used is given.
Butterfly Valve Styles - Butterfly valves contain a concentrically or eccentrically oriented disc which can be rotated in a normally sandwich-like housing or body. The angle of rotation is usually 90 degrees for ON-OFF service; for continuous control applications the aperture angle is normally limited to only 60 degrees. Because of the ease of manufacture and the cost-saving construction butterfly valves are - particularly at big nominal sizes and low pressure differentials - a more economical alternative to standard control valves.
Rotary Plug Valves - This valve construction, simply called “the rotary valve”- summarizes different valve styles under a generic term. All of them have one thing in common: a turning valve shaft for adjustments in valve opening. The form of the obturator varies between a simple drilled-through cylinder and a complicated eccentrically positioned plug with a spherical segment surface. To this category also belong armature types which are described as “cock” valves with a cylindrical or conical plug and a special opening cross-section whose profile is authoritative for the flow characteristics of the valve. The so called cock valve, with tapered plug, has been in use for more than 2000 years and was utilized in earlier days - carved out of wood - to tap wine. With the development of new, high corrosion resistant materials like PTFE or PFA which are frequently used for the lining of inferior metallic valve bodies, these well-known constructions have had a renaissance. This principle is used, however, principally for ON-OFF services and only seldom for continuous control applications.
Control Valve Trim Materials
Trim Materials - Gases Versus Liquids - Clean gases are not usually a source of trim erosion, even at high velocities. However, entrained solids or liquid droplets in high velocity gas can wear the trim rapidly. Depending on the fluid’s composition, liquids at high velocity can produce accelerated erosion. For example, at high velocities water causes more damage than lubricating oil. With liquids, another harmful effect is cavitation which can erode most trim material, even hardened trim. Liquid application valves require the use of hardened trim more often than gas application valves - from ValTek.
Control Valve Material Selection, Corrosion and NACE Applications
Selection of Suitable Materials for Control Valves - The sizing and specifying of control valves presupposes a high degree of experience in order to meet the requirements in an optimum manner. This applies particularly to the selection of the correct materials for the valve body, valve bonnet and internal parts (trim). A “low cost” control valve, composed of unsuitable materials soon becomes very expensive if it has to be replaced after only a short working life. On the other hand a valve consisting of expensive, exotic materials does not automatically ensure long durability if other important influential parameters have been disregarded. A selection of suitable materials is by no means made easy by the wide spread offering of valve manufacturers. One is reminded of pharmacies who also offer prescriptions identical or at least very similar under different names. As a kind of introduction, a systematic survey of common control valve materials should be examined in order to provide an orientation for valve designers and users - from Samson Controls.
Corrosion and Erosion in Control Valves - Attack by corrosion occurs especially on the inner walls and internal parts of control valves and is therefore often influential in the durability of a component or for the entire valve. If one examines this corrosion process more closely, one finds that insoluble corrosion products forming an oxide layer develop on the material surface. This layer causes a separation between the attacking fluid and the material. This normally very thin layer is designated as the „passivation layer“ which prevents or at least delays a further corrosion. For this reason, high quality austenitic steels are usually treated at first in a pickling plant before any further fabrication. In this passivation process old oxide layers along with scaling and iron dust are removed and a new, precisely controlled passivation layer is formed. It is obvious that this layer must not show cracks and must not be damaged, otherwise the corrosion attack will continue - from Samson Controls.
Valve Materials of Construction for NACE Applications - from Metso Automation.
How to Select Control Valves - This very useful information from the renowned Béla Lipták comes in three parts - Part 1 - Part 2 - Part 3 - When it comes to selecting and sizing control valves, the non-commercial chart in this article not only helps you pick the right one for the job, but also serves as a fantastic reference tool you can download! From Control Global.
Valve Material Selection Chart - from Turnkey Industrial Pipe & Supply.
Control Valve Maintenance
Overhaul & Repair Of Control Valves - The repair procedure is as follows;
Control Valve Sub-Assembly:
(1) Components are marked to ensure correct orientation upon reassembly, and are tested, to reflect an ‘as received’ condition. (2) Complete disassembly. (3) Grit Blast and inspect all pressure containing components' (4) Supply written inspection report. (5) Recut, polish and Lap seat angles. (6) Hone Packing bore area to ensure no leakage through packing box. (7) Remachine flange gasket surfaces. (8) Replace all soft parts and hard parts as required. (9) Reassemble. (10) Test and Calibrate. (11) Paint.
Actuator & Associated Instrumentation - (12) Complete disassembly and replace soft parts and hard parts as needed. (13) Reassemble. (14) Set Bench Range and calibrate. (15) Paint.
Re-Assembly - (16) Remount all accessories. (17) Replace all tubing and fittings with stainless steel tube/fittings. (18) Test and calibrate valve assembly, including accessories.
Enhanced Maintenance Efficiency with Third-Generation Control Valve Diagnostics - Niklas Lindfors and Juha Kivelä - For more than two decades, maintenance managers and engineers at plants and mills have had a chance to use control valve diagnostics as help when planning shutdown activities. The first diagnostics tools were developed during the 1980s, and since then the technology has taken giant leaps, further providing a wide range of new possibilities. For a rather long time, real-time diagnostic information has been available, including when the process is online, making it possible to predict—and prevent—possible process disturbances. Users are now taking advantage of the additional information available and adopting predictive maintenance strategies to gain more value in the process industry every year. The latest development in the field of diagnostics, the so-called “third generation of diagnostics,” is also playing a role in this transition by further smoothening the shift from traditional corrective and schedule-based to predictive maintenance - from the ISA and InTech.
How to Achieve Optimal Control Valve Performance - Shawn Anderson and Neal Rinehart. - Leaders in the process industries realise that good process control performance is an essential element in achieving world-class reliability as well as optimizing overall process efficiency. Since control valves are the only devices in the process loop that actually “move” to adjust the process, their performance is critical. The best way to achieve excellent performance is to initially select the most appropriate final control valve for the application and then to maintain its performance over time -from Emerson Process Management.
Rethink your Control Valve Maintenance - Neal Rinehart - Learn how new diagnostic tools can help make predictive maintenance a reality - Far too little has been done over the years to sustain the performance of control valves once they go into operation, despite widespread agreement on the impact that valves have on process efficiency. Rather than considering control valves as assets to be preserved, too many plants treat them as liabilities — frequently replacing critical valves during shutdown for no reason other than length of service. As a result, millions of dollars have been wasted and perfectly good control valves often have been discarded - from Emerson Process Management.
The Control Valve’s Hidden Impact on the Bottom Line (Part 1) - Bill Fitzgerald and Charles LindenMany of the profitability issues facing the process industries today can be linked directly to control valve performance. Are there valve-related issues in your plant that you should be concerned about? Part 1 of this article will address dynamic performance of the control valve and how it impacts your bottom line. Part 2 will speak to other valve characteristics that are typically ignored when selecting control valves, such as leakage past the seat, long-term reliability, and maintainability. It will conclude with some case studies that illustrate the dramatic impact that control valves can have on the bottom line - from Emerson Process Management.
The Control Valve’s Hidden Impact on the Bottom Line (Part 2) - Part 1 of this article (VALVE Magazine, Summer 2003) made the case that the control valve, as part of the overall process control infrastructure, is often overlooked when end users consider ways to improve financial performance in their plants. One of the prime reasons for this problem is that control valves are generally selected and maintained as if they were static devices and not part of the highly dynamic process control system - from Emerson Process Management.
Valve Wellness Programs - David W. Douglas - To maximize the utility of diagnostic equipment used in chemical processing, technicians must stretch their knowledge of control valves and related diagnostic equipment that keeps tabs on valve health and safety. Thanks to plantservices.com.
Improving Valve Life and Operating Efficiency The Easy Way - John C. Robertson - Valves are, unquestionably, the most important part of any piping and pumping system because they direct the flow of fluids and regulate temperatures. Properly used and maintained, they can improve process efficiency and lower costs. It is wise to apply the basics of proper valve maintenance in ways that improve their life cycle and operating efficiency. Here are eight often-overlooked valve maintenance basics that can help you do just that. From maintenanceresources.com.
Improving Valve Life and Operating Efficiency The Easy Way - John C. Robertson - Eight often-overlooked valve maintenance basics.
Use of Ultrasonic Analysis in the Testing of Isolating Valves - Offshore installations use a series of isolation valves to divert the flows from the various pumps. One of the main reasons a pump test can "fail", is if the isolating valves are passing. This article describes testing the isolating valves using ultrasonic analysis. Overhaul of an isolating valve costs significantly less than undertaking an unnecessary pump major overhaul.
Control Valve for Safety Instrumented Systems Applications
Functional Safety of Globe Valves, Rotary Plug Valves, Ball Valves and Butter?y Valves - This manual is intended to assist planners and operators during the integration of control valves into a safety loop as part of the safety function and to enable them to safely operate control valves. This manual contains information, safety-related characteristics and warnings concerning the functional safety in accordance with IEC 61508 and concerning the application in the process industry in accordance with IEC 61511 - from Samson Controls.
Reliability Data and the use of Control Valves in the Process Industry in accordance with IEC 61508/61511 - Thomas Karte, Eugen Nebel, Manfred Dietz and Helge Essig - IEC 61508 and IEC 61511 are the relevant standards for the speci?cation and design of safety-related control loops in the process industry. Control valves used in these loops play a key role when it comes to determining the safety integrity level (SIL) of the safety instrumented function (SIF). A wide variety of sensors and PLCs, the other key components in the safety loop, are available with validated data concerning their probability of failure. However, this sort of data is only available for a limited number of control valves as statistical proof is dif?cult to obtain due to the multitude of process conditions that exist in the chemical industry. This paper describes the investigation method used for a series of control valves. The user can determine the SIL achieved using this investigation data, the planned plant structure, and an exact analysis of the process - from Samson Controls.
Enhanced Reliability for Final Elements - Process valves, sometimes also addressed as final elements are in many cases the most decisive factor when it comes to calculating the SIL level for a safety instrumented function (SIF). Due to the large variety of conditions of usage in the process industry there is a lack of appropriate data and approved devices. Testing procedures like partial stroke testing can provide enhanced diagnostic coverage and therefore help to get improved reliability data for the total loop. Verification of this 'diagnostic data' and proper integration of these procedures into the safety instrumented system (SIS) and basic process control system (BPCS) environment at the same time poses a challenge. New developments on actors and relevant approvals are presented as well as instrumentation with new functionality to support diagnostic coverage, different topologies for connection to SIS and BPCS are discussed - thanks to SA Instrumentation and Control.
Split Range Control Valves
Implementing MPC to Reduce Variability by Optimizing Control Valve Response - Ever had a problem with split range valves, this paper may just help! Thanks to www.controlglobal.com.
Split Range Control Valves - This tutorial details just what split range is along with some examples - from Contek Systems.
Control Valve Actuator Design and Operation
The Fisher Control Valve Handbook - This superb 295-page PDF whitepaper is a control valve resource that has been consistently updated for 30 years. It contains vital information on control valve performance and latest technologies. Thanks to Emerson Process Management.
Control Valve Actuator Bench Set Requirements - Jerry Butz - Control Valve “Bench Set” is an often-misunderstood point of confusion, and sometimes incorrectly described part of a control valve’s actuator specifications. But not understanding it can set one up for a failure in the form of a mis-sized actuator and spring. Maybe this information can help to clear the cloud of confusion and make it easier for engineers, technicians, and operators to understand - from Flow Control.
Understanding Control Valve Bench Set - Dave Harrold-from Control Engineering.
Control Valve Actuators - This is ICEweb's Technical Information page on Control and Quarter Turn Valve Actuators.
Control Valve Actuators and Positioners - Control valves need actuators to operate. This tutorial briefly discusses the differences between electric and pneumatic actuators, the relationship between direct acting and reverse acting terminology, and how this affects a valve's controlling influence. The importance of positioners is discussed with regard to what they do and why they are required for many applications-from Spirax Sarco.
Control Valve Actuator Options - Today’s Actuators Offer Imposed Performance With Lower Life-Cycle Costs. The Challenge Is Choosing the Right One for the Application - George Ritz - Over the past several years, valve actuators have received relatively little attention while process control specialists concentrated on controllers, sensors, and other components of the control loop. This is borne out by the unglamorous nickname “pig iron” assigned to the actuator/control valve unit. With the onset of the smart-valve generation, it suddenly appears that the control valve actuator may get more respect along with its new electronics degree - from CCI.
Linear Pistion Actuators - Samy, Stemler - High Reliability of actuation is of paramount importance in the nuclear power industry. Pneumatic actuators form the largest installed base with many in safety significant applications. This paper addresses the issues related to actuation, such as available Thrust, Stiffness, Sensitivity, Hysteresis, Dead band, Dynamic Stability and a sizing example. This paper also presents comparisons between various types of linear actuators and their relative advantages and disadvantages. Also presented will be evaluation techniques for troubleshooting actuator problems and improving plant performance - from CCI.
Closed Loop Breathing - This is a technique to ensure that corrosive or saline air cannot enter the internals of the valve on the breathing side of the valve. It is very popular in the Offshore Oil and Gas Industry and on Coastal Refineries etc - thanks to Rotork for this excellent schematic.
How to Select an Actuator - Wayne Ulanski - As the process industry continues to achieve more efficient and productive plant design, plant engineers and technicians are faced, almost daily, with new equipment designs and applications. One product, a valve actuator, may be described by some as simply a black box, having an input (power supply or signal), an output (torque), and a mechanism or circuitry to operate a valve. Those who select control valves will quickly see that a variety of valve actuators are available to meet most individual or plant wide valve automation requirements. In order to make the best technical and economical choice, an engineer must know the factors that are most important for the selection of actuators for plant wide valve automation. Where the quality of a valve depends on the mechanical design, the metallurgy, and the machining, its performance in the control loop is often dictated by the actuator - from SVF Flow Controls, Inc.
Control Valve Actuators: Their Impacton Control and Variability - Chris Warnett, In a process plant, the general function of a control valve is to restrict the opening of the valve so it affects the flow or pressure of the liquid or gas that is passing through it. In anygiven application, an installed valve, whether it is a rotary or sliding stem valve, has one fundamental variable - the position of the moving element. That single moving element determines the exposed orifice that allows greater or lesser flow through the valve, which inturn provides the control of the process. The valve itself may be extremely sophisticated with exotic body and seat material, or it may have complex flow patterns that allow for a high pressure drop or some other function.However, the fundamental requirement to move the valve stem to position the control element remains the same regardless of whether it is a simple or a sophisticated valve.A control valve actuator is used to move the valve stem (which is attached to the internal control element) to the desired position and hold it in place. In addition to the act of moving and holding positions, there are many other parameters to that movement which determine the best type of actuator that should be used for every specific application. For example, other important considerations might include speed, repeatability, resolution, and stiffness - from Rotork Process Controls and Valve World.
Valve Actuator Accessories
The following links are provided thanks to Austral Powerflo Solutions.
Rotary Limit Switch Boxes - Rotary limit switch boxes provide a visual and remote electrical indication of quarter turn valve/actuator position (ball, butterfly and plug).
Bolt Switches - "Bolt" switches are magnetic proximity switch suitable for any type of position indication.
Valve Position Indicators - The 3D Series namur indicators provide high visibility verification of valve/actuator position. The indicator features a rotor with red and green quadrants that rotate to indicate valve open and valve closed positions.
Butterfly Control Valves
Why a Butterfly - Vinod Bhasin -thanks to Sigma Tech- This is a pretty old document but has some good information.
Application of Butterfly Valves for Free Discharge, Minimum Pressure Drop, and for Choking Cavitation - Flow Component and Control valve Research -Utah State University.
Control Valve Applications
The following links are from Masoneilan.
Avoid Control Valve Application Problems with Physics-based Models - Kinetic energy criteria have many limitations- from Masoneilan - This article explores the rationale for KE limitations and demonstrates that KE criteria often provide very rough approximations of the actual physical phenomena that cause valve problems.
Natural Gas Storage - Valve Solutions - by Larry Swartz.
Getting Optimum Performance through Feedwater Control Valve Modifications - by Brian Leimkuehler and Sanjay V. Sherikar - Reproduced with the permission of CCI Sulzer Valves.
The Application of Control Valves to Compressor Anti-surge Systems - E.W.Singleton - Pipelines transporting gases and vapours are invariably dependent on centrifugal or turbo-compressors for the propulsion of these fluids. Under normal operation, with the compressor running at any constant speed there is a specific relationship between the pressure head across the compressor and the flow through it. But this stable relationship can be disturbed by sudden changes in flow, pressure and density, usually caused by sudden variations in demand downstream of the compressor or in the case of systems requiring multiple compressors a disturbance can be caused by the switching of compressors in and out of service. All these can give rise to formidable pulsations of pressure and flow, better known as a surge. Under surge conditions the compressor may run erratically and a situation can arise where the pressure build up in the downstream pipe may overcome the delivery pressure of the compressor resulting in a flow reversal, reversing the compressor and causing mechanical damage - from Koso Kent Introl.
Control Valves for Pump Protection (Recirculation) Service - EW.Singleton - This paper discusses the essential procedures involved in the application of control valves for the protection of pumps operating at low flow conditions. Automatic Recirculating Valves (ARC Valves), although they do not fall into the category of control valves, do play an important role in pump protection, so a reference to these is also included - from Koso Kent Introl and Valve World.
Control Valve Sourcebook - Pulp & Paper - This Control Valve technical reference is focused on the selection, use and applications in a Pulp Mill - from Emerson Process Management.
Predicting Control Valve Reliability Problems and Troubleshooting in Petrochemical Plants - Critical Outlet Velocities - The Hidden Valve Enemy - Holger Siemers - In the complex area of the prediction control valve reliability, the various aspects of the cost-driven market, which have forced valve manufacturers to develop valves for typical market segments, have to be looked at. In the oil and gas market, a signi?cant portion of valves are severe service valves with high power consumption. A good balance between commercial aspects and necessary safety requirements for the long-term has to be found. This article recommends steps for long-term control valve reliability - from Samson Controls.
Control Valve Design Aspects for Critical Applications in Petrochemical Plants - Holger Siemers - Samson Controls - With three decades of experience in demanding applications, Mr Siemers has a deep appreciation of developments and trends in sizing control valves. In this paper, he reviews the past, present and future of valve design and sizing, taking all-important issues such as increasing cost pressure and time pressure into account. This paper is presented in two parts: firstly, how to use manufacturer independent software to analyse given or calculated plant parameters in more detail from an overall pointof view with a complete power check and optimizing possibilities. Some case studies are also discussed. The second section, scheduled for a future issue, includes information on to design, size and use severe service control valves with good performance for long maintenance intervals. Different philosophies of valve design (plug design), pressure balance systems, stem sealing, actuator sizing, cost philosophies for" high end" applications are discussed. The paper covers:
Accurate sizing & software tools.
Energy saving by plant and valve optimization.
Debottlenecking: Can the old valve do the new job ?
Predictable troubles with control valve sizing in case of sub-critical flow conditions and in case of flashing.
Control valve failures & troubleshooting.
The hidden valve enemy: Critical outlet velocities need to take priority.
Fugitive emissions philosophies for control valves.
Actuator sizing philosophies.
Control valve design and cost philosophies for "high end" applications.
A Valve as a Flowmeter - Because valves are already installed for process control, process optimization and performance can be further improved by using control valves to measure the flow rate - Technical information from Metso Automation.
Control Valve Positioners and Accessories
Smart Valves, Positioners and Flow Conditioning Technology - One of the newer devices that offer improved performance of control valves is the smart positioner. A smart positioner is a microprocessor-based electronic positioner that derives benefit from digital programming to obtain improved positioning performance. Some models offer predictive maintenance and diagnostic benefits as well. An advantage of the smart positioner is that it may be programmed to use a position control algorithm to achieve better dynamic response than standard pneumatic positioners.- from Masoneilan.
Doing Business Differently-Digital Positioners - from Masoneilan.
Smart Technologies Sustain Plant Reliability, Help Control Costs - Todd Gordon - This article highlights the benefits of DVC technologies in a power plant - from Emerson Process Management.
Positioner and Actuator Operating Modes - The terms "direct" and "reverse" are frequently used when discussing control valves, positioners, and controllers. While the definitions of direct and reverse seem pretty straightforward, they cause quite a bit of confusion - especially when split-ranging is done. From The Plant Maintenance Resource Center.
Mission Possible - Analog-to-Digital Valve Upgrades - Sandro Esposito - A transformation is underway in process control, as a wide variety of new digital devices have been introduced in recent years, and a growing number of facilities have installed them. The transition is still a work in progress, however. Some process control facilities have simply been a bit slower to adopt digital valve positioners, for example, as they seek to become more comfortable with this unfamiliar technology. Others have made the switch to digital devices, but have maintained an “analog mindset” and use the digital positioners as they did their analog predecessors. The status quo is maintained and technologies that could help plant operators save time, money and frustration while potentially improving product quality and enhancing safety, are either not adopted or are underutilized. The first step in making the transition to digital valve positioners is understanding how they can be easily and cost-effectively implemented in a facility. This article will begin to bridge that gap by reviewing the various technologies available and highlighting the steps that should be taken to help ensure a successful transition. In addition, it will explain how plant operators can achieve what many consider to be a “mission impossible” - i.e., “hot cutover,” or switching to a digital valve positioner while the process workflow continues uninterrupted - from Kentrol and Flow Control.
Upgrading to Digital Positioners on Feedwater Regulating Valves - Chuck Linden and Bill Fitzgerald - Positioner problems such as spool valve fretting, feedback arms and linkages have been an ongoing issue in the Nuclear Industry. The decision was made to look at new technology in an attempt to eliminate the problem(s). The option of a digital positioner was selected for the upgrade. Several features such as remote mounting capability, on board diagnostics capability and allow integration to a future Digital Process Control System modification at Fort Calhoun Station. Based on the experiences at Fort Calhoun Station and discussions with plants installing digital positioners on Feedwater Regulating valves many of the challenges were similar. This presentation is important because some of the issues were technical in nature but many revolved around cultural paradigms and work practices. To gain the full advantage of equipment upgrades such as this one, one must be ready to address culture and to change work practices - from Fisher.
Intrinsic Safety and Flameproof Enclosure - An Impossible Team in Explosion Protection? - Dipl.-Ing Guido König and Prof. Dr.-Ing. Heinfried Hoffmann - The increasing application of digital field devices in process automation has revived the discussion about the best types of protection for instrumentation used in hazardous areas. The large number of electrical components integrated in microprocessor based devices requires more precautions to be taken per field device in order to ensure explosion protection. A positioner designed for pneumatically operated control valves is used to demonstrate different solutions - from Samson Controls.
Smart Valve Positioners and their Use in Safety Instrumented Systems - Thomas Karte, Jörg Kiesbauer - As part of efforts to reduce life cycle costs of control valves in the process industry, smart electro-pneumatic positioners play an important role due to their self-adaptive features and their highly developed diagnostic functions. Their use can lead to decisive improvements in availability and reliability. To make full use of this potential, which has often been discussed in theory in the past but hardly been put into practice to date, NAMUR Recommendation 107 and Guideline VOl 2650 provide information on the scope of diagnostics and the generation of alarm states. Applications in safety instrumented systems are of particular interest as smart positioners are used more and more with on/off valves in place of classic solenoid valves. In the process industry, the use of on/off valves in safety instrumented systems is governed by the IEC 6 1511 standard. The basic principle behind this standard is the safety management life cycle, which can be effectively supported by the diagnostic functions of positioner - from Samson Controls.
Solenoid Valves - ICEweb's solenoid valve page has a vast amount of information on Solenoids.
Control Valve Education
Professional Certificate Of Competency in Control Valve Sizing, Selection And Maintenance - Control valves are the workhorse of our facilities, continually functioning to ensure our systems work as intended. A properly specified, engineered, designed, installed, and maintained control valve can be one of the most profitable investments a facility can have, while a control valve that "does not work well" can be an increased risk of injury (more exposure of maintenance personnel working on the valve), and disruption to your system. With today's focus on data management, the control valve is the part of the control loop that not only requires integration with modern data collection methods, but also involves mechanical features (moving parts, exposure to process fluids, material selection issues) as well as occupational health and safety issues not associated with other parts of the control loop (such as noise).Often the benefits of modern SCADA systems can be lost with inappropriate or minimal attention to the control valves. This comprehensive certificate course covers the essentials of control valves and actuators. With this knowledge, the user is better placed to fully realize the full potential and benefit of any control system. Selections of case studies are used to illustrate the key concepts with examples of real world working control valves. The course is aimed at those who want to get a solid appreciation of the fundamentals of their control valve design, installation and troubleshooting - from EIT.
Self Operated Regulators
For Details on Self Operated Regulators see ICEweb's Pressure Regulator Page.
ICEweb's comprehensive page on ESD and BDV valves contains a super vault of technical papers on this important subject.
Looking for a valve without corrosion problems? These valves made from plastics and potentially using Nanotechnology techniques may just solve them.
These valves are specific to those power plant issues such as de-superheaters, steam service etc.
HVAC Control Valves
HVAC Control Valves Ball vs. Globe - No longer a Cost Issue - In the past, ball valves had been attractive to HVAC control contractors primarily because they appeared to be half the price of a comparable globe valve. However, this included the purchase price of the valve only, and not the costs of extra pipe reducers and added installation time. That said, with the advent of new ball valves and more competitively priced globe valves, the decision on whether to use a globe or ball valve is no longer dictated by price. This paper addresses some technical differences between ball and globe valves and makes recommendations on factors to consider when selecting the proper valve - from Siemens.
Selecting HVAC Control Valves - from Siemens Building Technologies, Inc. The Tech Tips section from page 90 is particularly relevant.
HVAC Control Valve Characteristics - Amrish Chopra - In HVAC systems, control valves are primarily used to control the flow of chilled water, hot water or steam. To understand the importance of valve flow characteristics in HVAC control it is necessary to understand valve construction, type of valve flow characteristics and few basics of control theory - From - Anergy lnstruments.