Thoughts on fuel filters

[fisherman]

I, and some others, have long considered that many fuel filters are rigged backwards, particularly CAV. The fuel is fed down through the element, and the muck sits on top, when it would be better to have the muck underneath where it may drop off, and even be drained out. I have a sedimenter, the fuel comes in at the top, over a cone, and out through the middle, the muck sits on the cone and has to be shaken down to the drain off. Surely it would be better to let the fuel find its way up around the edge of the cone. My friend tried connecting up in reverse, but found to his frustration that there is a constriction, a step down in bore, that caused a blockage on the (now) inlet side.

He has now made a filter from an alloy cap and base, with a perspex tube, two rings inside. The fuel is delivered to near the bottom, and finds its way round the two rings to the outlet. Total cost about £20 and a few hours at the lathe. I think that a CAV filter could be modified satisfactorily with a bit of judicious drilling and maybe a perspex tube and longer centre bolt.

I also remember seeing an outfit, probably the result of similar problems, there was a half inch bore steel tube from the tank to just near the engine lift pump, and a 'T' with a drain on the end.

 

[smeaks]

Cav filters 296 cost £2-£4 and are very disposable... Better filters cost more but cav filters are cheap and work.

 

[duncan99210]

The filer elements are too cheap and easy to change to be worth worrying about.

 

[pvb]

I, and some others, have long considered that many fuel filters are rigged backwards, particularly CAV. The fuel is fed down through the element, and the muck sits on top, when it would be better to have the muck underneath where it may drop off, and even be drained out.

Whilst you may find it confusing, there's a good reason for it. As the fuel passes through the filter, tiny particles of water agglomerate into larger drops, which can fall to the bottom of the bowl.

 

[fisherman]

Aha! Except the water sits on the glass but not the ally base with the drain plug, but I accept the theory.

In re crosland filters above, yes they are cheap, no problem. I use a Delphi betweeen that and the injector pump, finer than the crosland 522, but not the finest, the supplier said some engines refuse service given the state of fuel these days.

 

[KellysEye]

> and the muck sits on top,

That's odd, filters should have a small, gap betwen the filter and the filter housing so the filter takes out the dirt. If the bowl gets dirt in it then the filter is blocked and needs changing fast. If the problem you have is the CAV design then change to Racor.

 

[Rossynant]

Yes, it's odd, in heavy duty old engines there were sometimes separator/filters with no 'filtering element' as such to change (only to clean when stuck) and those have been throwing off most of contaminants at bottom, to be drained. Those kept most dirt from the final filter on engine, which was only changed at leisure, when servicing, but not because it got blocked while on the way. Not to be seen now
Racor is probably best bet, still have separator/filter working in this mode, and fuel fed to filter from downside - this I found with pictures:
http://www.ariel-cd36.org/dualracorbig.jpg
http://www.maesco.com/products/racor/r_tbn_intro_hwy/r_tbn_intro_hwy.html
http://www.maesco.com/products/racor/r_tbn_intro/r_tbn_intro.html