Control Valve Guide
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Setpoint Integrated Solutions is an industry leader in applying Control Valve solutions across industry segments. Brannon Gant - Regional Sales Manager
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Control Valve Guide
- 1. WHEN ACCURACY MATTERS IntroductionIntroduction toto Control Valve TypesControl Valve Types
- 2. WHEN ACCURACY MATTERS • IEC Definition: A power operated device which changes the fluid flow rate in a process control system. It consists of a valve connected to an actuator that is capable of changing the position of the closure member in the valve in response to a signal from the system • ISA Definition: A power operated device which modifies the fluid rate in a process control system. It consists of a valve connected to an actuator mechanism that is capable of changing the position of a flow controlling element in the valve in response to a signal from the controlling system. Control Valve DefinitionControl Valve Definition
- 3. WHEN ACCURACY MATTERS 5050 PSIGPSIG TANKTANK PC Supply Steam P1 = 75-100 psig Positioner Analog Electro-Pneumatic Control Signal 4-20mA Process Variable 4-20mA Where does a CV fit in the Control SystemWhere does a CV fit in the Control System
- 4. WHEN ACCURACY MATTERS • Feature – Ruggedly built for high cycle service – Always provides tight shutoff – Valve bore approximates line size – Always provide system effect with travel change – Used to alter flow in response to control signal – “Absorbs "large amount of energy • On-Off Valve – No – Yes – Yes – No – No – No • Control Valve – Yes – No – No – Yes – Yes – Yes Control Valve vs On/Off ValveControl Valve vs On/Off Valve
- 5. WHEN ACCURACY MATTERS Typical Isolation ValvesTypical Isolation Valves HP Butterfly Full Port Ball Sleeve Lined Plug Manual Globe Manual Gate
- 6. WHEN ACCURACY MATTERS Control Valve HierarchyControl Valve Hierarchy Pressure Drop HPBV Ball Rotary Globe Globe Severe Duty
- 7. WHEN ACCURACY MATTERS Control Valve TypesControl Valve Types • Reciprocating – Globe – Angle – Severe Service • Rotary – Butterfly – Ball – Rotary Globe
- 8. WHEN ACCURACY MATTERS Basic Butterfly ValvesBasic Butterfly Valves Poor Control Valve
- 9. WHEN ACCURACY MATTERS High Performance Butterfly ValvesHigh Performance Butterfly Valves Better Control
- 10. WHEN ACCURACY MATTERS Types of Butterfly ValvesTypes of Butterfly Valves Concentric Centerline Single Offset (Eccentric) Double Offset (HPBV) 2 1 2 1 3 Tripple Offset
- 11. WHEN ACCURACY MATTERS Ball ValvesBall Valves
- 12. WHEN ACCURACY MATTERS Segmented BallSegmented Ball Control ValveControl Valve Un-Restricted Flow Path Un-Restricted Flow Path Partially Open
- 13. WHEN ACCURACY MATTERS Segmented Ball ValvesSegmented Ball Valves • Partial Ball – 90 Deg. Rotation • High Capacity & High Turndown • Characterized Segmented Ball • Single Metal or Soft Seat Notice the Single Clamped Seat Notice the Characterization
- 14. WHEN ACCURACY MATTERS Eccentric Rotary GlobeEccentric Rotary Globe
- 15. WHEN ACCURACY MATTERS CAMFLEX AnimationCAMFLEX Animation
- 16. WHEN ACCURACY MATTERS Reciprocating Control ValvesReciprocating Control Valves
- 17. WHEN ACCURACY MATTERS Single Port UnbalancedSingle Port Unbalanced • Globe Valve • Unbalanced Design • Post Guided • Lo-dB Trim • Class-IV & Class-V Shut- Off • Flow To Open • Flow To Close
- 18. WHEN ACCURACY MATTERS LEAKAGE CLASSESLEAKAGE CLASSES • CL IV, Standard – .01% of Rated Cv • CL V, Optional – Reduced Pressure Drop Capability Due to Higher Seat Loads Required • CL VI, Optional – Plug with PTFE Seal Ring
- 19. WHEN ACCURACY MATTERS QUICK CHANGE TRIMQUICK CHANGE TRIM • Maintenance Advantage • Seat Ring Held in Place by the Seat Ring Retainer (A Type of Cage) • Seat Ring Gasket Required
- 20. WHEN ACCURACY MATTERS TRIM TYPESTRIM TYPES • Contoured Trim – Full Area – Reduced Area • Single Stage Lo-dB and Anti-Cavitation • Two-Stage Lo-dB and Anti-Cavitation
- 21. WHEN ACCURACY MATTERS LOW NOISE PRODUCTSLOW NOISE PRODUCTS • LO-DB Trim Reduces the Sound Level up to 15 dBA Over Conventional Trim, Depending on the P1 /P2 Ratio. SINGLE-STAGE Lo-dB TRIM
- 22. WHEN ACCURACY MATTERS Angle Single Port UnbalancedAngle Single Port Unbalanced
- 23. WHEN ACCURACY MATTERS Venturi Seat RingVenturi Seat Ring Extreme Conditions High Pressure Drops Sever Coking Conditions Flashing Liquids Emergence Blow Down
- 24. WHEN ACCURACY MATTERS Single Port BalancedSingle Port Balanced • Globe Valve • Fully-Balanced Design • Cage Guided • Composite Polymer Balancing Seal • Class-V Shut-Off • Flow To Open
- 25. WHEN ACCURACY MATTERS Single Port BalancedSingle Port Balanced
- 26. WHEN ACCURACY MATTERS CAGE GUIDED VALVESCAGE GUIDED VALVES • The cage provides positive alignment and control of the plug • The cage can modify or “characterize” the flow The Cage Serves Two Major Functions
- 27. WHEN ACCURACY MATTERS CAGE GUIDED - PRESSURE BALANCEDCAGE GUIDED - PRESSURE BALANCED TYPICAL APPLICATIONS • Clean Process Fluids • High Pressure, High Temperature, Noise, and Cavitation LIMITATIONS • Slurries or Gritty or Dirty Processes • Less Capacity Compared to Rotary Valves • Larger and Heavier than Most Rotary Valves
- 28. WHEN ACCURACY MATTERS CAGECAGE • Acts as Sealing Surface for Plug Seal Ring • Retains Seat Ring • Provides Throttling Orifice • Guiding Surface
- 29. WHEN ACCURACY MATTERS SEAL RINGSSEAL RINGS • Metal Seal Ring – Class II – Temp: -320o F to 650o F • PTFE Seal with Backup – Meets Class IV Seat Leakage – Temp: -20o F to 300o F • Graphite Seal Ring – Meets Class IV Seat Leakage – Temp: -320o F to 1050o F
- 30. WHEN ACCURACY MATTERS Pressure Energized Seal RingPressure Energized Seal Ring • Pressure Energized PTFE Plug Seal • Class V Leakage • Max Temp: 450o F (600o F) • Uni-Directional • Higher Shutoff Capability
- 31. WHEN ACCURACY MATTERS AUXILIARY PLUGAUXILIARY PLUG • Flow-To-Close Direction Only – Approx. 10 dB Less Attenuation Than F-T-O • Tight Shutoff at High Temperature • Class IV, Class V Leakage • “Dead” Travel in Closed Position = 0.050”
- 32. WHEN ACCURACY MATTERS AUXILIARY PLUGAUXILIARY PLUG • Cage Guided • Balanced • Single Seated • Captured Seat Ring (QC) • Pilot Trim Stem Packing Ring (S) Cage Balancing Seal Packing Follower Auxiliary Pilot Plug Body Seat Ring Guide Bushing Plug (Main) Bonnet
- 33. WHEN ACCURACY MATTERS Double Port (Semi Balanced)Double Port (Semi Balanced)
- 35. WHEN ACCURACY MATTERS 80000 Series 3 Way80000 Series 3 Way 80000 Series 3 Way DivertingCombining
- 36. WHEN ACCURACY MATTERS Bellows SealBellows Seal
- 37. WHEN ACCURACY MATTERS Low / Micro FlowLow / Micro Flow
- 38. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Raised Face (RF)
- 39. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Weld Prep Butt Weld
- 40. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Socket Weld
- 41. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Ring Type Joint (RTJ)
- 42. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Clamp Connection (Graylok,ReFlange)
- 43. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Threaded (NPT,MS)
- 44. WHEN ACCURACY MATTERS Flangeless End ConnectionsEnd Connections
- 45. WHEN ACCURACY MATTERS End ConnectionsEnd Connections Separable Flange
Editor's Notes
- The Control Valve is a Pressure containment vessel consisting of an internal closure member referred to as Control Valve Trim. The closure member or trim is connected to a stem that is connected to a power operated device designed to modulate the internal trim. The power operated device could be air operated, electrically operated or hydraulically operated.
- The purpose of a control valve is to provide a means of implementing a control strategy for a given process operation. The Control Valve is considered the final control element in a process control loop. Control valves are normally regarded as valves that provide a continuously variable flow area for the purpose of regulating or adjusting the fluid flow rate or pressure in a piping system. The diagram depicts a Feedback Control Loop where the sensing element is downstream of the control valve monitoring adjustments that are made to maintain Setpoint.
- Isolation valves differ greatly from Control Valves. Friction is an enemy of a control valve simply because it prohibits the ability for high resolution control or inhibits the ability for small controlled micro adjustments. Control valves are designed to cause a permanent pressure loss in the system by adjusting the fluid flow rate and pressure. Isolation valves are often selected to have no system affect choosing full port line bore valves. Isolation valves are required to meet stringent shutoff requirements. A byproduct of meeting these shut off requirements is high static and dynamic friction not conducive for high resolution control or high cycle. Control valves are designed to manage the energy conversion taking place inside the control valve.
- Typical isolation valves include butterfly (Rubber lined, single, double and triple off set), Ball (reduced port & full port), plug, globe and gate. All of these valves require high static friction to seal along with high dynamic friction.
- When selecting control valves the objective is to select the best fit most cost effective (BFCE) solution for the given application. All of these valves could be used for continuous control depending on the process conditions and application requirements. Full Port, reduced port or butterfly valves are not ideal for continuous control applications but more suited for on/off control. Valves designed for continuous control applications are segmented ball, rotary globe, balanced & un-balanced globe and severe duty control valves for extreme conditions.
- Two primary types of control valves are rotary and reciprocating also known as rotary globe, rising stem, sliding stem and globe control.
- With Rubber lined butterfly valves notice how the shaft penetrates through the seat sealing area, this would not be a good valve for throttling service. These valves would be used in a very limited role for control applications for example very low pressure drop, very low cycle requirements and some on/off control applications. The weakness is where the stem penetrates the sealing surface through the liner at 6:00 & 12:00, risk of tearing the liner in throttling or high cycle applications is high. High static friction is required for isolation in rubber lined designs. In addition there are fully lined butterfly valves for corrosive service and swing through butterfly valves for damper control not requiring shutoff.
- Double off set butterfly valves are much better for throttling service with the disc never touches the seat until closure. HPBV are limited to medium P1 upstream pressure and low delta P applications with a minimum control range of 20% to 60% to min & max flow conditions.
- Single offset valves move the shaft out of the sealing area. Double offset valves (HPBV) move the shaft back and slightly off center producing an eccentric action where the disc does not touch the seat until closure is required. Triple offset moves the shaft back, slightly off center combining an elliptical ever changing angle on the disc seating surface. Triple offset valves are ideal for tight shutoff isolation applications in general service or severe service with extreme conditions typically never used in throttling applications. On the other hand (HPBV) or high performance butterfly valves are used in throttling applications but with limitations you will see later on in the training.
- Ball valve are available in full port where port ID approximates the ID of the pipe or reduced port where port ID is 1 line size smaller than pipe ID. As mentioned earlier a ball valve has high static and dynamic friction designed for tight shutoff. Ball valves can be used in throttling applications where position accuracy is not a requirement. Various terms apply – Split body valves, end entry valves, top entry valves, trunnion mount and seat supported ball.
- Segmented ball valves on the other hand are excellent in throttling applications with low pressure drops. A segmented ball valve is a portion of a spherical ball with one seating mechanism. These partial balls are also characterized producing equal percent or modified equal percent flow characteristic but more on that later. These type valves offer metal or soft seat designs, high turndown, much lower friction than standard ball valve, tight shutoff options in a variety of body and trim materials. Typical turndown of these valves are 500:1 or greater.
- Notice the clamped seat held in by the tail piece. Notice the shaped edge on the ball, characterization mentioned earlier is dictated by the shape of the segment ball. Notice as the ball rotates 90 degrees out of the flow path reducing line resistance. These type valve offer inherent =% flow characteristic, high capacity, high turndown for high flow low pressure drop applications.
- Rotary Globe Style valves entered the market in the late 1960’s building on the inherent features found in a globe style valve. Rotary Globe valves were designed to perform in applications intended for reciprocating globe valves capturing the inherent benefits of both designs. This valve offers high resolution control, high turndown, no metal to metal seat contact when modulating, tight shutoff and multiple CV reductions.
- Actuators for the rotary globe are extremely flexible where changing fail action you would disconnect the lever from the clevis, unbolt the actuator from the linkage box moving to the opposite side and reconnecting. The diaphragm is a top hat style spring opposed rolling diaphragm made of Buna-N material. Simple manual override hand wheels are threaded into the linkage box for manual positioning.
- There are two basic types of reciprocating Control Valves, Balanced and Unbalanced. As you can see from the pictorials the balanced style trim allows process pressure equalization of the plug where the unbalanced trim design requires brute force to over come full up stream pressure.
- Single port unbalanced valves have a drop in seat ring design that is clamped in place by a cage retainer compressed by the bonnet. This is referred to as top entry quick change trim. Unbalanced designs also use threaded seat designs typically used in high temperature applications. In this design the shaft is heavily guided preventing any potential misalignment of plug and seat during closure. Unbalanced valves must shutoff against full upstream pressure with no process assistance therefore sizes & pressure ratings are limited due to high thrust requirements calling for very large actuators.
- The standard leakage rating offered is Class IV. Class IV equates to a rate of leakage equivalent to approximately .01% of the rated CV. This is the most common leakage class for control valves. Class V is offered for additional seat leakage requirements. The Class V leakage is obtained with additional force being applied to the valve plug in the seat in an unbalanced design due to the additional forces required to load the seat, Class V shutoff pressure drop capabilities are reduced compared to Class IV. However, larger actuator sizes can be used to obtain the equivalent shutoff pressure capability with Class V seat leakage. The tightest seat leakage offered in the 21000 utilizes a soft Teflon insert to obtain Class VI seat leakage. The soft seat provides exceptional seat tightness but limit the valve application to 450o F due to the Teflon material
- As mentioned, 90% of the 21000’s Masoneilan provides are supplied with quick change trim. Quick change trim is a design where the seat ring is held in place by the seat ring retainer (cage). A gasket is utilized under the seat ring to seal the process fluid. The seat ring retainer is held in place by the valve bonnet and bolting which provides the loading of the seat ring. This design makes it easy to remove the seat ring for repair or replacement. The top entry - bolted bonnet design also makes it easier to change the plug and stem and/or the cage retainer. The screwed in seat design is not as easy to maintain because the valve seat ring is threaded into the valve body. However, the plug and stem is still easy to change because of the top-entry, bolted bonnet design utilized.
- As discussed, the 21000 is very versatile and rugged. It has many different trim types to suit a wide range of control valve applications. The standard contoured plugs are available in linear, equal percentage & modified =% characteristics. Additionally, the valve trim is available in full area and reduced CVs to provide wide rangeability. In addition to the standard plug contours, Lo-dB and cavitation containment trims are available. These trims are used in applications where noise is being generated or cavitation is occurring. For more severe conditions, the 21000 offers two-stage Lo-dB and anti-cavitation options.
- The single-stage Lo-dB trim in the 21000 Series is used to reduce the sound level by up to 15 dBA below the standard trim. The exact amount of noise reduction is relative to the ratio of P1/P2. The sizing and selection program will calculate the noise reduction for you. As you can see, the holes are drilled in the valve plug to produce the noise attention required. The 21000 Lo-dB trim must be utilized in the flow-to-open direction.
- Angle Valves are typically used in applications where there is flashing, heavy particulates, erosive service and high pressure drops.
- The 70000 Series is available in sizes 3/4” - 6” in the 150# - 600# ratings. It is also available in 3/4” - 2” sizes at pressure ratings of 900# - 2500#. The valve is available in standard materials of carbon steel, stainless steel, and chrome moly. The 70000 Series are ideally suited for special application such as hydrocarbon service involving severe operating conditions where high temperatures and / or high pressure, high pressure drops, severe coking conditions and flashing liquids may be encountered. They are especially suited to emergency blowdown or dropout service. Masoneilan also manufactures specially designed angle valves for operating conditions involving especially high pressure and /or high pressure drops. These models are in the Engineered Products Family which will be discussed later.
- In balanced single port designs notice how the process enters the area above the plug equalizing the pressure. Balancing the pressure reduces stem size and requires much less actuator thrust. Notice the small holes or balancing ports in the top of the plug, pressure is equalized on top and bottom where various seals are used between the plug and cage . The plug is guided by the cage through the entire stroke ensuring dynamic stability.
- This slide demonstrates one of many plug seals critical in determining shutoff requirements. This particular seal is an energized seal Masoneilan Model 413 series used in Class V applications.
- The cage in a cage-guided valve serves two main functions. The cage provides alignment of the main valve plug. This alignment precludes the plug from moving to one side or the other due to line pressure. It also ensures that the plug aligns properly with the main plug seat. This is one of the main reasons that cage-guided valves are used on high pressure applications. Stem-guided plugs and even in some cases, post guided plugs, can be loaded from high pressure to one side or the other and cause misalignments. The other function of the cage is to characterize the flow rates. The manner in which the holes are drilled in the cage determines if the flow will exhibit linear, equal percent, or quick opening characteristics. 25000’s, 21000’s, 28000’s and 70000’s exhibit flow characterization by contouring the plugs.
- Due to the nature of cage-guided designs, it is important that they only be applied in service application with clean process fluids. The plug is in contact with the cage for guiding and utilizes piston seals for shutoff. Therefore, there are tight clearances involved with valves that utilize cage-guiding. If particles were in the flow- stream , these would lodge in the clearances. This could cause the valve plug to become stuck or the piston seals to be damaged. If the seals become damaged, the valve won’t provide the necessary shutoff. Another limitation to cage-guided valves is the CV compared to an equivalent size rotary product. However, rotary valves are typically limited in the amount of pressure they can be applied in. Globe valves are heavier compared to an equivalent size rotary valves.
- The 41000 cage also serves other purposes in addition to providing guiding and alignment and characterizing the flow stream. The cage also acts as a sealing surface for the plug seal ring. The seal prevents process fluid from flowing between the plug and cage when the valve is shutoff. The cage, in a 41000, is also the throttling orifice in contrast with the seat orifice being the throttling orifice in a 25000, 21000, 28000 and 70000 design. As the plug is removed from the cage, the ports in the cage become increasingly exposed and the flow increases.
- The other 41005 seal rings available are the 41500, the 41600 and the 41900 seal rings. The 41500 is a in-resist metal seal ring. The 51600 seal ring is made of TFE material and is provided with a Nordel back-up ring to provide rigidity. This seal provides a Class IV shutoff low temperature service below 300oF. The 41900 provides Class IV shutoff up to 1050oF. The 41900 utilizes a graphite seal ring and is provided with a ni-resist backup ring to provide rigidity. Therefore, as you can see, there are several seal ring choices for the 41005 Series. It is important that the proper seal is chosen depending on the application and the customer requirements.
- As mentioned, what determines the ANSI Class shutoff of a 41000 is which type of seal is selected. The 41000 has five different seal types to select from. The first one we will discuss is the 41300 seal. This seal is a pressure energized PTFE seal. It provides the tightest shutoff Class available on a 41000 Class V. However, because of the seal material, the valve seal is limited to a maximum temperature in service of 450oF. Additionally, the 41300 is applied in the flow-to-open direction. This allows the pressure on the top of the seal to flex the seal outward and provide a tight seal between the valve plug and cage.
- A unique design that the 41000 offers is the 41400 design. This design utilizes a piloted plug to shutoff the main plug. The pilot plug controls the balancing port and the valve shutoff. It is only provided in the flow-to-close direction. The piloted design utilizes a ni-resist seal ring on the outside of the plug and cage. This option provides Class V shutoff at high temperatures. Therefore, if Class V shutoff is required at temperatures above 450oF, the 41400 is the only solution. The important thing to remember with the piloted design is that after the main plug is seated, there is approximately .050” over travel required to seat and shut the pilot.
- As you can see from the animation the pilot plug lifts off the pressurizing the area above the plug balancing the plug during modulation. When closing you can see the slight over travel after the main plug makes contact with the seat allowing the pilot plug to seat off. This design is available only in FTC orientation.
- Double Port valves are double seated, double post guided, top entry & bottom entry, high capacity with seat leakages ANSI/FCI Class 2 or better. Typical flow orientation is flow into the ports producing a semi-balanced effect with forces acting on each plug. These valves are rarely sold on projects mainly used to replace in kind or offer unique solutions in various applications.
- Three way valves are used in two primary configurations combining or diverting service.
- You can see the plug and flow orientation for typical combining or diverting service.
- The Bellows design is a multi-ply, formed construction that is welded on the ends. This type of design minimizes the amount of mechanical joints, i.e., minimizing the amount of potential leak paths. Metal Bellows Stem Seal are designed for toxic or lethal services, or other applications requiring zero emissions. The 21000 Series Bellows assembly is an Externally Pressurized design, thus the process fluid is sealed outside of the Bellows. The design includes a built-in anti-rotation feature, which minimizes torsional loading and stresses on the Bellows due to fluid rotational forces or due to handling. This will help maximize the service life of the Bellows. Other factors contributing to potential reduced Bellows life are radial and axial loading. The 21000 Series Bellows assembly includes an additional guide on top of the Bellows (in addition to the valve plug guide at the bottom), providing exceptional radial support and alignment. There is also a mechanical stop designed into the Bellows Bonnet, which prevents over extension of the Bellows in the axial direction. Standard safety features include a Leak Detector connection, and an additional redundant packing set between the process and atmosphere. The packing box design is identical to the standard 21000 Series bonnets, i.e., it can accommodate the standard Teflon, Graphite, and LE Packing sets.
- These type valves are designed for low flow applications to micro flow applications in low or high pressure drop conditions. Due to very tight tolerances applications are limited to clean media or filtered fluids to prevent plugging. The Masoneilan 28000 series design offers adjustable CV’s, multiple trim options and high pressure liquid let down trim option in a compact package.
- The Raised face is the most common of all flange faces. The Raised face is named like this because the gasket surfaces are raised above the bolting circle face (the raised face is only a slight step). Raised face flanges are therefore not full contact flanges. As such, some flange stress may be created when the bolting is tightened. The raised face is finished with a series of concentric circular grooves for keeping the gasket in place and providing a better seal. Raised face flanges are specified for low, medium and high pressure-temperature applications. The main advantage of using a flanged valve is that the valve can be easily removed from the line. However, it is to be noted that flanges are subject to thermal distortion and shock. Therefore a welded connection would be usually recommended for applications where significant temperature variations occur. Flanges are generally built to ANSI Standard B16.5 (or DIN or other international standards). Rating of flanges is made according to the type of service, material requirement, maximum service temperature and pressure.
- The butt-welding ends are prepared by beveling each end of the valve to match a similar bevel on the pipe. The two ends are then butted to the pipeline and joined with a full penetration weld. This type of joint is used on all valve styles and the end preparation must be different for each schedule of pipe. These are generally furnished for control valves in sizes 2-1/2-inch and larger. Care must be exercised when welding valve bodies in the pipeline to prevent excessive heat transmitted to valve trim parts. Trims with low-temperature composition materials must be removed before welding.
- 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 pipe slips into the socket where it butts against a shoulder and then joins to the valve with a fillet weld. Socket welding ends in a given size are dimensionally the same regardless of pipe schedule. They are usually furnished in sizes through 2-inch.
- Ring type joint flanges are actually a modification of the raised face design. RTJ flanges have grooves cut into their faces with steel ring gaskets. RTJ flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or "Coining") the gasket to make Intimate Contact inside the grooves, creating a metal to metal seal. RTJ flanges are usually specified for high pressure and high temperature applications.
- A Grayloc® connector has three components: a metal seal ring, two hubs and a clamp assembly. As the hubs are drawn together by the clamp assembly, the seal ring lips deflect against the inner sealing surfaces of the hubs. These connectors are sized according to pipe size and schedule available from ANSI / ASME 150# thru 2500# ratings.
- Thread connection is usually used on 2“ valves or under, and is not recommended for elevated temperature service. This connection is also used in low maintenance or non-critical applications.
- In a wafer connection the valve is installed between the pipe flanges and tightened to its place with the bolts for the pipe flanges. In some wafer types there are some centering holes on the body to ensure valve's correct position between the flanges. Wafer type body is the lightest body version for mounting between piping flanges. Therefore a wafer valve use to be cheaper than other valves. Also it is fast mounting. But wafer connection is not an option when one side is removed and you need to keep the sealing with the other side. Neither it is used with hazardous fluids such as hydrocarbons and chemicals. In case of fire bolts could dilate and displace the flanges resulting in leakage. Valves with wafer connection are common in butterfly and gate valves.
- Also known as a slip-on flange. A flange that fits over a valve body flow connection. It is generally held in place by means of a retaining ring. This style of flange connection conforms to ANSI/ISA 275. 20 and allows for the use of different body and flange materials. Example: A valve with a alloy body material construction could use carbon steel flanges for reduced cost. These valves have longer face to face than typical globe control valves conforming to ISA S75.03.