Valtek Severe Service Equipment
Valtek Severe Service Equipment Valtek Severe Service Equipment
Valtek Severe Service EquipmentChannelStream TrimPressure Reduction MechanismsAlthough ChannelStream trim uses many pressure reductionmechanisms, the gradual reduction in pressurethrough the trim occurs principally as a result of fivephysical mechanisms:1. Sudden expansion of the flow areas as the liquid exitsthe restrictive channels and enters the intersectingexpansion holes2. Frictional losses due to multiple, small passageways3. Turbulent mixing in the expansion holes4. Mutual impingement of opposing streams in the expansionholes5. Directional changes of the fluid as it passes throughthe retainerIn addition, the small channel size generates only small,rapidly dissipated vortex turbulence, reducing vortexcavitation associated with larger flow geometrics. Theabove mechanisms (occurring in multiple stages) minimizepressure recovery.Velocity and PressureThe velocities at the inlet and outlet of a Valtek controlvalve with ChannelStream trim are generally designedfor a maximum of 30 feet per second while fluid velocitiesinterior to the valve are also closely controlled. Inaddition, the valve is designed to ensure that the pressureof the fluid in the valve body (including theChannelStream cartridge) is always greater than theliquid vapor pressure.Flow CharacteristicsChannelStream trim offers a linear flow characteristic,producing essentially equal changes of flow with equalchanges in valve stroke. The linear characteristic cartridgedesign consists of an axially uniform hole andchannel pattern. The linear characteristic is most commonlyused for high-drop liquid applications. Non-linearcharacteristics are available by designing an appropriatenon-uniform hole pattern, along with a correspondingaxial change in the area of the restrictive channels toproduce the desired characteristic.FLOWFigure 18: ChannelStreamLow Flow DesignMaintenanceMany comparative anti-cavitation valves utilize cagedesigns that can experience sticking problems betweenthe plug head and the cage. The standard Channel-Stream cartridge avoids such problems since thecartridge’s smooth, continuous inner-stage surfaceallows close-clearance plug motion.Anti-cavitation valves are typically constructed with smallflow passages that can become plugged by dirt or otherdebris in the fluid stream. Such devices usually direct theflow initially to the throttling plug before passing itthrough the restrictive device. This results in stickingand galling as dirt and other material become trappedbetween the sliding plug and the inside surface of theanti-cavitation device. On the other hand, ChannelStreamis designed with two important protective features tominimize such plugging problems: First, flow is firstbrought through the cartridge; contaminants too large topass through the small outer channels are trapped at theouter-most stage of the cartridge preventing debris fromtraveling through the device to the throttling plug. Second,because the inner channels progressively becomelarger, small particles (which pass through the first set ofchannels) are easily passed through the rest of thecartridge. In the unlikely event that the cartridge doesbecome plugged, it can be easily disassembled andcleaned.12Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611
Valtek Severe Service EquipmentChannelStream TrimLow Flow DesignFor flows of between 0.5 and 2.5 C V, a specialChannelStream design is utilized where the cartridge isan integral part of the plug (Figure 18), instead of aseparate cartridge/seat retainer in the standard design.The cartridge/plug is closely guided in the seat ring.Within the plug head, the cylindrical stages of theChannelStream are retained. Although located in theplug head and not in the seat retainer, the stages areidentical in design and function to the standard cartridge.As the cartridge/plug strokes through the seat,the flow area increases as additional expansion holesare exposed to the flow. Some advantages of using theChannelStream low flow design is its simplicity; it doesnot require the use of an angle-style body and can beeasily retrofitted into a standard Valtek Mark One valve.With the ChannelStream low flow design, because ofthe extremely small holes and channels, it should onlybe applied in clean services.Flow CapacityIn choosing a valve for a particular application, the usershould consider not only the C V, but also the velocity andthe Sigma value that must be accommodated. Therequired flow capacity of an application can be determinedthrough the standard ISA sizing equations. Themain difference in sizing a standard globe valve and aChannelStream valve is that the ChannelStream valveis far less likely to choke, thus providing more flow for agiven flow capacity and pressure drop.Typical ChannelStream trim information is given in thetables on page 14 is not intended to provide a completelisting of all available designs. Rather, it can be useful inestimating capabilities of a particular valve size andpressure class.In choosing a valve for a particular application, the usershould consider not only the C V, but also the velocity andthe Sigma value that must be accommodated.Table 5: ChannelStream TrimMaterials of ConstructionTrim PartCartridge(standard design)Cartridge/Plug(low flow design)Plug(standard design)SeatRingAvailable Materials316, 410 or 416 stainlesssteel; Inconel; other alloysas required416 stainless steel316 stainless steel withAlloy 6 overlay; 416 or 420stainless steel; other alloysas required316 stainless steel withAlloy 6 overlay; 410, 416 or420 stainless steel; otheralloys as requiredSee Valtek Mark One Control Valves technicalbulletin for basic valve’s materials of construction.Table 6: Comparison of Typical Valve Recovery Coefficients,F Land F iwith σ choked* and σ incipientDamage*Valve Flow Trim F LF σchoked* σincipient*idamageType Direction SizeGlobe over full area 0.85 0.76 1.38 1.73under all 0.90 0.81 1.23 1.52Rotary Disk 90 O open full 0.56 0.49 3.17 4.16Ball 90 O open full 0.60 0.54 2.78 3.43CavControl over seat all 0.92 0.85 1.18 1.20ChannelStream over seat all ~1.0** *** ** 1.30 to 1.001*These Sigma values do not include size and pressure scale factors for proper application to actual service requirements.** Choking will not occur when properly applied. ***Does not apply to multi-staged trim valves.Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 861113
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<strong>Valtek</strong> <strong>Severe</strong> <strong>Service</strong> <strong>Equipment</strong>ChannelStream TrimLow Flow DesignFor flows of between 0.5 and 2.5 C V, a specialChannelStream design is utilized where the cartridge isan integral part of the plug (Figure 18), instead of aseparate cartridge/seat retainer in the standard design.The cartridge/plug is closely guided in the seat ring.Within the plug head, the cylindrical stages of theChannelStream are retained. Although located in theplug head and not in the seat retainer, the stages areidentical in design and function to the standard cartridge.As the cartridge/plug strokes through the seat,the flow area increases as additional expansion holesare exposed to the flow. Some advantages of using theChannelStream low flow design is its simplicity; it doesnot require the use of an angle-style body and can beeasily retrofitted into a standard <strong>Valtek</strong> Mark One valve.With the ChannelStream low flow design, because ofthe extremely small holes and channels, it should onlybe applied in clean services.Flow CapacityIn choosing a valve for a particular application, the usershould consider not only the C V, but also the velocity andthe Sigma value that must be accommodated. Therequired flow capacity of an application can be determinedthrough the standard ISA sizing equations. Themain difference in sizing a standard globe valve and aChannelStream valve is that the ChannelStream valveis far less likely to choke, thus providing more flow for agiven flow capacity and pressure drop.Typical ChannelStream trim information is given in thetables on page 14 is not intended to provide a completelisting of all available designs. Rather, it can be useful inestimating capabilities of a particular valve size andpressure class.In choosing a valve for a particular application, the usershould consider not only the C V, but also the velocity andthe Sigma value that must be accommodated.Table 5: ChannelStream TrimMaterials of ConstructionTrim PartCartridge(standard design)Cartridge/Plug(low flow design)Plug(standard design)SeatRingAvailable Materials316, 410 or 416 stainlesssteel; Inconel; other alloysas required416 stainless steel316 stainless steel withAlloy 6 overlay; 416 or 420stainless steel; other alloysas required316 stainless steel withAlloy 6 overlay; 410, 416 or420 stainless steel; otheralloys as requiredSee <strong>Valtek</strong> Mark One Control Valves technicalbulletin for basic valve’s materials of construction.Table 6: Comparison of Typical Valve Recovery Coefficients,F Land F iwith σ choked* and σ incipientDamage*Valve Flow Trim F LF σchoked* σincipient*idamageType Direction SizeGlobe over full area 0.85 0.76 1.38 1.73under all 0.90 0.81 1.23 1.52Rotary Disk 90 O open full 0.56 0.49 3.17 4.16Ball 90 O open full 0.60 0.54 2.78 3.43CavControl over seat all 0.92 0.85 1.18 1.20ChannelStream over seat all ~1.0** *** ** 1.30 to 1.001*These Sigma values do not include size and pressure scale factors for proper application to actual service requirements.** Choking will not occur when properly applied. ***Does not apply to multi-staged trim valves.Flowserve Corporation, <strong>Valtek</strong> Control Products, Tel. USA 801 489 861113
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