Practical Pointers | Fives North American

Combustion maintenance tips for operation and adjustment of industrial combustion systems.

Combustion

North American Combustion Practical Pointers

Operation and adjustment of pressure-balanced air/fuel ratio controls for industrial burners.

— Regulators — Premix systems — Nozzle-mix systems — Oil systems

— Dual-fuel systems — Pilots — Manifolds — Valve & linkages

COST EFFECTIVE COMBUSTION SOLUTIONS YOU CAN COUNT ON.

In additon to our broad offering of proprietary burners and combustion-related products, we are dedicated to providing services to you throughout all phases of your combustion system. Fives North American Combustion, Inc. is dedicated to being the combustion expert you can count on.

— Process Analysis — Application Experience — System Engineering — Proprietray Burners & — Maintenance — Steel Fabrication — Quality Manufacturing

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Fives North American Combustion, Inc. 4455 East 71st Street - Cleveland, OH 44105 USA Tel 216 271 6000 - Fax 216 373 4237 - email: fna.sales@fivesgroup.com www.fivesgroup.com

This book or any part thereof must not be reproduced in any form without written permission from Fives North American Combustion, Inc.

Fourth Edition First Printing

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CONTENTS

I NTRODUCTION ........................................................................................................................................................ 1

REGULATORS Simple (Line) Pressure-Reducing Gas Regulator.............................................................................................. 5 Atmospheric Regulator (Zero Governor)............................................................................................................ 6 Atmospheric Regulator Supplying a Premix Burner System.........................................................................7 Operation of a Cross-Connected Air/Gas Ratio Regulator Supplying a Nozzle-Mix Burner System.................................................................................................... 8 Pressure Taps for Cross-Connection Impulse Lines........................................................................................ 9 Taps for Measuring Chamber (Furnace) Pressure........................................................................................... 9 PREMIX SYSTEMS Operation of an Aspirator Mixer........................................................................................................................10 Installation and Lighting of Premix Systems.....................................................................................................11 Adjustment of Premix Systems............................................................................................................................12 Premix System in Use............................................................................................................................................13 Effect of Pressure or Suction in Combustion Chamber on Control with a Zero or Atmospheric System.....................................................................................14 Effect of Combustion Chamber Pressure or Suction on Burner Capacity - Premix System........................................................................................................15 Trouble-Shooting Air/Gas Ratio Regulators-- Atmospheric Service on Premix Systems.................................................................................................16 Trouble-Shooting Premix Burners....................................................................................................................... 17 Premix Burner Configurations.............................................................................................................................18 NOZZLE-MIX SYSTEMS Operation of a Cross-Connected Air/Gas Ratio Regulator..........................................................................19 Adjustment of High Fire Air/Fuel Ratio.............................................................................................................20 Adjustment of Air/Fuel Ratio at Low Fire Rate.................................................................................................21 Summary - Practical Air/Fuel Ratio Adjustment.............................................................................................23 Regulator Selection................................................................................................................................................24 Regulator Installation - General.........................................................................................................................25 Installation for Premix Burners...........................................................................................................................26 Installation for Nozzle-Mix Burners................................................................................................................... 27 Lighting and Adjustment......................................................................................................................................29 Servicing...................................................................................................................................................................30 Gas Pressure Requirements for Cross-Connected Air/Gas Ratio Regulators..........................................32 If Gas Supply Pressure is Low.............................................................................................................................33 Use of a Bleeder....................................................................................................................................................34 Effect of Pressure or Suction in Combustion Chamber on Control with a Straight Cross-Connected System...........................................................................35 Effect of Pressure or Suction in Combustion Chamber on Control with a Cross-Connected System with Bleeder..................................................................36 Effect of Pressure or Suction in Combustion Chamber on Burner Capacity with Nozzle-Mix Burners........................................................................................ 37 Checking Operation of a Cross-Connected Air/Gas Ratio Regulator.......................................................38

III

CONTENTS , cont.

Trouble-Shooting 7218 Air/Gas Ratio Regulators - Cross-Connected.......................................................39 Trouble-Shooting Nozzle-Mix Gas Burners.....................................................................................................40 XSA Operation - Variable Ratio Regulator.......................................................................................................41 XSA Operation - Full Air Pressure-Controlled Impulse.................................................................................43 For Most Accurate Control with High Pressure Gas, use Individual Cross-Connected Line Regulators..................................................................................45 Trouble-Shooting Pressure-Reducing (Line) Regulators................................................................................46 OIL AND DUAL-FUEL SYSTEMS Ratiotrol and Oil Burner....................................................................................................................................... 47 3 Pipe Dual-Fuel Burner.......................................................................................................................................48 4 Pipe Dual-Fuel Burner.......................................................................................................................................49 PILOT SYSTEMS Gas Supply to 4011 Pilots.....................................................................................................................................50 Pilot Piping.................................................................................................................................................................51 Pilot Adjustment......................................................................................................................................................52 Natural Gas Flames of a 4011 Premix Pilot Set.............................................................................................53 Trouble-Shooting Pilots - Spark Ignition...........................................................................................................54 Trouble-Shooting Pilots - Spark or Manual Ignition......................................................................................54 Trouble-Shooting Pilots.........................................................................................................................................55 Trouble-Shooting Pilots - Flame Detection......................................................................................................56

MANIFOLDS Gas and Air Manifolds Do's and Don'ts........................................................................................................... 57

VALVES, LINKAGES Adjustable Port Air Valve Adjustments..............................................................................................................58 Valve Linkage Adjustments..................................................................................................................................59

APPENDIX Judging Flames.......................................................................................................................................................61

INDEX, NOMENCLATURE ....................................................................................................................................62

Record Your Settings ..........................................................................................................................................63

INTRODUCTION

This is a guidebook of engineering practice and recommendations, all subject to local, state, and federal codes, and insurance requirements, and good common sense. No patent liability is assumed with respect to the use of information from this book. while every precaution has been taken in preparing this guidebook, the publisher assumes no responsibility for errors or omissions; nor is any liability assumed for damages resulting from use of this information.

- WARNING - Situations dangerous to personnel and property may exist with the operation and maintenance of any combustion equipment. The presence of fuels, oxidants, hot and cold combustion products, hot surfaces, electrical power in control and ignition circuits, etc., are inherent with any combustion application. Components in combustion systems may exceed 160°F (71°C) surface temperatures and present hot surface contact hazard. Fives North American Combustion, Inc. suggests the use of combustion systems that are in compliance with all Safety Codes, Standards, Regulations and Directives; and care in operation.

INTRODUCTION

PURPOSE This booklet will help you adjust your burners for (a) better fuel efficiency, (b) more production with fewer interruptions, (c) safer operation, and (d) improved uniformity.

Combustion systems covered include: 1. Premix Gas Burner Systems, 2. Nozzle-Mix Gas Burner Systems 3. Oil Burner Systems 4. Dual-Fuel Burner Systems 5. Pilot Systems

COVERAGE Simple straightforward explanations relate to installation, initial setup, start-up, operation, adjustment, servicing, and troubleshooting of pressure-balanced type air/fuel ratio controls (zero governors, atmospheric regulators, cross- connected governors, cross-connected regulators). Further information concerning adjustments for most efficient operation is contained in North American Handbook Supplement 149. SERVICING Please remember that cleanliness and routine maintenance can save a lot of future headaches. When your combustion system is not working properly, consult this booklet first. Service calls may be costly and there may be delays until a serviceman is available. Try to determine which component of the system is causing the trouble, and then (if you cannot fix it yourself) call the manufacturer of that component. It is wasteful of money and time to call a burner serviceman if a temperature control is at fault...and vice versa. WARNING Search through this book until you find a schematic that corresponds to your combustion system. Beware of seemingly small variations in equipment. These important differences affect the method of adjustment and operation.

INTRODUCTION

MEASURE PRESSURES An indispensable tool for trouble-shooting or servicing combustion equipment is a pressure measurement device: Pressure gauges, water manometers, or digital manometers are extremely valuable. After initial adjustment of the combustion system, the various pressures should be recorded. In the future, problems may be more easily solved by referring to those pressures and comparing them with the pressures at the time of the problem. See inside back cover. Using pressure measurement and the appropriate manufacturers' bulletins, you will be able to determine the burner firing rate, accuracy of the air/fuel ratio regulator, performance of the combustion air blower, pressure drops in existing piping, existence of blockages in the piping and their location, and utility supply pressures. Measurement of pressures for a combustion system should be performed under flow conditions. As an example, a partially open valve may allow full proper pressures under low flow conditions but excessive drop-off in pressure after burner is turned on. GOOD LUCK We trust that this booklet will make you more expert in industrial burner control systems.

REGULATORS

adjust spring to set desired outlet pressure (for example: 20 osi)

spring pressure set to counterbalance 20 osi outlet pressure

vent to atmosphere

gas flow

20 osi

regulator's valve opens until outlet pressure is 20 osi to balance spring pressure

SIMPLE (LINE) PRESSURE-REDUCING GAS REGULATOR

This type of regulator maintains a constant gas supply pressure upstream of control devices. A small regulator of this type is often used in pilot systems. (See "B'' on page 50) The schematic piping diagram on page 4 shows the main and pilot pressure- reducing regulators piped into a typical burner system. For trouble-shooting tips on pressure-reducing regulators, see page 46.

REGULATORS

gas flow

balancing diaphragm

balancing tube

gas flow to burner(s)

"A"

"L"

control diaphragm

spring "S"

adjust

ATMOSPHERIC REGULATOR (ZERO GOVERNOR)

This type of regulator is loaded by the controlled air pressure rather than by spring pressure and gives an outlet pressure at "A" equal to the pressure at "L" plus or minus the effect of the spring "S" adjustment. This type of regulator is shipped with spring set "Neutral", just supporting the internals. The balancing diaphragm minimizes the effect of inlet pressure changes on outlet pressure.

Bonded valve, facing

Valve seat

Body plug

Inlet test tap plug

Pressure tube

Balancing diaphragm

Spring

Gas diaphragm

Vent on diaphragm cover (not shown)

Cover plug

Spring adjusting plug

REGULATORS

Control valve

Air

Air and gas mix in venturi

Mixer

Gas

Atmospheric (0) pressure

Built-in limiting orifice

Atmospheric (0) pressure

Drip leg

Air/gas ration regulator

ATMOSPHERIC REGULATOR SUPPLYING A PREMIX BURNER SYSTEM

As air flow through the venturi increases, increased suction causes more gas flow through the limiting orifice valve. This in turn slightly reduces the pressure at "A" which causes the regulator to open and allow more gas to flow and maintain the atmospheric or "zero gauge" outlet pressure. Because a slight amount of force is required to raise the internals and open the regulator, the pressure at "A" may drop off 1 or 2 tenths of an inch w.c. at full flow. This "droop" has only a minor effect on accuracy of control when the regulator is properly sized.

REGULATORS

5 D

3 D

wide open when operating

"A"

air

control valve

to other burners

impulse line (cross- connection)

Limiting Orifice

4 pipe dia. (min) 10 pipe dia. (min)

gas

unions for easy removal

"C"

Burner (open or sealed-in type)

"D"

regulator diaphragm must be level

OPERATION OF A CROSS-CONNECTED AIR/GAS RATIO REGULATOR SUPPLYING A NOZZLE-MIX BURNER SYSTEM

The pressure at "A" goes through the impulse line to chamber "B." The regulator's valve then opens until the outlet pressure at "C" (and conveyed through a balancing tube to chamber "D") equals the pressure at "B." The diaphragm and valve then stop moving because pressures at "B" and "D" are balanced. The pressure in the chamber below the regulator diaphragm controls the flow through the regulator. The location and proper installation of the impulse tap is important. See page 9.

REGULATORS

PRESSURE TAPS FOR CROSS-CONNECTION IMPULSE LINES

GOOD

BAD

BEST

do not allow any protrusion into pipe

remove burrs

BEST

5 pipe dia .

3 pipe dia.

It is best to locate impulse tap on top or side of pipe, parallel to valve shaft, with undisturbed straight runs upstream and downstream. BAD ACCEPTABLE

Avoid elbows, tees, sharp edges and abrupt changes of flow direction. Burrs or nipples projecting into the pipe cause the air to speed up. Any change in velocity gives a false pressure reading. The off-center flow downstream of any valve will have less bad influence on an impulse if the tap is parallel to the valve shaft. Tap from the side or top of a pipe to prevent condensate or dirt from entering. Avoid dips or U's in impulse lines - condensed water could collect. Pitch the impulse line so water will run back to the air line - not to the regulator, where weight on the diaphragm could "fool" the regulator. Connect the regulator end of an impulse line last. Blow out the impulse line from the regulator end until air comes through the tapped pipe. Easiest is usually through a threaded connection provided in most burner mounting plates (see page 19), but internal flow of some burners creates a misleading negative pressure in the mounting plate. 4422, 4441, 4442, 4425, 6422, and 6425 burners may have as much as 22.2" wc suction (-8A size at 16 osi air pressure) at the mounting plate, but be positive at the ends of the air tubes, causing as much as 4% error in the air/ fuel ratio. If critical, relocate the chamber pressure tap as follows: Use a tee and large observation port on the end of a tap to permit easy checking for blockage. Locate taps well above a level where hearth scale or splashing liquids might plug them. A pressure tap should not be opposite a burner, or near a flue, or in any other position where velocities are high. A pressure tap should not be directly below a burner, else it could become a flue-way for hot gas circulation between the refractory and furnace shell. TAPS FOR MEASURING CHAMBER (FURNACE) PRESSURE

PREMIX SYSTEMS

OPERATION OF AN ASPIRATOR MIXER

The nominal pressure ratios for a North American premix system are 8 osi air pressure, 8 osi suction, 4"w.c. mixture pressure. These are approximate. There is a wide range of control from slightly lean to rich (depending on the burner) with gas of 800 Btu/ft3 or more. If these pressures (or the same ratio of pressures) do not exist, check for excessive restrictions in the mixture line or burner.

Control valve

Burner may be sealed-in or open type.

Air

8 osi

4"w.c.

Rod is used to size mixer to match nozzle(s)

Gas

8 osi with gas shut off

1st: Set high fire ratio using built-in limiting orifice.

Zero gas pressure

2nd: Set low fire ratio, see page 21.

PREMIX SYSTEMS

gas adjustment valve cartridge (self-contained)

turn gas adjustment plug clockwise to decrease gas

gas pipe connection can be either left-hand or righ-hand by reversing cartridge

remove cap to make gas adjustment

INSTALLATION AND LIGHTING OF PREMIX SYSTEMS

3065 Aspirator Mixers can be mounted in any position convenient to the user's piping. The gas adjustment valve cartridge is self-contained and can be mounted in either side of the mixer. Gas piping is perpendicular to the air line. It is satisfactory to use one mixer for two or more burners, but flow distribution and pressure drops should be considered carefully when designing the manifold. When mounting an Aspirator Mixer, allow side clearance for Allen wrench setting of the gas adjustment valve. All mixers are shipped with the gas adjustment valve closed and with right-hand assembly as shown. Plugged taps ( 1/8 ") are provided for pressure readings. To light the burner(s): Follow blower instructions to start the blower. All gas lines up to the 7218 Regulator must be purged. Before lighting any pilot or burner, purge the firing chamber - see Step 1, page 52. Follow pilot instructions to light the pilot(s). Set the main air valve at low fire position (1 or 2 osi air pressure). Open the gas adjustment valve 3 or 4 turns. Open the upstream gas shutoff valve(s) and the individual gas valve for one burner. If the burner does not light in a few seconds, close the nearest upstream gas shutoff valve (to prevent accumulation of unburned gas) and purge the chamber allowing sufficient time for a minimum of four changes of atmosphere. Then open the gas adjustment valve one more turn and reopen the shutoff valve. Repeat the procedure until the main flame lights.

PREMIX SYSTEMS

clearance for pullling displace- ment rod

8666 Testip

1 ½ " or larger mixer

pressure tap

1⁄8 " pipe size

pressure tap on opposite side

2 pipe dia. recommended minimum

identification markings

If an elbow is used in this section, allow at least 2 pipe diameters on each side of the elbow.

last figure denotes rod size in 32nds of an inch

gas adjustment valve gas inlet

mixture

outlet

interchangeable displacement rod

air inlet

ADJUSTMENT OF PREMIX SYSTEMS

Adjust the high fire air/gas ratio by slowly turning the air valve to high fire position while adjusting the limiting orifice gas valve as needed to maintain the desired air/gas ratio. † Replace the valve cover. Adjust the low fire air/gas ratio. Turn the air to low fire (about ½ osi). If more or less gas is required, remove the regulator's gas diaphragm cover plug and use a screwdriver to turn the spring adjusting plug - clockwise* for more gas. Replace the cover plug. On sealed-in burners where flame is not visible, the following is recommended for a 1 ½ " or larger mixer. Drill and tap a 1⁄8 " hole in the pipe from mixer to burner; screw an 8666 Testip into this hole and light it so that you can see a sample of main burner flame. Adjust the mixer for the type of flame desired †, using the flame from the Testip as a guide. (A purple-tinged flame denotes a lean fire; a greenish-blue inner-cone denotes a rich flame) The Testip can be removed, the hole plugged, and the Testip used on other burners. Mixers have interchangeable displacement rods that permit changing mixer orifices to conform to field conditions or to get lower or higher mixture pressures (with consequent more or less suction, respectively). Rods can be interchanged without breaking piping. Recommended rod diameters are listed on Bulletin 3065 for burner(s)., type of gas, and air pressure involved. * For North American 7218 Regulators. Others may be different. † See "Judging Flames," page 61.

PREMIX SYSTEMS

control valve

optional cross-connected impluse line if higher mixture pressure is required*

air

5 D

3 D

flame

8 osi

4 1/2 "w.c.

4"w.c.

gas

Limiting Orifice

gas pressure = zero (if no impulse) or equal to air impulse if used

required gas pressure = pressure drop through regulator + safety factor + air impulse (when used)

PREMIX SYSTEM IN USE

As restriction in the mixture line is increased, the mixture pressure will rise and the suction will be reduced. If the restriction is sufficient to cause the suction to be too low to supply enough gas, a smaller capacity mixer and rod (or less outlet restriction) is required. Mixture piping should be sized for a low pressure drop, 0.5"w.c. or less. In a typical installation, the regulator would be sized for a minimum 2 osi drop, and a safety factor of 1 osi would be allowed, requiring a gas supply pressure to the regulator inlet of 3 osi (See page 24 for detailed sizing instructions). * If necessary the 7218 Regulator may be cross-connected to the air or mixture line to overcome the effect of high restriction in the mixture line or nozzle.

PREMIX SYSTEMS

pressure variable or different from furnace room pressure

control valve

Mixer

-2 osi

built-in Limiting Orifice

EFFECT OF PRESSURE OR SUCTION IN COMBUSTION CHAMBER ON CONTROL WITH A ZERO OR ATMOSPHERIC SYSTEM With the lower side of diaphragm open to atmosphere (without line A), a suction in the furnace is transmitted along the dashed line to the upper side of the control of the system. Similarly, a positive combustion chamber pressure will add a closing force and upset control of the system Addition of dotted line (A) compensates for variable combustion chamber pressure or balances any combustion chamber pressure higher or lower than the room pressure adjacent to the regulator. Line (A) will not cause trouble if installed where not required, so if in doubt about combustion chamber pressure, install it. * * See page 9, regarding location of combustion chamber pressure tap.

PREMIX SYSTEMS

control valve

combustion chamber

air

8 osi

"A"

6 osi effective pressure 10 osi effective pressure

+2 osi

-2 osi

pressure drop across nozzle

Manometer

EFFECT OF COMBUSTION CHAMBER PRESSURE OR SUCTION ON BURNER CAPACITY — PREMIX SYSTEM

It is really pressure difference or pressure drop, rather than pressure, that affects flow rate (burner capacity). With 8 osi inlet air and a positive combustion chamber pressure of 2 osi, the pressure drop, or "effective pressure" will be 8 - 2 = 6 osi. The flow will be less. If the chamber has 2 osi suction, the pressure drop will be 8 - (-2) = 10 osi and the mixture pressure will be 5"w.c. The nozzle capacity will be based on 5"w.c. To actually measure pressure drop across the nozzle, measure the pressure at "A" in inches wc and subtract the inches wc of combustion chamber pressure † (or add if suction); base the capacity on this effective mixture pressure. The required gas pressure will be increased by the amount of the positive combustion chamber pressure, or decreased by the amount of the negative combustion chamber pressure.

† See page 9, regarding location of combustion chamber pressure tap.

PREMIX SYSTEMS

TROUBLE SHOOTING AIR/GAS RATIO REGULATORS ATMOSPHERIC SERVICE ON PREMIX SYSTEMS

A. Symptom: At high fire, outlet pressure goes negative or flame goes lean Causes:

1. Insufficient supply pressure or supply line is undersized. 2. Regulator is undersized. 3. Leak around lower diaphragm or adjustment plug. 4. Hole in large diaphragm.

B. Symptom: Fire goes rich at "Low"

Causes: 1. Spring adjustment set "positive." 2. Hole in small diaphragm.

3. Limiting orifice open beyond normal to compensate for any conditions under "A." 4. Regulator vent not cross-connected to combustion chamber which has negative pressure. 5. Valve not seating because of dirt or damage.

C. Symptom: Fire goes lean at "Low"

Causes: 1. Spring adjustment set "negative."

2. Regulator vent not cross-connected to combustion chamber which has positive pressure.

PREMIX SYSTEMS

TROUBLE SHOOTING PREMIX BURNERS

A. Symptom: Not enough gas to burners Causes: 1. Mixer too large for burner nozzle or nozzles causing low

suction at gas limiting orifice. Install larger displacement rod, smaller mixer, larger nozzle, or if necessary, cross connect the regulator to the air or mixture line. More gas supply pressure is required if cross-connected. 2. Regulator outlet pressure too low. 3. Mixer venturi dirty or obstructed. 4. Burner nozzle restricted by foreign matter or from being overheated. 5. Burner tile restricted. 6. Restricted mixture piping. 7. High positive pressure in combustion chamber without regulator vent being cross-connected, or with inadequate gas supply pressure. 8. Restricted gas piping between regulator and mixer.

B. Symptom: Burner flashing back (flame in mixture line) Causes: 1. Non-uniform mixture piping causing too low a mixture pressure. 2. Mixture pressure being turned too low. 3. Pulsating gas or air supply. 4. Turbulence in a burner nozzle caused by its being too close to a pipe fitting. 5. Nozzle being heated beyond ignition temperature of mixture.

C. Symptom: Burner unstable

Causes: 1. Mixture too rich or too lean.

2. On some types, no free air in combustion area. 3. On sealed-in tunnel type burners, no flame retention step from nozzle bore to tile. 4. On sealed-in type burners, tile in bad condition. 5. On sealed-in type burners, tile broken loose from, or plugs left out of, mounting plate. 6. On self-piloted burners, piloting holes partially or wholly clogged. 7. On self-piloting nozzles, nozzle too close to elbow tee.

PREMIX SYSTEMS

PREMIX BURNER CONFIGURATIONS

air-gas mixture

piloting holes

OPEN BURNER, SELF-PILOTING NOZZLE

tile

air-gas mixture

flame retention step

SEALED-IN TUNNEL BURNER (Tile required for stable flame)

NOZZLE MIX SYSTEMS

air

"A" 16 osi

5 D

3 D

Air Control Valve

4 pipe dia. (min.)

gas

Chamber Pressure Connection

Limiting Orifice Valve

10 pipe dia. (min.)

"C" 16 osi

"B"

16 osi

"D"

OPERATION OF A CROSS-CONNECTED AIR/GAS RATIO REGULATOR

The pressures used in the following discussions are for the purpose of explaining the regulator operations and may not be the same on an actual application of the equipment. The pressure at "A" goes through the impulse line to chamber "B." The regulator opens until the outlet pressure at "C" passing through balancing tube to chamber "D" equals the pressure at "B."

NOZZLE MIX SYSTEMS

air

16 osi

5 D

3 D

4 pipe dia.

gas

10 pipe dia.

16 osi

Limiting Orifice Valve high fire ratio adjustment

ADJUSTMENT OF HIGH FIRE AIR/FUEL RATIO

(Refer to page 29 and to "Sheet 7218-2 Instructions" regarding procedure for lighting and turning up to high fire rate) Set the limiting orifice valve for the desired air/fuel ratio on high fire. This gives the proper flow of gas at 16 osi to match the flow of air at 16 osi. If the air pressure is changed, the gas pressure will follow this change, and the air/ gas ratio will remain unchanged. This high fire ratio setting is an orifice size adjustment. Its setting at any pressure affects the air/gas ratio at all pressures. This high fire ratio adjustment should be made first, then low fire. Air capacities of burners are determined by their orifice sizes which are fixed. These capacities at various air pressures are listed in the burner bulletins.

NOZZLE MIX SYSTEMS

air

0.5 osi

5 D

3 D

Manual Valve

to other burners

Burner

impulse line

4 pipe dia.

gas

Limiting Orifice Valve

10 pipe dia.

0.5 osi

low fire ratio adjustment

ADJUSTMENT OF AIR/FUEL RATIO AT LOW FIRE RATE

After the high fire ratio is set, turn the air to the low fire pressure (about 0.5 osi). If more or less gas is required at this position, the low fire ratio may be adjusted by changing the compression of the regulator spring. (See step 3, page 29)

NOZZLE MIX SYSTEMS

0.6 osi

If the spring plug is screwed in the equivalent of 0.1 osi, the outlet gas pressure (vertical force) required to balance the spring will be the 0.5 osi impulse plus 0.1 or 0.6 osi.

0.5 osi

0.1 osi

If the spring plug is screwed out until the weight of the internals is equivalent to 0.1 osi, the outlet gas pressure (vertical force) required to balance the spring will be the 0.5 osi impulse minus 0.1 equals 0.4 osi.

0.4 osi

0.5 osi

0.1 osi

ADJUSTMENT OF AIR/FUEL RATIO AT LOW FIRE RATE, (cont.)

This example adds or subtracts 20% of the gas pressure at low fire, but at a high fire of 16 osi, adds or subtracts only 0.1 osi ÷ 16 osi = 0.6%. This affects low fire ratio considerably, but has practically no effect on the high fire ratio. The spring is adjustable up to about 1"w.c. positive or negative. If a large amount of adjustment is made, it may be necessary to return to high fire and correct the high fire ratio.

NOZZLE MIX SYSTEMS

air

5 D

3 D

Limiting Orifice Valve-- high fire ratio adjustment (1st ratio setting)

4 pipe dia.

10 pipe dia.

Air/Gas Ratio Regulator-- low fire ratio adjustment (2nd ratio setting)

SUMMARY — PRACTICAL AIR/FUEL RATIO ADJUSTMENT The pressures mentioned previously were used to illustrate the principles of operation, and are not necessarily for practical field adjustment. 1. Set the linkage on the air control valve for the desired high and low air pressure. 2. Light the fire at low air pressure with enough gas to maintain flame. 3. Turn to high fire, adjusting the high fire ratio adjustment to keep the flame burning. 4. Set the high fire ratio adjustment for the desired air/gas ratio, using an Allen wrench on the limiting orifice valve. 5. Turn to low fire position and if needed, adjust the low fire ratio by removing the gas diaphragm cover plug and using a screwdriver to turn the spring adjusting plug. 6. If a major adjustment was necessary on low fire, return to high fire and correct the ratio again with the limiting orifice valve. 7. Recheck the low fire ratio and correct it if needed using the regulator spring adjusting plug. 8. Replace caps on the limiting orifice valve and the regulator.

NOZZLE MIX SYSTEMS

REGULATOR SELECTION

To size a regulator, determine the required cfh of gas and pressure drop available at high fire. Divide required cfh by Table 2 Factor for available pressure drop. Select the smallest regulator with Table 1 (2 osi) capacity above this adjusted capacity. Never choose a regulator capacity based on more than 16 osi drop (even if more is available) EXAMPLES A nozzle-mix system requires 5000 cfh of natural gas. Gas inlet pressure is 12 osi; maximum air pressure at the burner is 8 osi. When cross-connected, outlet gas pressure is 8 osi at high fire; pressure drop across regulator is 12 – 8 = 4 osi. Table 2 factor for 4 osi is 1.41; 5000 cfh ÷ 1.41 = 3546 cfh. In the 0.6 sp gr column of Table 1, select a 7218-4 Regulator (rated at 4800 cfh.) If air pressure at the burner was 16 osi but available gas pressure was still only 12 osi, a bleeder would be required in the cross connection. For minimum bleed†, select regulator for required cfh directly from Table 1 (2 osi) capacities; then bleed cross-connected air impulse at high fire from 16 osi to 10 osi (12 osi available gas pressure minus 2 osi drop through regulator). For the required 5000 cfh in this example, select a 7218-5 from Table 1. If system was premix instead of nozzle-mix, regulator outlet pressure is zero, and pressure drop through the regulator would equal inlet gas pressure (12 osi). Table 2 factor is 2.45; 5000 ÷ 2.45 = 2040 cfh. Select a 7218-3 Regulator from Table 1.

Table 1. CAPACITIES scfh MAXIMUM WIDE OPEN with 2 osi drop through regulator and 2 psig inlet pressure Regulator gas gravity designation 0.6 1.5 7218-01 285 180 7218-0 540 341 7218-1 700 442 7218-2 1730 1090 7218-3 2800 1770 7218-4 4800 3030 7218-5 6900 4360 7218-6 9100 5750 7218-7 17600 11120

(For capacities at other drops, use square root law or Table 2 page 25.)

NOZZLE MIX SYSTEMS

Table 2 FACTORS for correcting capacity for pressure drop.

pr. drop, osi

factor 0.707

pr. drop, osi

factor

2.00 2.24 2.45 2.65 2.83

1.00 1.12 1.22 1.41

10 12 14 16

2 1/2

3 4 6

1.73

REGULATOR INSTALLATION - GENERAL

1. Install a gas shutoff valve upstream of the regulator. 2. Mount regulator horizontally. Regulator cannot function if the diaphragm is not horizontal. This arrow on the body must point in the direction of gas flow. 7218 diaphragm case should be below the gas line. 3. Install regulators in clean pipe lines of adequate size, free from dirt, scale and chips. Mount regulator close enough to mixers or burners to avoid excessive pressure drop. Install unions of flanges to permit removal for servicing. Protect the regulator from excessive heat. Ambient temperature should not exceed 180 degrees F (350°F if Viton diaphragms are used). Avoid welding near a regulator when installing adjacent piping as weld spatter may roll into a regulator and burn holes through the diaphragm. Apply pipe compound to threaded pipe ends, not to threads, on the regulator body. 4. One regulator should not supply more burners than served by one mixer or controlled by one air valve. 5. For aspirator mixer (zero gas) systems, best control is obtained with at least 2 osi† greater than air impulse pressure. When the regulator's vent is connected to the combustion chamber, the furnace pressure must be added to the gas pressure requirement. Gas inlet pressure should not exceed 2 psi except in special cases. 6. When cross-connecting the regulator's vent to the combustion chamber, main air line, or outside, use 3/8 " tubing for up to a 10 ft run; ½" (or larger) tubing for longer runs. 7. To attach the cross-connection or impulse line to an air line, install a tee or weld a half coupling on the top or side of the air pipe and then drill a hole through the pipe, (½" hole if a bleeder is used, otherwise about the ID of the tubing selected in step 6 above). † Or pressure drop for which the regulator size was selected.

NOZZLE MIX SYSTEMS

Remove burrs from the inside. To minimize turbulence effects, locate the connection on the air line at least 5 air pipe diameters downstream and 3 diameters upstream of any valve or fitting. If it is absolutely necessary to locate the connection less than 5 diameters downstream of the control valve, the hole should be drilled so that the drill is parallel to the shaft of the valve.

INSTALLATION FOR PREMIX BURNERS

1. For an open type premix burner, remove the thread protection cap from the vent and leave open to the furnace room atmosphere as shown in Figure 1. If the vent is piped outdoors, protect the end of the vent pipe from air currents, water, and dirt. 2. For a sealed-in type premix burner the vent of the 7218 Atmospheric Regulator should be cross-connected to the combustion chamber to correct the regulator action for any difference between furnace and atmospheric pressure. When one regulator is used for each burner, connect the vent through the burner mounting plate (as in figure 2) or to the combustion area.

Control Valve

air

Mixer

gas

Open Register Premix Burner

Figure 1

Air/Gas Ratio Regulator

Control Valve

Sealed-in Premix Burner

air

Mixer

gas

Figure 2

Air/Gas Ratio Regulator

NOZZLE MIX SYSTEMS

INSTALLATION FOR NOZZLE-MIX BURNERS

1. Install a limiting orifice valve between the regulator and burner. 2. If the minimum gas inlet pressure exceeds the maximum air pressure by 2 or more osi, simply cross-connect the regulator's vent to the main air line downstream of the control valve, as in Figure 3.

5 pipe dia. minimum

3 dia. min.

air

Control Valve

Limiting Orifice Valve impulse line

shutoff

Nozzle Mixing Burner

Air/Gas Ratio Regulator

Figure 3

3. If the minimum gas pressure at the regulator inlet is not at least 2 osi more than the maximum air pressure available at the burner, then a bleeder must be installed in the air pressure impulse line, as shown in Figure 4, with the amount of bleed set so that maximum impulse pressure is 2 osi less than the gas inlet pressure. (See page 34 and the Bleeder bulletin) This arrangement should be used only when combustion chamber pressures are atmospheric (open burner). 4. If gas and air pressure are not known, make a "trial and error" setting of the bleeder by lighting the burner and bringing it to high fire as described in step 3. Then successfully reduce the impulse to the regulator by means of a bleed until you find a bleeder setting that produces an effect on the flame. This is the correct bleeder setting for all firing rates. Readjust the limiting orifice gas valve. (If gas pressure is not constant set the bleeder for the next lower impulse pressure)

† Or pressure drop for which the regulator size was selected.

NOZZLE MIX SYSTEMS

5 pipe dia.

8654 or 8655 Bleeder

Control Valve

air

impulse line

Limiting Orifice Valve

shutoff

gas

Nozzle Mixing Burner

Air/Gas Ratio Regulator

Figure 4

5. If the combustion chamber pressure fluctuates or is not atmospheric (sealed-in burners) and if gas pressure is less than air pressure, use a 3-pipe bleeder, as shown in Figure 5: this arrangement bleeds off a portion of the air impulse pressure to the combustion chamber so that fluctuations in combustion chamber pressure are neutralized by being applied to both sides of the controlling diaphragm in the gas regulator. Note: A 3-pipe bleeder can be used as a 2-pipe bleeder when the combustion chamber is at atmospheric pressure. In this case the piping connection to the combustion chamber can be omitted.

5 pipe dia.

minimum min.

Control Valve

8654 or 8655 Bleeder

air

impulse lines

Metering Orifice

10D

shutoff

gas

Nozzle Mixing Burner

Air/Gas Ratio Regulator

Limiting Orifice

Figure 5

4D min.

NOZZLE MIX SYSTEMS

LIGHTING AND ADJUSTMENT

1. Light the burner. Follow the blower instructions to start the blower. All gas lines up to the 7218 Regulators must be purged. Before lighting any pilot or burner, make sure that all manual fuel valves are closed, and purge the firing chamber . Follow the pilot instructions light the pilot. Set the main air valve at the low fire position (1 or 2 osi air pressure). Open the limiting orifice gas valve 6 to 6½ turns. Open the upstream gas shutoff valves(s). If the burner does not light in a few seconds, close the nearest upstream gas shutoff valve to prevent accumulation of unburned gas, purge the chamber allowing sufficient time for a minimum of 4 changes of atmosphere, then open the limiting orifice gas valve one more turn and reopen the gas shutoff valve. Repeat this procedure until the main flame lights. 2. Adjust the high fire air/gas ratio. Slowly turn the air valve to high fire position while adjusting the limiting orifice gas valve as needed to maintain the desired air/gas ratio. Replace the limiting orifice valve cover. 3. (For 7218 only, not 7216) Adjust the low fire air/gas ratio only after step 2 is completed. Turn the air valve to low fire position. Remove the gas diaphragm cover plug on the bottom of the regulator. Use an Allen wrench to turn the spring adjusting plug clockwise for more gas, or counterclockwise for less gas, to obtain the desired air/gas ratio. † Replace the gas diaphragm cover plug. 4. (For 7218 only, not 7216) On-off control. To adjust the regulator for on-off control, turn the spring adjusting plug counterclockwise until the compression spring is completely relaxed. NOTE: While the soft seat in this regulator provides good closing characteristics with zero impulse pressure. It is not meant to be used as a shutoff valve. If the burner is to be held in a "off" cycle for periods which exceed normal cycle times, an approved shutoff valve must be installed to prevent fuel leakage. 5. Dual-fuel burners. When a nozzle-mix burner of the dual-fuel type is being operated on gas with atomizing air left on, the regulator must supply a constant amount of gas to match the atomizing air plus a varying amount to match the main air at any firing rate. To adjust the regulator for this situation, first operate on main air only and follow the instructions under nozzle-mix burners for making the cross-connection, adjusting the limiting orifice gas valve, and adjusting the bleed if any is required. Next turn off the main air (the flame will go out), and remove the gas diaphragm cover plug. Turn on the atomizing air at the pressure suggested for gas operation and screw the spring adjusting plug clockwise until the pilot relights the burner and the desired air/gas ratio is found.

NOZZLE MIX SYSTEMS

Replace the cover plug. The regulator is then adjusted for atomizing air plus main air at any firing rate, and the burner will have the same capacity when operating on gas as on oil. (If the burner cannot be lighted on atomizing air only, adjust the spring adjusting plug with the main air at low fire setting)

SERVICING

To check regulator operation, 1⁄8 " pipe taps are provided on the body for inlet and outlet pressure readings. UNABLE TO ACHIEVE MINIMUM OR "0" FLOW 1. Make sure that the regulator has been adjusted correctly as in steps 3 or 4 (under Lighting and Adjustment). 2. Disconnect the air impulse line at the regulator to ensure that there is no loading pressure. 3. Connect a manometer to the 1⁄8 " outlet tap to determine if the combustion chamber is under a negative pressure. If so, cross-connect the regulator vent to the combustion chamber as shown in Figure 2 or 5 on previous pages. 4. Shut off gas supply, remove body plug, apply air impulse (about 16 osi) to the vent to raise regulator valve off seat, wipe seat surfaces with cloth to remove possible pipe scale, dirt, pipe thread chips, or other foreign matter. Remove the air impulse and replace the body plug. 5. Shut off gas supply, remove body plug and inlet test tap plug. While pressing gently downward on regulator valve, attempt to blow through a rubber tube attached to the inlet test tap. If back pressure dœs not build up, the balancing diaphragm is ruptured and must be replaced. (As an alternate test, try to wobble the regulator valve with a finger. If the balancing diaphragm is intact, it will hold the valve fairly rigid)

NOZZLE MIX SYSTEMS

5. Shut off gas supply, remove body plug and inlet test tap plug. While pressing gently downward on regulator valve, attempt to blow through a rubber tube attached to the inlet test tap. If back pressure does not build up, the balancing diaphragm is ruptured and must be replaced. (As an alternate test, try to wobble the regulator valve with a finger. If the balancing diaphragm is intact, it will hold the valve fairly rigid) REGULATOR NOT RESPONSIVE 1. Make sure thread protection cap is removed from vent. If impulse line is used, make sure it is not clogged, undersized, or inoperative due to bad installation. 2. Make sure of mixer suction by shutting of gas supply and reading water gauge attached to outlet test tap while air flows through the mixer. If impulse line is used, disconnect from regulator vent and attach it to water gauge to observe impulse magnitude and changes. 3. If suction or impulse is satisfactory but regulator still is not responsive, shut off gas supply, remove outlet test plug, connect rubber tube to regulator vent, and blow through tube. If pressure does not build up in the tube, the gas diaphragm is ruptured and must be replaced.

NOZZLE MIX SYSTEMS

air

16 osi

4 pipe dia.

2 osi minimum drop

10 pipe dia.

19 osi

16 osi

GAS PRESSURE REQUIREMENTS FOR CROSS-CONNECTED AIR/GAS RATIO REGULATORS

Operation of this system depends on an adequate gas supply pressure. With 16 osi impulse the regulator will open until an outlet pressure of 16 osi is reached. If the regulator is sized to take a 2 osi pressure drop at full fire conditions, an inlet pressure of 18 osi or more is required. A little extra inlet pressure is desirable as a safety factor; thus . . .

Air pressure..................................................................16 osi Pressure drop through regulator.............................. 2 osi Safety factor................................................................. 1 osi Required supply pressure . 19 osi or, if a regulator is sized for a 6 osi drop............16 osi 6 osi 1 osi 23 osi

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