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FISHER CONTROL VALVE HANDBOOK PDF

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Fisher is a mark owned by one of the companies in the Emerson Automation The Control Valve Handbook has been a primary reference since its first printing . Fisher, ENVIRO-SEAL and FIELDVUE are marks owned by Fisher Controls The Control Valve Handbook has been a primary reference for more than 30 years. Control valves are an increasingly vital component of modern manufacturing around the world. sppn.info


Fisher Control Valve Handbook Pdf

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Fisher Control Valve Handbook - Fourth Edition. It appears you don't have a PDF plugin for this browser. No biggie you can click here to download the PDF file. sppn.info - Ebook download as PDF File .pdf), Text Fisher, ENVIRO-SEAL and FIELDVUE are marks owned by Fisher Controls. sppn.info ASIA PACIFIC Emerson Process Management The Control Valve Handbook has been a primary reference since its first printing .

Printed in U. Well—selected and maintained control valves increase efficiency, safety, profitability, and ecology. The Control Valve Handbook has been a primary reference for more than 30 years. This third edition is a complete revision and update that includes vital information on control valve performance and the latest technologies.

D Chapter 1 offers an introduction to control valves including definitions for common control valve and instrumentation terminology. D Chapter 2 develops the vital topic of control valve performance. D Chapter 3 covers valve and actuator types. D Chapter 4 describes digital valve controllers, analog positioners, boosters, and other control valve accessories.

D Chapter 5 is a comprehensive guide to selecting the best control valve for an application. D Chapter 6 covers the selection and use of special control valves. D Chapter 7 covers desuperheaters, steam conditioning valves, and turbine bypass systems. D Chapter 8 offers typical control valve installation and maintenance proce- dures.

D Chapter 9 includes information on control valve standards and approval agencies throughout the world. D Chapter 10 offers useful tables of engineering reference data. D Chapter 11 includes piping reference data.

D Chapter 12 is a handy resource for common conversions. The Control Valve Handbook is both a textbook and a reference on the strongest link in the control loop: the control valve and its accessories. This book includes exten- sive and proven knowledge from leading experts in the process control field includ- ing contributions from the ISA and the Crane Company.

Subscribe to view the full document. Introduction to Control Valves 1. For those rotary. Fail-safe action can involve the valve under stated conditions.

Rate of flow through a cess. The effective bulence. This ence between the high and low values term should always be designated as of the diaphragm pressure range.

It is the number of U. Introduction to Control Valves designed for rotary valve service. A condition wherein the valve closure member moves to an open position when the actuating en- Control Valve Functions ergy source fails. This area of a diaphragm might change as seal permits the actuator stem to it is stroked.

A condition wherein the valve closure member moves to a Trunnion Mounting: A style of closed position when the actuating en- mounting the disk or ball on the valve ergy source fails.

The calibration of the ac. A characteristic of a valve Terminology and its actuator. Molded dia- sure. This either inherent flow characteristic or can be stated as an inherent or installed flow characteristic. High-Recovery Valve: A valve de- Effective Area: In a diaphragm ac.

Equal Percentage Flow Charac- site the seal ring. Sometimes called teristic. Clearance Flow: That flow below the Flow Characteristic: Relationship minimum controllable flow with the between flow through the valve and closure member not seated. Flow Coefficient Cv: A constant Double-Acting Actuator: An actua. See also Reverse Flow. Cv related to the geometry of a tor in which power is supplied in either valve. Also pressure range can differ from the called direct acting.

Process Control Terminology: Linear Characteristic.

See Seat Leakage. Quick Opening Flow Characteristic: See Process Control Terminology: Low-Recovery Valve: A valve de. It is because constructions where linear extension of the forces acting on the closure of the actuator stem moves the ball or member that the inherent diaphragm disk toward the closed position.

The ratio of the largest turbulence created by the contours of flow coefficient Cv to the smallest the flowpath. Push-Down-to-Open Construction: Installed Flow Characteristic: The A globe-style valve construction in relationship between the flow rate and which the seat ring is located between the closure member travel as it is the actuator and the closure member.

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Quick Opening Characteristic. A control valve that still does a 17 www. Also called reverse acting. See Fail- bench. This range is often referred to for upper portions of closure member as a bench set range because it will travel. Normally Open Valve: See Fail- Inherent Flow Characteristic: The Open.

The high and low values of istic: An inherent flow characteristic pressure applied to the diaphragm to that provides equal percent character- produce rated valve plug travel with istic at low closure member travel and atmospheric pressure in the valve approximately a linear characteristic body. The term varying process conditions. Although individual designs value. Straight-through flow valves. Introduction to Control Valves stream of the valve vena contracta re.

See tion. The term can also produce rated travel with stated condi. The high and low values of toward the seat ring. Abbreviation for American Na- tional Standards Institute. In diaphragm control valves. A graphical rep- rate is usually stated in pounds force resentation of the calibration report per inch compression. A plot of log ampli- with pressure differential and tempera. Abbreviation for American mended by the manufacturers. ISA to minimum controllable flow rates.

Others included are also popularly used throughout the control Rated Flow Coefficient Cv: The valve industry. Process Instru- pressed as the ratio of the maximum mentation Terminology. It is the most common form of graphically present- Spring Rate: The force change per ing frequency response data. ANSI leakage clas. Relative Flow Coefficient: The ratio ASTM: A calibration curve obtained by downstream of the actual physical re. It is usually shown as percent output span versus percent input span and Other Process Control provides a measurement of hystere- Terminology sis.

Rated Travel: The distance of move- ment of the closure member from the API: Abbreviation for American Pe- closed position to the rated full-open troleum Institute. Steady state output of a device plotted as a function of its Stem Unbalance: The rated full-open position is the maximum opening recom. A con- trol system that operates without hu- Seat Leakage: The quantity of fluid man intervention.

Rangeability can also be ex. Introduction to Control Valves good job of controlling when flow in. Society of Mechanical Engineers. The following terms and definitions Clearance Flow: That flow below the not previously defined are frequently minimum controllable flow with the encountered by people associated closure general member not seated. The curve is usual- duced on the valve stem in any posi. Some of the terms controllable flow has a rangeability of indicated with an asterisk are quoted to 1.

The application Vena Contracta: The portion of a of known values of the measured vari- flow stream where fluid velocity is at able and the recording of correspond- its maximum and fluid static pressure ing values of output readings. In a control valve. Graphic Representation of Various Control Terms 19 www.

Introduction to Control Valves Figure In control sured as a non-repeatability and ex- valve applications. An undesirable oscillation secutive measurements of the output of appreciable magnitude. This is the pressure that actual- Entropy: The theoretical measure of ly works on the actuator diaphragm or energy that cannot be transformed piston and it can be the instrument into mechanical work in a thermody. The region between the limits control device.

NACE is no longer an abbreviation. For a came international. It does not include hyesteresis pressure to the actuator caused by figure The range of op- and the resulting fundamental sinusoi.

A device that operates as the International Society for Mea- automatically to regulate a controlled surement and Control. Instrument Pressure: The output Enthalpy: A thermodynamic quantity pressure from an automatic controller that is the sum of the internal energy that is used to operate a control valve.

Output amplitude and can be subjected without permanent phase shift are observed as functions impairment of operating characteris- of the input test frequency and used to tics. The ratio of the change in output magnitude to the change of ISA: Abbreviation for the Instrument the input that causes it after the Society of America. Operating Medium: This is the fluid.

The return signal Association of Corrosion Engineers. Resistance of metal to stating the lower and upper range val- plastic deformation. Also called the heat content. Abbreviation for Fluid Controls Institute. It is usually mea- at or near the stability limit. Abbreviation for Occupational Safety and Health Act.

The frequency-dependent rela. Now recognized steady-state has been reached. Loading Pressure: The pressure ume multiplied by the pressure: A physical variable. Action in which two or values of control valve supply pres- more signals are generated or two or sure are 20 psig for a 3 to 15 psig more final controlling elements are ac. Error of a device operat- that input signal figure The pressure at Signal Amplitude Sequencing Split the supply port of a device.

It is usually expressed as per- tween the upper and lower range val. The algebraic difference be. Introduction to Control Valves 22 www.

Reducing process variability through better process control allows optimiza- Process Variability tion of the process and the production of products right the first time. Reducing pro. These specification means lost profit due to marketing challenges must be met al. A quality product mize plant throughputs with fewer re. To deliver acceptable returns to their shareholders.

Control valve

Market process control technology is recog- globalization is resulting in intense nized as an effective method to im- pressures to reduce manufacturing prove financial returns and meet glob- costs to compete with lower wages al competitive pressures. Competition exists between The basic objective of a company is to international companies to provide the make a profit through the production highest quality products and to maxi.

Most on this distribution. These are typi- cally performed in a flow lab in actual The problem. This band is the variability of the instrumentation to address the prob- process. Fur- set point needs to be established at a thermore.

Reducing process variability is a key A statistically derived band of values to achieving business goals. Process Variability variable both above and below the set The most desirable solution is to re- point. Evalu- and resources are being wasted by ating control valve assemblies under making a large percentage of the closed-loop conditions provides the product to a level much greater than only true measure of variability perfor- required by the specification see up.

Pro- cess Variability see definition in Unfortunately. Closed-loop performance data per distribution in figure It is a measure of how tightly lem of process variability reduction. A process that is in control.

More than one isolated parameter must be considered. Some of the output CO values fails to produce a most important design considerations change in the measured process vari- include: Control Valve Performance Figure When a load disturbance occurs..

Each of these design features will be considered in this chapter to provide The ability of control valves to reduce insight into what constitutes a superior process variability depends upon valve design.

Dead Band search within the industry has found the particular design features of the Dead band is a major contributor to final control element. Valve compo. Most importantly. Only when the controller output has changed enough to progress through the dead band does a corresponding change in the process variable occur.

This is misleading because it ignores engineered valve should respond to the performance of the valve itself. The valves are subjected to a nal changes. Control Valve Performance back through the process. Effect of Dead Band on along with shaft wind-up in rotary Valve Performance valves. Any time the controller output re- verses direction. Only then can a corrective action occur.

In a recent plant audit. Figure 2—3. Because tions. The presence of dead band in the process ensures the process variable deviation from the set point will have to increase until it is big enough to get through the dead band. Valve B requires input sig- 26 www. A well. This diagram represents an In all three valve tests figure On the other hand. Rack-and-pinion actuators are particu- ability. Piston actua- siderably worse. In addition. The ability of and the elastomer degrades.

Packing friction is the primary source of friction in sliding stem valves. This illustrates entirely. Spline valve seals during manufacture. As a result. An additional advantage of of control valve applications specified 27 www.

For best performance in reducing pro- ing effect these higher friction torque cess variability. In Actuator-Positioner Design these types of valves.

Some valve shaft connections Manufacturers usually lubricate rotary also exhibit dead band effects. Valve C is con. Valves B and C figure show the devastat. Rotary valves are tenance is not performed.

Positioners are used with the majority tuators. Because of the high Backlash see definition in Chapter 1 seal friction and poor drive train stiff.

This does not translate motion to the con. If that main- in control valves. The combina- valve styles and packing arrange. A well-engineered control the misleading performance conclu.

Backlash commonly occurs in significant dead band that clearly has gear drives of various configurations. Control Valve Performance today. With the increasing emphasis Spool valve positioners are relatively upon economic performance of pro.

The namic gain. Unless the device is sensitive these devices by using spool valves to these small signal changes. These microprocessor- Although the positioner preamplifier based positioners provide dynamic can have high static gain.

Chapter 4. Positioner gain is composed of type of device generally has low sen- two parts: Many high gain spool valve device serves as this high static gain positioners have static instrument air preamplifier. In many pneumatic consumption of these high gain spool positioners. Relays are preferred be- move rapidly to provide a timely cor. This power amplifier positioning accuracy and faster re. The input stage of these posi- tioners is often a low static gain trans- The most important characteristic of a ducer module that changes the input good positioner for process variability signal electric or pneumatic into reduction is that it be a high gain de.

They also provide valve moni- tion must be supplemented by a high toring and diagnostic capabilities to dynamic gain power amplifier that help ensure that initial good perfor- supplies the required air flow as rapid. Positioners allow for precise ly as needed. This increases the dy- process variable. This high static gain namic power gain of the device. In other less subject to fluid contamination. Positioner designs are changing dra- tuator to make it respond promptly.

In automatic. This can be a dangerous loop where the process time constant combination of factors from a stability approaches the dead time. These two cess variability will be improved. For affect the dead time of the valve as- example. Some valve any given valve assembly. T63 is the must have a high dynamic gain to time measured from initiation of the minimize the dynamic time of the input signal change to when the out.

This type of behavior is typically induced by the asymmetric For optimum control of many pro. Control Valve Performance In summary. If the valve assembly is in a fast that easy.

Gen- the slower the valve response time. A the loop for best overall performance. On these fast loops. It is important to keep the the actuator air chamber to be filled. This dynamic time ler are for small changes in position. The dynamic time is ume of air to the actuator.

Of friction in the valve body and actuator course. In a pneumatic valve parameter called T63 Tee At first. It includes both the valve as. Recognizing that the po- time can dramatically affect loop per. If will be determined primarily by the dy- a control valve assembly can quickly namic characteristics of the positioner respond to these small changes.

In other sembly dead time. Supply pressure also affects the vol- One way to reduce the actuator air ume of air delivered to the actuator. On rotary valve actuators. This higher been optimized for a particular supply thrust-to-friction ratio reduces dead pressure. Actuator style alignment. This gain. It is also directly linked to air phragm actuator.

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Instrument supply pressure can also have a significant impact on dynamic performance of the valve assembly. In addi. To minimize the valve assembly dead ally necessary to use a higher air time. To obtain the required thrust with a piston actuator. These friction problems also valve assembly friction. As indicated. As mentioned. This means that a packing friction.

These fric- go into an unstable oscillation. Control Valve Performance used. The tradeoff is a psig might find its gain cut in half possible detrimental effect on the when the supply pressure is boosted valve response time through in- to 35 psig. Piston actuators usually have valve positioners can consume up to higher thrust capability than spring. If the overall thrust-to-friction ratio is For example. For both of these alternatives mean that a example. Good engineering judgment must One of the surprising things to come go into the practice of valve assembly out of many industry studies on valve sizing and selection to achieve the response time has been the change in best dynamic performance from the thinking about spring-and-diaphragm loop.

Extensive testing of constant. Higher friction in 1. This mistaken belief arose from many Valve Type And years of experience with testing Characterization valves for stroking time. Control Valve Performance Having a positioner design with a high valves has shown that spring-and-dia- static gain preamplifier can make a phragm valve assemblies consistently significant difference in reducing dead outperform piston actuated valves on band.

This can also make a significant small signal changes. Research has shown this to valve assembly design. Many pro. It assembly is installed in a fast process is not simply a matter of finding a loop. It has long been a misconception in the Figure shows the dramatic differ- process industry that piston actuators ences in dead time and overall T63 re- are faster than spring-and-diaphragm sponse time caused by differences in actuators.

While a valve assembly to complete its full valve must be of sufficient size to stroke in either direction. In normal pro. Since valve flow 3 for a complete description. Valve Response Time Summary Typically. The greatest of the valve. This is not a which caused the flow change is de- normal situation in practice.

These characteristics are gain that is the greatest at the lower called the inherent flow characteristic end of the travel range. Typical valve characteris.

The installed drop across the valve is allowed to process gain at any operating condi- change naturally. Installed flow characteristic curves larly rotary ball valves. Many valve designs. An illustration of such change in output flow to the percent an installed flow characteristic is change in valve assembly input sig- shown in the upper curve of figure nal.

Installed Flow Characteristic and Gain centage valve is at the largest valve The flow in this figure is related to opening. A Knowledge of the inherent valve char.

Installed gain. The loop is placed in manual valve cages or plugs that can be inter. The slope of this process optimization is the installed flow curve is then evaluated at each flow characteristic of the entire pro. The installed part of figure Inherent valve characteristic is an in- herent function of the valve flow pas.

Although the 4-to-1 ratio of gain ing gain of the unit being controlled. If too much point flow condition. There is nothing magic gain get too large. Version 2. It is Loop gain should not vary more than good operating practice to keep valve a 4-to-1 ratio.

In gains of such devices as the control this case. EnTech Control Inc. Because Ontario. Control Valve Performance The reason for characterizing inherent agree produces an acceptable range valve gain through various valve trim of gain margins in most process con- designs is to provide compensation trol loops. The end goal is to maintain a This guideline forms the basis for the loop gain.

In other words. Because these two inverse relationships should the valve is part of the loop process balance out to provide a more linear as defined here. As the flow varies gain variation occurs in the control about that set point. The loop can be- about this specific ratio. It is good possible to maintain optimum perfor. Some industry experts installed process gain.

There is also a danger that is still a 4-to-1 ratio. The potential dan- the loop gain might change enough to ger inherent in using this reduced gain cause instability. If the loop gain change due to gain in the controller as possible. For ex. March flow characteristic for the process The control range of a valve varies dramatically with valve style.

If the inherent characteristic of a valve could be selected to exactly compen- Process optimization requires a valve sate for the system gain change with style and size be chosen that will keep flow. The nonlinear feedback Other valve styles.

Effect of Valve Style on Control Range point in the travel. Because butterfly valves typically namic performance and loop stability have the narrowest control range. Figure This condition can be alleviated by shows a line-size butterfly valve changing the inherent characteristics compared to a line-size globe valve.

To ensure good dy. The best process performance occurs when the required flow characteristic Regardless of its actual inherent valve is obtained through changes in the characteristic. Using cams performance through a reduction of to characterize the valve is usually not process variability. Control Valve Performance the entire valve assembly. This technique recalibrates the ing the controller. Proper selec- simply relying upon a change in the tion of a control valve designed to pro- design of the valve trim.

This technique is sometimes re. Oversizing of valves sometimes oc- which severely limits the dynamic re. The second way oversized valves hurt however. Because an over- process to only a 0. For example. This is because the cam also dramatically Valve Sizing changes the positioner loop gain.

Best performance valve input signal by taking the linear results when most loop gain comes mA controller signal and using a from the controller. Many increment of valve travel.

This method. Some electronic devices attempt to Oversizing the valve hurts process produce valve characterization by variability in two ways. It variability. This results from as effective as characterizing the using line-size valves.

For valve travels above about 50 an open-loop situation. Valve A in figure sense to select a control valve for does a good job of following the present conditions and then replace trend of the minimum variability line the valve when conditions change. Although it is pos- low travel. This situation came about be. Valve A. This diagram plots process variability as a percent of the set point variable The valve shown in figure is totally versus the closed-loop time constant. Economic Results All three valve designs are capable of controlling the process and reducing Consideration of the factors discussed the variability.

Valves B and C characteristic. Consider what would hap- impact on the economic results of an pen if the poorer performing Valve B operating plant. The closed-loop test re- ing zero and the valve must undergo sults shown in figure demonstrate wide changes in travel with very little the ability of three different valves to resulting changes in flow. This valve shows excellent dy- When selecting a valve.

More and more con. The line slop- chosen. Control Valve Performance opening valve.

Control Valve Handbook.Pdf - Process Control and Instrumentation

While it might seem counter. Process control studies Not all valves provide the same dy- show that.

In contrast. All real valve assemblies valve. While the initial cost might vide this much improvement every be higher for the best control valve. This 1. This example is ciently adequate to deal with the dy- 38 www. While important. A valve that can pro. Decreased energy costs. Closed-Loop Performance a 2. Often the extra initial cost of the the set point. This might not seem like ways a good control valve can in- much.

The excellent performance of the bet. The is imperative that these specifications valve is called the final control ele. Control Valve Performance namic characteristics of process con. Although extremely important role in producing traditional valve specifications play an the best possible performance from important role. Process optimization must also address real dynamic per- means optimizing the entire process.

Parts of the loop cannot be tion system capable of achieving 0. Profitability in. Iso- formed on thousands of process con. It makes no sense to Finally. Audits per. It the control room equipment. Summary Control valves are sophisticated. They use shaft. Chapter 3 Valve and Actuator Types Control Valves Many styles of control valve bodies have been developed through the The control valve regulates the rate of years.

D Contain the fluid without external leakage. Some have found wide applica- fluid flow as the position of the valve tion. D Single port is the most common valve body style and is simple in D Be capable of withstanding the construction. To do this. Angle valves are nearly always single ported figure The valve shown has cage-style construc- tion. Others might have screwed-in Bar-stock valve bodies are often spe- seat rings. Flanged Angle-Style Con- where space is at a premium and the trol Valve Body valve can also serve as an elbow.

D Cage or retainer-style single- seated valve bodies can also be easi- ly modified by change of trim parts to provide reduced-capacity flow. Retainer-style trim also offers ease of Figure They for reduction of erosion damage. Figure shows two of the more popular styles of single-ported or single-seated globe-type control valve bodies. D Many modern single-seated valve bodies use cage or retainer- style construction to retain the seat- ring cage.

They are widely used in pro- cess control applications. Normal flow direction is most often up through the seat ring. Single-port valves can handle most service requirements. D Because high-pressure fluid is normally loading the entire area of the port. Balanced Valve Plug. Flanged versions are available with ratings to Class Variations permits choice of several flow charac- available include cage-guided trim.

Reduced un- duced from a casting. Cage-style trim provides valve plug guiding. Valve Body with Cage- Style Trim. Interchangeability of trim gas and oil figure Bar Stock Valve Bodies Figure High Pressure Globe-Style plug and the wall of the cage cylinder Control Valve Body virtually eliminates leakage of the up- stream high pressure fluid into the bar-stock material and from some lower pressure downstream system.

For most 43 www. When exotic metal alloys are Downstream pressure acts on both required for corrosion resistance. This adaptation of the cage-guided D Many double-ported bodies re- bodies mentioned above was de- verse. D Port-guided valve plugs are Use of noise abatement trim reduces often used for on-off or low—pressure overall noise levels by as much as 35 throttling service.

D Port-guided single-port valve bodies are typically provided with screwed in seat rings which might be difficult to remove after use. These are available in various material combinations. The provides only Class II shutoff capabili- design incorporates oversize end con.

Cage-Guided Valve pacity than single-ported valves of the Bodies same line size. D Metal-to-metal seating usually tional valve bodies figure D Bodies normally have higher ca- High Capacity. D They are susceptible to velocity- induced vibration.

The valve with unbalanced constructions nor. The control valve body shown in fig- vice. Top-and-bottom- decibels. Also available in cageless guided valve plugs furnish stable op- versions with bolted seat ring. Flow direction depends on the ure 3—7 is assembled for push-down- intended service and trim selection.

Class High Capacity Valve Body one port and close the other. This position opens the bottom common port to the right-hand port D Butterfly valve bodies offer econ- and shuts off the left-hand port. D Actuator selection demands careful consideration. Control Valve Standard end connections flanged. D Best designs use cage-style trim for positive valve plug guiding and ease of maintenance. The omy. Typical Butterfly selected for high temperature service. Reverse—Acting Double.

Three-Way Valve Bodies D Three pipeline connections pro- vide general converging flow-mixing or diverging flow-splitting service. D Bodies require minimum space Balanced valve plug style three-way for installation figure Larger cous fluids.

D Ball remains in contact with seal tained by using a liner or by including during rotation. D Bodies are available with either D A dynamically contoured disk.

Control Valve Application Tools

These control valves have good rangeability. This construction is similar to a con- ventional ball valve. The paper industry. Smaller sizes can use versions of traditional diaphragm or piston D V-notch ball control valve bodies pneumatic actuators. Valve with V-Notch Ball quire high-output or large actuators if the valve is big or the pressure drop is high.

D Conventional contoured disks provide throttling control for up to degree disk rotation. Rotary-Shaft Control D Butterfly valve bodies might re. The V-notch produces an very stringent leakage requirements. Soft-seat construction can be ob. D Units are available for service in contoured V-notch in the ball figure nuclear power plant applications with D Standard butterfly valves are available in sizes through inch for D Straight-through flow design pro- miscellaneous control valve applica.

They can be used for piston rotary actuators. Butterfly valves exhibit an approximately equal percentage flow D They use standard diaphragm or characteristic. Valve and Actuator Types terms of flow capacity per investment dollar. D Valve assembly combats ero- sion. Conse- quently. D Path of eccentric plug minimizes ies are available in sizes through contact with the seat ring when open- inch compatible with standard ing.

They are fre- quently applied in applications requiring large sizes and high temper- body end connections. D They use standard pneumatic diaphragm or piston rotary actuators. ASME flanges. Both flanged atures due to their lower cost relative and flangeless valves mate with Class to other styles of control valves.

Chapter D Self-centering seat ring and rugged plug allow forward or reverse D Standard flow direction is depen. They control. D Eccentric-disk control valve bod.

The Eccentric-Disk Rotary-Shaft Control Valve Eccentric disk rotary shaft control valves are intended for general ser- vice applications not requiring preci- sion throttling control. D Eccentric-disk control valve bod- ies provide linear flow characteristic Eccentric-Plug Control Valve through 90 degrees of disk rotation Bodies figure They are used on all Screwed Pipe Threads valve sizes.

This style of rotary control valve suits erosive.

Valve and Actuator Types cluding ceramics. Valve maintenance might The raised face flange features a cir- be complicated by screwed end con. This kind of flange is used with a variety of gasket materials and flange materials Bolted Gasketed Flanges for pressures through the psig Flanged end valves are easily re.

Flanged end connections end connections. The most common Screwed end connections. D Designs offering a segmented V-notch ball in place of the plug for higher capacity requirements are available. The breaking a flanged joint or union con. This construction is commonly male threads on the pipeline ends. The flanged or flangeless valves feature streamlined flow passages and rugged metal-trim components for dependable service in slurry applications.

The threads usually specified are tapered female The flat face variety allows the match- NPT National Pipe Thread on the ing flanges to be in full face contact valve body. They form a metal-to-met. Trims face concentric with the valve open. Generally rotary valves do not have bonnets. This makes an excellent joint at ies. On some rotary-shaft valves. They are usual- ly furnished in sizes through 2-inch.

Valve and Actuator Types styles. The gasket consists of a metal terials must be removed before weld- ring with either an elliptical or octago. Welding ends come in two equivalent forged material because it 49 www. When the flange bolts are tightened. Care must be exercised The ring-type joint flange looks like when welding valve bodies in the the raised-face flange except that a pipeline to prevent excessive heat U-shaped groove is cut in the raised transmitted to valve trim parts. Common Welded End two ends are then butted to the pipe- Connections line and joined with a full penetration weld.

The socket welding ends are prepared by boring in each end of the valve a socket with an inside diameter slightly larger than the pipe outside diameter. The The bonnet of a control valve is that gasket is generally soft iron or Monel part of the body assembly through Trademark of Inco Alloys Internation.

The pipe slips into the socket where it butts against a shoulder and then joins to the valve with a fillet weld. The Figure These are generally furnished and all steel and alloy steel bodies. Welding end valves are On a typical globe-style control valve more difficult to take from the line and body. Socket welding ends in a given size are dimensionally the same regard- less of pipe schedule. On globe or angle bod- al. This type of joint is used on all valve styles and the end preparation This style of flanging is normally stan.

It is means of mounting the actuator to the furnished only on steel and alloy valve body and houses the packing box. The bonnet normally provides a ly not used at high temperatures.

Several area on the side of the packing box styles of valve body-to-bonnet con. Extension cage. Typical Bonnet. This alternate is compact.

The bonnet also provides alignment for the cage. The compresses a flat sheet gasket to seal frost crystals can cut grooves in the the body-bonnet joint. Extension bonnets are used for either high or low temperature service to On control valve bodies with cage.

The most opening is closed with a standard pipe common is the bolted flange type plug unless one of the following condi- shown in figure showing a bon. The damage at low process temperatures tightening of the body-bonnet bolting if frost forms on the valve stem. The packing is most often retained by a packing fol- lower held in place by a flange on the yoke boss area of the bonnet figure An alternate packing retention means is where the packing follower is held in place by a screwed gland figure Stan- nishes loading force to prevent leak.

D It is necessary to purge the ble. Most bolted-flange bonnets have an rosion effects as the body.Response Time: Figure illustrates a top-mounted dictive maintenance. Relationship minimum controllable flow with the between flow through the valve and closure member not seated.

Using cams performance through a reduction of to characterize the valve is usually not process variability. The closeness to which a the vertical axis is labeled as percent curve relating to two variables approx- flow or Cv figure Examples ers.

Push-Down-to-Open Construction: In other sembly dead time. Selection of a bellows from stainless steel tubing.