cavitation-control.pdf

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Flowserve Cavitation Contro

Experience In Motion


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IndexSection Page

1 Introduction to Cavitation ................................... 3

2 Product Comparison ........................................... 7

3 ChannelStream.................................................... 10

4 Multi-Z ................................................................ 11

5 TigerTooth ........................................................... 12

6 CavControl .......................................................... 12

7 ChannelStream Low Cv ....................................... 13

8 MicroCav ............................................................. 13

9 CavStream .......................................................... 14

10 MultiStream ........................................................ 14

11 Gestra ZK ........................................................... 15

12 Kammer CageControl Type III ............................. 16

13 Kammer StreamControl Type II-1 ....................... 17

14 NAF Z-Trim .......................................................... 18

15 NAF A-Trim.......................................................... 19


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1. Introduction to Cavitation1.1 Velocity Profle Through Control Valves

As a liquid travels through a control valve, a vena con-tracta (point o narrowest ow restriction) develops di-rectly downstream o the throttling point. The ow areaat this point is smaller than the rest o the ow path. Asthe ow area constricts, the velocity o the uid rises. A-ter the uid passes the vena contracta the velocity dropsagain. See Figure 1, Velocity Through a Control Valve,or a velocity profle through a conventional single-seatedglobe-style control valve.

1.2 Pressure Profle Through Control ValvesThe increase in velocity at the vena contracta is causby a transer o pressure energy in the ow to velocity eergy in the ow, resulting in lower pressures. As the leaves this high-velocity area, the velocity energy is coverted back into pressure energy, and the pressure recoers. See Figure 2, Pressure Through a Control Valve,a pressure profle through a conventional single-seatglobe-style control valve.

Figure 2: Pressure Through a Control ValveFigure 1: Velocity Through a Control Valve

As a uid travels through a

conventional single-seated

globe-style control valve, a

vena contracta (point o nar-

rowest ow restriction) de-

velops directly downstream

o the narrowest throttling

point.


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1.3 Cavitation ProfleIn many control valves, the pressure at the vena contractawill drop below the vapor pressure o the liquid. Whenthis occurs, small bubbles o gas will orm as the liquidvaporizes. As the pressure then rises above the vaporpressure again, these small bubbles collapse or implode

as the vapor turns back into liquid. The damage is inict-ed as the bubbles implode. The implosion o the vaporbubbles is very energetic and orms jets o uid which cantear small pits into the metal. See Figure 3, Pressure Pro-fle or Cavitation, or an illustrated profle o cavitation.

1.7 Cavitation SoundWhen cavitation bubbles implode they make a distinc-tive sound. Low level, or incipient cavitation is heard ina piping system as intermittent popping or crackling. Asthe pressure drop increases and the cavitation becomesmore severe, the noise becomes a steady hiss or rattle thatgradually increases in volume. Fully-developed or chokedcavitation is oten described as a sound like gravel or smallrocks owing through the pipe.

1.4 FlashingIn some cases the liquid pressure will not rise above thevapor pressure again. This is a special case known asashing. Flashing has a distinct set o issues and solu-tions. Flashing requires special handling and is not cov-ered in this document. See Figure 4, Pressure Profle orFlashing, or an illustrated profle o ashing.

Figure 3: Pressure Profle or Cavitation

1.5 Cavitation EectsCavitation damage destroys both piping and controlvalves, oten resulting in catastrophic ailure. It causesvalves to leak by eroding seat suraces. It can drill holesthrough pressure vessel walls. Even low levels o cavita-tion will cause cumulative damage, steadily eroding partsuntil the part is either repaired, or it ails.

1.6 Cavitation DamageCavitation damage orms a rough surace o small micro-sized pits which are easy to identiy with a magniyingglass or microscope, see Figure 5, Cavitation DamagedParts. Certain types o corrosion can mimic the eects ocavitation. In these cases, the location o the damage willhelp distinguish cavitation. It rarely orms in narrow gapsas is common with crevice corrosion. Cavitation damageis almost always located downstream o the control valveseating areas. Occasionally cavitation bubbles can dritdownstream, causing damage to piping and fttings.

Figure 4: Pressure Profle or Flashing

Figure 5: Cavitation Damaged Parts

ConceptionDevelopment

Manuacture


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1.8 Cavitation ControlThe ideal solution to cavitation is to reduce the pressurerom inlet to outlet gradually, thus avoiding a large pres-sure drop at the vena contracta. Cavitation can be avoidedentirely by not permitting the pressure to all below thevapor pressure, thereby eliminating any bubble ormationand subsequent collapse. See Figure 6, Gradual PressureReduction Profle, or an illustrated example o cavitationelimination. Another solution that can be used or lowerlevels o cavitation involves controlling or dissipating theenergy o the imploding bubbles by isolating them awayrom the metal suraces. This greatly reduces the amounto energy that the exposed suraces o a valve need toabsorb, allowing the components to resist damage.

1.10 Sigma: The Cavitation IndexVarious cavitation indices have been used to correlate peormance data to improve designs o hydraulic proceequipment. A cavitation index, called Sigma (), has bedeveloped and applied to quantiy cavitation in contvalves. Sigma represents the ratio o the potential or sisting cavity ormation to the potential or causing cavormation. This cavitation index is defned as ollows:

(P1 - Pv) =

(P1 - P2)

Where:

P1 = Upstream pressure (psia), measured two pipediameters upstream rom the valve

P2 = Downstream pressure (psia), measured six pipediameters downstream rom the valve

PV = Vapor pressure o the liquid at owing temperatur

Through laboratory and feld testing results, acceptaboperating Sigmas or eliminating cavitation (and its asociated choking, noise, and damage) have been estalished.

In general, globe valves experience minimal cavitatidamage when operating at low pressure. Generally, these cases, no cavitation control trim is necessary. Haened trim may be all that is needed to provide a satactory level o protection. At a medium pressure socavitation control is usually required. A trim that usmutual impingement (directs opposing cavitation streaminto each other) will generally sufce in this range. At hipressure drops the potential or severe cavitation damaexists and a staged pressure drop trim designed or svere service must be included in the valves sizing.

1.9 Cavitation MeasurementCavitation in uid ows can be measured using the vi-bration o imploding bubbles as the indicator. Anothermethod is to examine damaged parts. Using the vibrationmethod has obvious advantages, but this method requirescareul isolation o the process ow that is not practicalin the feld. However, under lab conditions this methodcan provide a quick way to identiy and measure the cavi-tation severity. Fortunately there are methods to predictand eliminate cavitation beore a valve is ever exposed todamaging conditions.

Figure 6: Gradual Pressure Reduction Profle


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We thus have the ollowing general categories or a typicalglobe valves operating conditions:

> 2.0 No cavitation is occurring.

1.7 < < 2.0 No cavitation control required.

Hardened trim provides protection.

1.5 < < 1.7 Some cavitation control required. Mutual impingement trim may work.

1.0 < < 1.5 Potential or severe cavitation.Use staged pressure drop trim.

< 1.0 Flashing is occurring.

In actual application there are additional actors that needto be considered in sizing the valve and selecting the typeo trim. However, the various types o calculated and test-ed Sigmas can be compared to these general categories to

show how they are used. For example:

Tests indicate that water owing over-the-plug through aully open, single-seated globe valve at 200 psia and 80F (vapor pressure = 0.5 psia), chokes or attains maximumow at a downstream pressure o 56 psia. The chokedcavitation index is then:

(200 - 0.5) choked= = 1.39 (200 - 56)

These tests also indicate that cavitation damage (damage)or this particular style o valve in continuous operation be-gins at about damage = 1.73 which is sooner than choked.

The point at which cavitation frst occurs (incipient) can alsobe deduced rom tests and starts at a smaller pressuredrop resulting in a somewhat higher value than damage.

I this same valve operates wide open at an upstream pres-sure (P1) o 500 psia and a downstream pressure (P2) o200 psia, and the water temperature increased to 180 F(vapor pressure = 7.5 psia), the operating Sigma is:

(500 - 7.5) operating= = 1.64 (500 - 200)

Because this operating value is greater than choked, the valveis not choked at these conditions. However, the operating isless than damage; thereore, the valve may experience cavi-tation damage unless cavitation control trim or harder ma-terials are used. In this example, our general categoriesshow that a hardened trim using the principle o mutual

impingement to control the cavitation is appropriate.

Some o the other actors that aect the intensity o cavita-tion are the magnitude o the actual service pressure com-pared with test pressures, the ow path geometry, andthe uid purity. By researching these actors, methods oscaling the index or such variables have been established.This geometry and pressure scaling is not accounted or incalculating the liquid pressure recovery actor (FL) and theliquid cavitation actor (Fi) when they are used or controlvalve sizing. This can slightly aect the estimated Cv andpossibly the valve size actually required.

It should be noted that the valve type used in an applica-

tion makes a dierence in the level o resistance to cavita-tion that will be achievable or a given process. Figure 7 ,Typical Valve Recovery Coefcients, lists some generalsigma limits o various valve types and trims.

Figure 7: Typical Valve Recovery Coefcients

* Size and pressure scale actors not included in these values.

** Choking will not occur when properly applied.

*** Does not apply to multi-staged trim valves.

ValveType

FlowDirection

TrimSize

FL Fi choked* incipient*damage

Rotary Disk 90o open ull 0.56 0.49 3.17 4.16

Ball 90o open ull 0.60 0.54 2.78 3.43

Globe overunder

ullall

0.850.90

0.760.81

1.381.23

1.731.52

Single Stage over seat all 0.92 0.85 1.18 1.20

Multi-Stage over seat all ~1.0** *** ** 1.30-1.001


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2. Product ComparisonDesign

Globe & Angle, Multi-StageCavitation Elimination

Globe & Angle, Multi-StageCavitation Elimination

Type ChannelStream Multi-ZBase Valve Mark Series Kmmer SeriesSize Range 1.5 to 36 1 to 8 (DIN 25 to 200)

Cv Range 6 to 720 0.03 to 137Flow Direction Flow over the plug Flow under the plug

Pressure Stages 2 to 6 3 to 6Features Tolerates Sigma as low as 1.002.

Works best in mild to moderate cavitation and can han-dle heavy cavitation applications.

Eliminates cavitation through a series of holes and chan-nels to reduce the pressure in stages.

Optimized and characterized for an application withstages added as needed.

Uses small passages, impingement, expansion andcontraction to reduce pressure.

Tolerates Sigma as low as 1.002. Forgiving of solids in the process. Linear multistage plug and retainer. Optimized for the application. Eliminates cavitation. Certied and tested by boiler feed-pump manufacturers. Seat is protected from high velocity. Unique venturi outlet nozzle in angle valves.

DesignGlobe & Angle, Multi-Stage

Cavitation EliminationGlobe & Angle, Single Stage

Cavitation Control

Type TigerTooth CavControlBase Valve Mark Series Mark SeriesSize Range 1 to 36 1 to 24

Cv Range 4 to 4000 1.5 to 1,000Flow Direction Flow under the plug Flow over the plug

Pressure Stages 2 to 8 1

Features Tolerates Sigma as low as 1.002. Eliminates cavitation. Stacked disks with concentric rows of teeth that increase

in size provide sudden expansions and contractions todrop the pressure in stages and slow velocity.

Tolerant of dirty services. Optimized for a given application. Disk stacks can be characterized.

Tolerates Sigma as low as 1.2 Uses a drilled hole seat retainer with stepped holes tomove the vena contracta away rom metal suraces.

Controls cavitation by directing the cavitation bubblesaway rom the metal suraces and into opposing streamsrom the opposite side o the retainer. Impinging jets create a column o cavitation in the center o the retainer.

Works best in low to mild cavitation. Can be characterized.


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2. Product ComparisonDesign

Globe & Angle, Multi-StageCavitation Elimination Plug Head

Globe & Angle, Multi-StageCavitation Elimination Plug head

Type ChannelStream Low Cv MicroCavBase Valve Mark Series Mark SeriesSize Range 1 to 3 1, 1 and 2

Cv Range 0.25 to 50 0.0007 to 1.25Flow Direction Flow over the plug Flow over the plug

Pressure Stages 2 to 4 4 to 6Features Tolerates Sigma as low as 1.002.

Uses the same technology as ChannelStream to elimi-nate cavitation, except that the stages are built into theplug head instead o the retainer.

Same performance as ChannelStream at much lowercapacities.

Can be used in conjunction with ChannelStream retain-ers.

Tolerates Sigma as low as 1.006.

Exceptionally low flow capabilities. Utilizes a special close-guided plug with continually ex-panding grooves that intersect each other thus providingstaged pressure drops as the uid impinges upon itselwhile expanding.

DesignGlobe & Angle, Single StageCavitation Control Plug Head

Globe, Multi-StageCavitation Control

Type CavStream MultiStreamBase Valve Mark Series FlowTop (16), FlowPro (12)Size Range to 3 to 16 (DN 15 to 400)

Cv Range 0.4 to 88 4.6 to 578 (12)Flow Direction Flow over the plug Flow under the plug

Pressure Stages 1 4Features Tolerates Sigma as low as 1.2.

Uses the same technology as CavControl to control cavi-tation, except the holes are drilled into a special close-guided plug head rather than in the seat retainer.

Impinging jets create a column of cavitation in the centero the plug head, keeping the bubbles away rom metalsuraces.

Same performance as CavControl with much lowercapacities.

Can be characterized.

Efcient, modular design with standardized combina-

tions or cavitation elimination. Allows for an easy upgrade from standard trim sets. Works well with low to mild levels of cavitation. Optimized for the process conditions.


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Globe, Multi-StageCavitation Elimination

Globe, Multi-StageCavitation Elimination

Globe, Multi-StageCavitation Control

Design

ZK CageControl - Type III StreamControl - Type II-1 TypeGestra Series Kmmer Series Kmmer Series Base Valve

1 to 3 (DN 25 to 150) to 4 to 4 Size Range2.7 to 20 1.8 to 228 1.8 to 228 Cv Range

Flow over the plug Flow under the plug Flow over the plug recommended Flow Direction4 1 or 2 1 Pressure Stage

Excellent sealing and control charac-

teristics. Extremely wear-resistant. Designed on a modular assembly

principle. Easy assembly and inspection of

nozzle insert. Works well with high pressure drops

and heavy cavitation potential.

Works best in low to mild cavitation.

Plug and/or cage characterizeddesigns available Optimized for the service conditions. As the plug opens in the seat, it

simultaneously opens the cage oreective staged pressure drops overthe entire stroke length.

Used for low levels of cavitation.

Optimized for the service conditions. Plug can be used in combinationwith Type I trim.

As the plug opens in the seat, itsimultaneously opens the cage oreective staged pressure drops overthe entire stroke length.

Features

Rotary Characterized BallCavitation Control

Rotary BallCavitation Control

Rotary Ball, Multi-StageCavitation Elimination

Design

Z-Trim Z-Trim A-Trim TypeNAF-Setball NAF-Duball NAF-Duball Base Valve

2 to 20 (DN 50 to 500) 2 to 20 (DN 50 to 500) 2 to 10 (DN 50 to 250) Size Range0.73 to 925 90 to 15950 6 to 3340 Cv Range

Bi-directional Bi-directional Bi-directional Flow Direction

1 to 5 1 to 5 6 Pressure Stage

Tight shutoff.

A V-shaped sector provides accuratecontrol over a wide range.

Works well with media containingsolids or pulp without plugging.

Can manage high pressure drops atlow ow and high capacity at largeopenings.

Splits the ow into many smallerows providing 3 steps o pressurereduction.

Used in low levels of cavitation.

Tight shutoff.

Works well with media containingsolids or pulp without plugging.

Can manage high pressure drops atlow ow and high capacity at largeopenings.

Splits the ow into many smallerows providing 3 steps o pressurereduction.

Used in low levels of cavitation.

Tight shutoff.

A large number of zigzag channelstake the pressure drop in stages al-lowing cavitation to be eliminated.

From open to 45o ow passesthrough the channels twice as theow circles around the ball and exitsthrough the passages not yet directlyexposed. This allows extra protec-tion at low ow/high pressure dropconditions.

Up to moderate levels of cavitation.

Features

2. Product Comparison


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Introduction

ChannelStream trim prevents cavitation rom orming andminimizes hydrodynamic noise in the most severe liquid ap-plications. This design not only eliminates cavitation damage,

but also provides easy maintenance and long lie, even wheninstalled in the most difcult applications. The Channel-Streamcartridge may appear similar to other competitive designs be-cause o its drilled holes and close-ftting cylinders but herethe similarity ends. Rather than acting as a ow restriction, thedrilled holes in the ChannelStream cartridge are used as expan-sion areas or the uid as it enters rom restrictive channelsmachined in the outside o all interior cylinders. This preventsthe uid recovery rom occurring adjacent to a critical trim sur-ace. Successive intersections and impingement o the uidin the restrictive channels result in additional pressure losseswhile expansion holes connected to the channels create a serieso expansions and contractions that result in a series o highlyefcient pressure drops. This staged pressure drop eliminatescavitation in most applications and minimizes the energy ocavitation that may still occur in others.Design

The standard ChannelStream trim is designed or ows o 6 CVand higher, and utilizes a cartridge design in lieu o a standard seatretainer. With this design, ow is directed over the plug througha series o close-ftting cylindrical stages, called the cartridge(Figure 3.1). Flow travels frst through the expansion holes inthe outer cylinder and then enters the specially-engineered chan-nels machined into the outer surace o the second cylinder. Theliquid is confned to the channel until it reaches the intersecting

expansion hole in the second cylinder and passes through to thenext restrictive channel, and so orth.

The number o stages and the ow area o the channels in eachstage o the ChannelStream cartridge are designed to producethe desired overall pressure drop, while avoiding cavitation atany point. The ow area o the channel is usually greater in eachsuccessive stage in order to minimize the number o stages. Thisresults in higher pressure drops being taken in the outer (or initial)stages as compared with the inner (or fnal) stages.

A number o pins near the top o the cartridge, held in place witha small bead weld, hold the trim together in the correct alignment.

Figure 3.1: Cutaway o a ChannelStream cartridge

3. ChannelStream

The welds can be easily ground or machined out to allow disas-sembly and cleaning. The plug fts closely inside the cartridgebore, controlling the ow. Unbalanced and pressure-balanceddesigns are available.

Valtek control valves with ChannelStream trim are manuacturedin sizes 1.5 through 36-inch, using conventional Valtek globe-stylebodies up to Class 4500. Many parts are interchangeable withconventional Valtek Mark One valves. Angle bodies in Classes 150through 600 valves in sizes 16 through 36-inch may be custom-abricated. For applications requiring long strokes, long-strokingpneumatic cylinder, electric and hydraulic actuators are avail-

able.

Base Valve DesignThe Mark series o valves.Mechanisms at Work Sudden expansion and contraction Frictional losses in small passages Turbulent mixing Mutual impingement of opposing streams Directional changes


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4. Multi-Z

Figure 4.1: Cutaway o a Multi-Z Valve

Introduction

Users rom the power generation, petrochemical and industrialchemicals industries are requently conronted with extremepressure dierentials in their process systems - dierentials oup to 400 bar are common. For this reason these customersdesire continuous, steady-state ow curves with appropriateow characteristics, long and uniorm service lie, as well aslow maintenance costs. The valves used must satisy certainprerequisites, such as accommodating solids in liquid media,high sound levels, high temperatures, cavitation ormation, andcorrosion. The Multi-Z was made or these conditions.

Design

Multi-Z valves are used i solids are entrained in the mediumand i there is a possibility o cavitation orming. In additionthis multi-stage valve is capable o reducing high-pressure di-erentials through a staged relie process. Multi-Z trim reducespressure by partition division - an approach which is dierentthan that pursued by other suppliers. The major advantage isa noticeable reduction in wear combined with extremely low-noise.

The valves are optimally tailored to the specifc operating condi-tions o the customer thus achieving signifcantly better resultsin perormance characteristics. The individual stages o the plugare confgured in such a manner that cavitation is impossible.Through the appropriate design o transitions and passages inthe plug, solids as large as .5 in the process can be saelymanaged without destroying the fttings or the valve. The addi-tion o a unique venturi outlet nozzle provides urther trim andseat protection rom high velocity, cavitation and ashing. Thedesign of the linear / equal percentage multi-stage plug resultsin greater rangeability and outstanding control characteristicsor the installed strokes.

The trim can be used in both in-line globe style valves and anglestyle bodies currently up to 8 and Class 1500 in size.

Base Valve DesignThe Multi-Z series o valves.Mechanisms at Work Sudden expansion and contraction Frictional losses in small passages Turbulent mixing Mutual impingement of opposing streams Directional changes


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Introduction

Decades o feld experience has proven the sophisticated de-sign o the TigerTooth to be very eective at cavitation elimina-tion.

Design

The TigerTooth design employs highly engineered concentricgrooves (or teeth) machined into the ace and backside o aseries o circular stacked discs which orm the seat retainer.Legs separate one disc rom another, providing a gap betweenindividual discs, orming concentrically expanding ow pas-sages. An additional beneft o this is that the passages in theTigerTooth design are sel-cleaning as they grow wider romthe inside to the outside. This allows large solids to easily passthrough the trim.

TigerTooth trim causes sudden expansion and contraction othe uid as it passes over the teeth. The TigerTooth valves

ability to gradually reduce pressure without generating highvelocities is important or operation in service with entrainedsolids as well as or minimizing uid noise.

Base Valve DesignThe Mark series o valves.

Mechanisms at Work Sudden expansion and contraction Frictional losses in small passages Directional changes Velocity reduction

Figure 5.1: Cutaway o TigerTooth Trim Figure 6.1: CavControl Seat Retainer

6. CavControl5. TigerTooth

Introduction

A very eective and simple method o controlling cavitation inlow to mild conditions, the CavControl trim does not attemptto eliminate cavitation but rather contain the cavitating bubblesin the center o the retainer away rom the metal suraces othe valve.

Design

The CavControl design employs matched pairs o holes thatcause diametrically-opposed jets o uid to create a conditiono mutual impingement in the center o the retainer. As theexpanding jets o bubbles collide with each other the turbu-lence created dissipates the energy o the cavitating streamsbeore they come in contact with the downstream suraces othe valve. A small step in the drilled holes o the retainer movethe vena contracta away rom the inside surace o the retainerthus protecting it rom the energy o the cavitation bubblesas they implode. Standardized designs are available or most

applications; however characterization is possible to cover awider range o applications.


Mechanisms at Work Mutual impingement Turbulent mixing Area expansion


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Introduction

For very low ows at high pressure drops the MicroCav plhead is used to eliminate cavitation. Close guided in a specseat ring, this trim can handle Sigmas as low as 1.006 and Cbetween 0.0007 and 1.25. This trim is used in valves rangrom 1 to 1.5 to 2 in size.

Design

This operating mechanisms o this trim involve multiple contually expanding grooves that intersect each other as they spiaround the plug head. Not only does this create areas o su

den contraction and expansion at the groove intersections bit allows the uid to impinge upon itsel while expanding. Tgradually expanding grooves also serve to reduce the velocitythe uid as it travels along the length o the plug head.


Mechanisms at Work Sudden expansion and contraction Turbulent mixing Mutual impingement of opposing streams Velocity reduction

Figure 7.1: Low Cv ChannelStream Plug Head

7. ChannelStream Low Cv

8. MicroCav

Figure 8.1: MicroCav Plug HeadIntroduction

For low ows at high pressure drops, the Low Cv Channel-Stream uses the same technology to eliminate cavitation as isused in the larger capacity Channelstream retainers except it isbuilt into a close-guided plug head. As the plug is stroked inthe seat ring the holes are exposed or hidden as required orthe needed ow capacity in its range.

Design

With a Cv capacity as small as 0.25 and as large as 50 this trimis intended or valves in the 1 to 3 size. This trim can also beused in conjunction with ChannelStream retainers with in this

range to provide additional stages o protection. The limita-tions o control are set by the clearance ow passing throughthe tolerance gaps as the plug comes o the seat.

Base Valve DesignThe Mark series o valves.Mechanisms at Work Sudden expansion and contraction Frictional losses in small passages Turbulent mixing Mutual impingement of opposing streams Directional changes


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Introduction

Using a ow-under-the-plug confguration this trim is capable ocontrolling mild levels o cavitation.

Design

Using our drilled hole stages (one upstream o the plug andthree downstream) and a contoured plug, the MultiStreamprovides good cavitation control and excellent turndown. Us-ing small holes in each stage as contraction points and largeopen areas between them as expansion points the MultiStream

drops the pressure in stages and divides the uid into numer-ous smaller streams. This modular trim can be optimized as theprocess conditions require.

Base Valve DesignAvailable in the FlowTop and FlowPro valve series.

Mechanisms at Work Sudden expansion and contraction Frictional losses in small passages Surface impingement and turbulent mixing Directional changes

Figure 10.1: MultiStream Trim

Introduction

The CavStream plug head uses the same technology to controlcavitation as the larger CavControl trim with the exception thatit is built into the plug head instead o the retainer. As the plugis stroked in the seat ring the holes are exposed or hidden asrequired or the needed ow capacity in its range.

Design

Tolerating Sigmas as low as 1.2 and covering a Cv range o 0.4to 88 or valves 0.5 to 3 the CavStream trim controls cavitationthrough the mutual impingement o opposing jets o uid. Asthe expanding jets o bubbles collide with each other the tur-bulence created dissipates the energy o the cavitating streamsbeore they come in contact with the downstream suraces o

the valve. A small step in the drilled holes o the retainer movethe vena contracta away rom the inside surace o the retainerthus protecting it rom the energy o the cavitation bubbles asthey implode.


Mechanisms at Work Mutual impingement Turbulent mixing Area expansion

Figure 9.1: CavStream Plug Head

10. MultiStream9. CavStream


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Introduction

Used in Leak-o control, drainage and warm-up, level controland injection cooling, the Gestra ZK model comes in 6 confgu-rations. These include the ZK 29, ZK 210, ZK 412, the ZK 313,the ZK 513, and the ZK 213. The ZK has excellent sealing andcontrol characteristics and is extremely wear-resistant whileeliminating cavitation. With a unique arrangement o concentricholed sleeves this trim can be confgured or a variety o operat-ing conditions and handle extremely high pressure drops rom1,400 psi to 8,120 psi. The same trim set can be confgured orlinear or equal percent characteristics. All this while keeping thesound level below 85 dBA.

Design

The main operating principle is based around the radial stagnozzle design which consists o several concentric sleeves wia large number o radial orifces. The orifces are arranged parallel, but are shited rom sleeve to sleeve so that they partoverlap orming nozzles arranged in series with intermediaash chambers. The ow through the nozzles is determined the plug. As the plug is stroked it will either partially or copletely set ree the nozzles o a stage. Depending on how tholes are aligned, the characteristic o the trim can be changerom linear to equal percent. The control edge on the plug thseals the holes allows or the plug to lit well out o the se

beore main ow begins, reducing wear on the seating suraand allowing the trim to maintain tight shut-o. For higher presures a tandem shut-o confguration is employed that allowthe ow velocity to be zero as the main seat opens or closethus excluding wire draw.

An additional principle o reducing pressure drop involves drillhole sleeves that pass ow through to channels in the next sleeand then out the holes in that sleeve to an expansion area beopassing through a fnal stage o holes. The plug varies the voume o the expansion area as it strokes up and down to maintathe proper expansion ratio or the uid. The gradually increasiareas o expansion ater each contraction reduce the pressurestages to eliminate or prevent cavitation.

Base Valve DesignThe Gestra series o valves.

Mechanisms at Work Sudden expansion and contraction Frictional losses in small passages Turbulent mixing Surface and mutual impingement Directional changes

Figure 12.1: Gestra ZK 313 Cutaway

11. ZK


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Introduction

This heavy gauge trim set can be used or reducing mild cavita-tion and eliminating low levels o cavitation. Three (3) confgu-rations are possible depending on the application requirements.

The possible components consist o a heavy drilled-hole cage,a skirt guided drilled-hole plug or a parabolic plug. Depend-ing on the combination o these components, a single stage orcavitation control can be confgured either with the cage andthe parabolic plug or just the drilled-hole plug. A two stagecavitation control/elimination conguration can be provided bycombining the drilled-hole cage with the skirt guided drilled-holeplug which also guides against the cage. The heavy duty con-struction o this trim allows the Type III system to be eective athigher pressure drops than the Type II-1 .

Figure 13.1: Kammer CageControl - Type III Trim

12. CageControl -Type III

Design

The main operating principle used in the CageControl Type IIItrim is alternating areas o expansion and contraction. As the

valve strokes the plug open to expose the holes, it simultaneous-ly opens the cage. This keeps the area o expansion between thetwo stages o holes proportional to the ow through the valveproviding an area o staged pressure drop. As the ow passesthrough the plug holes it is constricted and the ow is broken upinto multiple streams. These streams exit into an area o expan-sion between the stages and then are constricted again by theholes o the second stage. The streams again exit in to an areao expansion as they enter the upper gallery o the valve body.

When all the drilled hole components are used together this canbe eective in eliminating cavitation in low conditions and con-trolling it in mild conditions. This confguration can be opti-mized to match the process conditions. Where the cavitation is

low and only control is needed either the drilled hole plug or thecage can be used alone as dictated by the process Cv require-ments.

This trim is used in a ow-under confguration to protect theparabolic plug rom cavitation damage while in a control con-fguration. This also allows the uid streams to be directed intogradually expanding areas as they pass through the drilled holesthus reducing the pressure in stages and controlling velocity.

Standardized designs allow or quicker deliveries and lowercosts.

Base Valve Design

Available in a number o Kammer platorms, the most commonlyused is the TotalFlow 035000 series control valve.

Mechanisms at Work

Sudden expansion and contraction Frictional losses in small passages Turbulent mixing Surface impingement


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Introduction

There are 3 confgurations o this multi-purpose trim available.The Type II-1 confguration o this trim, that uses just the skirt-guided drilled-hole plug component, is the only one recommend-

ed or use in low levels o cavitating service. No screens or drilledcages are used. This Trim can be used to control low levels ocavitation in either a ow over (recommended) or a ow underdirection.

Design

In a ow-over confguration, using just the plug, this trim workson the principle o mutual impingement and turbulent mixing tocontrol cavitation. This works well or controlling low levels ocavitation.

In a ow-under application and at lower levels o cavitation the

Figure 14.1: Kammer StreamControl - Type II Trim

13. StreamControl - Type II-1

Kammer

TotalFlow035000

same plug works on the principle o creating a restriction by spting the uid into many small streams and allowing them to epand into a larger area.

Standardized designs allow or quicker deliveries and low

costs.

Base Valve Design

Available in a number o Kammer platorms, the most commonused is the TotalFlow 035000 series control valve.

Mechanisms at Work

Mutual impingement Turbulent mixing Area expansion


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18

Introduction

Z-Trim is oered in a notched V-ball or a ull-port ball and com-bines the benefts o an advanced control valve with the simplic-ity o a ball valve. Most eective with medium pressure dropsand able to handle low ows at higher pressure drops, the Z-trimcan be used to eectively control cavitation. The trim also works

very well with media containing particles like fbers without risko clogging. Using the standard Setball or Duball as a platorm,adding the Z-Trim requires only one part to be changed.

Design

The simple design o the Z-Trim controls low levels o cavitationby passing the uid through as many as fve stages o pressurereduction. The passages rom one stage to the next split theow in to many smaller streams creating alternating areas o ex-pansion and contraction. The increasing passage areas in eachsubsequent stage o the Z-Trim allows the uid to expand whilecontrolling velocities.

Figure 16.1: Setball Control Valve with Z-Trim

As the valve opens, ewer stages are taken until the ball is openand the valve develops ull capacity. This eature gives eectivecavitation control at the low end, where pressure drops are high,and still delivers the high capacity expected rom a ball valvewhen ully open.

Base Valve Design

The Z-Trim is available in the Duball, Setball, and ShearStreamSB control valves.

Mechanisms at Work

Sudden expansion and contraction Turbulent mixing Directional changes

14. Z-Trim

Figure 16.2: Duball Control Valve with Z-Trim


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Introduction

Capable o eliminating moderate cavitation completely, theA-Trim provides exceptional control in the simplicity o a ballvalve. Very eective at low ows and higher pressure drops,this trim works best in clean media.

DesignThe ball o the A-Trim is made up o many small zigzag channelscreating a large number o deections as well as small areas oexpansion and contraction. This allows the pressure drop tobe taken in many small steps. The area o each channel can bevaried in order to optimize the trim or specifc process condi-tions.

This design is particularly eective in eliminating cavitationwhen the valve is frst opened and up to 45 0 o rotation. It isduring this stage o orientation that the lowest ows and high-est pressure drops are encountered and the greatest amount oprotection is required. As the uid enters an exposed channel

on the upstream side o the ball it is orced to pass around tball between the seals and through the channels that are nyet exposed in order to exit the trim. The passing o the uthrough the channels twice provides additional stages o presure reduction where it is needed most. As the ball continuto open past 450 to its ull capacity the uid passes througmore and more o the channels only once. As a result the val

capacity will increase appreciably and still maintain the abilto eliminate cavitation.

Base Valve Design

The A-Trim is available in the Duball.

Mechanisms at Work

Sudden expansion and contraction Frictional losses in small passages Directional changes

Figure 17.1: A-Trim or Duball

15. A-Trim


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To find your local Flowserve representative:

For more information about Flowserve Corporation, visit

www.flowserve.com or call USA 1 800 225 6989

Flowserve Corporation has established industry leadership in the design and manuacture o its products. When properlyselected, this Flowserve product is designed to perorm its intended unction saely during i ts useul lie. However,the purchaser or user o Flowserve products should be aware that Flowserve products might be used in numerousapplications under a wide variety o industrial service conditions. Although Flowserve can (and oten does) providegeneral guidelines, it cannot provide specific data and warnings for all possible applications. The purchaser/user mustthereore assume the ultimate responsibility or the proper sizing and selection, installation, operation, and maintenanceof Flowserve products. The purchaser/user should read and understand the Installation Operation Maintenance (IOM)instructions included with the product, and train its employees and contractors in the sae use o Flowserve products inconnection with the speciic application.

While the inormation and speciications contained in this literature are believed to be accurate, they are supplied orinormative purposes only and should not be considered certiied or as a guarantee o satisactory results by reliancethereon. Nothing contained herein is to be construed as a warranty or guarantee, express or implied, regarding anymatter with respect to this product. Because Flowserve is continually improving and upgrading its product design, t hespeciications, dimensions and inormation contained herein are subject to change without notice. Should any questionarise concerning these provisions, the purchaser/user should contact Flowserve Corporation at any one of its worldwideoperations or oices.

2006 Flowserve Corporation, Irving, Texas, USA. Flowserve is a registered trademark o Flowserve Corporation.

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