Join Date: Jul 2000
Thanked 176 Times in 165 Posts
Rep Power: 17
Re: diesel filter size 2 micron or 10?
At constant pressure/vacuum a 10然 Racor will filter at a rate of 5 times the amount of fuel than with a 2然. Filters are 'sized' based on GPM vs. 'differential pressure across the filter'. Filtering takes 'work'. So, in a system that develops a maximum vacuum (or pressure) by its lift pump using a 2然 instead of a 10然 .... you will get only 1/5th the flow of fuel oil. ..... and this relates to only clean filters and not filters that have trapped debris.
If for some reason you NEED (and you shouldn't) to filter with a 2然 instead of the 10然 to get the same amount of oil flow, you will need to increase the SURFACE AREA of the 2然 by 5 TIMES.
Without increasing the filter surface area AND if there is sufficient debris in the oil, that 2然 will also 'choke' with debris at 'more' than 5 TIMES FASTER than a 10然 .... simply because in nature there are exponentially more smaller sized particles than larger sized particles. Putting an undue load on your engine's lift pump (5 times more vacuum needed to deliver the SAME amount of fuel) by using a 2然 instead of the spec'd 10然 will increase the potential of breaking the diaphragm in your engines lift pump.
However in your case, the average RACOR is soooooo 'oversized' for small hp diesel engines that I would guestimate that the filters are not the cause of you not reaching max rpm in your engine .... check for too tight stuffing box, wrong prop pitch, errant rpm gage, etc.
Best way to check rpm is with an optical rpm gage vs. the flywheel; most 'tachometers' on small boats are usually in great error - either use a mechanical or optical tach.
There are other reasons why a 2然 should not be used, but the above should be sufficient 'for starters' on a sound technical filtration basis.
Last edited by RichH; 07-08-2012 at 01:22 PM.