Siemens Industry, Inc. INSTALLATION AND SERVICE INSTRUCTION SD74 Rev.
SD74 TABLE OF CONTENTS SECTION AND TITLE PAGE 1.0 INTRODUCTION .................................................................................................................................................4 1.1 MODEL DESIGNATION...................................................................................................................................4 1.2 SPECIFICATIONS ..............................................................................................................................
SD74 LIST OF ILLUSTRATIONS FIGURE AND TITLE 2-1 2-3 2-4 2-5 4-1 4-2 5-1 5-2 5-3 PAGE Installation Dimensions........................................................................................................................................10 Rotary Range Spring Kit Assembly and Parts List ..............................................................................................13 Rotary Range Spring Assembly ........................................................................................
SD74 1.0 INTRODUCTION This instruction describes the installation, operation, and maintenance of the Model Series 74 Valve Positioner and Motion Transmitter. The Model Series 74 is a two-stage, high frequency response valve positioner. The positioner incorporates dual outputs which makes it ideally suited for double-acting cylinder operators. When one output is supplying air, the other is exhausting it. This action provides large differential forces to drive the actuator to the desired position.
SD74 1.3 ORDERING RANGE AND SUPPRESSION SPRING KITS Order either a rectilinear spring kit or a rotary spring kit for each Model 74, depending upon the intended actuator. • For a rectilinear actuator, refer to Table 1-1 and, considering actuator stroke length and Model 74 input pressure range, select the needed kit. • For a rotary actuator, refer to Table 1-2 and, considering actuator direction of stem rotation and Model 74 input pressure range, select the needed kit.
SD74 TABLE 1-1 Rectilinear Range Spring Kits, Continued ACTUATOR STROKE IN INCHES 36-48 48 INSTRUMENT INPUT PRESSURE RANGE IN PSIG KIT AND PARTS Kit No. Spring No. Color Code Screw No. Kit No. Spring No. Color Code Screw No. 3-15 3-9 3-27 14997-1 14996-111 2 None 12372-296 14995-121 14996-1112 None 12372-296 0-30 0-15 Not Available Not Available TABLE 1-2 Rotary Range Spring Kits See Figure 2-3 for an exploded view of the kit and a parts list.
SD74 1.4 CUSTOMER/PRODUCT SUPPORT For support and the location of your local Siemens representative, refer to the table below for the URL of the Process Instrumentation (PI) portion of the Siemens public Internet site. Once at the site, click Support in the right column and then Product Support. Next select the type of support desired: sales, technical (see the table below), documentation, or software. Online Support Request http://www.siemens.
SD74 2.0 INSTALLATION See Figure 2-1 for mounting dimensions and connections. The two basic mounting positions of the positioner are normal, where the nameplate is on the bottom, and inverted, where the nameplate is on top. Valve design and desired valve position when the input is at maximum determine whether the positioner should be mounted normal or inverted. Table 2-1 shows various positioner-actuator combinations when using a double-acting cylinder operator.
SD74 CAUTION Synthetic compressor lubricants in the air stream at the instrument may cause it to fail. The requirements for a quality instrument air supply can be found in the Instrument Society of America's "Quality Standard for Instrument Air" (ISA-S7.3). Basically, this standard calls for the following: Particle Size — Maximum particle size in the air stream at the instrument should be no larger than 3 microns.
SD74 6 PSI INSTR. PRESS. SPAN. 12 PSI INSTR. PRESS. SPAN 15 PSI INSTR. PRESS. SPAN 24 PSI INSTR. PRESS. SPAN 30 PSI INSTR. PRESS. SPAN Stroke “C” Dim. Stroke “C” Dim. Stroke “C” Dim. Stroke “C” Dim. Stroke “C” Dim.
SD74 TABLE 2-1 Double-Acting Cylinder Operators VALVE DESIGN Valve Action Down to Close Up to Close Down to Close Up to Close Maximum Controller Output, Valve Closes Opens Opens Closes For Controller Air Failure, Valve Opens Closes Closes Opens Positioner Mounting Inverted Inverted Normal Normal TABLE 2-2 Single-Acting Operators VALVE DESIGN Actuator Top Top Bottom Bottom Valve Action Air Closes Air Opens Air Opens Air Closes Desired Valve Action Maximum Controller Output, V
SD74 2.5 RANGE AND SUPPRESSION SPRING KITS There are three spring kits: rectilinear range, rotary range, and suppression. Each is packaged separately and is assembled on the Model 74 by the instrument installer. Available kits are listed in Section 1.3. Springs are colorcoded and spring colors are included in the tables in Section 1.3. IMPORTANT Install the suppression spring kit (if needed) before installing a range spring kit; see Section 2.5.3 Suppression Spring Kit. 2.5.
SD74 ITEM 1 2 3 4 5 6 DESCRIPTION Model 74 Enclosure Assembly Spring Assembly (includes: range spring, traveling washer, span adjusting screw, and link) Split Clamp 6-32 x 3/8 lg. Socket Hd. Screw Mounting Plate, when ordered; plate mounting hardware (A) is installer supplied FIGURE 2-3 Rotary Range Spring Kit Assembly and Parts List FIGURE 2-4 Rotary Range Spring Assembly 1. If a kit without a mounting plate was ordered, fabricate a plate. Refer to the dimensions in Figure 2-5.
SD74 4. Place range spring assembly on actuator shaft. 5. Attach the range spring link to the input diaphragm assembly stem (See Figure 4-1). 6. Align the split clamp so that its slot is 90° from the slot in the range spring assembly. Tighten slightly. 7. Position the traveling washer on the span adjustment screw in its approximate center. 8. Calibrate the Model 74. Refer to Section 3 Calibration. 9. Lock the split clamp in place by tightening the clamp screw. Torque to 15-20 in lbs.
SD74 3.0 CALIBRATION 3.1 VALVE POSITIONER The Model 74, when used as a valve positioner, has three calibration adjustments: Zero, span and output pressure level. Make all adjustments with the positioner mounted on the actuator. 3.1.1 Rectilinear Range Spring ZERO AND SPAN (See Figure 2-2) 1. Turn on supply air. 2. Set input signal at its minimum range pressure (3 psig for a 3 to 15 psig range). 3.
SD74 This section gives a procedure for each type of actuator. Needed equipment: 1. A pressure regulator capable of providing a mid-scale input for the positioner input range. 2. Three pressure gauges: one for the input and one for each of the positioner valve connections. Additional gauges are not required if the positioner is equipped with optional gauges. 3.
SD74 6. Loosen the spring seats and adjust the zero screw for a 3 psig output. 7. Position the valve to its maximum stroke position. 8. Turn both spring seats at the same time to increase or decrease the number of active coils, for a 15 psig output. 9. Repeat steps 5 through 8 until the transmitter is calibrated. 10. Lock the zero screw by holding the lower spring seat and turning the upper spring seat clockwise approximately 3/4". Rotary Range Spring ZERO AND SPAN (Figures 2-1 and 2-3) 1.
SD74 On spring-loaded and cushion-loaded operators, only one of the positioner outputs is used; the other is plugged. The Model 74 is then a single-acting positioner, working against the operator spring force or cushion load. The previous principle of operation describing the double-acting positioner applies also to the single-acting positioner. FIGURE 4-1 Valve Positioner Schematic 4.2 MOTION TRANSMITTER The Motion Transmitter works on the force-balance principle.
SD74 FIGURE 4-2 Motion Transmitter Schematic 5.0 MAINTENANCE A spring return pushbutton restriction cleaner is built into the body of the valve positioner. Push this button to clear the restriction and eliminate problems caused by build-up on the restriction. Pushing the button will not interrupt operation of the valve. A build-up of dirt on the pilot plungers or their seats may cause erratic operation. To clean these, turn off the supply, remove the retaining nuts, and drop the plungers out.
SD74 • Plungers – The plungers differ in shape, as shown in this figure. • Diaphragm Rings – The Model 74S diaphragm ring has a nozzle. The Model 74 ring does not. • Diaphragm Assemblies – The Model 74S has a diaphragm spacer with a small hole drilled in it, as shown by the cutaway view in this figure. The Model 74 spacer does not have this hole. • Housings – The housing for the Model 74 has a positioner nozzle. The Model 74S housing does not.
SD74 5.1 DISASSEMBLY If it is necessary to disassemble the positioner, refer to Parts List No. 12372PL and proceed as follows: 1. Remove the pilot plunger sealing screws, plunger springs and plungers. 2. Remove the six body screws and separate the upper and lower housings. 3. Pull the baffle and grommet from the input diaphragm assembly stem. 4. Remove the two small screws that hold the beam to the output diaphragm assembly. Be careful not to lose the spacers and washers. 5.
SD74 5.2 ASSEMBLY To assemble, reverse the disassembly procedure and take into account the following: 1. Exercise care when installing the output diaphragm assembly. Carefully guide the capillary tube into the small hole in the upper housing. Be certain the capillary is engaged in the hole before installing and tightening the clamping plate. 2.
SD74 6.0 PARTS LIST Model Series 74 H/FR Valve Positioners Drawing No. 12372PL 11/94 Supersedes 1/88 IMPORTANT Service Parts Kits are available for servicing the instrument. Contact Siemens for available kits; refer to the Customer/Product Support section of this instruction. Some parts in this Parts List may not be available for separate purchase.
SD74 Symbol *1 Part No.
SD74 Symbol Part No. Description Req’d 40 14923-52 Mounting Plate (not shown) As Req’d 41 14923-49 Enclosure (not shown) 1 A 1-0265 2-56 x 1/4 Rd. Hd. 2 B 1-2565 10-32 x 7/8 Rd. Hd. 6 C 1-2450 10-32 x 9/16 Fill. Hd. 4 D 1-2550 10-32 x 7/8 Fill. Hd. 2 E 1-7216 #2 Med. Lwr. 2 F 1-7288 #10 Med. Lwr 12 G 1-1335 #6-32 x 1/2 Truss Hd. 1 *Recommended On-Hand Spare Parts: Always specify range, serial number or other nameplate information when ordering spare parts.
