How about a sight tube?

I forgot to draw my sight-tube on the diagrams above.

A sight tube is very handy to show you volume when filling.

It can also show you the pump performance, (when the pump is not performing well, perhaps is it blocked, or is working with thick, cold oil, the level in the sight tube will be higher than normal).

You can use it to see the colour of the tank contents, settling rates etc.

My sight tube has a tap at the bottom so I can isolate it. It is open at the top, going about 20cm above the max liquid level, so is not pressurised and won't overflow.

The same simple PVC tube has lasted me 2 1/2 years of heavy use.

sight tube


Here's the top end of the sight tube. I've pushed a large funnel in there so I can return any drained-off samples to the tank. If I slightly close valve V2 while the sight tube tap is open, I can empty the sight tube completely.

Notice the max level I fill to, this is including methoxide. The level never quite comes up as high as the venturi.

sight tube top

State diagram for the New Eco-System

This table tells you about the status of each valve, the heater and pump at various stages of the process.

State diagram: Green = open valve, or power applied
Step Heater Pump V11 V2 V3 V4 V5 V6 V7 Notes
Oil in                   Pre-filtered
Heat Oil 50C                 Check level before applying heat
Dewater oil 90C                 Switch to 50C when O/P slows
Cool oil 50C                 Titrate oil now. Empty collector. I use NaOH
Inject Methoxide           Adj.       Allow 20 mins to inject.
Reaction Stage                   Allow 90 mins at 50C
5% Prewash                   Mix 15 mins
Settle Glycerol                   Wait 90 mins
Drain Glycerol                   Drain slowly to avoid whirlpool
Distil methanol 90C                  
Drain Biodiesel off           Adj.     Ensure heater is OFF first! Caution - Hot! Wear breathing apparatus.
Take sample and perform 23/7 test before discharging whole batch.


Description of what's going on in the Process...

1. Oil In

Remove the glycerol collection tank from V3.

Turn on the pump, and open valve V6 only. Shut all other valves.

Your oil storage tank is piped to the 'Oil In' port. It should be above the level of the pump if your pump is not self-priming.

Your oil must be free of large chunks of debris, so your pump doesn't jam. There is no need to filter it (all the fine bits and pieces will end up in your glycerol layer). It must have no visible water in it.

Open valve V1 to load oil into the reactor. Shut valve V1 when the oil level in the reactor reaches 75% of its capacity.

This will leave the correct amount of space for the methoxide which you will add later. Don't under-fill the reactor - too much air space will affect your distillation performance.

2. Heat Oil

Open valves V2 and V6, with the pump running, to recirculate oil around the tank.

Double check that your reactor is filled with the correct amount of oil. (75%)

Switch on the heater now, but ONLY if you are CERTAIN that the reactor is filled to 75% AND that the pump is running.

It is dangerous to add heat if the level is too low, because you may expose the heating element, which would then overheat and ignite the oil in the tank. You could have a tank explosion.

You must run the pump whenever the heater is on, so that there is a steady flow of oil to cool the element.

3. De-water Oil

Dry oil is vital. Wet oil can create a soap-gel in your processor, which can easily block your pipework. Most used oil contains a large amount of water, even though it may look clear, so I recommend you de-water oil every time. This process is unique - you can de-water your oil in the processor, without any smelly, oily steam being given off. Here's how...

  • Open V2 and V6 and V7
  • Switch on the pump
  • Heat the oil to 90C
  • Circulate cold water thru the condenser

When the oil reaches 90 degrees C, switch everything off and let the oil settle for an hour. It will now be thin because it is hot, so any particles of food will drop quickly to the bottom of the tank. After an hour, carefully open V3 and drain off 5% of the tank volume into a container (leaving the tank 70% full of oil). This drained off oil will contain most of the damp food particles which settled out. You can leave these to settle, then pour the remaining oil back into your WVO tank (not the processor).

Switch on the pump.

The venturi will drag dry air from the bottom of the condenser into the wet oil. As the oil sprays into the processor, it will carry the air with it, which becomes filled with moisture from the oil. The air now escapes out the top of the reactor and down through the condenser, where the water vapour condenses and drips into the distillate tank. The now dried air then goes back up to the venturi to be returned to the wet oil, for the process to repeat until the oil is dry. (You can fill the airspace with CO2 or N2 if you want an inert atmosphere)

You don't need to have a fresh supply of water for the condenser. I use a 45 gallon drum of rainwater, which I pump thru the condenser and back into the drum again, in a closed loop. I use a household heating circulator pump for this. A few litres a minute is enough if your heater is rated at 3kW.

4. Cool the Oil

Maintain circulation of water through the condenser.

By the time the oil has cooled to 50C, it should be dry enough for you to start the reaction...

Take a sample of oil from V3, leave it to cool to around 20C and titrate it, to see how much lye you will need to add to the methanol.

To be safe, unplug your heater completely now, so that there is no way you can accidentally switch it on. Click >here< to see what may happen if you accidentally switch your heater on, while the element is exposed to methanol-laden air.

Close valve V7, and switch off the water pump feeding the cooling water thru your condenser.

Empty the water which collected in the distillate tank. You can put it into the cooling-water reservoir.

Refit the distillate tank.

Fit the glycerol collection tank to V3.

5. Methoxide mixing and injection

Maintain circulation of water through the condenser.

You titrated your dried oil, so can now make up your methoxide.

Calculate how much oil is in your tank. Multiply by 0.22. That is how much methanol you must measure put into the methoxide tank.

If you are using NaOH, you will need 5 grams of NaOH as your base amount, plus titration amount, for every litre of oil. If you are using KOH, the base amount will be 7 grams. Pour the NaOH or KOH into the methanol and agitate until it is all dissolved.

Connect the methoxide tank to V4 and the vent.

Switch on the pump. Gradually open V4 to allow the suction to draw methoxide out of the carboy.

Aim for a feed rate slow enough so the methoxide is fully dosed into the reactor over a period of around 20 minutes. If you dose too fast, the methoxide may flood into the processor so concentrated, that it just floats on top of the oil. You may also get an unwanted gel forming in the piping or tank, which can cause blockages.

As the tank fills up, the air it displaces (the same volume of air as there was methoxide in the carboy) passes thru the condenser and back into the methoxide carboy. The condenser helps to reduce any outgassing of methanol - don't worry about the drips of methanol which collect in the distillate collection tank. It will be very little, and will not affect your reaction. At least you have saved the methanol, rather than venting it out to the air.

When the dosing is complete, shut off valve V4 and stop the flow of cooling water thru the condenser.

6. The reaction stage

V2 and V6 should be fully open. Check that V4 and V7 are closed, and that the heater is OFF.

Allow the pump to run for around 90 to 120 minutes, which should be long enough for your reaction to reach its peak of conversion from oil to biodiesel. Your temperature should remain at around 50C throughout the reaction, if your insulation on the tank and piping is adequate.

After the reaction period has elapsed, switch off the pump, close V2 and carefully remove the methoxide container - be careful not to spill any methoxide on yourself, wear suitable body protection.


7. The 5% prewash

Fill the methoxide container with water; the amount should be 5% or 1/20th of the amount of oil you dosed the tank with.

Re-connect the container, open valve V2 and switch on the pump. Open V4 fully to allow the pump to draw the water out of the carboy. You can close V2 to allow the pump to draw water fast out of the container, as it is not important for it to be gradually introduced.

When all the water has been pumped out of the container, close V4 and fully open V2. Allow the pump to recirculate the mixture for around 15 minutes to ensure the water has been evenly blended throughout the mixture.

When the 15 minutes have elapsed, switch off the pump and close valve V2. The water will tend to attract soap from the biodiesel, along with glycerol and caustic soda, and together they will drop to the bottom of the tank, where they can then be easily drained off, leaving semi-purified biodiesel behind ...

8. Settle the glycerol

Glycerol and water are both denser than biodiesel so will drop to the bottom of the reaction vessel, carrying with them most of the soap which is formed as a byproduct, and the catalyst. Allow 90 minutes or more for this settling to happen. Be aware that if you leave the processor too long, say more than a few hours, the settled glycerol in the pipework may form a thick gel, especially in cold weather. This can block your pipework and jam the pump.

To prevent this from being a big issue if you need to leave the processor like this for a few hours, you can part-drain the pipework after around 30 minutes. Ensure V2 and V1 are closed, and V6 is open. Open V3 slightly, to drain off the dark glycerol in the pipework. Stop draining when you see the liquid colour turn much lighter, as this will be biodiesel, which you don't want to drain off just yet.

9. Drain the glycerol

Slowly open valve V2. open valve V3 slightly to allow a slow trickle of glycerol to fall into the glycerol collection container. Depending on your oil quality, you can typically expect to collect from 15% to 25% of the volume of the oil you used, as glycerol. You will be able to see when all the glycerol has been drained, because the drained liquid will suddenly become much lighter - biodiesel. Close V3 completely now and wait a couple of minutes. Re-open V3 very slightly and you should be able to drain off a little more glycerol. When no more glycerol flows, close V3.