Hot swap fuel pre-filters

[noelex 77]

The ability to hot swap primary filters is a valuable option that is worth considering.

However, I sometimes see this implemented with small primary filter housings. These can clog very quickly. I have seen boats with only a moderate diesel bug problem where each new element provided less than 15 minutes run time before it was overwhelmed.

Avoiding diesel bug problems is obviously the best defence, but it is wise as a backup to consider a filter system that could still provide a reasonable run time in the event of a problem. Two small primary filter units will not necessarily achieve this.

Large filters have a enormous advantage in this regard.

Look at the difference between the popular Racor 500 series and increasing this just one size to a Racor 900 unit. The table below shows the difference before these filters clog enough to stop the engine running. For example, if you take the 4psi limit with a Racor 500 series (top graph), the engine would stumble when the filter had trapped 62 grams of material. It would take 270 grams to do the same to the larger 900 filter (bottom graph). So a single 900 filter is the equivalent of more than four 500 sized filters.

The Racor 500 series is already a reasonably large primary filter, but many boat owners fit much smaller units not realising that it takes very little foreign material to clog these units. The ability to hot swap the elements even with a reasonable quantity of spare elements still only provides a very limited run time in the event of an issue.

Fit a dual hot swappable system, or even better a day tank system, but also consider implementing this with larger filter housings if this feasible.

[daletournier]

Originally Posted by timb7734

Probably this has been covered before ad nauseum:

Per Steve D’Antonio and many manufacturers:
The average 2-micron secondary filter is especially efficient at capturing millions of fine particles until called upon to also capture larger gravel-sized particles as well. The reason for this is straightforward; in spite of their absolute-sounding ratings of 2, 10 and 30 microns, these filters do not possess an absolute ability to capture all particles of their respective ratings and larger. Some larger-sized dirt inevitably slips through. However, because of a phenomenon known as micro-caking, as the filter begins to capture some contaminants, it becomes more efficient at capturing more of the smaller particles — the dirt actually becomes part of the filtering process. If, however, both large and small particles are included in the mix, then the micro-caking process is hindered; the larger “gravel” leaves holes in the caked surface layer, allowing some debris to pass through the (secondary) filter. Picture a bucket with a few holes placed in the bottom; if you pour fine sand into the bucket, some of the sand will filter through the holes, but eventually the sand will capture more new sand than is filtering through the holes. If, however, you poured a mixture of fine sand and gravel into the same bucket, the gravel would keep pathways open for the sand to continue to filter through to the holes in the bottom.

Additionally, operating a 2-micron element as the primary filter means, in theory, all or most of the contamination will be captured in this element and virtually nothing will be captured by the secondary on-engine filter. Thus, you’ve effectively halved your filter media surface area — you now have only one filter that must contend with all of the contamination. If you should happen to take on a batch of particularly dirty fuel, this primary filter may quickly become overwhelmed. If, on the other hand, your primary filter is a 30- or 10-micron rating, then the contamination can be divided between the two filters, offering greater overall media surface area with the finer filter because of the lack of large particles, operating more efficiently to boot. While anecdotal evidence may suggest that 2-micron primary filtration works, this is likely more so the case when dealing with relatively clean fuel. Once comparatively dirty fuel is encountered, segregating the contamination into two locations is simply more efficient and desirable.

Personal experience with a bad load of fuel taken on a week before contamination issues arose, had the 30 micron Racors becoming totally blocked in less than 30 minutes, and the fuel system limiting RPM to idle. The problems arose after a second fueling where we left right away with stirred up tanks.

I disagree with him. Yer, sure by running 2 micron you are cutting the secondary out of the equation, I think this is good because the racors are easy to change and the secondary isnt. Also it's easy to carry quite a few racors, they are much better priced than the yanmar secondary.

I've had bad fuel twice in places like west Sumatra which was very inconvenient.

Everything that goes into my tank now goes through a 2 micron racer, I pump it from jerry cans through my little polishing system into the tank. I then run 10 micron racor primary's (couldn't buy 2 micron when I stocked up) Two tanks ,two filters, two vacuum gauges.

[jhulmer]

Originally Posted by AKA-None

Couldn’t you use a small pump plumbed in the fuel and the vent going back to the tank. Use that to prime the new second filter?

Yes, a squeeze bulb pump rated for diesel installed in the supply line from the tank, works great for this. However, I prefer to limit the number of fittings inline to prevent leaks.
https://www.amazon.com/Rubber-Transf...a-571000993864

[gold]

The Keenan rig doesn't rely on anything electrical to work, the valves are normal hand operated valves. But the electrical connection allows the switch to be remote from the engine and operate an actuator to move the valve remotely. The only engine problems I've ever had happened in situations where there was no time to go below and mess with the engine, I had to sail out of several very sketchy situations with very little wind. With this rig, you can remotely trigger the filter swap with a switch. This rig is not cheap, I think it was $2800 or so, but In my mind it was well worth adding for a long-cruise vessel to have peace of mind coming and going from tricky places.