Selecting an Air Compressor (from Free to Expensive) for a Waste Oil Syphon Burner

Working on a heater is dangerous. Modify your heating system at your own risk. Do not try to work on a heater if you do not know what you are doing. You can be electrocuted or cause a fire.

After getting through one heating season using a waste oil pressure conversion I wanted to upgrade to a syphon conversion to have more control over the combustion and hopefully less maintenance. Since a syphon conversion is made up of three basic parts, this article is one of a three part series that covers the syphon burner, constant level tank and the air compressor.

See the other parts of this series of articles by clicking on my screen name or visiting my blog.

In a nutshell a syphon burner works like a fertilizer sprayer that attaches to a garden hose or an air powered paint sprayer that a body shop would use. They both function the same way. The air or water are forced through the spray can where the fertilizer or paint is drawn up the feed tube and broken into small droplets as it exits the spray nozzle. Portable "torpedo" heaters use this principle. There is a Yahoo group called Altfuelfurnace that has all of the details on converting a standard home heating oil burner to run on waste oil. Craig from CK Burners make a conversion kit. He offers everything from basic parts to complete kits.

A syphon burner requires compressed air to atomize the waste oil into small particles to allow them to burn cleanly. There are several ways to supply air to your syphon burner. If you have a large shop compressor you just need to run a line to the air pressure regulator on the burner. A cheap way to supply the air is to use a small pancake compressor. Harbor Freight and other import suppliers have them. They are cheap, but they are noisy, which can be a problem if it is installed inside the house. The cheap imported compressor can have issues with longevity too.

A lot of guys use a Gast compressor. They sell on eBay for about $100. They make less noise than shop compressors and have a good reputation. There are parts available online to rebuild them when they wear out. I have a used Gast pump and I set it up to pressurize a small air tank but it would not cycle correctly. I used an inexpensive pressure switch for a shallow well. It does not have an internal pressure relief so the compressor could not start against the pressure from the tank. It does run well without the tank and pressure switch. I have a 35 psi spring loaded pressure relief valve to limit the pressure. The downside is that the compressor must run constantly anytime the burner is operating. The upside is a simpler set up with less parts to fail. I found a crank case breather in the high performance isle at my local auto parts store. It makes a nice intake filter to protect the compressor. I mounted the run capacitor inside of a plastic electrical job box and mounted it to a length of wood with the pump.

I am experimenting with another, cheaper option. I get a good feeling from using free "junk" or salvaged parts to build my projects. I had a couple old refrigerator compressor motors around because I used them to draw a suction on my waste oil collection tank. I used one to pressurize my burner but it was only able to make 4-5 psi and the burner would not fire. I need 10-12 psi to get a clean burn in my heater, so I just added a second compressor. I can now supply 10-11 psi to my burner. I mounted both motors on a piece of wood. One motor had the factory rubber mounts. I used some scrap rubber hose to make a vibration resistant mount for the other motor. I have test run these compressors for a couple hours and they worked well, but I don't know how long they will last. I plan to add a few drops of light oil to the intake of the compressors to make up for some of the lubrication that the freon provides. Since I am not working the compressors too hard by building high pressure or vacuum, I think they should hold up pretty well. If not, they are cheap enough to replace. Beside the cost (FREE!) these motor run silently compared to any other compressor. The only noise is the excess air escaping from the vent. I have found that beside running very quietly these pumps also run much cooler than the Gast pump or a shop compressor. I plan to build a duplicate double compressor set up and have it ready to go into operation if my first one fails.

The compressors will have a suction and pressure line. They probably won't be labeled, but it is easy to figure out which is which. Just plug it in and put your finger over the tubes to feel if it is sucking in air or pushing out air. I slipped a rubber air line over the copper tube and secured it with a hose clamp. I used a NPT tee with hose barbs to connect the two supply lines together. You should add a small air filter to the suction line. A foam sponge filter like a lawn mower uses should do the trick and it's washable. I have thought about including a automatic oiler for an air tool to the suction port, but I haven't done it yet. I never oiled the motor I used for my wvo suction tanks. It took 2 years of regular use before I burned out my first pump and that pump had a hard life. I used it to draw about 28" of vacuum on a 80 gallon tank. It didn't quit running, it just began to draw less and less vacuum in the tank.

Window air conditioners, freezers and refrigerators all have similar compressors. An old large window a/c unit may be able to supply your burner with enough air on it's own. These compressor motors require a capacitor. It's best to remove your motor from the donor appliance with as much of the wiring intact as possible that way you don't have to figure out how to put it back together. They might run without the capacitor but they probably won't last as long. My motors had a built in low pressure switch. The switch prevents the motor from running if the refrigerator losses it's freon charge. I bypassed the switch by moving my "hot" wire from the switch and placing it directly to the compressor (see photo). These motors don't provide a lot of volume but they can build a lot of pressure, so be sure to use a relief valve along with a pressure switch or other safety device. If you are going to salvage a motor from an appliance do not vent the freon into the air. It's a violation of the clean air act. If the charge has already been lost than you can cut out the compressor and the wiring. If not the charge must be recovered and recycled.

I used a water trap and a relief valve along with the air pressure regulator from CK's kit. I mounted a spring loaded relief valve on the bottom of a vertical section of black iron pipe. I hope that most of the moisture in the air will collect inside the pipe and run down to the valve where it will be automatically vented out (see photo). The rest of the moisture should be eliminated by the water trap where it can be bleed out through the drain fitting.

Please view all of the photos with this article.