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There are a number of places in the process where biodiesel filters should be used.
The first of these is on the infeed oil. A number of people believe that it is necessary to filter the infeed oil down to a very fine particle size. Personally, I remove the big particles, the fish heads, etc. I use a 1 mm mesh screen to remove these particles.
Once the infeed oil has been filtered and fed into the biodiesel processor, it is not necessary to filter it again until just before it is transferred into final storage, or it goes into a vehicle.
Duda Biodiesel has a selection of filters available.
A number of different types of filter can be used.
Sock filters look just like socks and are usually used in conjunction with a special housing. they can also be used in a specially made frame. There are many manufacturers who will make a sock filter up to any size, and they're available in many different micron ratings. Sock filters are useful for filtering the raw oil, but only have limited function in final filtering.
A filter mesh can be placed over the infeed tank and the raw oil can be poured through this. A mesh size of 1 mm is adequate. A good material to use is commonly available mosquito or fly screen. Other good materials to use are stainless steel mesh and plastic mesh.
There are also manufacturers who manufacture special plastic tops that fit on 200 liter drums as well as buckets. These filters work very well and make filtering simple.
As water filters are commonly available, they are often used for filtering biodiesel. There are however a number of issues to watch out for.
Spin on diesel filters are the best choice for final biodiesel filters. If the filter is suitable for low sulfur diesel, then it should be just fine for biodiesel. There are a number of manufacturers who sell special biodiesel filters, but these are generally not needed.
It is good design practice to a have a water trap in the final filter system. Putting a 10 micron spin on filter with a water trap in series with a 5 micron or less final filter works very well. I like to filter the biodiesel as it comes out of the storage tank, just before it goes into the vehicle.
Most auto spares shops will have a selection of spin on diesel filters. Remember that you will need the top housing as well as the filter in order to use them.