Picking the correct nozzle takes a little experience, but hollow and semi-solid nozzles usually give a shorter and wider flame pattern than solid nozzles. If you have a nozzle recommended by the manufacturer, use it first. Pick the correct size nozzle from a nozzle flow chart.

I like to set American burners between 140 and 150 psi and Riellos between 160 and 200 psi. The increased pump pressure will give you better atomization and a cleaner burn. I have not found any negative aspects when increasing pump pressure. All nozzles should be tight in the adapter. The correct torque is 100 inch-pounds, which is about as tight as the average person can get it using two 6-inch wrenches with one hand.

On initial fire off, I look at the fire and set the burner by eye to get what I believe is a clean fire without smoke. At this point, take a smoke test and a CO2 reading. I then adjust the burner to obtain the highest possible CO2 with just a slight trace of smoke, which is done by gradually reducing the air and taking smoke tests.

When the point of a slight trace is found, I record the CO2 reading. At this point, I also check for flame shape and impingement (I realize that this is not always possible) and adjust the over-fire draft to the recommended level (usually 0.02 inches water column). I do not like to leave burners on the edge of smoke.

I always record the final numbers for smoke, over-fire draft, breach draft, CO2, gross stack temperature, net stack temperature, and steady-state efficiency.

The last thing that I do - and probably the most important step - is test the oil burner safety lockout. When I do this, I do two things. The first thing I do is record the ohm reading that I get on the cad cell. Ideally this should fall between 200 to 800 ohms. The second thing I do is to remove the cad cell and fire the burner. I then record the number of seconds it takes the burner to go off on safety.

This should be part of everyone's routine every time they work on a burner. Having this information on file will be your protection if the control ever fails.

Always file for a permit and an inspection if available in your area. In today's lawsuit-prone society, it is always better to protect yourself, which is why we have to add this final line. Remember, these recommendations are placed here for your evaluation only.

The Advantages Of Pre-Purge

Have you ever wondered why one burner seems to operate so much cleaner than another? It can't be burning any cleaner - zero smoke is zero smoke, right? The big difference is pre-purge.

During start-up of a burner without pre-purge, the oil valve in the pump opens at about 2,400 rpm. At this point, you only have 80 percent of the required air available. The end result is smoke (sometimes higher than No. 6) until everything gets ironed out.

You might say that it is only a few seconds and won't make any difference, but let me remind you that the average oil burner starts thousands of times a year, and soot is accumulative. Now if you use pre-purge, the burner has time to come up to speed and some draft will be established. The end result is a sharp, clean light off with close to zero smoke.

Adding pre-purge is relatively easy and inexpensive. I just install an oil valve and add a 5- to 10-second electronic delay. These electronic delays are inexpensive and can be purchased at any supply house where A/C controls are sold.

Pump Pressure

The main reason to raise pump pressure is the better atomization it provides. Better atomization means smaller droplets with better ignition and a cleaner burn.

Spray angle - Once the spray pattern is established, raising the pump pressure will not actually change the spray angle. However, the fire shape (in a flame retention burner) will give the appearance of increasing the spray angle. This is because the smaller droplets are being consumed at a much faster rate, thereby giving a much shorter fire. The smaller droplets also allow the retention head to pull the flame back a little more, which results in a slightly wider flame. This is more apparent with hollow and semi-solid nozzles than it is with solid nozzles.

Spray pattern - As the pressure is increased, the spray pattern becomes better defined.

Flow rate - The flow rate increases as the pressure increases but not as much as one might think. A one-gallon nozzle will produce 1 gallon per hour (gph) at 100 psi, but it will only produce 1.41 gph at 200 psi. The formula for calculating flow rate is: The square root of (new pressure divided by 100) multiplied by the nozzle rating. In this example, 200 psi ÷ 100 = 2, and the square root of 2 is 1.414. If a one-gallon nozzle is used, 1.414 x 1 = 1.41 gph. It is much easier to use a nozzle chart provided by either a nozzle or burner manufacturer.

As far as I can tell, increasing the pump pressure and reducing the nozzle size accordingly will only give positive results (with cold oil it may become necessary). However, it should not be considered a cure-all.

Publication date: 12/15/2003