How to Build a Constant Level (CL) Tank for a Waste Oil Syphon Burner

How to Build a Constant Level Tank 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, CL 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.

It is important to keep the surface of the fuel oil at constant level a few inches below the nozzle in the burner. Changes in the fuel level will effect the firing rate and air/fuel mixture of the burner. A higher level will allow more fuel to be drawn into the burner and a lower level will make harder for the burner to drawn in the fuel. I built my burner using a conversion kit from CK Burners. They recommend using a brass float valve part number 4652K11 from McMaster-Carr. Some guys have used toilet tank fill valves or other float valves. Anything that can hold up to your waste oil will work. The brass valve was only about $20, so I followed Craig's advice and used it. It is recommended to to avoid zinc or galvanized parts because it can react with waste vegetable oil.

Almost any small container can be used for the tank. Some guys have welded a custom tank or used plastic tanks, but most use a .50 caliber military ammo can. It's the right size, made from steel and has a locking lid with a seal. Used ammo can can usually be found for $10-$15, so it's hardly worth the effort and time to build one. I already had one so I used the can to build my tank. I like the idea of using an all metal fuel tank and metal connections to reduce the risk of a fire. I have viewed some pics and read a few reviews of how other guys built their tanks. Many placed the feed tube near the bottom of the tank. I wanted to keep all of my penetrations above the oil in the tank to minimize the chance of leaks. Since it is a syphon feed system the fuel line can penetrate the CL tank above the level of the fuel. It does not have to be at the bottom like a gravity fed fuel line would need to be located. I placed the fill valve on the hinge end of the tank, just below the hinge. I located the pick up or feed tube on the side of the tank next to the fill valve, leaving room for the toilet float ball. The valve has 3/8"NPT threads. I used a 3/8" to 1/2" bushing to allow me to use rubber o-rings and electrical conduit nuts to secure the parts where they exit the tank. The pick up tube is 3/8" steel pipe. CK Burners recommends that the feed line should be at least 3/8" and should be kept as short as possible. It's probably overkill, but I added and overflow/vent fitting to vent the CL tank back to the fuel tank. In the unlikely event that the fill valve sticks and the tank floods the overflow should help to minimize leaks by routing the extra fuel back to the main fuel tank. Of course some fuel will leak from my tank penetrations and from the burner nozzle, but I hope the vent will reduce the mess and allow the tank to breath since the lid is sealed. All three fittings have 3/8" flare adapters so I can 3/8" copper fuel lines. I used a step bit or uni bit to drill the holes in the ammo can. They can be pricey, but Harbor Freight sells them at a good price and they hold up well.

Most CL tanks are gravity fed from a standard 275-300 gallon fuel tank or even just a 55 gallon drum. I wanted to use the pump on my burner to feed the CL tank for a few reasons. I haven't installed a 275 tank yet, so I'm using a steel 55 gallon drum as a fuel tank. Just like making the penetrations in the CL tank, I did not want to have a fitting on the bottom of my drum that can cause a leak. Using the standard burner pump with a two pipe set up ( supply and return lines ) will enable me to use a standard home heating oil fuel filter on the supply line and it will allow me to draw fuel from the top of the drum with a stand pipe. A two pipe system is also very tolerant of air. It will quickly bleed the air from the lines when a new filter is installed. I reduced the feed pressure to the high pressure port on the fuel pump and plugged the high pressure port with a npt fitting. I placed a tee in the return line to feed the CL tank. The float valve in the CL tank can open and close as needed while the extra fuel can just flow through the return line back to the drum. Do not supply your CL tank directly from return line without a tee. The float valve can create excess pressure in the return line and cause the seals in the pump to fail, flooding the burner with fuel. If your oil burner is above your fuel tank you can build an overflow CL tank that doesn't require a float valve. Just install a return line from the CL tank to the main fuel tank. Since the fuel tank is below the CL tank you will need a pump to bring the oil up to the CL tank. Gravity will take any excess fuel from the CL tank back down to the main tank through the overflow/return line. Since my tank is in the basement with the heater I needed to use a float valve.

Be sure to view all of the photos attached to this article. This is another case where a picture is worth a thousand words.