An Introduction To Oil Burner Components And Operation

Although there are several different types of oil burners used in high-pressure cleaners and their appearance may differ radically, each one must have the same basic components.

Almost every oil burner system is made up of:

· A fuel pump
· A fuel nozzle
· A fuel storage and handling system including a fuel tank, lines and filter
· A blower
· A transformer
· Electrodes for ignition
· A power source to drive the pump and blower
· An electrical power supply.

Most cleaners equipped with a trigger or shut-off gun also have a solenoid valve to control fuel flow.

Note: A gasoline-powered hot water cleaner will require an electrical power supply for burner ignition. This may be an 115V AC generator, a magneto or a 12-volt battery. Using a gasoline engine to power a generator means less power to the pump so a somewhat larger gasoline engine is needed.

What An Oil Burner Does
An oil burner must do at least three things just to work at all:
· Deliver the fuel in properly atomized form
· Deliver the proper amount of air with the fuel
· Provide for ignition of the mixture of atomized fuel oil and air

Remember: The oil burner is made up of three systems: The fuel handling, which delivers the right amount of properly atomized fuel, the air handling, which delivers the proper amount of air to meet the oxygen requirement for proper combustion, and the ignition to start and help maintain the combustion process.

What An Oil Burner Needs
An oil burner must have adequate, properly atomized, clean fuel; the proper amount of clean air; a combustion chamber temperature high enough to promote vaporization of the fuel; and sufficient spark at the electrodes for ignition of the fuel and air mixture.

Just enough fuel for clean combustion should reach the combustion chamber. This means nozzle sizing and pump output flow and pressure should be precise. Clean fuel and a clean, clear strainer are essential to proper burner operation. For efficient operation the combustion chamber must be hot enough for proper fuel combustion. This is usually 700 to 900 degrees Fahrenheit. Fuel that is not completely burned exits through the stack as smoke or is deposited as soot inside the heat exchanger.

The blower must deliver the proper amount of air to complement the amount of fuel atomized in the combustion chamber. Electric current provided by the transformer must be adequate to jump the gap between the electrodes. Jumping this gap is called "arcing". This is simply a controlled dead short which produces the heat necessary to ignite the fuel oil and air mixture.

The electrodes may require adjustment from time to time. Electrode adjustments should be made with care. Remember; an oil burner must have clean fuel, sufficient air and ignition spark.

Gun-Type Burners
The most common burner type used in United States-produced equipment, the gun-type oil burner, a design used for home heating and incinerators, is a single unit incorporation fuel pump, blower, nozzle, motor, ignition transformer and electrodes in a single unit. Gun-type burners are also produced in Europe. This unit is then mounted on a separately designed coil assembly.

The Burner Integrated Into the System

The down-fired boiler design popular into European-produced equipment uses a different configuration from the gun-type burner. Shown to the right is the boiler’s combustion area. Air moves around the outside of the coil from the bottom to the top where it enters the air tube and combustion area. The tube and electrode and fuel nozzle assembly are installed and can be removed as a single unit, allowing easy testing and inspection.

European-style or full-featured equipment generally has the burner’s components integrated into the boiler system rather than into a single unit like the gun-type burner design. With this design the blower can be at one end of the coil, the fuel nozzle and ignition at the other, the fuel pump in another location and the ignition transformer mounted with other electronic components.

Remember: A burner, which is integrated into the system, has the same or equivalent components as the gun-type burner; they are simply installed at strategic places in the system.

Fuel Delivery
The fuel pump moves the fuel oil from the fuel tank to the fuel nozzle. The pump uses a gear set to squeeze the fuel through the pump at about 100 psi. Different equipment manufacturers may set fuel pumps at different pressure ratings up to 125 psi or more.

Fuel pumps are basically self-lubrication; the flow of fuel oil through the pump lubricates and cools its moving parts. Operating a fuel pump with no fuel or a clogged strainer will starve the pump. Without the lubricating and cooling effect of the fuel oil, the pump will overheat and seize up. When the pump seizes up, a drive coupling may break or increased demand on the motor will blow a fuse or trip a thermal reset.

The fuel pump’s action forces the flow of fuel through the nozzle orifice into the combustion chamber. The size of the orifice can regulate the amount of fuel pumped into the combustion chamber. Nozzles are generally rated according to the gallons of fuel flow they will allow in an hour. This gph rating is based on a pressure of 100psi. An increase in operating pressure will result in a small but perceptible increase in flow.

Passage through the fuel nozzle into the atmosphere breaks the fuel up to a mist of fine droplets. This misting process is called atomization. For fuel to burn properly, efficiently and completely it must be properly atomized. The atomization process mixes the fuel droplets with air in the combustion chamber. Fuel is atomized to allow more air to surround the tiny droplets and provide a mix of oxygen and fuel sufficient for proper combustion.

Remember:
Fuel pumps are generally set to produce 100 psi.
Fuel nozzle flow ratings assume the 100 psi setting.
Fuel must be properly atomized for efficient combustion.

Improper atomization will result in unburned fuel in the chamber and visible smoking. The amount of fuel flow is controlled by the size of the fuel nozzle orifice. Fuel nozzles are rated according to their flow in gph at 100 psi pump pressure.

A rule of thumb in sizing nozzles for United States-produced cleaners is to use a fuel nozzle producing a flow in gph one-half the system water flow in gpm. In other words, a 2 gpm machine would work with a 1 gph nozzle. For a European-design cleaner this would be a .75 gph nozzle. Boiler inefficiency may cause a system to require a nozzle rated for a flow larger than indicated by this estimating technique. The extra fuel must be consumed to overcome the poor boiler design.

Air Delivery
A fan or blower delivers air to the oil burner. On a gun type burner this fan is mounted on the side of the burner housing. The burner motor drives this squirrel cage type fan. Air bands regulate the amount of air delivered. On an integrated style burner the blower will probably be driven by the same motor as the pump. The blower may be driven directly by the motor or a drive belt may be used. A fiber air tube or bag moves air flow from the blower to the boiler. An air damper is used to control the amount of air delivered to the combustion chamber.

Ignition
The ignition transformer provides the electric spar for ignition of the fuel / air mixture in the combustion chamber. On the gun-type burner the transformer is mounted on the top of the burner housing and bus bars and spring contactors provide power to the electrodes. If the burner is integrated into the total system the ignition transformer is usually mounted with other electrical components and connected to the ignition electrodes with wires much like spark plug wires.

Air Delivery

In a forced-draft pressure-atomizing gun type oil burner, a blower that is mounted inside of the burner housing moves air to the combustion area. The squirrel cage blower is directly driven by a fractional horsepower burner motor, which also drives the fuel pump. Air enters the blower through the bands, an outer and an inner, which may be moved to control the amount of air, which may be moved by the blower. Air adjustments should be relatively permanent and should not change unless the conditions in which the burner operates (available air or fuel type) change.

Note: Air adjustments on some equipment designs, especially those with the fan driven by the pump motor, are made with an air damper instead of with air bands. The air damper is simply a door, which may be moved to regulate airflow. The air damper must be located in the airflow path to the burner and can be located by tracing airflow from the fan to the burner.

Adjusting The Air Bands

To adjust the air bands, simply loosen the screw, which holds the outer band together in its circular shape. Rotate the band until the match-up of the slots in the two bands produces the size of air opening desired. Naturally, the larger the opening size, the more air will be introduced into the combustion chamber.

Note: On equipment with an air damper, air adjustments are made by loosening a locking setscrew and then moving the air damper to create the size of air opening desired. Most dampers will not be visible because they are located inside the air supply ducts. Usually an indicator or lever will protrude from the duct at the point where the damper is installed. In some machines this lever will be located underneath the cleaner.

The Deflector And Air Tube
From the blower the air is forced into the air tube through the deflector, which resembles a small, stationary fan blade with angled blades. Air exiting the air tube passes the deflector in a swirling pattern rather than a straight blast of air. Swirling the air leaving the air tube allows for better mixture of air and fuel for more efficient combustion.

The electrodes and fuel nozzle are mounted inside the air tube at the outlet and of the burner assembly. Air tubes vary in size, depending on desired burner output. Most used in the industry are eight inches long with a circular opening on each end that may be from three inches to slightly over three-and-one-half inches in diameter.

Note: Down-fired burners in European cleaners also have air tubes although they are of a somewhat different shape and are smaller.

Ignition Spark

The electrodes may require adjustment from time to time. Electrode adjustments should be made carefully and only when necessary. Gradual wear will appear at the very end or tip of the electrode. Electrode wear is the result of extreme heat produced at the point of arc contact. The electrode will appear to get shorter and shorter. Wear can continue until the high voltage arc can no longer cross the gap between the electrodes. At this point, electrode adjustment will be necessary.

For a gun-type oil burner the electrodes should generally be set 1/8 inch forward of the front of the fuel nozzle. (This setting may vary for different manufacturers and types). The tips of the electrodes should be ½ inch above the center of the fuel nozzle. This adjustment allows the electrodes to provide adequate arcing or spark for ignition without being in the fuel spray or allowing flame to impinge on the electrodes.

Service Hint: When adjusting the forward setting on the electrodes, care should be taken not to adjust the setting too far forward. This may cause arcing between the electrodes and the deflector plate. Such arcing will prevent ignition and result in excess fuel buildup in the boiler assembly.

Servicing The Electrode Assembly

An electrode assembly is composed of three separate components. The electrode itself is a metal rod that is threaded on one end and bent or curved on the other end. Two of these rods are paired and curved toward each other so that electrical arcing will occur at, and only between the tips of the rods.

Each electrode rod is inserted through a ceramic insulator. The insulator prevents arcing between the back portions of the rod and other metal components. A special nut called a palnut is screwed onto the electrode rod, preventing the insulator from sliding off. To service the electrode assembly, simply remove the palnut and the ceramic insulator will slide off the electrode rod.

While the ceramic insulator is removed, inspect it for chips or cracks. Carbon buildup in areas where the insulator is damaged may lead to carbon arcing or arcing between the carbon buildup and the other electrode rather than between the tips of the electrodes. Any carbon buildup on and around the electrode assemblies may lead to carbon arcing.

The Ignition Transformer

The ignition transformer takes line voltage and steps it up to the approximately 10,000 volts to create the spark that jumps the gap between the ignition electrodes. The voltage and amperage supplied to the cleaning system are not appropriate for creating the needed ignition spark. The pump motor requires 115, 230 or 460 volts for operation. The ignition electrodes for the oil burner, however, will require a much higher voltage (usually 8000 to 10,000 volts) for the ignition spark to arc across the gap between the electrodes.

What The Ignition Transformer Does
A transformer is used to increase the voltage from the voltage from the voltage supplied by the electric utility to the voltage required by the ignition electrodes. The power supplied to a transformer always equals the power provide by the transformer. This basic expression of a fundamental physical principle is expressed as "power in = power out."

A transformer increases or decreases amperage exactly inversely to any increase or decrease in voltage. In other words, if a transformer doubles the voltage of a 20 amp, 115 volt current, the result would be a 230 volt, 10 amp current. Transformers come in two basic types: step-up, which increase voltage and step-down, which reduce voltage. A step-up transformer is used in the ignition transformer role.

The Flip-Up Top
In most modern gun-type burners the ignition transformer is mounted on a hinge on the burner assembly. When ignition transformer swings shut like a door, the bus bars on the transformer make contact with the electrodes. When power is provided to the transformer, a spark is created at the gap between the electrodes. The transformer can be swung back for testing or inspection of the bus bars to see if they are properly aligned. Look for signs of arcing within the burner housing. If the transformer is bad, it should be replaced. Replace with a transformer of the same rated output.