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Instruction Manual Form 5295 August 1998

Design DVG/AF

Design DVG/AF Variable Geometry Desuperheater Contents Introduction

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

Principle of Operation Installation

................... 2

................................ 3

Maintenance Instructions

............... 4 Servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Troubleshooting

......................... 5

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

6

Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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W6981/IL

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

Description

Scope of Manual This instruction manual includes installation, maintenance, and operation information for the Design DVG/ AF variable orifice desuperheater. Refer to separate instruction manuals for information on the actuator and accessories. Only personnel qualified through training or experience should install, operate, and maintain a Design DVG/AF desuperheater. If you have any questions about these instructions, contact your Fisher Controls sales office or sales representative before proceeding.

The Design DVG/AF variable orifice desuperheater (figure 1) provides a convenient and efficient method of reducing superheated steam, and some other vapors, to desired temperature levels. The variable orifice design allows precise temperature control under widely fluctuating process conditions. The DVG/AF assures: 1. Fine atomization over a wide range of operating conditions assuring rapid and complete vaporization of injected water. 2. No pipe liners, atomizing steam, or separate spraywater control valves are required. 3. Temperature control to within 10 - 15째F (6 - 8째C) of saturation. D101616X012

Introduction


Design DVG/AF Table 1. Specifications

Steam Line Sizes J 8 to 60-inch

Inherent Rangeability(3)

Steam Line Connection Sizes J 3, J 4, and J 6-inch ANSI Class J 150, J 300, J 600, J 900, and J 1500 raised-face flange (consult factory for higher ratings)(1)

Spraywater Pressure Required

Spraywater Connection Sizes J 1, J 1-1/2, and J 2-inch ANSI Class J 150, J 300, J 600, J 900, and J 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

Up to 25:1

50 to 500 psig (3.5 to 35 bar) greater than steam line pressure Minimum Steam Velocity(4) 30 feet per second (9.1 meters per second) Yoke Boss Sizes and Valve Stem Diameters 2-13/16 inch (71mm) yoke boss diameter with 1/2 inch (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 the pressure or temperature limits in this instruction manual, nor any applicable code or standard limitations. 3. Ratio of maximum to minimum controllable Cv, 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.

Principle of Operation The Design DVG/AF desuperheater reduces steam temperatures by introducing cooling water directly into the hot steam. Heat transfer accomplishes the desired temperature reduction. The cooling water absorbs heat by conduction and forced convection until the water absorbs sufficient heat for vaporization. By regulation of the water quantity, the degree of heat absorption can be controlled and a specified final steam temperature maintained.

W6982-1 / IL

Figure 2. Detail of Design DVG/AF Desuperheater

4. Simple in line installation is accomplished through a standard flange connection. Installation can be in a vertical-up or horizontal pipe. 5. High turndown capability.

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The linear positioning of the plug regulates water flow to the sprayhead of the DVG/AF. The main body diameter controls the flow of water, via radially drilled orifices, in the guide cage. A cross sectional drawing of the DVG/AF appears in figure 2. The Design DVG/AF desuperheater utilizes the proven, spring-loaded AF (Anti-Flash) nozzle to provide a uniform hollow cone spray pattern over a wide range of flow conditions (see figure 3). The water is injected through holes drilled at a compound angle to induce spin as the AF nozzle plug is opened with increasing water pressure. The design of the AF nozzle is such that water flows only after sufficient backpressure is available to provide a good spray pattern. The full opening of the AF nozzle is limited by a travel stop to ensure that the spring is kept within its proper working range and the water film thickness is maintained at the necessary thickness for proper atomization.


Design DVG/AF Table 2. “T” Dimensions T(1)

D STEM BODY SPRING

NUT PIN

PLUG

WATER INJECTION HOLES

Nominal Pipe Size, Inches

Inches

mm

8 10

9-3/4 8-1/2

248 216

12 14 16 18

11 10-1/2 9-1/2 8-1/2

279 267 241 216

20 22 24 >24

10-1/2 9-1/2 8-1/2 8-1/2

267 241 216 216

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

A7191 / IL

Figure 3. AF Nozzle Cross Section

2. Clean and flush out the cooling water line before connecting to the desuperheater. Use only clean sources of cooling water. Use of clean water decreases wear to the valve trim and prevents clogging of desuperheater orifices by solid particles. Note

Installation WARNING Personal injury or equipment damage caused by sudden release of pressure may result if the desuperheater is installed where service conditions could exceed the limits of the pressure class noted on the nameplate. To avoid such injury or damage, provide a relief valve for over pressure protection as required by government or accepted industry codes and good engineering practices.

CAUTION When ordered, the desuperheater configuration and construction materials were selected to meet particular pressure, temperature, pressure drop, and fluid conditions. Do not apply any other conditions to the desuperheater without first contacting your Fisher Controls sales office or sales representative. 1. Insert the Design DVG/AF desuperheater into the flanged pipe stud on the steam pipe (see table 2 and figure 4 for the proper ”T” length dimension). Bolt the unit to the pipe stud flange in accordance with standard piping practice.

Fisher Controls recommends installation of a strainer and isolating valve on the waterline leading to the desuperheater. Failure to do so may result in clogging of the desuperheater by solid particles, thus hampering temperature control of the steam. 3. A straight run of pipe is required downstream of the desuperheater to ensure complete vaporization of cooling water. Consult the desuperheater certified drawing for the required distance of straight pipe. 4. Typically, a temperature sensor should be mounted at a minimum distance of 30 feet (9.1 m) downstream of the desuperheater. This distance will vary depending on steam velocity and percentage of spraywater. Consult the installation drawing provided with the unit for this distance or call your Fisher Controls sales office or sales representative. 5. The steam line should have no branch lines between the desuperheater and the downstream temperature sensor. 6. A typical control loop is illustrated in figure 5. A temperature sensor (TE) measures changes in temperature and transmits a signal to a remote temperature-indicating controller or distributed control system (DCS). The output signal from the controller is sent to the positioner on the desuperheater. The positioner output signal is piped to the actuator, which strokes the stem/plug of the desuperheater. A rising stem opens the desuperheater to allow additional water flow.

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Design DVG/AF Drain the process media from both sides of the valve. J Vent the power actuator loading pressure and relieve any actuator spring precompression.

WATER FLANGE MOUNTING FLANGE

T

HEIGHT

NOMINAL PIPE SIZE

A7192 / IL

Figure 4. DVG/AF “T” Location

WARNING Personal injury could result from packing leakage. Valve packing was tightened prior to shipment; however it should be checked for possible loosening due to shipping and handling.

J Use lock-out procedures to be sure that the above measures stay in effect while you work on the equipment. Shut off water and steam flow and vent all system pressure before removal of the desuperheater from the steam line. Disconnect the desuperheater from the flanged pipe stud and water flange. Withdraw the unit from the line. Temporarily connect the desuperheater to the air supply and verify proper action. To check for seat leakage, connect a water line to the unit and pressurize to service conditions.

Disassembly CAUTION Residual system pressure may be released during the following steps if the system was improperly isolated or vented. Use extreme care to prevent personal injury while loosening any fasteners in the pressure boundary.

Maintenance Instructions

1. Disconnect all field connections to the positioner and actuator. Remove the mounting and water flange bolting and remove the DVG/AF from the steam line.

Servicing

2. Remove the actuator from the DVG/AF using the actuator manufacturer’s removal instructions. Reference figure 6 for assistance in disassembly in the following steps.

Due to the care Fisher Controls takes in meeting all manufacturing requirements (heat-treating, dimensional tolerances, etc.), use only replacement parts manufactured or furnished by Fisher Controls.

WARNING Avoid personal injury from sudden release of pressure or uncontrolled process fluid. Before starting disassembly: J Disconnect any operating lines providing air pressure, electric power, or a control signal to the actuator. Be sure the actuator cannot suddenly open or close the valve. J Use bypass valves or completely shut off the process to isolate the valve from process pressure. Relieve process pressure on both sides of the valve.

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3. Slowly loosen the bonnet nuts (key36) approximately 1/16” in a uniform manner. 4. Break the bonnet (key 13) loose from the body (key 01). 5. After ensuring that the system is depressurized remove the bonnet nuts (key 36) and washers (key 35). 6. Remove the bonnet (key 13) from the body (key 01) taking care to avoid damage to the stem (key 17). 7. Remove the plug/stem assembly (keys 8, 17 and 18), cage guide (key 15) and seat (key14) for inspection. 8. Examine the removed parts for unusual wear and replace if necessary. 9. Remove and discard the seat gasket (key 30), bonnet gasket (key 31) and stem packing (key 24).


Design DVG/AF

TC

SPRAYWATER

           TE

STEAMFLOW

C0817/IL

Figure 5. Typical DVG/AF Installation

10. Remove the spray nozzle(s) (key 9) by unscrewing them from the nozzle holder after removing the anti-rotation tab(s). 11. Inspect the spray nozzles. The nozzles should be completely closed with no evidence of foreign debris or uneven action when opened and closed. If this is not the case and the nozzle(s) cannot be disassembled for cleaning; the nozzle(s) must be replaced to correct the problem. 12. Flush the desuperheater to remove any debris. Clean all gasket and part mating surfaces.

Assembly 1. Reassemble the unit with new gaskets and packing following a reverse sequence of the disassembly. Lubricate all sliding surfaces and the bonnet studs and washers with a quality high temperature lubricant. The nozzle antirotation tabs can be replaced with any similar sized SA182-F22 (2-1/4 Cr—1 Mo) material or 9018 weld rod if required. Take care to avoid overheating the nozzle or getting weld spatter on the nozzle opening surface. 2. Tighten the bonnet bolts in a multi-step uniform cross pattern. It is recommended that the bonnet bolt torquing be carried out in a minimum of four torque

levels until the final torque is achieved. Torquing values are shown in table 3. 3. Reinstall the packing ring, a new packing set, packing follower, flange and nuts. 4. Mount the actuator. When mounting the actuator it is critical to ensure that the stroke is set to ensure that proper seating load is available. Follow the guidelines set forth by the manufacturer in setting up the actuator. In general, position the plug on the seat, move the actuator to full open position, close the actuator for the length of the DVG/AF stroke and then connect actuator and DVG/AF stems. If more complete information is required, consult the actuator documentation. 5. Tighten the packing nuts as required. Torquing values are shown in table 4. Recheck the stem packing for leakage after the system is returned to service and retighten the packing nuts if required.

Troubleshooting The following guide (table 5) is intended as a basic first line troubleshooting guide. Contact your Fisher Controls sales office or sales representative for assistance if you are unable to resolve your field operation problem.

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Design DVG/AF 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 needed

Actuator 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/AF

Actuator 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 pressure

Temperature 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 reached

Temperature 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/replace

Temperature 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 properly

Water 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. Ensure bonnet bolts are properly torqued.

Table 4. Recommended Bonnet Bolt Torque Bolt Size, Inch

Threads per Inch

5/8

11

Recommended Bolt Torque, LbfJft(1) 125

3/4

10

200

Table 5. Recommended Packing Nut Torque Stem Diameter, Inch

1. Torques for studs with heavy hex nuts.

1/2

DVG/AF Parts Ordering Each desuperheater assembly is assigned a serial number which can be found on the mounting flange of the desuperheater. The serial number will have the form ATL-XX-YYYY-Z, where XX is the project year, YYYY is the specified sequence of numbers and/or letters identifying the project, and Z is the item number identifying the desuperheater on that project. Refer to the serial number when contacting your Fisher Controls sales office or sales representative for technical assistance. When ordering numbers for each part required, the key numbers on figure 6 can be used to help in part identification.

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3/4

ANSI Pressure Class

Maximum Torque, LbfJft

Minimum Torque, LbfJft

150

6

4

300

7

5

600

10

7

900

13

9

1500

16

11

2500

18

13

150

12

8

300

15

10

600

22

15

900

30

20

1500

37

25

2500

45

30


Design DVG/AF

B2603 / IL

Figure 6. Design DVG/AF Assembly

Parts List Key 1 2 3 4 5 7 8* 9* 13 14* 15* 17*

Description Valve Body Valve Body Pipe Water Flange Water Pipe Valve Body Flange Nozzle Mount Plug Spray Nozzle Bonnet Seat Cage Guide Stem

*Recommended spare parts

Key 18* 23 24* 25 26 27 28 30* 31* 34 35 36

Description Stem Pin Gland Ring Packing Set Gland Follower Gland Flange Gland Stud Gland Nut Seat Gasket Bonnet Gasket Bonnet Stud Bonnet Stud Washer Bonnet Stud Nut

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Design DVG/AF

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

                         

                                                                                       

For information, contact Fisher Controls: Marshalltown, Iowa 50158 USA Cernay 68700 France Sao Paulo 05424 Brazil Singapore 128461 8 Printed in U.S.A.


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