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BOILER OPERATION AND CONTROLS

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Boiler Starting and Operating Instructions

Before starting the boiler, the operator should be familiar with the burner, boiler, and all controls and components. To quickly locate and identify the various controls and components mentioned in the following paragraphs, refer to the ''Cleaver-Brooks Operation, Service and Parts Manual''. Instructions for adjusting major components should be reviewed prior to firing. The wiring diagram should also have been studied, along with the firing sequence.

WARNING!

Be sure the starting instructions are read completely until they are thoroughly understood, before attempting to operate the boiler, rather than performing each operation as it is read for the first time. Failure to follow these instructions could result in serious personal injury or death!

Verify supply of fuel and proper voltage. Check for blown fuses, open circuit breakers, dropped out overloads, etc. Check reset of all starters and controls having manual reset features. Check the lockout switch on the programmer and reset if necessary.

The boiler should be filled with water to the proper operating level using water of ambient temperature. Be sure that treated feedwater is available and used. In heating applications, the entire system should be filled and vented. On a steam boiler, open the test valve to vent air displaced during filling. Leave the test valve open until the escape of steam is noted after the burner is operating.

WARNING!

Prior to firing a boiler, be sure that discharge piping from safety valves or relief valves, and discharge piping from all blowdown and drain valves, is piped to a SAFE point of discharge, so that discharge of hot water or steam cannot possibly cause injury. Failure to follow these instructions could result in serious personal injury or death.

Check all linkage for full and free movement of the damper and metering valves and cams. The check can be done by loosening the linkage at the damper motor connecting arm and manipulating the linkage by hand.

Check for rotation of all motors by momentarily closing the motor starter or relay. The blower impeller rotation is counter-clockwise for the CB-LE, when viewed from the front of the boiler. The air pump rotation is clockwise when viewed from its drive end.

Before operating the boiler feed pump or oil supply pump, ensure all valves in the line are open or properly positioned. For safety reasons, perform a final pre-startup inspection, especially checking for any loose or incomplete piping or wiring or any other situations that might present a hazard.

Menu

Control Settings Steam and Hot Water

Inspect the '''Operating Limit Control '''for proper setting.

The operating limit pressure control of a steam boiler should be set slightly above the highest desired steam pressure, but at least 10% lower than the setting of the safety valve.

The operating limit temperature control on a hot water boiler should be set slightly above the highest desired water temperature and within the limits of the pressure vessel.

Inspect the '''High Limit Control '''for proper setting.

On a high pressure steam boiler, the high limit pressure control should be set approximately 10 psig above the operating limit pressure control setting, if feasible, or midway between the operating limit pressure and the safety valve setting. The setting on a low-pressure steam boiler may be two or three psig above the operating limit setting, but must not exceed the safety valve setting.

On a hot water boiler, the high limit temperature control should be 5-10?F above the operating limit temperature control setting, but within the limits of the design pressure of the pressure vessel.

Inspect the '''Modulating Control '''for proper setting. The control must be set and adjusted so that the modulating motor returns to low fire position before the operating limit control opens. It is desirable to have its low point setting somewhat below the cut-in setting of the limit control so that the burner operates in low fire''' '''position for a brief period on each start rather than immediately driving to a high fire position.

NOTE:

The settings of all the above controls may require some readjustment after the boiler is started and running for a short period. The scale settings on the controls are relatively accurate, but are principally for use as guides. Final adjustment should be based on and agree with the reading of the steam pressure gauge or the water temperature thermometer.

Inspect the '''Low-water Cutoff''' and '''Pump Control''' as well as the '''Auxiliary Low-water Cutoff''' (if equipped with this optional device). Check for freedom of float movement. Float movement can be verified by observing the level of water in the gauge glass when the water supply has been cut off either by the stopping of the feed pump or by the closing of a valve, and the restarting of the pump or opening of the valve when water is drained from the pressure vessel. The importance of proper functioning of low-water controls cannot be over-emphasized. Be sure that the control and the piping is level.

The settings of controls relating to fuel, either oil or gas, are covered in subsequent sections.

In the event the boiler is equipped with optional control devices not listed here, be certain to ascertain that their settings are correct. If additional information is required, see your local Cleaver-Brooks authorized representative or contact Cleaver-Brooks.

On initial startup or whenever the boiler is placed into operation from a "cold" start, the '''Manual-automatic Selector Switch''' should be set at "manual" and the '''Manual Flame Control''' set at "close." After the boiler is in operation and thoroughly warmed, the selector switch should be turned to "automatic," so that the burner firing rate may be controlled by the '''Modulating Control '''in accordance with load demands.

Close all power entrance switches (supplied by others).

Gas Pilot

The gas pilot should be checked for satisfactory performance prior to initial firing.

On initial starting attempts, several efforts might be required to fully bleed the pilot line. While checking pilot adjustment, observe whether the pilot flame is extinguished promptly when the burner switch is opened. A lingering flame indicates a leaking gas pilot valve, which is a condition requiring correction before proceeding.

Atomizing Air

The supply and pressure of the atomizing air on an oil-fired burner should be checked. Before starting, inspect the oil pump lube oil level. Add oil if necessary to bring the level to the mid-point or slightly higher of the sight glass. Use the correct grade of SAE 20 detergent oil.

Check the oil level of the air intake strainer. When operating a standard 78" boiler, make certain that the V-belt which drives the air pump is in place and has proper tension.

To verify airflow and pressure, place the burner '''Run/test Switch '''on the program relay to the test position. If the burner is a combination fuel burner, be sure that the gas/oil selector switch is set to "oil." Turn the '''Burner Switch '''on. The burner will cycle to the low fire pre-purge position and stop there.

Observe the reading on the air pressure gauge. With no oil flow, the pressure should be a minimum of seven psi.

If there is no pressure, determine the cause and correct it before proceeding. Check for obstructions in the air inlet line, incorrect rotation, or a loose oil nozzle or other leaks. If the pressure is much higher without any oil flow, check for obstruction in the discharge line or at the oil nozzle. If there is no obstruction, restrict the airflow by adjusting the air intake valve screw.

The air pressure will increase when an oil flow exists. At low firing rate, the air pressure may rise to 12 psi or more.

NOTE:

The air pressure should not exceed 35 psi at high fire. Greater air pressure causes excessive wear of the air pump, increases lute oil usage, and can overload the motor, thus causing damage to the equipment. Abnormally high pressure indicated on the nozzle air pressure is an indication that the burner nozzle has become clogged. In the event of clogging, check the nozzle and clean as necessary.

After airflow has been verified, turn the burner switch off and return the run/test switch to the run position.

Depending upon the fuel being burned setup the fuel system, see the Cleaver-Brooks operation manual. When firing with oil, be certain that the '''Burner Gun''' is in its most forward position and latched in place. When firing with gas, the burner gun should be properly withdrawn and latched in place. The fuel selector switch should be, accordingly, set to either oil or gas.

Set the '''Manual-Automatic Switch''' to "manual" and turn the manual flame control to "close."

Turn burner switch to "ON." The load demand light should glow. The low-water level light should remain out, indicating a safe water level in the boiler. The programmer is now sequencing.

On an initial starting attempt, several efforts might be required to accomplish "bleeding" of main or pilot fuel lines. If ignition does not then occur, do not repeat unsuccessful attempts without rechecking the burner and pilot adjustment.

On ignition failure, the flame failure light will glow and the blower will purge the boiler of unburned fuel vapors before stopping. After ignition failure, wait a few moments before resetting the lockout switch.

WARNING!

Do not relight the pilot or attempt to start the main burner, wither oil or gas, if the combustion chamber is hot and/or if gas or oil vapor combustion gases are present in the furnace or flue passages. Failure to follow these instructions could result in serious personal injury or death!

WARNING!

The burner and control system is designed to provide a "pre-purge" period of fan operation prior to establishing ignition spark and pilot flame. Do not attempt to alter the system or take any action that might circumvent the "pre-purge" feature. Failure to follow these instructions could result in serious personal injury or death!

After main flame ignition, the burner should be set on manual control at its low fire setting (that is, with manual flame control at "close") until the boiler is properly warmed. Close the steam header.

In the case of a steam boiler, close the test valve when the steam begins to appear.

A hot water boiler must have a continuous flow of system water through the vessel during the warm-up period. The entire water content of the system and boiler must be warmed prior to increasing fuel input.

If the flame at low fire provides insufficient heat to reach normal operating pressure or temperature after 30 minutes, gradually increase the firing rate by turning the '''Manual Flame Control '''in one point increments to no higher than the third cam screw. Operate at the increased fuel input rate for a period of time until an increase is noted in pressure or temperature.

After the boiler is thoroughly warmed, turn the manual flame control to high fire. At this point a combustion analysis should be made, with instruments, and fuel flow regulated as required. After making the high-fire adjustment, manually decrease the firing rate, stopping at each cam screw to analyze combustion gases, and adjust as required.

To properly perform the testing and adjusting, it is necessary that the burner be allowed to fire at a maximum rate long enough to achieve desired results.

Boiler Operation

Normal operation of the burner should be with the switch in the automatic position and under the direction of the modulating control. The manual position is provided for initial adjustment of the burner over the entire firing range. When a shutdown occurs while operating in the manual position at other than low fire, the damper will not be in a closed position, thus allowing more air than desired to flow through the boiler. The hot flame to cool air cycling subjects the pressure vessel metal and refractory to undesirable conditions.

With the switch set at "Auto," the burner will operate on a modulating basis according to the load demand.

The burner will continue to operate with modulated firing until the operating limit pressure or temperature is reached, unless:

  • The burner is manually turned "off."
  • A low-water condition is detected by low-water level control.
  • The electrical or fuel supply is interrupted.
  • The combustion air pressure or atomizing air pressure drops below minimum level.

NOTE:

There can beother reasons for shutdown such as motor overload, flame outages, tripped circuit breakers, blown fuses, or through other interlock devices in the circuitry.

When the burner is shut down normally, by either the '''Operating Limit Control '''or by manually switching the burner off, the load demand light no longer glows.

Shutdown through conditions causing safety or interlock controls to open will actuate the '''Flame Failure Light '''(and alarm if so equipped) and the '''Load Demand Light '''will remain lit. The cause of this type of shutdown will have to be located, investigated, and corrected before operation can be resumed.

Shutdown

When the '''Operating Limit Control '''setting is reached to open the circuit or if the burner switch is turned "off," the following sequence occurs:

  • The fuel valve is de-energized and the flame is extinguished.
  • The timer begins operation and the blower motor continues running to force air through the furnace in the post-purge period.
  • At the end of the programmed post-purge period, the blower motor is turned off.
  • The air pump motor of an oil-fired burner is also turned off.
  • The timer has returned to its original starting position and stops.
  • The unit is ready to restart.

Safety Valves, Safety Relief Valves, and Temperature/Pressure Relief Valves

The safety relief valve is one of the most important devices on any boiler. It is the boiler’s last measure of protection against overpressure. It must be adequately sized and of the correct pressure rating for the boiler. But getting a safe installation is only the beginning. The safety relief valve also must be inspected and tested regularly. Mud and scale from the boiler can interfere with the operation of the relief valve. Plugged discharge lines can prevent proper operation or allow discharged water and steam to come in contact with equipment or operating personnel.

Lifting the test lever while the boiler is operating will confirm its proper operation. At no time should technicians test the valve by increasing the pressure of the boiler to a level higher than the safety-valve setting. They should exercise caution when testing relief valves, as steam or hot water will be discharged through the valve at the operating pressure of the boiler. Valves should be tested every time a boiler is started and at the interval recommended by the manufacturer.

This section provides you with the knowledge you need to inspect and test relief valves and safety valves. Specifically, this section covers:

  • How relief valves and safety valves are categorized and characterized
  • How relief valves and safety valves are constructed and how these valves operate
  • Data that is marked on relief valves and safety valves to permit accurate identification and assessment for proper application
  • Relief and safety valve terminology

The table below provides terminology associated with relief and safety valves.

TERM

DEFINITION

Fluid

Any substance that will flow and assume the shape of the container it is held in is known as a fluid. This term includes both liquids and gasses.

Liquid

A liquid is a substance with no definite shape but a definite volume. A liquid will take the shape of its container. Pressure is exerted on all surfaces that contact the liquid.

Gas

A substance that has no definite volume or shape. A gas must be enclosed in a container to prevent escape to the atmosphere. A gas exerts pressure on all sides of a container; it can also be compressed.

Vapor

A fluid that is a combination of gas with liquid mixed in it. The liquid is said to be entrained in the gas.

Blowdown

This term relates to both safety and relief valves. It is defined as the difference in pressure between the valve’s set pressure, and the pressure at which a valve reseats. It is expressed as a percentage of the valve’s set pressure.

Accumulation

This term relates to both safety and relief valves. It is defined as the difference in pressure between the pressure at which the valve is fully open, and the valve’s set pressure. It is expressed as a percentage of the valve’s set pressure.

Set Pressure

The pressure at which a safety or relief valve first begins to open in response to an overpressure condition. This is also known as a valve’s setpoint.

Categorization and Characterization of Relief Valves and Safety Valves

'''Table 1''' provides a basic overview of relief valves and safety valves.

Table 1: Overview of Relief Valves and Safety Valves

PRESSURE-RELIEVING VALVES

General Purpose: Avoid equipment damage and personnel injury caused by overpressure in piping systems and pressure vessels.

General Function: Automatically provides relief action in response to overpressure.

Relief Valves

Service Application

Distinguishing Feature

Action

Spring-Operated

Pilot-Operated

Both types used for incompressible fluids. (i.e., liquids).

Both types used where there is no danger of explosion from overpressure.

  • Downward seating, relying on spring pressure to seal.
  • "Lifts" upward when pressure is at setpoint.
  • Reverse (upward) seating, relying on system pressure to seal.
  • Downward acting when pressure is at setpoint, gradually opens.
  • Relies on pilot valve to actuate relief action.

Safety Valves

Service Application

Distinguishing Feature

Action

Spring-Operated

Pilot-Operated

Both types used for compressible fluids (i.e., gases and vapors).

Both types used where there is danger of explosion from overpressure.

  • Downward seating, relying on spring pressure to seal.
  • "Pops" fully open when pressure is at setpoint.
  • Blowdown setpoint adjustable
  • Downward seating, relying on system pressure and spring pressure to seal.
  • "Pops" fully open when pressure is at setpoint.
  • Relies on pilot valve to actuate relief action.

Blowdown setpoint adjustable.

Valve Identifications and Markings

This section covers identifications and markings that permit identification of individual relief valves and safety valves and the symbolism used in piping and instrumentation diagrams (P&ID) to designate these valves. Safety valve capacity and blowout information is listed on the name/data plate on the safety valve.

Accurate valve identification is critical to valve installation, removal for inspection/maintenance or testing/adjustment, and reinstallation. To permit accurate identification, most manufacturers mark data on the body of a valve and/or on a manufacturer’s plate that is attached to the valve body. This data includes the following:

  • '''Manufacturer’s Name, Trademark, or Symbol''': Specifies the valve manufacturer.
  • '''Rating Designation''': Specifies the appropriate pressure rating class designations or specific maximum pressure/temperature designations for the valve.
  • '''Cold Working Pressure''': The letters and designations listed below stand for the following parameters at normal-range ambient temperatures (-20 to 100degrees Fahrenheit; -29 to 36degrees Celsius):

1. WO - Water and oil pressure

2. OWG - Oil, water, and gas pressure

3. WOG - Water, oil, and gas pressure

4. GLP - Gas and liquid pressure

5. WWP - Working water pressure

6. W - Water pressure

7. WSP - Working steam pressure

  • '''Material Designation''': Specifies the materials of construction for the body and the bonnet of the valve. Forged and fabricated valves are usually identified with () American Society for Testing Materials (ASTM) numbers and grade identification symbols.
  • '''Melt Identification''': Cast valves are marked with the melt numbers or melt identification symbols.
  • '''Valve Trim Identification''': Identifies materials of construction for internals such as the stem and the disc when these materials differ from the materials of construction for the valve body.
  • '''Size Designation''': Specified in nominal pipe size.
  • '''Identification of Threaded End''': Standard ring joints that comply with applicable ANSI and API standards are marked with ''R''.
  • '''Special Function Requirements''': Manufacturers may place catalog numbers, dates, reference numbers, and other data to distinguish valves used for special functions.

Safety and Relief Valve Inspection and Maintenance Guidelines

Safety and relief valves are normally tested after major repairs or overhaul. There are normally four items that can be tested on a safety valve or a relief valve: Valve setpoint, blowdown, accumulation, and seat leakage. A brief discussion of the various testing methods follows, in addition to a diagram of a safety valve test stand ('''Figure 1'''). The type of method used depends upon the individual requirements and circumstances.


'''Figure 1: Safety Valve Test Stand'''

Safe operation of a boiler is dependent on a vital accessory, the safety valve. Failure to test the safety valve on a regular basis or to manually open it periodically can result in heavy accumulations of scale and deposits of sediment or sludge near the valve. These conditions can cause the safety valve spring to solidify or the disc to seal, ultimately rendering the safety valve inoperative. A constantly simmering safety valve is a danger sign and must not be neglected.

Your preventive maintenance program includes the documentation and inspection of the safety valve. A daily test must be performed when the boiler is in operation. Simply raise the hand-operating lever quickly to its limit and allow it to snap closed. Any tendency of a sticking, binding, or leaking of the safety valve must be corrected immediately.

External Inspections

Before testing, a simple external inspection of a relief or safety valve can identify some fundamental problems that may affect the valve’s operation. The following items should be checked when performing an external inspection:

  • Check the valve for signs of leakage or leak-through at the discharge piping bolts and around the yoke bolts.
  • Inspect the general physical condition of the valve and the piping attached to the valve. Minor physical damage can result in improper valve operation.
  • Look around the valve for signs of steam or warm condensate leakage around the drain plug and around the bolts on the yoke.
  • If the valve is of the huddling chamber variety, check the lock wire on the adjusting ring pins. If the lockwire is missing or appears to be tampered with, the valve setpoints may not be correct and valve testing is necessary.
  • Check the temperature of the valve and discharge piping. If the outside surface of the discharge piping is abnormally hot or abnormally cold, it is usually a sign of leakage.

Hand Lifting Relief/Safety Valves

If an external inspection of the valve reveals that a valve is leaking between the seat and the disc, it may be a result of foreign matter such as ash, dirt, or rust particles trapped between the seat and disc. It is also possible that the valve did not re-seat correctly after the last time it popped. In many cases, a mechanic can correct either of these two causes of leakage by manually lifting or hand lifting the valve.

Hand lifting clears foreign matter out of the valve and gives the disc a chance to reseat properly. However, any time a safety valve is lifted, there is a corresponding drop in system pressure.

Before the valve is hand lifted, the appropriate operating personnel should be notified so that they can compensate for the drop in system pressure and keep it from interfering with normal operations.

If operating personnel are not forewarned, when pressure drops as the valve is hand lifted, they might take emergency measures to raise pressure or shut down the system. Such actions could be costly and perhaps dangerous.

Anyone who hand lifts a valve must take appropriate personal safety precautions. These precautions include using the required personal protective equipment and connecting a hook and lanyard or similar device to the valve’s release lever.

Attaching a hook to the valve’s release lever enables the mechanic to position himself as far away from the valve as possible. This is important because when a valve is hand lifted, a great deal of hot, pressurized fluid could be released.

To lift the valve, the mechanic pulls the hook hard enough to open the valve all the way.

The valve is then held open for only two or three seconds. If the valve is held open any longer, the rush of steam could damage the disc.

After the valve closes, the external inspection is repeated to check for leaks and more heat than would normally be expected after hand lifting. If the valve seats properly after lifting, it should cool down immediately.

If the second inspection indicates that the problem was not solved by hand lifting the valve or if hand lifting was not a possible solution for the initial problem, follow plant procedures to have the valve examined and the problem corrected.

A relief valve or a safety valve can be removed from the system in which it is installed to permit inspection and repair, and to permit bench testing for the actual pressure at which the valve provides relief action.

Inspections

Relief valves, safety valves, and pilot valves should be inspected according to a periodic schedule and repaired as necessary to ensure effective operation. Inspection schedules for individual valves vary, depending on the severity of the service in which the valves are employed. As rules of thumb:

  • Valves used for non-corrosive fluids are inspected on a yearly basis.
  • Valves used for corrosive fluids are inspected more frequently.

Repairs

Repairs performed on safety valves and safety relief valves by groups or individuals other than the manufacturer must be performed by an organization in possession of a current National Board VR Certificate of Authorization.

Testing and Adjustment Guidelines for Relief and Safety Valves

Basic Terms

Maximum Operating Pressure (MOP)— The maximum pressure at which a natural gas facility can be operated without further review, facility modifications, or documented operating procedures. This pressure can be limited by customer piping, downstream piping, operating agreements, etc.

Maximum Allowable Operating Pressure (MAOP) – Maximum established pressure at which a facility can be operated without documented operating procedures.

Maximum Inlet Operating Pressure – Maximum pressure the inlet piping can experience during normal operation.

Outlet Maximum Operating Pressure – Maximum pressure the outlet piping at a facility can be operated without further review, facility modifications, or documented operating procedures. This can be limited by customer piping, downstream piping, operating agreements, etc.

Outlet Maximum Allowable Operating Pressure – Maximum pressure at which the outlet piping can be operated without documented operating procedures.

Testing and adjusting relief and safety valves is important to safe system operation. This section discusses the various methods available to perform these tests safely and accurately.

Safety valves are normally tested both for relieving and closing pressure. This requires that the boiler pressure be raised until the valve opens and relieves sufficient pressure for the valve to close. Safety valve seats are susceptible to damage caused by wet steam or grit. Cleaning of the boiler and steam lines before testing safety valves is necessary.

Testing safety valves always requires special precaution. Safety valve exhaust piping and vent piping should not exert any excessive forces on the safety valve.

When a boiler inspector is carrying out an examination of a boiler, he must, by sealing the safety valve, ensure that the safety valve is so adjusted as to prevent the boiler from being operated at a pressure greater than the maximum permissible working pressure. The maximum permissible working pressure can be obtained from the certificate of fitness.

The seal attached to the safety valve should be maintained intact and the setting of the safety valve should not be altered by a person who is not a boiler inspector.

The setpoint of the valve is the system pressure at which the valve begins to open. The following general guidelines apply to setpoint testing of relief valves, safety valves, and pilot valves:

  • Only qualified personnel are to conduct setpoint tests.
  • Tests are normally conducted after a valve has undergone major repairs or overhaul.
  • Setpoint tests are conducted through use of nitrogen, natural gas, or, for compressed air systems, air.
  • Bench testing and in-place testing are both used as applicable. For bench testing, the guidelines outlined above in Inspection Repair/ Removal are to be followed.
  • Personnel in the area in which a setpoint test is to be conducted are to be notified.
  • Personnel involved in setpoint testing are to use personal protective equipment and are to make proper selection and use of tools.
  • Personnel involved in setpoint testing are to follow applicable depressurization/pressurization procedures and also follow lockout/tagout procedures where these procedures are applicable.

During setpoint testing, the following environmental protocols are to be followed:

  • Contamination of soil, surface waters, and ground water is to be avoided.
  • Any waste materials that are generated are to be collected in approved containers and are to be disposed of properly.
  • Testing is to be documented through use of correct forms, with the forms completed properly.

Boiler System Controls

The control configuration for a boiler installation depends on the size of the boiler, the requirements of the insurance company providing coverage for the facility, and the building codes of the locality in which the facility is located. The overall boiler control system is typically integrated through a control panel known as the burner management system, which controls the boiler operation to maintain the system setpoint conditions and shuts down the boiler if an equipment damaging and life threatening condition is sensed.

For most packaged boiler installations, the basic boiler control is a single -element, proportional control device. In the case of a steam boiler, the control device is a pressure sensing element that sends a signal to the burner management system to adjust the burner firing rate to maintain a set pressure in the steam distribution system.

In a hot water boiler, the control device is a temperature-sensing element. In large steam boiler installations, the control system may be a three-element, proportional-integral-derivative controller that not only responds to the system set pressure, but may also respond to the rate of change in parameters such as pressure, steam flow, or water level.

In multiple boiler installations, the burner management systems of each boiler may be controlled by a master plant controller (sometimes referred to as a lead-lag controller) to stage boiler operation to minimize on/off operation. They may also minimize frequent burner cycling, which can cause thermal stresses leading to tube and tube sheet leaks.

While a brief description of the common types of control components associated with packaged boilers follows, the best guide to facility boiler operation and boiler controls is the manufacturer’s operating and maintenance instructions provided with the boilers.

'''Figure 2''' shows the boiler system’s major components for a Cleaver-Brooks model CB-LE 200 series boilers with a CB-HAWK boiler management control system.


'''Figure 2: Boiler Components'''

  1. '''LOW WATER CUTOFF'''
  2. '''BLOWER MOTOR AND FAN'''
  3. '''TUBES AND TUBE SHEET'''
  4. '''REAR HEAD REFRACTORY'''
  5. '''GAS TRAIN'''
  6. '''BURNER HOUSING AND DIFFUSER'''
  7. '''FLAME SAFEGUARD CONTROLS'''
  8. '''THROAT AND LINER'''

Common Controls

The following control devices are common to all boilers:

  1. The '''forced draft fan motor''' drives forced draft fan directly to provide combustion air.
  2. The '''forced draft fan motor starter''' energizes the forced draft fan motor.
  3. The '''forced draft fan''' furnishes all air, under pressure, for combustion of pilot fuel and main fuel, and for purging prior to burner ignition and after burner operation termination.
  4. The '''ignition transformer''' provides high-voltage spark for ignition of the gas pilot or light oil pilot.
  5. The '''modulating motor''' operates the rotary air damper and fuel valves through a cam and linkage system to provide proper air-fuel ratios under all boiler load conditions.
  6. The '''low fire switch''' is an internal auxiliary switch, cam-actuated by the modulating motor shaft, which must be closed to indicate that the air damper and fuel metering valve are in the low fire position before an ignition cycle can occur.
  7. The '''burner switch''' is a manually operated start-stop switch for directly starting and stopping operation of the burner.
  8. The '''manual-automatic switch''', when set at "automatic," subsequently operates at the command of the modulating control which governs the position of the modulating motor in accordance with load demand. When set at "Manual," the modulating motor, through the manual flame control, can be positioned at a desired burner firing rate. The primary purpose of the manual position is for testing and setting the air-fuel ratio through the entire firing range.
  9. The '''manual flame control''' is a manually operated potentiometer that permits the positioning of the modulating motor to a desired burner firing rate when the manual-automatic switch is set on manual. It is used primarily for initial or subsequent setting of fuel input throughout the firing range. It has no control over the firing rate when the manual-automatic switch is set on "automatic."
  10. The '''modulating motor transformer '''reduces control circuit voltage to required voltage for operation of modulating motor (typically reduces 115 volt alternating current to 24 volt alternating current).
  11. '''Indicating lights''' provide visual information of flame failure, load demand, fuel valve (valve open), and low water.
  12. The '''program relay and flame safeguard control''' (flame safety system) automatically programs each starting, operating, and shutdown period in conjunction with the operating limit and interlock devices. This includes, in a timed and proper sequence, the operation of the blower motor, ignition system, fuel valve(s), and damper motor. The sequence includes air purge periods prior to ignition and upon burner shutdown. The flame detector portion of this control monitors both oil and gas flames and provides protection in the event of loss of a flame signal. The control recycles automatically during normal operation, or following a power interruption. It must be manually reset following a safety shutdown caused by a loss of flame. An internal checking circuit is incorporated that is effective on every start. The circuit will prevent burner operation in the event anything causes the flame relay to hold in during this period.
  13. The '''combustion air proving switch''' is a pressure sensitive switch actuated by air pressure from the forced draft fan. Its contacts close to prove presence of combustion air. The fuel valves cannot be energized, unless this switch is satisfied.
  14. The '''combustion air damper''' controls combustion air in proportion to fuel input for various load demands. The damper may be of the butterfly, opposed blade, or rotary type.

Steam Controls

The following control devices are used with steam systems:

  1. The '''steam pressure gauge''' indicates boiler internal pressure.
  2. The '''operating limit pressure control''' breaks a circuit to stop burner operation on a rise of boiler pressure above a selected setting. It is adjusted to stop or start the burner at a preselected pressure setting.
  3. The '''high limit pressure control''' breaks a circuit to stop burner operation on a rise of pressure above a selected setting. It is adjusted to stop the burner at a preselected pressure above the operating limit control setting. This control is normally equipped with a manual reset.
  4. The '''modulating pressure control''' senses changing boiler pressures and transmits this information to the modulating motor to change the burner firing rate when the manual-automatic switch is set on automatic.
  5. The '''low water cutoff and feedwater pump control''' (typically float-operated) responds to the water level in the boiler. The control starts and stops the feedwater pump or operates the feedwater control valve to maintain the proper water level in the boiler. If the water level drops below the lowest safe water level for the boiler, the control shuts down the boiler.
  6. Most jurisdictions require two independent '''low water cutoff devices'''. The auxiliary low water cutoff also provides a signal to shut down the boiler if the water level drops below the lowest safe water level for the boiler.
  7. The '''water column''' provides visual indication of the boiler water level. The water column and low water cutoff devices for a boiler are typically incorporated in the same piping assembly.
  8. The '''test valve''' allows the boiler to be vented during filling and facilitates routine boiler inspection. The test valve is typically incorporated in the same piping assembly as the water column and the low water cutoff.
  9. '''Safety valves''' relieve the boiler of pressure higher than the design pressure. Safety valves and discharge piping must conform to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code requirements.

Hot Water Controls

The following control devices are used with hot water systems:

  1. The '''water temperature gauge''' indicates the internal water temperature.
  2. The '''water pressure gauge''' indicates the pressure in the boiler.
  3. The '''operating limit temperature control''' breaks a circuit to stop burner operation on a rise of boiler temperature above a selected setting. It is adjusted to stop or start the burner at a preselected operating temperature.
  4. The '''high limit temperature control''' breaks a circuit to stop burner operation on temperature rise above a selected setting. It is adjusted to stop the burner at a preselected temperature above the operating control setting. The high limit temperature control normally is equipped with a manual reset.
  5. The '''modulating temperature control''' senses changing boiler temperature and transmits this information to the modulating motor to change the burner firing rate when the manual/automatic switch is set on automatic.
  6. The '''low water cutoff''' breaks the circuit to stop burner operation if the water level in the boiler drops below a safe operating level.
  7. Most jurisdictions require two independent devices to terminate boiler operation in the event of low water. The '''auxiliary low water cutoff''' also provides a signal to stop burner operation if the water level in the boiler drops below a safe operating level.
  8. '''Relief valves''' relieve the boiler of pressure higher than the design pressure. Relief valves and discharge piping must conform to the ASME Boiler and Pressure Vessel Code requirements.

Gas Controls

The following control devices are used with '''gas-fired boilers''':

  1. The '''gas pilot valve''' is a solenoid valve that opens during the ignition period to admit fuel to the pilot. It closes after main flame is established. The sequence of energizing and de-energizing is controlled by the program relay and flame safeguard control. Some jurisdictions may require two independent gas pilot valves installed in series.When two independent gas pilot valves are required, a normally open vent valve is usually required to vent the section of gas piping between the valves whenever both gas pilot valves are de-energized. The vent valve closes when the gas pilot valves are energized.
  2. The '''gas pilot shutoff cock''' is a manually operated, non-lubricated plug valve for isolating the gas supply from the gas pilot valve.
  3. The '''gas pilot adjusting cock''' is a manually operated valve used to regulate the size of the gas pilot flame.
  4. The '''gas pilot aspirator''' is a venturi device using combustion air to improve the flow of gas to the pilot burner.
  5. The '''gas pilot pressure gauge''' indicates gas pressure in the supply line to the gas pilot.
  6. The '''gas pilot pressure regulating valve''' reduces incoming gas pressure to suit the requirements of the pilot burner. Most pilot burners require a gas pressure in the range of 5 to 10 inches of water column.
  7. The '''main burner gas flow control valve''' is modulated through a mechanical linkage to the modulating motor to regulate the flow of gas to the burner in proportion to the boiler load.
  8. The '''gas modulating cam''' is an assembly consisting of a quadrant, a series of adjustable Allen head screws, and a contour spring to adjust gas input at any boiler load condition to attain the required air-fuel ratio. The position of the quadrant is controlled by the modulating motor.
  9. The '''main gas cock''' is a manually operated, non-lubricated plug valve for isolating the gas supply from the main gas valves.
  10. Most jurisdictions require two independent '''main gas valves''' in series. Main valves will open only after the program relay and flame safeguard control signals that a pilot flame has been established.
  11. The '''main gas vent valve''' is a normally open solenoid valve installed between the two main gas valves to vent gas to atmosphere should any be present in the main gas line when the gas valves are de-energized.
  12. The '''low gas pressure switch''' is a pressure-actuated switch that is closed whenever the pressure in the gas supply line is above a preselected pressure. If the gas pressure in the gas main drops below the set pressure, the low gas pressure switch opens, breaking the circuit to the main gas valves which causes the main gas valves to close, terminating burner operation.
  13. The '''high gas pressure switch''' is a pressure-actuated switch that is closed whenever the gas supply line pressure is below a pre-selected pressure. If the gas pressure in the gas main rises above the set pressure, the high gas pressure switch opens breaking the circuit to the main gas valves which causes the main gas valves to close, terminating burner operation.

Oil Controls

The following control devices are used with oil-fired (or dual fuel) boilers:

  1. The '''oil drawer switch''' is a limit switch which remains open, preventing the burner from operating until the oil drawer burner gun is latched in the forward position.
  2. The '''atomizing air proving switch''' is a pressure switch that closes allowing the burner to operate when there is sufficient atomizing air pressure for proper burner operation. Oil valve(s) will not operate, or will not remain open, unless the atomizing air proving switch remains closed.
  3. The '''air pump module''' provides the compressed air required to atomize the fuel oil for proper burner operation. It is started automatically by the program in the program relay and flame safeguard control system.
  4. The '''air pump motor''' drives the air pump and an air-cooling fan. The control for the motor operates in parallel with the forced draft fan motor.
  5. The '''air pump''' provides air for atomizing the fuel oil.
  6. The '''air filter''', typically an oil bath or viscous film filter element, is used to clean the air supply prior to entering the air pump.
  7. The '''check valve''' prevents lubricating oil and compressed air from surging back through the pump and air filter when the air pump stops.
  8. The '''air-oil receiver''' tank holds a supply of oil for lubricating the air pump. It separates lube oil from atomizing air before delivery to the burner nozzle.
  9. The '''atomizing air pressure gauge''' indicates the pressure in the atomizing air supply system near the connection to the burner.
  10. The '''lube oil level sight glass''' indicates the level of lubricating oil in the air-oil receiver tank.
  11. The '''lube oil cooling coil''' cools the lubricating oil before the oil enters the air pump. A fan driven by the air pump motor circulates cooling air over the coil.
  12. The '''lube oil strainer '''filters lubricating oil before the oil enters the air pump.
  13. The '''lube oil fill pipe and strainer''' are used when adding oil to the air-oil receiver tank.
  14. Some jurisdictions require a '''low oil pressure switch'''. When required, this pressure-actuated switch opens when the pressure in the fuel oil supply system drops below a set value.
  15. The '''oil solenoid valve''' opens when energized by the program relay and flame safeguard control system allowing fuel oil flow from the oil metering valve to the burner nozzle. Many jurisdictions require two independent oil solenoid valves in series for boiler fired-on light oils.
  16. The '''fuel oil controller''' is an assembly hat combines the gauges, regulators, and valves required for regulating the flow of fuel oil into a single unit. Most controllers have the following integral parts. In addition to the parts listed below, controllers on systems burning No. 6 or heavier fuel oil require additional parts.'''a.''' The oil metering valve is operated through a mechanical linkage to the modulating motor. The valve regulates the fuel oil supply to the burner nozzle in proportion to the boiler load.'''b.''' The oil modulating cam is an assembly consisting of a quadrant, a series of adjustable Allen head screws, and a contour spring to adjust gas input at any boiler load condition to attain the required air-fuel ratio. The position of the quadrant is controlled by the modulating motor.'''c.''' The oil burner pressure gauge indicates the pressure in the fuel oil supply line at the inlet connection to the oil metering valve.'''d.''' The oil pressure regulator may be required to reduce the pressure in the facility fuel oil delivery system to a pressure compatible with the oil burner fuel oil supply regulating components.
  17. The '''oil relief valve''' bypasses excess fuel oil and maintains the fuel oil system pressure indicated on the oil supply pressure gauge.
  18. When a '''light oil pilot system''' is used, a solenoid valve is provided to control the flow of fuel to the pilot nozzle. The pilot valve is energized at the appropriate time by the program in the program relay and flame safeguard control system. It shuts off the flow of fuel to the pilot when the control system receives a signal that the main burner flame has been established. Note that many oil burners use a gas pilot system.
  19. The '''back pressure orifice''' is a restriction located in the oil return line immediately downstream of the fuel oil controller to maintain a set pressure in the fuel supply system. A back pressure orifice is generally only used on systems that do not use an oil relief valve.

Heavy Oil Controls

The following additional control devices are used when firing heavy oil:

  1. The '''oil heater switch''' is a manual disconnect for electric power to fuel oil heater system.
  2. The '''oil heater – electric''' is used for heating sufficient fuel oil for operating the burner at low fire during cold starts before steam or hot water is available for fuel oil heating. On steam boiler units, the electric heater is typically integral with the steam fuel oil heater. On hot water boiler units, the electric heater is typically a stand-alone unit. The electric heater must be turned off during extended boiler lay-up or at any time fuel oil transfer is terminated.
  3. The '''oil heater – steam or hot water''' heats the fuel oil to attain the proper fuel oil viscosity for full atomization of the fuel oil. On steam boilers operating at 15 psig or less, the steam heater typically operates at the same pressure as the boiler. On higher pressure steam boiler units, a pressure reducing station is typically installed in the supply line to the fuel oil heater to limit the steam pressure in the oil heater to 15 psig or less.
  4. The '''oil heater thermostat – electric and steam''' senses fuel oil temperature. On electric heaters, it energizes or de-energizes the electric heater to maintain the proper fuel oil temperature. On steam heaters, it controls the operation of the steam flow control valve in the supply line to the heater to maintain temperature.
  5. The '''oil heater thermostat – hot water''' – senses fuel oil temperature and starts and stops a booster water pump which circulates hot water from the boiler through the oil heater to control the temperature of the fuel oil.
  6. The '''booster water pump''' circulates water from the hot water boiler through a hot water fuel oil heater. Operation of the pump is controlled by the hot water oil heater thermostat.
  7. The '''oil heater valve''' is a normally open solenoid valve opened by the steam boiler heater thermostat to allow flow of steam to the steam heater to maintain the temperature of the fuel oil.
  8. The '''steam heater supply check valve''' is installed in the steam supply line ahead of a steam oil heater, the check valve prevents oil contamination of the waterside of the pressure vessel should any leakage occur in the oil heater.
  9. The '''steam heater pressure regulator''' is used on steam boiler units that operate at pressures higher than 15 psig to reduce the steam pressure supplied to the steam oil heater to pressures compatible with the equipment.
  10. The '''steam trap''' drains condensate and prevents loss of steam from the steam oil heater. The discharge of the steam trap on the steam oil heater unit is typically discharged rather than recovered to eliminate the possibility of contaminating the waterside of the boiler in the event of a leak in the oil heater unit.
  11. The '''steam heater discharge check valve''' prevents air entry during shutdown periods when cooling action may create a vacuum within the steam heater.
  12. The '''oil supply pressure gauge''' is installed in the fuel oil supply line between the discharge of the fuel oil heater and the inlet to the fuel oil controller unit oil pressure regulator.
  13. The '''low oil temperature switch''' is a temperature-actuated switch that prevents the burner from firing or terminates burner operation if the fuel oil temperature is lower than required for proper oil burner operation.
  14. '''High oil temperature switch'''. Some jurisdictions require a temperature-actuated switch that prevents the burner from firing or terminates burner operation if the fuel oil temperature is above a set temperature. This is the high oil temperature switch.
  15. The '''fuel oil controller''' units for boilers firing heavy oil require the following:'''a.''' The '''fuel oil thermometer''' indicates temperature of fuel oil being supplied to the fuel oil controller.'''b.''' The '''back pressure valve''' ensures that a minimum fuel oil supply system pressure is maintained for proper fuel oil controller operation.'''c.''' The '''oil return pressure gauge''' indicates the oil pressure on the return side of the fuel coil controller.'''d.''' The '''manual bypass valve''' is used when making a cold start. When open, it bypasses control elements and allows oil circulation through the supply and return system to allow oil heaters to adjust the temperature of the fuel oil before firing the burner is attempted. The valve must be closed prior to firing the boiler.'''e.''' The '''orifice oil control valve''' may be opened prior to startup to aid in establishing fuel oil flow through the controller. Prior to firing the boiler, the valve must be closed.
  16. The '''air purge valve''' is a solenoid valve that opens simultaneously with the closing of the oil solenoid valve at burner shutdown, allowing compressed air to purge oil from the burner nozzle and adjacent piping. This oil is burned by the diminishing flame which continues burning for approximately four seconds after the oil solenoid valve closes.
  17. The '''air purge orifice nozzle''' limits purging air to the proper quantity for expelling unburned oil at the normal delivery rate.
  18. The '''air purge orifice nozzle''' '''filter''' filters the purging air of any particles that might plug the air purge orifice nozzle.
  19. The '''air purge check valve''' prevents fuel oil from entering the atomizing airline.
  20. The '''air purge relay''', when energized, controls the operation of the air purge valve.

Additional Controls for Dual-Fuel Burners

Boilers with dual-fuel burner systems require a selector switch to tell the control system which set of fuel controls to operate.