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Filtering WVO before using it to make biodiesel is very important. There are many
different types of filters to be found,
and a few different methods of filtering as well; these are discussed below.
Heating the oil:
Heat the oil up to 160°F before you filter; this speeds up the process of filtering WVO, and will not clog the filter with thickened oil.
You can pre-filter using an old t-shirt:
Get a 5 gallon bucket, put a few 2 inch holes in the bottom, drape the t-shirt in it, attaching it to the top of the bucket with the lid (hole cut out on top). Pour the oil through the hole on top and have something to catch the oil beneath.
When buying a filter, get a 200 or 400-micron filter to get the crispies and other large food chunks out. The higher the micron number, the larger the filter holes.
Gravity Fed Filtering:
WVO is generally gravity fed through filters with the higher micron ratings since the oil will flow pretty quickly through these. This is either accomplished by hand pouring the WVO through the filter, or setting a tank of WVO above a catching tank, allowing the oil to flow down through a filter.
Before you filter out the really small stuff, it is a good idea to
De-watering before fine filtering will help get out stuff that may clog your filters prematurely. Often, de-watering is done by heating and mixing simontaineously. Over time the water will evaporate out.
Filters with a low micron rating allow the oil to pass through very slowly when gravity fed. Therefore, the finer filters are are often pumped to speed up the process.
Oil can be pumped through bag filters as long as they are enclosed in housing.
It is recommended that WVO be filtered down to 5 microns, so the finished biodiesel will not damage the engine.
If patience and space allow, you could do a mix of settling and filtering WVO. Store enough WVO so that it can settle for 2 weeks. Pump off the top 90%. On the bottom will be the vast majority of the crud and water. It will still need to be put through a very fine filter as a precautionary measure and be tested for the presence of water. Doing this will save time and money by not having to build an elaborate filtering system and change large amounts of filters.
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