Control Settings Steam and Hot Water in Boiler

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.

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.

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.

image 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!

image 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.