8/11/2019 C5295

1/8

Design DVG/AF Variable Geometry DesuperheaterContents

Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Scope of Manual 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .Description 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Principle of Operation 2. . . . . . . . . . . . . . . . . . .

Installation 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maintenance Instructions 4. . . . . . . . . . . . . . .Servicing 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Disassembly 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Assembly 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Troubleshooting 5. . . . . . . . . . . . . . . . . . . . . . . . .

DVG/AF Parts Ordering 6. . . . . . . . . . . . . . . . . .

Parts List 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction

Scope of ManualThis instruction manual includes installation, mainte-nance, and operation information for the Design DVG/ AF variable orifice desuperheater. Refer to separateinstruction manuals for information on the actuator andaccessories.

Only personnel qualified through training or experienceshould install, operate, and maintain a Design DVG/AFdesuperheater. If you have any questions about theseinstructions, contact your Fisher Controls sales officeor sales representative before proceeding.

Figure 1. Design DVG/AF Variable Geometry Desuperheater with Pneumatic Actuator

W6981/IL

DescriptionThe Design DVG/AF variable orifice desuperheater(figure 1) provides a convenient and efficient methodof reducing superheated steam, and some other va-pors, to desired temperature levels. The variable ori-fice design allows precise temperature control underwidely fluctuating process conditions.

The DVG/AF assures:

1. Fine atomization over a wide range of operatingconditions assuring rapid and complete vaporization of

injected water.2. No pipe liners, atomizing steam, or separate spray-water control valves are required.

3. Temperature control to within 10 - 15 F (6 - 8 C) ofsaturation.

Instruction ManualForm 5295August 1998 Design DVG/AF

8/11/2019 C5295

2/8

Design DVG/AF

2

Table 1. Specifications

Steam Line Sizes8 to 60-inch

Steam Line Connection Sizes

3, 4, and 6-inch ANSI Class 150, 300,600, 900, and 1500 raised-face flange (con-sult factory for higher ratings) (1)

Spraywater Connection Sizes1, 1-1/2, and 2-inch ANSI Class 150,300, 600, 900, and 1500 raised-face

flange (consult factory for higher Ratings) (1)

Maximum Inlet Pressures (2)

Consistent with applicable Class 150, 300, 600,900, and 1500 (consult factory for higher ratings)pressure-temperature ratings per ASME B16.34

Inherent Rangeability (3)

Up to 25:1

Spraywater Pressure Required

50 to 500 psig (3.5 to 35 bar) greater than steamline pressure

Minimum Steam Velocity (4)

30 feet per second (9.1 meters per second)

Yoke Boss Sizes and Valve Stem Diameters2-13/16 inch (71mm) yoke boss diameter with 1/2inch (12.7mm) stem diameter

Valve Travel (Standard)1-1/2 inch (38mm)

1. Alternate pressure classes may be available. Consult factory.2. Do not exceed t he pressure or temperature limits in this instruction manual, nor any applicable code or standard limitations.3. Ratio of maximum to minimum controllable C v, dependent on available water pressure differential.4. Minimum steam velocity is a function of several application parameters and may be adjusted upward or downward from this standard.

W6982-1 / IL

Figure 2. Detail of Design DVG/AF Desuperheater

4. Simple in line installation is accomplished through astandard flange connection. Installation can be in avertical-up or horizontal pipe.

5. High turndown capability.

Principle of OperationThe Design DVG/AF desuperheater reduces steamtemperatures by introducing cooling water directly intothe hot steam. Heat transfer accomplishes the desiredtemperature reduction. The cooling water absorbsheat by conduction and forced convection until the wa-ter absorbs sufficient heat for vaporization. By regula-tion of the water quantity, the degree of heat absorp-tion can be controlled and a specified final steamtemperature maintained.

The linear positioning of the plug regulates water flowto the sprayhead of the DVG/AF. The main body di-ameter controls the flow of water, via radially drilledorifices, in the guide cage. A cross sectional drawingof the DVG/AF appears in figure 2.

The Design DVG/AF desuperheater utilizes the prov-en, spring-loaded AF (Anti-Flash) nozzle to provide auniform hollow cone spray pattern over a wide rangeof flow conditions (see figure 3). The water is injectedthrough holes drilled at a compound angle to inducespin as the AF nozzle plug is opened with increasingwater pressure. The design of the AF nozzle is suchthat water flows only after sufficient backpressure isavailable to provide a good spray pattern. The fullopening of the AF nozzle is limited by a travel stop toensure that the spring is kept within its proper workingrange and the water film thickness is maintained at thenecessary thickness for proper atomization.

8/11/2019 C5295

3/8

Design DVG/AF

3

Figure 3. AF Nozzle Cross Section

STEM

SPRING

NUTPIN

WATER INJECTION HOLES

PLUG

BODY

A7191 / IL

Installation

WARNING

Personal injury or equipment damagecaused by sudden release of pressuremay result if the desuperheater isinstalled where service conditions couldexceed the limits of the pressure classnoted on the nameplate. To avoid such

injury or damage, provide a relief valvefor over pressure protection as requiredby government or accepted industrycodes and good engineering practices .

CAUTION

When ordered, the desuperheater con-figuration and construction materialswere selected to meet particular pres-sure, temperature, pressure drop, andfluid conditions. Do not apply any otherconditions to the desuperheater withoutfirst contacting your Fisher Controlssales office or sales representative.

1. Insert the Design DVG/AF desuperheater into theflanged pipe stud on the steam pipe (see table 2 andfigure 4 for the proper T length dimension). Bolt theunit to the pipe stud flange in accordance with stan-dard piping practice.

Table 2. T Dimensions D T(1)

Nominal Pipe Size,Inches Inches mm

810

9-3/48-1/2

248216

12

141618

11

10-1/29-1/28-1/2

279

267241216

202224

>24

10-1/29-1/28-1/28-1/2

267241216216

1. For the 6-inch mounting flange, add 2-3/4 inches (70 mm) to the T dimension.

2. Clean and flush out the cooling water line beforeconnecting to the desuperheater. Use only cleansources of cooling water. Use of clean water de-creases wear to the valve trim and prevents cloggingof desuperheater orifices by solid particles.

Note

Fisher Controls recommends installa-tion of a strainer and isolating valve onthe waterline leading to the desuper-heater. Failure to do so may result inclogging of the desuperheater by solidparticles, thus hampering temperaturecontrol of the steam.

3. A straight run of pipe is required downstream of thedesuperheater to ensure complete vaporization ofcooling water. Consult the desuperheater certifieddrawing for the required distance of straight pipe.

4. Typically, a temperature sensor should be mountedat a minimum distance of 30 feet (9.1 m) downstreamof the desuperheater. This distance will vary depend-ing on steam velocity and percentage of spraywater.Consult the installation drawing provided with the unitfor this distance or call your Fisher Controls sales of-fice or sales representative.

5. The steam line should have no branch lines be-tween the desuperheater and the downstream temper-ature sensor.

6. A typical control loop is illustrated in figure 5. Atemperature sensor (TE) measures changes in tem-perature and transmits a signal to a remote tempera-ture-indicating controller or distributed control system(DCS). The output signal from the controller is sent tothe positioner on the desuperheater. The positioneroutput signal is piped to the actuator, which strokesthe stem/plug of the desuperheater. A rising stemopens the desuperheater to allow additional waterflow.

8/11/2019 C5295

4/8

Design DVG/AF

4

Figure 4. DVG/AF T Location

WATERFLANGE

MOUNTINGFLANGE

T HEIGHT

NOMINALPIPE SIZE

A7192 / IL

WARNING

Personal injury could result from pack-ing leakage. Valve packing was tight-ened prior to shipment; however itshould be checked for possible loosen-ing due to shipping and handling.

Maintenance Instructions

ServicingDue to the care Fisher Controls takes in meeting allmanufacturing requirements (heat-treating, dimension-al tolerances, etc.), use only replacement partsmanufactured or furnished by Fisher Controls.

WARNING

Avoid personal injury from sudden re-lease of pressure or uncontrolled pro-cess fluid. Before starting disassembly:

Disconnect any operating lines pro-viding air pressure, electric power, or acontrol signal to the actuator. Be surethe actuator cannot suddenly open orclose the valve.

Use bypass valves or completelyshut off the process to isolate the valvefrom process pressure. Relieve processpressure on both sides of the valve.

Drain the process media from bothsides of the valve.

Vent the power actuator loadingpressure and relieve any actuator springprecompression.

Use lock-out procedures to be sure

that the above measures stay in effectwhile you work on the equipment.

Shut off water and steam flow and vent all systempressure before removal of the desuperheater fromthe steam line. Disconnect the desuperheater from theflanged pipe stud and water flange. Withdraw the unitfrom the line.

Temporarily connect the desuperheater to the air sup-ply and verify proper action. To check for seat leak-age, connect a water line to the unit and pressurize toservice conditions.

Disassembly

CAUTION

Residual system pressure may be re-leased during the following steps if thesystem was improperly isolated orvented. Use extreme care to prevent per-sonal injury while loosening any fasten-ers in the pressure boundary.

1. Disconnect all field connections to the positionerand actuator. Remove the mounting and water flangebolting and remove the DVG/AF from the steam line.2. Remove the actuator from the DVG/AF using theactuator manufacturers removal instructions. Refer-ence figure 6 for assistance in disassembly in the fol-lowing steps.3. Slowly loosen the bonnet nuts (key36) approxi-mately 1/16 in a uniform manner.4. Break the bonnet (key 13) loose from the body (key01).5. After ensuring that the system is depressurizedremove the bonnet nuts (key 36) and washers (key35).

6. Remove the bonnet (key 13) from the body (key01) taking care to avoid damage to the stem (key 17).7. Remove the plug/stem assembly (keys 8, 17 and18), cage guide (key 15) and seat (key14) for inspec-tion.8. Examine the removed parts for unusual wear andreplace if necessary.9. Remove and discard the seat gasket (key 30), bon-net gasket (key 31) and stem packing (key 24).

8/11/2019 C5295

5/8

Design DVG/AF

5

Figure 5. Typical DVG/AF Installation

SPRAYWATER

STEAMFLOW

TC

TE

C0817/IL

10. Remove the spray nozzle(s) (key 9) by unscrew-ing them from the nozzle holder after removing theanti-rotation tab(s).

11. Inspect the spray nozzles. The nozzles should becompletely closed with no evidence of foreign debrisor uneven action when opened and closed. If this isnot the case and the nozzle(s) cannot be disas-sembled for cleaning; the nozzle(s) must be replacedto correct the problem.

12. Flush the desuperheater to remove any debris.Clean all gasket and part mating surfaces.

Assembly1. Reassemble the unit with new gaskets and packingfollowing a reverse sequence of the disassembly. Lu-

bricate all sliding surfaces and the bonnet studs andwashers with a quality high temperature lubricant. Thenozzle antirotation tabs can be replaced with any simi-lar sized SA182-F22 (2-1/4 Cr1 Mo) material or9018 weld rod if required. Take care to avoid over-heating the nozzle or getting weld spatter on thenozzle opening surface.

2. Tighten the bonnet bolts in a multi-step uniformcross pattern. It is recommended that the bonnet bolttorquing be carried out in a minimum of four torque

levels until the final torque is achieved. Torquing val-ues are shown in table 3.

3. Reinstall the packing ring, a new packing set, pack-ing follower, flange and nuts.

4. Mount the actuator. When mounting the actuator itis critical to ensure that the stroke is set to ensure thatproper seating load is available. Follow the guidelinesset forth by the manufacturer in setting up the actua-tor. In general, position the plug on the seat, move theactuator to full open position, close the actuator for thelength of the DVG/AF stroke and then connect actua-tor and DVG/AF stems. If more complete informationis required, consult the actuator documentation.

5. Tighten the packing nuts as required. Torquing val-ues are shown in table 4. Recheck the stem packingfor leakage after the system is returned to service andretighten the packing nuts if required.

TroubleshootingThe following guide (table 5) is intended as a basicfirst line troubleshooting guide. Contact your FisherControls sales office or sales representative for assis-tance if you are unable to resolve your field operationproblem.

8/11/2019 C5295

6/8

Design DVG/AF

6

Table 3. Troubleshooting Guide Problem Corrective Action

Stem packing is leaking Tighten stem packing nuts

Stem packing is leaking after tightening stem packing nuts Repack and replace worn parts as neededActuator cannot open desuperheater Check actuator calibration.

Actuator cannot open desuperheater Check for over-tightening of the packing nuts

Actuator action is sticky Check for alignment between actuator and DVG/AFActuator action is sticky Check positioner calibration

Actuator action is sticky Replace plug, cage, stem guide and/or packing follower

Temperature setpoint is not reached Check water source availability and pressureTemperature setpoint is not reached Check nozzle(s) for plugging

Temperature setpoint is not reached Make sure that steam saturation pressure is not above setpoint

Temperature setpoint is not reached Check to ensure full actuator stroke is reachedTemperature setpoint is not reached Check for proper orientation of nozzle in steam flow

Temperature is below setpoint Check temperature control loop reset

Temperature is below setpoint Check nozzle for fouling/poor spray pattern clean/replaceTemperature is below setpoint Check temperature sensor location relocate per guidelines.

Temperature is below setpoint Check for proper orientation of nozzle in steam flow

Water in steam line Check that steam traps are functioning properlyWater in steam line when steam line isolated Check for proper desuperheater actuator installation

Water in steam line when steam line isolated Replace desuperheater seat and plug assembly

Bonnet gasket is leaking Inspect body/bonnet mating surfaces, replace bonnet gasket. Ensurebonnet bolts are properly torqued.

Table 4. Recommended Bonnet Bolt Torque

Bolt Size, Inch Threads per Inch Recommended BoltTorque, Lbf ft(1)

5/8 11 125

3/4 10 2001. Torques for studs with heavy hex nuts.

DVG/AF Parts OrderingEach desuperheater assembly is assigned a serialnumber which can be found on the mounting flange ofthe desuperheater. The serial number will have theform ATL-XX-YYYY-Z, where XX is the project year,YYYY is the specified sequence of numbers and/orletters identifying the project, and Z is the item numberidentifying the desuperheater on that project. Refer tothe serial number when contacting your Fisher Con-trols sales office or sales representative for technicalassistance. When ordering numbers for each part re-quired, the key numbers on figure 6 can be used tohelp in part identification.

Table 5. Recommended Packing Nut Torque

StemDiameter, Inch

ANSI PressureClass

MaximumTorque,

Lbf ft

MinimumTorque,

Lbf ft150 6 4300 7 5600 10 7

1/2900 13 9

1500 16 112500 18 13150 12 8300 15 10600 22 15

3/4900 30 20

1500 37 252500 45 30

8/11/2019 C5295

7/8

Design DVG/AF

7

Figure 6. Design DVG/AF Assembly

B2603 / IL

Parts ListKey Description

1 Valve Body2 Valve Body Pipe3 Water Flange4 Water Pipe5 Valve Body Flange7 Nozzle Mount8* Plug9* Spray Nozzle

13 Bonnet14* Seat15* Cage Guide17* Stem

Key Description

18* Stem Pin23 Gland Ring24* Packing Set25 Gland Follower26 Gland Flange27 Gland Stud28 Gland Nut30* Seat Gasket31* Bonnet Gasket34 Bonnet Stud35 Bonnet Stud Washer36 Bonnet Stud Nut

*Recommended spare parts

8/11/2019 C5295

8/8

Design DVG/AF

8

For information, contact Fisher Controls: Marshalltown, Iowa 50158 USACernay 68700 FranceSao Paulo 05424 BrazilSingapore 128461

Printed in U.S.A.

Fisher Controls International, Inc. 1990, 1998; All Rights Reserved

Fisher, Fisher-Rosemount, and Managing The Process Better are marks owned by Fisher Controls International, Inc. or Fisher-Rosemount Systems, Inc.All other marks are the property of their respective owners.