Primary Filter Micron Rating?

[dickh]

Have had to replace my Primary filter 3 weeks ago because it was blocked. Fine, engine now back to full power. But it got me thinking about Micron ratings - I remember talking to a very helpful guy at Sabre Diesels(Perkins) who had advised that the Primary filter should be 20-30 Micron and the Engine filter 5-10 microns. As I have always used Fram/Crosland/Delphi 296 filters I checked up and they all are betwen 6-8 microns and no-one appears to do a 20/30 micron filter of this size. The only ones I can trace are by Racor, who of course are much more expensive.
I replaced both filters, took them home and cut them open - only the primary filter was contaminated, the engine filter was quite clean, which strikes me that the primary was doing all the work and what the Sabre engineer said was a lot of good sense.
The Primary filter is the standard LUCAS/CAV type.
Does anyone else have this problem? It's going to be a drag to renew the filter halfway through the season, this is the first time I've had this problem -
Oh and I've dosed the fuel with S****N !


<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[seaesta]

Hi Dick
Filter Micron ratings are interesting. I was a mobile diesel equipment engineer for a few years and saved the company a fortune by sorting out filtration issues. Micron ratings are either "Nominal" or "Absolute". Absolute means the size of the largest holes and Nominal means the size of a typical hole. Absolute filters tend to be the best quality and typically used in high performance hydualics where the inclusion of particulates leads to degradation of performance by abbrasive wear (oil travels at a fair speed through appertures with 200 bar pressure difference across them and any muck acts like grit blast). You can go too far with filtration - I once put in a filter that took out the larger viscosity regulating molecules from an oil. Nominal filter ratings are pretty meaningless and only good for comparison purposes
If your primary is catching muck then it is doing its job - especially if the secondary remains uncontaminated. Why not have a bifurcated primary so that you can switch between filters or install a larger capacity filter or get cleaner fuel?
Martin

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[dickh]

Martin,
Thanks for the reply. not sure wether the ratings I got from the manufactures were absolute or nominal - they didn't say. Clean fuel could be an issue, I filled the tank at layup time last year and for various reasons the boat has not been used much - in fact I've barely used ½ tank(8 gallons).
Fitting a twin filter is a good idea, I will have to investigate this. I have considered removing the tank and giving it a good cleanout but as it is 17 gallons and sits behind the engine, I would have to remove the engine to get the tank out!!
I can get a larger capacity filter and this is an option.
Another option is to fit a RACOR conversion kit with a 20 micron filter and the normal filter on the engine.


<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif