Designed and constructed to accept pressure drops of the ... docs/Pentair Valves and Controls/1.6... · pipeline reducers or expanders can be eliminated. ... To steam turbine 3-way
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Flow ControlYarway is either a trademark or registered trademark of Tyco International Services AG or its affiliates in the United States and/or other countries. All other brand names, product names, or trademarks belong to theirrespective holders.
Designed and constructed to accept pressure drops of the highest magnitude.
Potentially destructive erosive forcesexist in high velocity flow through avalve. Their effects can show up asgrooves cut into the valve’s internalsurfaces by an erosive process calledwiredrawing.
Or the pressure drop can causecavitation damage which occurs as aconsequence of the collapse of vaporbubbles in the fluid flow stream. Thebubbles are formed when the fluidpressure is reduced below its vaporpressure at a given temperature. Whenthe system pressure again rises abovethe vapor pressure, the bubblescollapse or implode. Accompanied by a cracking noise, the implosionsrelease vast amounts of energy whichcan tear holes in the walls of the valvebody and destroy internal parts.
The Need for High Pressure ValvesControl of erosive and cavitationalforces is a primary objective of thedesign of high pressure valves. Various stacked disc designs, forinstance, operate on the principle offixed orifices, or flow paths, in parallel.As such a valve opens, the fixed flowareas are progressively uncovered bythe valve plug. Individual flow area does not increase.
These small flow areas act as fluidstrainers and the valve can becomeclogged with debris causing a loss of both flow and control.
Other designs take an approach basedon multiple orifices only one of which isvariable. But this means that the singlevariable orifice must handle the entirepressure differential across the valve.
Yarway’s Design ApproachYarway’s Turbo-Cascade control valve,on the other hand, is based on theprinciple of multiple variable orifices inseries. In this design, which has thebenefit of more than a decade ofrefinement by Yarway engineers, thetotal flow area increases as the valvemodulates toward the open position.Angular passages or flutes, in abushing, direct the fluid through the flowareas or stages which increase in areatoward the valve outlet, thus providinghigher pressure drop on the inlet stagesof the valve and a decreasing pressuredrop in each stage toward the valveoutlet.
In this design, all pressure drops andpressure recovery occur above thevapor pressure, so no cavitation willoccur within the valve.
Turbo-Cascade valves aremanufactured from forged steel bar to assure homogeneity. Connections are available to match inlet and outletline sizes. In many applications,pipeline reducers or expanders can be eliminated.
How it WorksThe valve divides the fluid flow intomultiple streams and breaks down thehigh pressure in separate stages byinducing 90 degree changes in flowdirection to dissipate energy.
As shown in Figure 2, the total pressuredrop of 2800 psi is broken down into foursuccessive breakdowns of 1297 psi (firststage), 793 psi (second stage), 465 psi(third stage), and 245 psi (fourth stage).
Because the reducing pressure spike atno time goes below the vapor pressureof 35 psia, cavitation will not occur.
Each stage of pressure letdown is at right angles to the following stage.This causes the fluid passing throughthe valve to change flow direction as it cascades down through the valve,dissipating additional energy. Inaddition, each Turbo-Cascade valvehas a fixed orifice in its outlet to provideyet another stage of pressure drop thateliminates the possibility of cavitation in the last stage.
As shown in the cutaway illustration(Figure 3), the cage or bushing throughwhich the cascade piston travels hascast grooves which provides anincrease in flow area as the fluid passesthrough the valve. The cascade shafthas precisely machined lobes thatmove up and down inside the flutedbushing. Varying the position of thelobes within the fluted bushing variesthe area exposed to flow and thuscontrols valve capacity.
To increase flow area further, thediameter of the cascade shaft betweenthe lobes decreases toward the valveoutlet.The increasingly larger flow areaforces higher pressure drop on theupper inlet stages. This is to assure thatthe pressure at all points within thevalve remains above the vapor pressureof the liquid, thus preventing cavitation.
ΔP1 = 1297 psig
1803 psig
ΔP2 = 793 psig
1010 psig
#1Stage
ΔP3 = 465 psig
545 psig ΔP4 = 245 psigPd = 300 psig#4
Stage
#3Stage
#2Stage
= 35 psia
P(psig)
Pv
Pi =3100psig
ValvInlet
e
Typical Applications
To H.P.Heater Controller
positioner
Steam flow fromsuperheater outlet
Desuperheatersprayhead
Thermalshield
Temperaturesensor
Manual bypassvalve
Temperaturetransmitter
B.F. Pump
Gatevalve
Gatevalve
Check valve
Manualisolationvalve
Manualisolation
valve
Turbo-cascadevalve
Turbo-cascade
valve
To H.P. Heater
Flow sensor orifice
Deaerator
Flow-meter
To steam turbine
3-way airsolenoid
valve
Desuperheating Spray Water Control System
Boiler Feed Pump Recirculation Control System
Application ConditionsQb = 600 gpm
Pi = 3100 psig
Pd = 300 psig
DP = 2800 psi
T = 260°F
Pv = 35 psia
G = 0.94
Cv = 11 (4 stages)
Figure 2 - Controlled pressure reduction in Yarway valves helps prevent cavitation, whichcan occur if pressure drops below the vapor pressure of the liquid. Consult Yarway if thepressure at the outlet of the Turbo-Cascade valve is near liquid vapor pressure.
Pressure Reduction CapacityThe Turbo-Cascade valve’s pressure-reduction capability depends on thenumber of pressure-reduction stagesincorporated into the valve for a givenset of conditions. Normally, 600 psi is the upper limit for one stage, twostages are used for 1500 psi, fourstages for 3000 psi and six stages for pressures over 3000 psi.
The cutaway section of the bushing(Figure 3) shows the fluid flow passagesthat provide staged pressurebreakdown. Three stages are illustrated,but up to six can be provided for veryhigh pressure differentials. With thecascade shaft in the closed position inthe bushing (Fig. 3a), drop-tight shut-offcan be achieved. Throttling position anda full open position are shown in Figs.3b and 3c.
With the cascade shaft in the full openposition, the lobes are at mid-point ofthe flutes in the bushing and maximumflow occurs.
Valve ActuationThe valve is designed for compatibilitywith a variety of actuators andpositioners – pneumatic, hydraulic orelectric. A simple form of actuator is a cylinder for on-off operation. Theposition of the actuator is controlled by a solenoid valve that opens or closesthe Turbo-Cascade on signal. Valvesrequiring flow modulation are equippedwith cylinder or diaphragm actuatorsand appropriate positioners.
A hydraulic balancing technique is usedin larger Turbo-Cascade valves for veryhigh pressures to provide automaticoperation. Smaller valves, with up to 2"intervals, are unbalanced and caneasily be operated by pneumatic pistonor diaphragm actuators. In larger sizes,most have balanced pistons so thatpneumatic actuators can be used.
Turbo-Cascade valves are quiet bydesign. The fluted flow configuration of the internals effectively limits fluidvelocity at all points within the valve,
thus preventing a high operating sound-pressure level in even the most severepressure letdown situations.
The design of the valve places theseating surfaces on the upstream orhigh pressure side with flow over theseat. A slight deadband protects theseating surfaces, allowing them toseparate before appreciable flowbegins. These features combine toprovide tight shut-off in high pressureservice over extended periods of time.
Figure 3 – Yarway technique for pressure letdown.
Fig. 3a Fig. 3b Fig. 3c
Seatless Valves for Pressures to 935 psi – Class 250 to 600
rc = Critical Pressure Ratio(Use Specific Gravity)
P1 = Inlet Pressure (psia)
Pv = Vapor Pressure (psia)
P2 = Outlet Pressure (psia)
DPtrue = P1 - P2
In sizing, use the smaller of the DPwhich will result in a larger Cv required.
A sample calculation follows:
Flow Q = 248 gpm
Inlet Pressure P1 = 1500 psia
Outlet Pressure P2 = 250 psia
Shut-off Pressure Pso = 1500 psia
Temperature T = 364°F
Vapor Pressure Pv = 164 psia
Specific Gravity SG = 0.88
Critical PressureRatio rc = 0.88
Recovery Factor FL = 0.93(since a 2 stage is chosen for 1250DP)
True DP = P1 - P2
= 1500 - 250
= 1250 psi
DPallowed = FL2[P1 - (rc x Pv)]
= [1500 - (0.88 x 164)]
= 1168 psi
Use the smaller of DPtrue or DPallowed inthe above equation.
Q
Cv = √ DP
SG
248Cv = √ 1168
0.88
Cv = 6.8
Select Class 900 ANSI Valve with 2 stages, Trim Number 0903 (Cv = 7.6).Select desired end connections.
Control valve for ____________________service, Tag No. ____________________ , in accordance with data sheet attached,shall be a Yarway Turbo-Cascade valve,Series 5400, forged steel body,incorporating separate elements fortight shut-off and throttling.
Pressure reduction shall beaccomplished in stages to dissipatepressure and control velocity bydirecting the fluid through a series ofvariable orifices whose individual flowarea increases as the valve is opened.
The fluid pressure breakdown shall takeplace through a series of characterizedpassages between the stem and thebushing whose flow area will be ofsufficient cross-sectional area topreclude the possibility of obstructionby foreign particles. Valve shall operatewith a sound pressure level of 90 dBAor less measured three feet from thevalve, three feet downstream.
Tyco Flow Control (TFC) provides the information herein in good faith but makes no representation as to its comprehensiveness or accuracy. This data sheet is intended only as a guide to TFC products and services. Individuals using this data sheet must exercise their independent judgment in evaluating product selection and determining product appropriateness for their particular purpose and system requirements. TFC MAKES NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE WITH RESPECT TO THE INFORMATION SET FORTH HEREIN OR THE PRODUCT(S) TO WHICH THE INFORMATION REFERS. ACCORDINGLY, TFC WILL NOT BE RESPONSIBLE FOR DAMAGES (OF ANY KIND OR NATURE, INCLUDING INCIDENTAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES) RESULTING FROM THE USE OF OR RELIANCE UPON THIS INFORMATION. Patents and Patents Pending in the U.S.and foreign countries. Tyco reserves the right to change product designs and specifications without notice. All registered trademarks are the property of their respective owners. Printed in the USA.