Emerson Process Management Product Bulletinlogo
Dirty Service Trim Tables Figures Print Version Collapse Expand
 
Fisher ® Dirty Service Anti-Cavitation Trim (DST)

Dirty Service Trim Description Fisher Dirty Service Trim (DST) (figure 1) is a patented multi-stage, anti-cavitation control valve trim for use in services where the fluid may have entrained particulate that could plug the passages, or cause erosion damage to conventional anti-cavitation trims. DST is frequently used in high pressure drop applications up to 4200 psid in the chemical, refining, oil and gas production, and power industries.
       Close Section Above

Features

  • Cavitation Control—2-, 3-, 4-, 5-, or 6-stage DST used in a valve properly selected for flow conditions can eliminate cavitation and associated damage and noise.
  • Versatility—Available in globe and angle valves, flow down (figure 3) or flow up (figure 4), from NPS 1 to 16 having weld-end or flanged-end connections. Can be used in easy-e®, EH, EHA, EW, HP, and HPA valves.
  • Long Trim Life—This patented trim concept uses a combined axial and radial flow that features large, open flow paths and decreased clearance flow erosion.
  • Flexibility— In many cases DST can be retrofitted to replace Cav III trims that are currently in service. DST can pass 1/4 to 3/4 inch particles without plugging.
  • Easy Maintenance—In-line trim removal allows inspection of parts without taking the valve body out of the pipeline.
  • Trim Materials—Typical trim materials include 17-4PH SST cages, 440C SST valve plug and seat, 316/ENC/alloy 6 cages with 316/alloy 6 valve plug and seat, or S32550/ENC/alloy 6 cages with S32550/alloy 6 valve plug and seat. Other materials are available to satisfy application requirements.
  • Sour Service Capability—Materials are available for applications handling sour fluids. Please contact your local Emerson Process Management sales office for additional information.
  • Shutoff—DST also features a protected seat design where the shutoff function of the valve is separate from the throttling areas of the trim.

       Close Section Above

Principle of Operation DST provides cavitation control for applications with entrained particulate that could potentially plug the inlet passages or cause severe erosion damage to conventional anti­cavitation trim. The DST design uses a combined axial and radial flow path that features large openings allowing particulate up to 3/4 inches in diameter to pass through the valve.
Due to the need for tight shutoff, the multi-stage design incorporates a protected seating surface that separates the shutoff and the throttling locations. All significant pressure drops are taken downstream of the seating surface. As a result, the seating surfaces are not worn away by throttling control action, (valve must always be throttled above the min Cv) resulting in extended shutoff capabilities.
In conventional staged-trim designs, cavitation usually does not exist until the final stage. Figure 2 illustrates why this happens. As shown, the greater the pressure drop through the final stage, the lower the vena contracta pressure (Pvc). If Pvc is less than or equal to Pv, and P2 is greater than Pv, then cavitation will result.
The DST valve avoids this by means of its unique expanding flow area design. Each of the stages has a successively larger flow area. The result is a very efficient operation because more than 90 percent of the overall pressure drop is taken in the stages prior to the final stage where there is little danger of bubble formation. Consequently, a relatively low inlet pressure to the final stage is achieved. Figure 2 also compares the pressure drop pattern through the four stages in the expanding area DST design with a pattern representing a six-stage trim design with each stage taking an equal portion of the total pressure drop. As can be seen, the inlet pressure to the last stage of DST trim is always less than the inlet pressure to the sixth stage of an equal-drop cage. Therefore the Pvc of the DST cage remains higher than the Pvc of an equal-drop cage. If the pressure drops were all equivalent to that of the last stage in DST trim, 11 stages would be required in the equal-drop trim.
       Close Section Above

Availability DST trim is available in numerous body designs and pressure classes. Table 1 shows the pressure drop limits for each design relative to the number of stages used.
Table 2 shows the different valve constructions that DST can be used in. It also shows typical min and max Cv values each valve can achieve. Any deviation from the sizes listed in table 2, or temperatures in table 3, will result in different Cv limitations. Please contact your Emerson Process Management sales office for any requests that do not fall within these ranges.
       Close Section Above

Trim Selection Guidelines The standard trim materials are listed below, and in table 3. Other materials such as superaustenitic SST, 347 SST, Solid Alloy 6, N08800, and tungsten carbide trim are available upon request. Contact your Emerson Process Management sales office for more information.

  • Trim A: Trim A is the typical trim used with carbon steel and alloy steel valve bodies. It can generally be used in severe service applications up to 316°C (600°F). Higher temperature can be achieved with alternate trim parts. Contact your Emerson Process Management sales office for higher temperature requirements. Typical applications for Trim A include boiler feedwater, water, non-sour hydrocarbons, and other non-sour liquids.
  • Trim B: Trim B is the typical trim used with stainless steel valve bodies. It can generally be used in severe service applications up to 316°C (600°F). Higher temperatures can be achieved with alternate trim parts. Contact your Emerson Process Management sales office for higher temperature requirements. Typical applications for Trim B include produced water, water, sour hydrocarbons, and other sour liquids. Not for use with boiler feedwater.
  • Trim C: Trim C can commonly be seen in carbon steel and Duplex SST valve bodies. This trim is most commonly used in sea water applications, produced water, and other offshore crude oil applications.

Please contact your Emerson Process Management sales office for more information on DST trim.

       Close Section Above

Characteristics The DST trim is designed to have a linear flow characteristic. It is also designed to have no significant flow for the first 10-15% travel. Special characterizations may be possible, including special low minimum Cv designs. Please contact your Emerson Process Management sales office for assistance.
       Close Section Above

Valve Sizing Guidelines Sizing procedures from Catalog 12 or Fisher Specification Manager can be used to size DST control valves. Noise calculations are best performed by using Fisher Specification Manager. The multi-stage configuration of the DST design reduces valve trim noise significantly. Select CAV III 2-Stage as the valve type in Fisher Specification Manager to perform the noise prediction calculation.
       Close Section Above

Ordering Information When ordering, specify:
Application Information
1. Process Liquid: State particle size and type of entrained impurities, if any.
2. Specific gravity of liquid
3. Temperature and vapor pressure of liquid
4. Critical pressure
5. Range of flowing inlet pressures
6. Pressure dropsa. Range of flowing pressure drops
b. Maximum at shutoff 7. Flow ratesa. Minimum controlled flow
b. Normal flow
c. Maximum flow 8. Required Cv
9. Line size and schedule        Close Section Above

Specifications

Available Valves

easy-e, EH, EHA, EU, EW, HP, and HPA.
See table 2

End Connection Styles

Refer to appropriate valve bulletin

Valve Body Dimensions and Weights

Valve type, pressure class, and number of stages will result in changes to these values. Please consult your Emerson Process Management sales office for more information on finished dimensions and weights

Shutoff Classifications

Class V per ANSI/FCS 70-2 and IEC 60534-4

Maximum Inlet Pressures and Temperatures(1)

Consistent with applicable CL600, CL900, CL1500, and CL2500 pressure/temperature ratings according to ASME B16.34 ratings unless limited by individual temperature and pressure limits shown in tables 1 and 3

Maximum Pressure Drop(1)

See table 1

Construction Materials

Trim Parts: 17-4PH SST cages, 440C SST valve plug and seat or 316/ENC/alloy 6 cages with 316/Alloy 6 valve plug and seat. S32550/ENC/alloy 6 cages, S32550/alloy 6 valve plug and seat. Trim can be made from several other bar stock alloys. Consult your Emerson Process Management sales office for your specific application

Temperature Capabilities

Valve Body/Trim Combinations: See table 3 All Other Parts: Consult your Emerson Process Management sales office

Flow Coefficients

See table 2

Flow Characteristic

Linear

Flow Direction

Flow down (typical) or Flow up (available)

Valve Cavitation Coefficient

Kc = 1.0 for all valves when trim is used within applicable pressure drop limits.

Maximum Valve Plug Travel

Typical plug travels are 0.75 inch through 2 inch. Contact your Emerson Process Management sales office for your specific application

Minimum Seating Force

Use Class V seat load requirements

1. The pressure/temperature limits in this bulletin and any applicable standard or code limitation for valve should not be exceeded.

Note
Neither Emerson, Emerson Process Management, nor any of their affiliated entities assume responsibility for the selection, use, or maintenance of any product. Responsibility for the selection, use, and maintenance of any product remains with the purchaser and end-user.

       Close Section Above


Table Table 1. Allowable Pressure Drop Limits
PRESSURE DROP LIMITS
Number of Stages Flowing Pressure Drop Limit (bar) Flowing Pressure Drop Limit (psi) Fl Kc
2 52 750 0.95 1.0
3 103 1500 0.97 1.0
4 207 3000 0.99 1.0
5 241 3500 0.99 1.0
6 289 4200 0.99 1.0

       Close Section Above

Table 2. Fisher DST Flow Down Availability(4)
VALVE DESIGN PRESSURE RATING VALVE SIZE PORT SIZE TRAVEL UNBALANCED AREA MINIMUM AND MAXIMUM CAPACITIES(3)
2-Stage 3-Stage 4-Stage 6-Stage
NPS inch inch inch2 Min Max Min Max Min Max Min Max
easy-e Globe CL600 (5) 0.875 0.63 0.610 (1) 0.15 4.4 NA(2) NA(2)
1.5(5) 1.125 0.75 0.800 (1) 0.22 8.9 NA(2) NA(2)
2 1.75 0.75 0.029 0.3 23.1 0.22 18.5 NA(2) NA(2)
2.5 2.188 0.75 0.061 0.5 30.5 0.4 23.4 NA(2) NA(2)
3 2.50 0.75 0.041 0.8 46 0.8 36 NA(2) NA(2)
4 3.438 1.25 0.118 1.7 81 1.5 64 NA(2) NA(2)
6 4.375 1.50 0.154 2.8 174 2.8 128 NA(2) NA(2)
8 5.375 2.00 0.206 5.5 253 5 185 NA(2) NA(2)
easy-e Angle CL600 (5) 1.125 0.75 0.800 (1) 0.22 8.9 NA(2) NA(2)
3 2.188 0.75 0.061 0.5 30.5 0.4 23.4 NA(2) NA(2)
4 2.50 0.75 0.041 0.8 46 0.8 36 NA(2) NA(2)
6 3.438 1.25 0.118 1.7 81 1.5 64 NA(2) NA(2)
EH CL1500 2 1.50 0.75 0.051 NA(2) (1) 0.3 7.5 (1)
3 1.875 1.00 0.031 NA(2) (1) 0.58 23 (1)
4 2.875 1.50 0.047 NA(2) 1.4 54 1 44 (1)
6 3.625 1.75 0.118 NA(2) 1.2 106 1 88.5 (1)
8 5.375 1.50 0.142 NA(2) 4 147 3 115 (1)
10 5.375 1.50 0.142 NA(2) 4 147 3 115 (1)
12 8.00 2.00 0.350 NA(2) (1) 10 298 (1)
14 8.00 2.00 0.350 NA(2) (1) 10 298 (1)
CL2500 (5) 1.50 0.75 0.780 NA(2) NA(2) (1) 0.4 9.4
(5) 1.875 0.75 1.534 NA(2) NA(2) 0.5 16 0.5 13.7
EHA CL1500 4 1.875 1.00 0.031 NA(2) (1) 0.45 19.2 (1)
6 2.875 1.50 0.047 NA(2) 1.4 54 1 44 (1)
8 3.625 1.75 0.118 NA(2) 1.2 105 1 88.5 (1)
CL2500 (6) 3.625 1.75 0.118 NA(2) NA(2) 1 86 (1)
(6) 2.875 1.50 0.047 NA(2) NA(2) 1 46 1 28
EU CL600 12 8.00 1.50 0.350 10 382 10 292 NA(2) NA(2)
16 11.00 4.00 0.490 (1) 10 617 NA(2) NA(2)
EW CL600 4X2 1.75 0.75 0.029 (1) 0.22 18.5 NA(2) NA(2)
6X4 3.438 1.25 0.118 1.7 81 1.5 64 NA(2) NA(2)
8X6 4.375 1.75 0.154 2.8 187 2.8 150 NA(2) NA(2)
12X8 5.375 2.00 0.142 5.5 253 5 185 NA(2) NA(2)
HP &
HPA		 CL1500 (5) 0.875 0.63 0.589 NA(2) (1) 0.09 3.2 (1)
(5) 1.25 0.75 0.785 NA(2) 0.2 8.3 0.28 7.1 (1)
3 1.875 1.00 0.031 NA(2) 0.65 24.8 0.45 19.4 (1)
4 2.875 1.00 0.047 NA(2) 1 39.5 1 34.6 (1)
6 3.625 1.50 0.118 NA(2) 1.2 89.3 1 71 (1)
CL2500 (5) 0.875 0.63 0.589 NA(2) NA(2) (1) (1)
(5) 1.00 0.75 0.785 NA(2) NA(2) (1) 0.3 4.3
1. Consult your Emerson Process Management sales office.
2. Construction not available.
3. 5-stage DST is available upon request.
4. For flow up constructions consult your Emerson Process Management sales office.
5. Unbalanced constructions.
6. These valves are from block forged angle valve bodies. Cast valve bodies are available and may change these values.

       Close Section Above

Table 3. Trim Combinations for Fisher DST(1)
TRIM DESIGNATION VALVE BODY MATERIAL VALVE PLUG CAGE SEAT RING MAXIMUM TEMPERATURE LIMIT
°C °F
A WCC 440C 17­4PH 17­4PH or
440C		 316 600
B WCC 316/CoCr­A 316/CoCr­A/ENC 316/CoCr­A/ENC 204 400
SST 316 600
C WCC S32550/
CoCr­A		 S32550/CoCr­A/ENC S32550/CoCr­A/ENC 316 600
SST 204 400
1. Contact your Emerson Process Management sales office for higher temperature capabilities.

       Close Section Above

Table 4. Typical Applications
POWER/COGENERATION Boiler feed pump recirculation
Desuperheater spray water control
Feedwater start-up regulators
Condensate pump recirculation
Superheater bypass
OIL AND GAS PRODUCTION Water injection pump recirculation
Produced/waste water injection well control
Separator letdown
Chemical injection pump bypass
NATURAL GAS PROCESSING Contactor (rich amine) letdown
Rich and lean amine pump spillback
REFINING Contactor letdown
Rich and lean amine pump spillback
Pump spillback/recirculation
Various high pressure and low pressure separator letdown

       Close Section Above

       Close Section Above


80.2:021
October 2009
©Fisher Controls International LLC 1997, 2009; All Rights Reserved
Notices