Honeywell Boiler L91D User's Manual
Contents
1. Mounting at a Remote Location If there is excessive vibration at the boiler that may adversely affect the operation of the controller mount the controller at a remote location All piping from the boiler must be suitable and solidly mounted The piping must be properly pitched to drain all condensation back to the boiler If this causes the controller to be located at an inconvenient height on large boilers it may be mounted at a lower level if the connecting piping is filled with clean water A steam trap siphon loop must be mounted between the remote piping and the controller 60 2152 08 L91A B D PROPORTIONING PRESSURETROL CONTROLLERS ACTION ON PRESSURE FALL ACTION ON PRESSURE FALL REAR POTENTIOMETER ACTION ON PRESSURE FALL FRONT POTENTIOMETER A TERMINALS ARE LABELED M8522A Fig 3 L91 terminal blocks and internal schematics WIRING 1 Disconnect power supply before beginning installation to prevent electric shock and equipment damage All wiring must comply with applicable electrical codes ordinances and regulations Use NEC Class 1 line voltage wiring 2 For normal installation use moisture resistant No 14 wire suitable for at least 167 F 75 C if you are using the controller with a flame safeguard primary control or at least 194 F 90 C if you are using it with a program ming control 3 Forhigh temperature installations use moisture resistant No 14 wire selected for a temper2. 8 When the controller is operating properly reconnecting the wires replacing the cover tightening the cover screw and resetting the controller to the desired value 9 Reconnecting power to the controlled motor or valve 60 2152 08 MAIN SCALE PROPOTIONING ADJUSTING SCREW RANGE ADJUSTING A SCREW L91B D ONLY MAIN SCALE SETTING INDICATOR OUTPUT SETPOINT INCREASE 135 SN Wy 1 2 INCREASES TO 135 OHMS A KNURLED ADJUSTMENT KNOB ON 10 TO 300 PSI 0 07 TO 2 07 MPA MODELS A TERMINALS ARE LABELED A 135 OHMS ON L91A B OR D M8546A Fig 7 Checking L91 Proportioning Pressuretrol Controller CAUTION Equipment Damage Hazard Failure to follow checkout instructions can damage components or systems Do not put the system into service until you have satisfactorily completed all applicable tests described in this Checkout section all tests in the Checkout section of the applicable instructions all tests for the flame safeguard control and any tests required by the burner and boiler manufacturers L91A B D PROPORTIONING PRESSURETROL CONTROLLERS SERVICE INFORMATION CAUTION Electrical Shock Hazard 1 Only qualified service technicians should attempt to service or repair flame safeguard controls and burner systems 2 Disconnect power supply before cleaning the potentiometer windings or wiper or before replacing the controller potentiometer Calibration All c
3. MODELS INTERNAL THREADS ON ALL OTHER MODELS TABLE SOME MODELS ARE ALSO AVAILABLE WITH 1 4 19 BSP TR INTERNAL THREADS SEE TABLE 1 A PROPORTIONING RANGE ADJUSTING SCREW ON L91B D MODELS ONLY A 33312B KNURLED ADJUSTMENT SCREW KNOB 7 8 IN 22 2 MM DIAMETER KNOB IS INCLUDED WITH 10 TO 300 PSI 0 07 TO 07 MPa MODELS OPTIONAL ACCESSORY FOR OTHER MODELS A FOR 10 TO 300 PSI 0 07 TO 2 07 MPa MODELS DIM C INCLUDES THE KNURLED ADJUSTMENT KNOB TABULATION OF DIMENSIONS_A AND C CUSTOMARY UNITS METRICUNTS n w w w 0 TO 15 PSI 0 TO 103 kPa 2 7n6 1 7 32 6 7 8 174 6 53 10 TO 300 PSI 0 07 to 207 MPa 1 1 4 6 116 1540A M29781 Fig 1 Mounting dimensions of the L91 Proportional Pressuretrol Controllers in in mm 60 2152 08 4 INSTALLATION When Installing This Product 1 Read these instructions carefully Failure to follow them could damage the product or cause a hazardous condition 2 Check the ratings given in the instructions and on the product to make sure the product is suitable for your application 3 Installer must be a trained experienced service technician 4 After installation is complete check out product opera tion as provided in these instructions A WARNING Electrical Shock Hazard Can cause severe injury death or property damage 1 Disconnect power supply before beginning installation to prevent electrical shock and equipment damage 2 When using th
4. controller is operating properly If it runs in the wrong direction reverse the B and W wires Observe the action of the motor or actuator until it stabilizes If the motor or valve is moving constantly widen the proportioning range not adjustable on an L91A incrementally until the system is stable If a Controller Seems to Operate Improperly Ifthe controller is suspected of operating improperly it may be further checked by 1 Leaving the controller installed where it is but discon necting all power to the controller motor or valve 2 Loosening the cover screw below the main scaleplate and removing the cover 3 Disconnecting the wires from the controller 4 Connecting an ohmmeter between controller terminals B and W to measure the resistance for the potentiometer in the controller The ohmmeter should read about 135 ohms for an L91A B or D 5 Connecting the ohmmeter between controller terminals W and R Fig 8 and raising the setpoint of the controller above the actual pressure being measured The ohmme ter should read the full value of the potentiometer mea sured in step 4 135 ohms for an L91A B or D 6 Slowly lowering the setpoint of the controller while observing the ohmmeter reading The resistance should drop to zero at some setpoint below the actual pressure 7 Making an approximation of the proportioning range by observing the change in setpoint required for a resis tance change from zero to full value
5. FF IS ADDITIVE FIT HOLE IN BOTTOM OF BRACKET OVER SCREW PROTRUDING UPWARD FROM BOTTOM OF CASE M8548A Fig 10 Replacing terminal block bracket L91A B D PROPORTIONING PRESSURETROL CONTROLLERS 11 60 2152 08 L91A B D PROPORTIONING PRESSURETROL CONTROLLERS Automation and Control Solutions Honeywell International Inc 1985 Douglas Drive North Golden Valley MN 55422 Honeywell Limited Honeywell Limit e 35 Dynamic Drive Toronto Ontario M1V 4Z9 customer honeywell com U S Registered Trademark J 2009 Honeywell International Inc 60 2152 08 Rev 12 09 Printed in U S A
6. Honeywell L91A B D Proportioning Pressuretrol Controllers APPLICATION L91 Proportioning Pressuretrol Controllers are Series 90 Modulating Pressure Controllers that provide direct control of modulating motors or valves used on automatic burners or steam heating systems PRODUCT DATA FEATURES Models available for pressure systems up to 300 psi 2068 kPa May be used with steam air noncombustible gases or other fluids noncorrosive to brass or phos bronze 300 psi model bellows When used with steam boilers a steam trap siphon loop is recommended Wiper on controller potentiometer moves in response to pressure changes L91D has two potentiometers for unison control of two motors L91B D models have adjustable proportioning throttling range to allow selection of desired pressure control range Adjustments made with screws on case top Large easily read scaleplates in both U S customary oz sq in psi or in Hg and metric kPa MPa mm Hg units Steel case with clear plastic cover to observe pressure settings and potentiometer action Fitting with 1 4 18 NPT threads allows rapid installation Surface mount with screws through knockout holes in case back Contents Application Features Specifications Installation Wiring Checkout Service Information 60 2152 08 o O Q N L91A B D PROPORTIONING PRESSURETROL CONTROLLERS SPECIFICATIONS Table 1 Mod
7. TER WIPER ARM S PROPORTIONING RANGE SCALEPLATE L19B D ONLY PROPORTIONING RANGE SETTING INDICATOR L91B D ONLY TERMINAL BLOCK T BELLOWS HOUSING MAIN SCALE SETTING INDICATOR MAIN SCALEPLATE A KNURLED ADJUSTMENT KNOB ON 10 TO 300 PSI 0 07 TO 2 07 MPa MODELS M8525 Fig 6 Setting L91 Proportioning Pressuretrol Controller A proportioning controller is used most often to regulate the firing rate of a burner by controlling a modulating motor Fig 4 or a modulating valve The controller potentiometer the feedback potentiometer in the motor or in the valve actuator and a balancing relay in the motor or actuator form an electric bridge circuit As long as the pressure of the controlled medium remains at the setpoint of the controller the circuit is balanced that is equal the relay contacts are open When the circuit is balanced the motor or actuator does not run If the pressure of the medium rises the wiper in the controller moves toward W This unbalances the circuit so a larger current flows through one side of the balancing relay The close contacts in the relay make causing the motor or valve actuator to drive toward its closed position As the motor or actuator runs the wiper on the feedback potentiometer moves in a direction to balance the circuit When the circuit is again in balance the balancing relay contacts open and the motor or actuator stops The valves and damp
8. ain scale setpoint for the desired operating pressure by turning the main scale adjusting screw Fig 7 or knurled adjustment knob on 10 to 300 psi 0 07 to 2 07 MPa models on the top of the case until the main scale setting indicator is at the minimum pressure desired The proportioning range extends above this value The scaleplate is marked in both customary 02 sq in psi or in Hg and metric kPa MPa or mm Hg units Use of L91 Proportioning Controller with Limit Controllers The L91 main scale setpoint plus the value of the differential proportioning range must be less than or equal to the limit controller s L404 main scale setpoint For example to control system pressure between 70 and 80 psi select an L91B 5 150 psi operating range adjustable differential proportioning throttling range of 5 to 23 psi and an L404A 10 150 psi adjustable differential of 8 to 16 psi Set the L404A main scale setpoint at 80 psi and its adjustable differential at 10 psi The L404A settings will then provide boiler pressure limit control between 70 and 80 psi An L91B differential proportioning range pressure of 5 psi is desired Therefore an L91B main scale setpoint of between 70 and 75 psi is required L91 main scale setpoint plus its differential must be less than or equal to the limit controller main scale set point The L91B settings provide system modulation between 70 and 75 psi or between 75 and 80 psi depending on the e
9. ature rating above the maximum operating temperature 4 Disconnect the power supply before beginning wiring to prevent electrical shock and equipment damage 5 Allmodels have a terminal block inside the cover Fig 3 and two 7 8 in 22 2 mm holes in one side for 1 2 in conduit cable or wires Remove the front cover by loos ening the screw at the bottom of the scaleplate 60 2152 08 6 Refer to Fig 4 for typical hookup W and B connections may be interchanged at the motor for reverse action cooling Follow the burner or boiler manufacturer s wiring diagram if provided Also refer to the wiring diagrams in the motor instructions 7 Replace the front cover when wiring is completed SERIES 90 MODULATING MOTOR L91 PROPORTIONING CONTROLLER CLOSED LOW FIRE OPEN HIGH FIRE A WIPER MOVES TOWARD W END OF A POTENTIOMETER ON PRESSURE RISE AND TOWARD B END ON PRESSURE FALL HOT L1 L2 A TERMINALS ARE LABELED POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED M8520A Fig 4 Hookup of L91 Proportioning Pressuretrol Controller to Series 90 Modulating Motor Setting In all models the proportioning range also called throttling range extends above the main scale setpoint Fig 5 The proportioning range is fixed on L91A models but is adjustable on L91B D models For values refer to Table 1 in the Specifications section Main Scale Set Point All models Adjust the m
10. e controller with a compressor install a dampening device such as a needle valve header or surge tank to dampen pulsations that can damage the controller or reduce its life IMPORTANT 1 Locate the controller where the ambient temperature will not exceed 150 F 66 C 2 When the controller is used on a boiler be sure to connect a steam trap siphon loop between the controller and the boiler 3 Before installing controller be sure the siphon loop has enough water in it to fill lower trap 4 Use pipe compound sparingly to avoid clogging the hole in the pipe or bellows fitting 5 Do not tighten the controller by hand by holding onto the case and turning it Location and Mounting When used with steam boilers always mount the controller above the water line in the boiler A steam trap siphon loop must always be connected between the controller and the boiler Fig 2 to prevent boiler scale and corrosive vapors from attacking the bellows Before installing controller be sure the siphon loop has enough water in it to fill lower trap The controller can be mounted 1 beside the pressure gauge 2 in a fitting on the boiler provided by the manufacturer or 3 at a remote location in case of excessive vibration Make all pipe connections in accordance with approved standards Use only a small amount of pipe compound to seal the connection joints Excess pipe compound may clog the small hole in the fitting and prevent t
11. e termi nals as in the old potentiometer Consult sketch in step 6 13 Carefully fit the hole in the bottom of the terminal block bracket over the screw protruding upward from the bot tom of the case Fig 10 Insert the screw removed in step 4 through the hole in the top of the case Fig 8 and into the top of the bracket and tighten it 14 Reconnect the wires from the external device motor or actuator to the terminal block 15 Replace the cover and tighten the cover screw 16 Reconnect power to the controller 60 2152 08 L91A B D PROPORTIONING PRESSURETROL CONTROLLERS REMOVE BRACKET SCREW FROM TOP OF CASE TERMINAL BLOCK BRACKET TS TERMINAL wP AYN BLOCK 8521 Fig 8 Removing terminal block bracket ACTIVE WINDING BARE WIRES POTENTIOMETER BRACKET ENAMEL REMOVED POTENTIOMETER c BOLT PETS 5 f WIPER ARM MAIN DIFF D 16 f 144 be re 12 5 FE 10 8 4 Y 6 3 2 q J 2 2 hi ra 5 TERMINAL of fo l BLOCK ozs ore is IN ADDITIVE lt 9 gt gt POTENTIOMETER WIRES THE POTENTIOMETER IN AN L91A IS MOUNTED AT A 45 DEGREE ANGLE INSTEAD OF HORIZONTALLY AN L91D HAS TWO POTENTIOMETERS A TERMINALS ARE LABELED M8547A Fig 9 Replacing potentiometer in L91 60 2152 08 10 TERMINAL BLOCK BRACKET TERMINAL BLOCK j MIN DI
12. els available Maximum Surge Operating Ranges Proportioning Throttling Range at Midscale Pressure U S U S Customary Potentiometer Customary Model Units Metric Units Part No Adjustable Units Metric Units psi kPa L91A 0 to 15 psi 0 to 103 kPa 23176CB No 0 5 psi 3 4 kPa 25 172 5 to 150 psi 0 03 to 1 03 MPa 23176CB No 5 psi 0 03 MPa 225 1551 10 to 300 psi 0 07 to 2 07 MPa 23176CB No 12 psi 0 08 MPa 350 2413 L91B 0 to 15 psi 0 to 103 kPa 23176CF Yes 1 5 to 12 psi 10 to 83 kPa 25 172 5 to 150 0 03 to 1 03 MPa 23176CB Yes 5 to 23 psi 35 to 160 kPa 225 1551 10 to 300 psi 0 07 to 2 07 MPa 23176CB Yes 12 to 48 psi 85 to 330 kPa 350 2413 10 to 300 psi 0 07 to 2 07 23176 Yes 30 to 110 psi 0 21 to 0 76 350 2413 L91D Oto 15 psi 0 to 103 kPa 23176CF Yes 1 5 to 12 psi 10 to 83 kPa 25 172 5 to 150 psi 0 03 to 1 03 23176 Yes 13 to 52 psi 0 09 to 0 36 MPa 225 1551 10 to 300 0 07 to 2 07 MPa 23176CF Yes 30 to 110 psi 0 21 to 0 76 350 2413 Models Table 1 L91A Single potentiometer nonadjustable proportioning range L91B Single potentiometer adjustable proportioning range L91D Two potentiometers allow unison control of motors adjustable proportioning range Electrical Rating 24 Vac Potentiometer Action Wiper moves toward W on pressure rise toward B on pressure fall Potentiometer is field replaceable Pot
13. entiometer Resistance 140 ohms nominal for L91A B and D models Pressure Sensing Element Brass bellows 10 300 psi models phos bronze bellows Minimum Ambient Temperature 32 F 0 C Maximum Ambient Temperature 150 F 66 C ORDERING INFORMATION Adjustment Means Screws on controller case top knurled knob for main scale setting on 10 to 300 psi 0 07 to 2 07 MPa models Setpoint At low pressure end of proportioning throttling range Main Scaleplate Marked in both U S customary oz sq in psi or in Hg and metric kPa MPa or mm Hg units Proportioning Range Scaleplate L91B D only Gradu ated from A to F with a MIN minimum value below A See Table 2 for the value of each division Mounting Means Fitting on bellows has 1 4 18 NPT threads external on 0 to 16 oz sq in 0 to 4 psi and 0 to 15 psi models internal on all other models for mounting on a pipe or steam trap siphon loop NOTE Some models are available with 1 4 19 BSP TR internal threads see Table 1 Also can be surface mounted by screws through two knockout holes in case back When purchasing replacement and modernization products from your TRADELINE wholesaler or distributor refer to the TRADELINE Catalog or price sheets for complete ordering number If you have additional questions need further information or would like to comment on our products or services please write or phone 1 Your local Honeywell A
14. ers connected to the motor or actuator will be partially closed decreasing the firing rate and reducing the pressure Similarly if the pressure of the controlled medium falls the wiper on the controller potentiometer moves toward B and the open contacts in the balancing relay make The motor or actuator drives toward its open position until circuit balance is achieved The valves and dampers will be opened wider and the firing rate will increase thus increasing the pressure small change the pressure of the controlled medium will cause a change in the firing rate to compensate for it thus keeping the pressure constant This process is called modulation 60 2152 08 L91A B D PROPORTIONING PRESSURETROL CONTROLLERS CHECKOUT After the controller is installed wired and set it should be tested with the system in operation First allow the system to stabilize Then observe the operation of the controller while raising and lowering its setpoint Pressure should increase when the setpoint is raised and decrease when the setpoint is lowered Use accurate pressure testing equipment when checking out the controller Do not rely on inexpensive gauges The controllers are carefully calibrated at the factory Make sure the modulating motor or modulating valve actuator reaches the low and high fire positions at the proper points If the motor or actuator runs in the proper direction when the setpoint is adjusted assume that the
15. he controller from operating properly To avoid leaks and damage to the case use a parallel jaw wrench on the controller fitting Do not tighten the controller by hand by holding onto the case and turning it L91A B D PROPORTIONING PRESSURETROL CONTROLLERS L91 PRESSURETROL CONTROLLER PRESSURE GAUGE STEAM TRAP A SIPHON LOOP 4 1 2 114 TO 5 1 2 140 A 50024585 001 STEAM TRAP IS A 1 4 IN BRASS PIPE WITH 1 4 18 NPT EXTERNAL TRHEADS ON BOTH ENDS A FITTING ON BELLOWS HAS 1 4 18 NPT EXTERNAL THREADS ON 0 TO 16 OZ SQ IN AND 0 TO 15 PSI MODELS INTERNAL THREADS ON ALL OTHER MODELS SOME MODELS ARE ALSO AVAILABLE WITH 1 4 19 BSP TR INTERNAL THREADS SEE TABLE 1 M23884 Fig 2 Approximate dimensions in in mm for mounting L91 Pressuretrol Controller beside Pressure Gauge on Steam Trap Siphon Loop Mounting Beside a Pressure Gauge To mount the controller beside a pressure gauge Fig 2 remove the gauge In its place install a steam trap siphon loop with a tee on top Using elbows and pipe nipples mount the controller and pressure gauge on the ends of the tee Mounting on a Boiler If it is not convenient to mount the controller beside the pressure gauge install a steam trap siphon loop in the fitting provided by the boiler manufacturer If there is no fitting mount the steam trap at a location recommended by the boiler manufacturer Screw the controller directly to the steam trap if possible
16. nt ranges includes 129564 Range Stop 107194 Range Stop Screw and 23466 Wrench Table 2 Approximate value of each division A to B B to C etc on proportioning throttling range scaleplate L91B D F only Operating Range Value of Each Division U S Customary U S Customary Units Metric Units Units Metric Units 0 to 10 oz sq in 0 to 7 kPa 6 2 oz sq in 2 7 kPa 0 to 15 psi 0 to 103 kPa 1 8 psi 12 4 kPa 5 to 150 psi L91B 0 03 to 1 03 MPa 7 8 psi 0 054 MPa 5 to 150 psi L91D 0 03 to 1 03 MPa 6 7 psi 0 046 MPa 10 to 300 psi L91B with 7 64 in potentiometer 0 07 to 2 07 MPa 16 4 psi 0 113 MPa 10 to 300 psi L91B D with 1 4 in potentiometer 0 07 to 2 07 MPa 13 8 psi 0 095 MPa 3 60 2152 08 L91A B D PROPORTIONING PRESSURETROL CONTROLLERS N 4 12 1143 COVERE L91A B D 411 82 110 3 CASE a lt 2 3 4 69 gt P 3 57 64 98 8 a lt 3 13 32 86 5 n lt gt 1 3 16 30 2 a 1 5 32 29 4 A A 1 1 16 27 0 Y 4 3 23 32 1 3 32 27 8 94 5 3 7 8 2 5 64 984 ALL OTHER DIM C SEE MODELS 1 13 16 2 2 2 TABULATON 46 0 TABLE 13 16 10 300 PSI 20 1 0 15 PSI 0 TO 16 OZIN 2 7 2 1 8 535 gt 1 116 270 DIM A SEE TABULATION TABLE DMB SEE TABULATION A EXTERNAL THREADS ON 0 TO 15 PSI
17. olvent type electrical contact cleaners can deteriorate plastic components and wire insulation and leave an oily residue that accumulates particulate matter dust etc The residue can break down to form various carbonaceous substances that cause early potentiometer failure Use of abrasive materials results in wearing of the potentiometer windings and accumulation of particulate matter that changes the resistance between the windings and the wiper Replacing the Controller Potentiometer Fig 8 10 IMPORTANT 1 Replace the controller potentiometer only when nec essary to obtain proper operation 2 When replacing the potentiometer be very careful not to bend or damage the wiper arm and not to change the wiper tension Any damage or change in tension will decrease the life of the new potentiometer 1 Disconnect all power to the controller 2 Loosen the cover screw below the main scaleplate and remove the cover 3 Mark the wires to the external device motor or valve actuator and disconnect them from the terminal block 4 Remove the screw holding the terminal block bracket to the top of the case Fig 8 Put this screw in a safe place because it will be needed later 5 While careful not to damage the potentiometer wiper or any of the internal wiring lift out the terminal block and bracket 6 Before removing any potentiometer wires carefully note and record sketch the position off center of the active winding on
18. ontrollers are carefully tested and calibrated at the factory under controlled conditions If the actual operating pressure does not match the setpoint move the main scaleplate slightly up or down until the setpoint agrees with the actual pressure Maintenance Keep the cover of the controller in place at all times to protect the internal components from dirt dust and physical damage Perform routine maintenance occasionally by inspecting and blowing or brushing away any accumulated dirt and dust To assure proper functioning of the controller at all times perform an operational check of the entire system during routine maintenance checks Be sure to handle controllers carefully at the time of installation during actual use and during maintenance Cleaning the Potentiometer Windings or Wiper Occasionally the windings or wiper on the potentiometer two on the L91D may need cleaning Disconnect the power supply before removing the cover from the controller and before cleaning the potentiometer IMPORTANT 1 Use an electrical contact cleaner that does not con tain solvents 2 Use extreme care to avoid bending the wiper arm changing the wiper tension and damaging the potenti ometer windings 3 Do not use an abrasion or burnishing tool to clean the potentiometer windings or wiper 4 Do not use hard paper such as a business card or abrasive materials sandpaper emery boards file etc to clean the windings or wiper S
19. the potentiometer and the location and con nections of all wiring terminals The new potentiometer must be inserted and connected the same Example In Fig 9 the active winding is on the left half of the potentiometer the wire from the left end of the wind ing is connected to the W terminal on the terminal block and the wire from the right end of the winding is connected to the B terminal on the terminal block 7 Loosen the W and B screws on the terminal block and remove the two wires to the active winding of the potentiometer Leave the wire to the wiper arm intact 8 Carefully unscrew the bolt that holds the potentiometer to the bracket Make sure the potentiometer wires do not entangle with the wiper and bend it 9 Carefully slide the old potentiometer off the bolt 10 Carefully slide the bolt through the new potentiometer Make sure that a The off center position of the winding on the new potentiometer is the same as the old potentiometer Consult sketch in step 6 b The wiper will contact bare wires Rotate the potenti ometer on the bolts so the surface of the winding where the brown enamel was removed is toward you 11 Screw the bolt into the potentiometer bracket Make sure the wiper is contacting bare wires step 10 b then tighten the bolt 12 Connect the two potentiometer wires to the W and B terminals on the terminal block and tighten the screws Make sure these wires are connected to the sam
20. utomation and Control Products Sales Office check white pages of your phone directory 2 Honeywell Customer Care 1885 Douglas Drive North Minneapolis Minnesota 55422 4386 In Canada Honeywell Limited Honeywell Limit e 35 Dynamic Drive Toronto Ontario M1V 429 International Sales and Service Offices in all principal cities of the world Manufacturing in Australia Canada Finland France Germany Japan Mexico Netherlands Spain Taiwan United Kingdom U S A 60 2152 08 Electrical Connections Internal screw terminals Hole inside of case for 1 2 in conduit Dimensions See Fig 1 see Fig 2 for mounting steam trap siphon loop Weight 1 Ib 15 oz 0 88 kg Finish Gray Replacement Parts 129178 Thermoplastic Cover 23176CB Potentiometer For all L91A models and a few L91B models see Table 1 140 ohms nominal length of active winding is 7 64 in 2 8 mm L91A B D PROPORTIONING PRESSURETROL CONTROLLERS 23176CF Potentiometer For all L91D models and most L91B models see Table 1 140 ohms nominal length of active winding is 1 4 in 6 4 mm Accessories 50024585 001 Steam Trap siphon loop 1 4 in brass pipe with 1 4 18 NPT external threads on both ends 14026 Steam Trap siphon loop 1 4 in steel pipe with 1 4 18 NPT external threads on both ends 33312B Knurled Adjustment Knob With setscrew fits on main scale pressure adjusting screw 4074BWJ Limit Stop Assembly To limit setpoi
21. xact setting of the L91B main scale setpoint Due to device tolerances the scaleplate settings are approximate and therefore the settings should be fine tuned with the system operating Proportioning Range L91B D Only Adjust the proportioning range throttling range by turning the proportioning range adjusting screw Fig 6 on the top of the case until the proportioning range setting indicator is at the desired value The proportioning range scale is graduated from A to F with a MIN minimum value below A The value of each division depends on the operating range of the controller Refer to Table 2 in the Specifications section Typical Operation Pressure variations cause the bellows to expand or contract Linkage between the bellows and the potentiometer wiper causes the wiper to move across the potentiometer windings This varies the resistance between R and B and between R and W causing an unbalance in the circuit connected to the controller See Fig 7 LOW FIRE r gt CLOSED I PRESSURE RISE PROPORTIONING RANGE A 4 POTENTIOMTER I WIPER 1 A MAIN SCALE I SETPOINT I gt HIGH FIRE gt OPEN A FIXED ON L91A ADJUSTABLE ON L91B D A L91D HAS TWO POTENTIOMETERS OPERATING IN wgs49A Fig 5 L91A B D operating points L91A B D PROPORTIONING PRESSURETROL CONTROLLERS MAIN SCALE ADJUSTING PROPORTIONING RANGE ADJUSTING SCREW L91B D ONLY CONTROLLER POTENTIOME
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