A black human hair is 56-181µm

Most of the human hairs that I've measured fall between .002" and .0025"...........50 to 62 µm...........but, I'm sure you can find different data if you goggle it.

There you go again guys. Splitting hairs.
The original question or how I interpreted it was the specific injector nozzle size opening. It is large but primarily filled by the tapered needle. At a certain pressure called the pop pressure the needle is hydrallically forced open. That does not mean the needle is still not obstructing the hole to some degree. Theoretically all fuel above that pressure is expelled. The amount of fuel above the opening pressure may have a lot to do with how far it opens in concert with how far the pressure is elevating above the initial opening or pop pressure. Again in theory the needle probably tries to balance the loading or buffer it bringing the pressure down to a median operational average..
Thats why increasing the element size in the pump gives more flow. Plus simutainiously a larger combined opening cross section between the needle and seat. The needle is only responding to the need to attempt to average the pressure after it opens. So the actual passage size is the space between the needle and it's seat above the nozzles end hole. It will and does vary. depending on viscosity of the fuel and other factors. If it is pushed too hard the nozzle end size will have to be further increased to cope with it for the engineered time frame of expusion of the fuel. If not perhaps the pump pressure goes too high.
Particles of any size are going to affect the ability of the needle and its seat to shut off cleanly. If they do stick either by composition or pressure between the needle and seat they should be washed through on the next cycle. Thats one strong pressure washing operation going on in there.
The higher the pop pressure of an injector probably the smaller the cross sectional area develops for the fuel to flow through with the same pump.

It never fails to amaze me how they got it all together long ago to actually make it work and last in service. Probably every last thing was hand lapped before machine lapping came along.
In respect to the people who slaved over the designs and fabricators back then. It is not unreasonable to do our part by putting the cleanest water free fuel through their system as practical or possible. This little episode sure beat me trying to measure the physical opening diameter of the nozzle hole itself. It is quite large in comparison to the minumin width of the actual passsage the fuel usually sees. This whole thing is getting or has gotten a little hairy.

The fuel filter on the car is a standard item, guess a 10uM....

I filter all the fuel prior to the car using 'Aqua' 10" filters, first 20, 10, 1 and then 1uM Absolute...(These are allegedly according to the makers, the sort of filter that are capable of removing 'cryptosperydium' bacteria etc from water)

As has been said, WVO contains all sorts of crud. During the making of BioDiesel, Most but Not All comes out anyway. Whats left apart from the usual soaps that have to be dealt with, who knows, But best filter properly. There's never been a case of 'Too Good' a filtered fuel causing a problem that I know of, and since I have adopted this filtration I have never had a case of a blocked vehicle fuel filter....

Here is an interesting item on fuel-filtration by 'Racor'.... It specifically mentions a 1uM Running Clearance of pump internals....http://www.encyclopedia.com/doc/1G1-72983644.html

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Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

What material are the Aqua 10 filters made of? Are they Cord/string wound filters? How much did the filter housings cost?

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84 300D, 82 Volvo 244Gl Diesel

They are of the 'Melt-blown' variety, a 'depth' filtration media...

Check out here, where I get mine from...http://www.mearesolutions.co.uk/

UK based, but I guess you must have summit similar there....

__________________
http://i190.photobucket.com/albums/z...0TDnoplate.jpg

Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

I understand they are polypropholyene I believe. Are these filters on your CAR or are you filtering the fuel before it goes into the tank.
In the US the filters you describe can cost as low as $1.59 (10 inches long) but for use on a vehicle you need a steel or aluminum filter housing and they are expensive.
When I started my searches I was looking for a 1 micron filter element that would be suitable for a by-pass oil filter that did not cost $30 or so as the Amsoil spin on dose. I looked into the Aqua type filters and found that they have String/Cord wound 1micron filters (also used for water filtration) the Cotton and Polyester Cord ones appear to be able to with stand the heat. The Cotton ones appear to be the best balance of price and suitability for the job. Problems: The sizes their out side diameters are 2 5/8 inch or less and have lengths of 9 5/6". 10", 20" on up to 40" and the long expensive filter housing.
I had not until reading your post thought to use them as a fuel filter.
There is a By-pass Filter Company; Gulf Coast I believe that uses a 4 inch outside diameter Cord wound filter but again the filter housing is expensive. So my searc continues.

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84 300D, 82 Volvo 244Gl Diesel