Valtek Severe Service Equipment

More documents

Recommendations

Info

Valtek Severe Service EquipmentTiger-Tooth TrimIntroductionWhen installed in a globe-style control valve, Tiger-Tooth trim effectively reduces sound pressure levels upto 30 dBA. Tiger-Tooth trim can also be used to eliminatethe damaging effects of cavitation – making it an effectivechoice for either gas or liquid processes with highpressure drop conditions.DesignA cross-sectioned view of the Tiger-Tooth control valvestack is shown in Figure 8. The basic Tiger-Tooth designinvolves highly engineered concentric grooves (or teeth)machined into the face and backside of a series ofcircular stacked discs (called a stack), which also acts asa seat retainer. Legs separate one disc from another,providing the correct distance between individual discs.For easy assembly, the entire stack is tack-welded intoone concentric unit and clamped in a conventional globeor angle body valve.With Tiger-Tooth trim, flow passes from the center of thestack through the teeth in a radial, wave-like manner tothe outlet, undergoing a series of sudden contractionsand expansions. This process reduces fluid pressure insteps without the large, single pressure drop typical ofconventional trims.Valtek control valves with Tiger-Tooth trim are manufacturedin sizes 1.5 through 36-inch, utilizing conventionalValtek globe-style bodies. Both unbalanced and pressure-balanceddesigns are available (Figures 9 and 10).For smaller parts inventory and lower cost, many partsare interchangeable with conventional Valtek Mark Oneglobe valves. To minimize costs associated with largeglobe valve bodies, valves in sizes 16 through 36-inchmay be custom-fabricated using an angle body configurationwith the inlet at the bottom and the outlet on theside. For applications requiring long strokes, specialpneumatic cylinder, hydraulic or electric actuators areavailable.Figure 9: Unbalanced Tiger-ToothTrim DesignFigure 8: Tiger-Tooth Stack Featuring aFive-tooth DesignFigure 10: Pressure-balanced Tiger-ToothTrim Design6Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611
Valtek Severe Service EquipmentTiger-Tooth TrimGas ApplicationsWith gases, the Tiger-Tooth design features a uniqueflow path that permits radial expansion of the fluid. Thetrim is effective on large pressure reductions in gases,because an additional flow path expansion is providedto handle the increasing volume as the pressure isdecreased. This is accomplished by making each toothand resulting flowpath somewhat larger than the precedingtooth. The increased flow area maintains acceptablegas velocity at every point across the discs.Liquid ApplicationsWith Tiger-Tooth trim, a series of small, multiple pressuredrops prevent cavitation from occurring at any pointinside the valve. The amount of pressure drop that canbe taken without cavitation occurring is proportional tothe difference between the local static pressure andvapor pressure. The expanding Tiger-Tooth design isused with liquids to eliminate most of the pressure dropas the flow first enters the trim. Because the fluid flowsunder the plug, the smaller teeth in any passage areencountered first, resulting in a higher pressure drop. Asthe fluid progresses through the stack, the expandingtooth pattern allows the pressure to be reduced in aseries of successively smaller pressure drops withoutexcursions below the vapor pressure – avoiding theformation of cavitation altogether.Velocity ControlOne of the fundamental design considerations withValtek control valves with Tiger-Tooth trim is the establishmentof acceptable velocities at every point as theflow passes through the valve. For liquid applications,maintaining valve outlet velocities below 30 feet persecond is desirable – although higher velocities maybe acceptable depending upon the application andprocess fluid.For gaseous control valve applications, keeping themaximum outlet gas velocity below 0.33 Mach is desirable,although higher velocities may be acceptablebased on the application.Velocities must be assessed for the most difficult flowingconditions at the following critical points (as shown inFigure 11):1. The inlet passageway to the valve2. The internal flow area of the Tiger-Tooth stack at allplug positions3. The flow area between the teeth, including inlet andoutlet area of the stack342FLOWFigure 11: Tiger-Tooth Velocity Check Points4. The gallery flow area formed between the outsidediameter of the Tiger-Tooth stack and the insidediameter of the valve body5. Outlet passage flow areaPressure Reduction Through SuddenExpansion and ContractionAn important mechanism acting to reduce the pressurein Tiger-Tooth trim is the sudden expansion and contractionphenomenon that takes place as the flow passesover the teeth. Figure 12 illustrates this mechanism. TheTiger-Tooth valve’s ability to gradually reduce pressureis important for the reduction of noise in the process line.Figure 13 is a graphic illustration of the noise attenuationcapabilities of Tiger-Tooth valves when installed in highvelocity applications.Flow CharacteristicsTiger-tooth trim is generally designed with a linear flowcharacteristic. Deviation from the linear characteristicinherent in a stacked disc design is reduced by lead-inareas machined into the valve plug and each individualdisc. This permits the next flow passage to begin passingflow before the first passage has reached full capacity.Bi-linear or tri-linear trim can be furnished withportions of the stack having different flow capacities,permitting a flow characteristic approaching an equalpercentage characteristic. Tiger-Tooth trim can also bemanufactured with a full-open area at the top of the stackto provide additional flow capacity and tolerance forlarge solids entrained in the process.51Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 86117
Page 1 and 2: Severe Service Equipment
Page 3 and 4: Valtek Severe Service EquipmentIntr
Page 5: Valtek Severe Service EquipmentIntr
Page 9 and 10: Valtek Severe Service EquipmentTige
Page 11 and 12: Valtek Severe Service EquipmentChan
Page 13 and 14: Valtek Severe Service EquipmentChan
Page 15: Valtek Severe Service EquipmentMicr
Page 19 and 20: Valtek Severe Service EquipmentMega

Valtek Severe Service Equipment

Create successful ePaper yourself

Delete template?

Save as template?