Combined Dual Filter and Fuel Polishing System?

[Wee Rascal]

After an unpleasant and nausea-inducing experience conking out and changing a CAV filter in choppy conditions due to diesel bug muck I’m looking at improving my fuel delivery system to incorporate both dual filters and polishing functionality.

Does anything in the following plan look like it wouldn’t work?

• Selector ball valve to allow fuel to be drawn either from the sender or from a hose connected to the fuel tank drain.
• Back to back selector valve allowing the selection of the CAV primary filter OR a parallel Racor primary water separator filter. (Seamless switch between primary filters in case of one being clogged.)
• Electric fuel pump (e.g. Facet) downstream of the primary filter(s), in series with the engine mechanical lift pump to make bleeding quicker, and to allow for polishing.

The idea of the connection to the tank drain would be to allow the electric pump to power a polishing function with the engine not running, drawing from he bottom of the tan to get water and gunge. The clean fuel return would be via the engine’s fuel return.

This assumes that the electric fuel pump would be able to create a flow around the circuit through the mechanical lift pump when the engine is off. Would that be the case or would the lift pump prevent flow? (It’s a Betamarine 38).

Similarly, are there any 12v fuel pumps which would allow passive flow when not powered (flow driven by the mechanical fuel pump) so that the engine wouldn’t become dependent on the electric fuel pump to keep running? (Not a major issue but it would be nice if it was no issue).

Or am I overthinking it all and maybe should simply swap out my CAV for an easy to change Racor and just build a separate standalone polisher?

 

[Cptsideways]

I built a system on my boat the simple solution is one way valves and change over valves in the system. But effectively the polishing system can run with or without the engine running. Either filter can become the primary engine filter. It'll also prime the engine side for bleeding by shutting off a valve. Uses the existing intake from the aft tank but returns to the foreward one (mines a duel tank system)

There's a fuel pump, two Racors, a couple of one way valves and several change over valves but in normal use not needed. All pretty inexpensive using copy Racors but genuine filters.

A picture before I finished it. I'll try and find a current one...

 

[noelex]

A polishing system is only one element in ensuring your engine is fed with clean fuel. However, it is a very beneficial system.

Ideally the polishing system should be independent of the fuel delivery to the engine. Usually this is not difficult to arrange. If installing a new system this would be the preferred option.

The polishing filter will likely process many thousands of litres per week when running. If there is a fuel contamination problem the polishing filter will clog relatively quickly. Likewise if there is any water in fuel, this will be extracted rapidly. Ideally this filter needs to be kept seperate from the engine supply.

If used regularly the polishing system should prevent, or at least significantly reduce the chance of fuel problems occurring, but it does this by filtering vast quantities of fuel. The fuel filter for the main engine supply should be separate.

 

[pandos]

After an unpleasant and nausea-inducing experience conking out and changing a CAV filter in choppy conditions due to diesel bug muck I’m looking at improving my fuel delivery system to incorporate both dual filters and polishing functionality.

Does anything in the following plan look like it wouldn’t work?

• Selector ball valve to allow fuel to be drawn either from the sender or from a hose connected to the fuel tank drain.
• Back to back selector valve allowing the selection of the CAV primary filter OR a parallel Racor primary water separator filter. (Seamless switch between primary filters in case of one being clogged.)
• Electric fuel pump (e.g. Facet) downstream of the primary filter(s), in series with the engine mechanical lift pump to make bleeding quicker, and to allow for polishing.

The idea of the connection to the tank drain would be to allow the electric pump to power a polishing function with the engine not running, drawing from he bottom of the tan to get water and gunge. The clean fuel return would be via the engine’s fuel return.

This assumes that the electric fuel pump would be able to create a flow around the circuit through the mechanical lift pump when the engine is off. Would that be the case or would the lift pump prevent flow? (It’s a Betamarine 38).

Similarly, are there any 12v fuel pumps which would allow passive flow when not powered (flow driven by the mechanical fuel pump) so that the engine wouldn’t become dependent on the electric fuel pump to keep running? (Not a major issue but it would be nice if it was no issue).

Or am I overthinking it all and maybe should simply swap out my CAV for an easy to change Racor and just build a separate standalone polisher?

The facet posiflow pump will allow unimpeded pass through whilst it is not powered up.
A word of warning, I fitted a posiflow and a Racor type filter to my new to me boat. In a moment of blind stupidity I used the supplied connections on the pump which were too small to allow sufficient fuel to flow when the engine was working hard...result engine sucked in air and died...several times...but at least was simple to restart...

 

[Wee Rascal]

The facet posiflow pump will allow unimpeded pass through whilst it is not powered up.
A word of warning, I fitted a posiflow and a Racor type filter to my new to me boat. In a moment of blind stupidity I used the supplied connections on the pump which were too small to allow sufficient fuel to flow when the engine was working hard...result engine sucked in air and died...several times...but at least was simple to restart...

That's interesting about the posiflow, thanks. So that gives an option to have that pump in the system, but for its operation not to be vital to keep the engine running.

I'm assuming that the mechanical lift pump would also allow pass through without the engine running, since it seems to be normal to fit in series without problem.

I understand that it's optimal to keep the polishing separate from the fuel delivery for the engine as noelex suggests. I suppose it's the skin-flint in me trying to avoid duplicating the purchase of elements of a polishing system that would already exist in the fuel delivery circuit and could be put to dual purpose by including some diverter valves. (Return line, pump, water separator/filter.)

That said, the additional expense isn't much, especially if I look at the unbranded Racor-alike units. I may end up keeping it all simpler.

Thanks for all the above responses. Appreciated.

 

[geem]

I think fuel polishing sound like something special but for a marine diesel tank all you can do it fuel filter. Sucking from a single point at the bottom of the tank will not ensure a spotless tank. To create a spotless tank, you need to vacuum the bottom of the whole tank. The suction velocity at the inlet to a typical low capacity fuel pump is insufficient to draw debris from all corners of the tank bottom. If you have suspended solids, the fuel filtering system will remove this but still leave a tank with a dirty bottom. There is a risk that this will get stirred up when you get in some boisterous conditions. A scouring velocity on the bottom of the tank is extremely difficult to achieve.
If your tank is dirty, I would remove it and have it cleaned so you are starting from new. If you can install a good inspection hatch at the same time and or add a 1" screw opening, this will allow you to periodically insert a length of flexible copper tube with fuel pump and filter to vacuum the bottom of the tank. You do this by moving the pipe all over the tank bottom. Clear fuel pipe and filter will allow you to watch dirt being sucked up the pipe. In my opinion, this is a far better approach than simply filtering you diesel on a regular basis.

 

[Roberto]

I think fuel polishing sound like something special but for a marine diesel tank all you can do it fuel filter. Sucking from a single point at the bottom of the tank will not ensure a spotless tank. To create a spotless tank, you need to vacuum the bottom of the whole tank. The suction velocity at the inlet to a typical low capacity fuel pump is insufficient to draw debris from all corners of the tank bottom. If you have suspended solids, the fuel filtering system will remove this but still leave a tank with a dirty bottom. There is a risk that this will get stirred up when you get in some boisterous conditions. A scouring velocity on the bottom of the tank is extremely difficult to achieve.
If your tank is dirty, I would remove it and have it cleaned so you are starting from new. If you can install a good inspection hatch at the same time and or add a 1" screw opening, this will allow you to periodically insert a length of flexible copper tube with fuel pump and filter to vacuum the bottom of the tank. You do this by moving the pipe all over the tank bottom. Clear fuel pipe and filter will allow you to watch dirt being sucked up the pipe. In my opinion, this is a far better approach than simply filtering you diesel on a regular basis.

+1
I open the inspection hatch and clean the tank once or twice a year by filtering/recirculating the whole fuel while scraping and sucking all the dirty material with a pipe, most of it basically sticks to the tank walls or accumulates along the corner welds, there is barely anything freely floating in the liquid. Give it a decent stir (like chop) and some of them mixes up, with lumps here and there. Besides cleaning the inside, I change the primary filter every 100 hour and I find it almost clean.
On a few occasions I would have lost the boat if the engine had failed, it's very nice to have the peace of mind of knowing for sure to have a clean tank (like not having to vomit while soaked with diesel while changing filters in a hurry).

 

[jaminb]

I made a standalone polishing system as described above but with a caravan (mini) dishes brush tie wrapped to the cranked copper pipe wand. I didn't have a stand alone inspection hatch and went in via the fuel gauge sender hole. I couldn't reach all of the tank but could reach the sump / lowest point and I did dredge up some gunk. This was the beginning of the season. I have just done a precautionary mid season primary filter change and all was good despite having had a few bumpy sails. I did use Marine 16 and now dose with the Diesel Fuel Complete when I fill up (2 x per season).

 

[Wee Rascal]

I think fuel polishing sound like something special but for a marine diesel tank all you can do it fuel filter. Sucking from a single point at the bottom of the tank will not ensure a spotless tank. To create a spotless tank, you need to vacuum the bottom of the whole tank. The suction velocity at the inlet to a typical low capacity fuel pump is insufficient to draw debris from all corners of the tank bottom. If you have suspended solids, the fuel filtering system will remove this but still leave a tank with a dirty bottom. There is a risk that this will get stirred up when you get in some boisterous conditions. A scouring velocity on the bottom of the tank is extremely difficult to achieve.
If your tank is dirty, I would remove it and have it cleaned so you are starting from new. If you can install a good inspection hatch at the same time and or add a 1" screw opening, this will allow you to periodically insert a length of flexible copper tube with fuel pump and filter to vacuum the bottom of the tank. You do this by moving the pipe all over the tank bottom. Clear fuel pipe and filter will allow you to watch dirt being sucked up the pipe. In my opinion, this is a far better approach than simply filtering you diesel on a regular basis.

You're correct of course.

My engine is brand new, and not long before it was installed I had paid an engineer to clean out the tank as best as possible. (The access to the fuel tank is very difficult and for me that's compounded by a "mobility in constrained spaces" issue following knee surgery, hence this was a "get someone in" rather than a DIY situation!)

So it was rather annoying to get a fuel starvation breakdown at 15 hrs run time on the new engine. I initially didn't believe it would be the filter due to the recent supposed clean out of the tank, but of course it was indeed a bug-gunged primary filter. This did happen in F6 to F7 conditions with big waves and was probably therefore a textbook example of the "boisterous conditions" stir-up mentioned above. The engine has run another 50 hours since then (in calmer conditions). I'll get an idea when I pull the filter next week whether it was a one off chunk or a gradual build up.

Removing the tank from this boat looks like a major undertaking requiring boat surgery. It sits under the cockpit floor between the space under the cockpit floor hatch and the lazarette. To my eye (I haven't measured) I can't see how it would fit through either that hatch or the lazarette opening. I (or more likely my teenage son) may be able to move it forward into the hatch space and cut better inspection panels into it without a complete removal. Will assess next week.

I might first try getting in to hoover it out a bit through the sender hole as jaminb did. I anticipate there are probably internal baffles that may limit the effectiveness of this strategy. But this together with changing to parallel filters and incorporating an easier-to-change-at-sea Racor clone, seem to be the easier route for now than tank removal.

 

[noelex]

The suction velocity at the inlet to a typical low capacity fuel pump is insufficient to draw debris from all corners of the tank bottom.

Fuel polishing works better to keep the tank clean, rather than a method to clean up a really dirty tank (although it will help). If you have a very dirty tank it is better to physically clean the tank and then install a polishing system (and other steps) to ensure you never have to do it again.


If the boat has a polishing system installed then this is continually removing water and other contaminants from the fuel. This reduces the chance of diesel bug forming. As you indicate the pumps on these polishing systems are not powerful enough to significantly stir up the tank contents, but the boat’s movement when sailing will do this quite nicely. For this reason it is helpful to always run the polishing system when sailing.

 

[rogerthebodger]

I built a fuel polishing machine with a high flow pump so the return to the tank will stir up the Contants of the tank and scour and much at the bottom of the tank to remove much

My polishing includes a water separator a cause filter and a fine filter all at least 1 " BSP fittings

 

[geem]

I built a fuel polishing machine with a high flow pump so the return to the tank will stir up the Contants of the tank and scour and much at the bottom of the tank to remove much

My polishing includes a water separator a cause filter and a fine filter all at least 1 " BSP fittings

I have worked on designs for very large fuel polishing systems for standy generator tanks for data centres. We found it was very hard to create enough scouring of the bottom of a tank. There are always spots that see very little velocity from fuel wash. It takes a lot of velocity to dislodge some of the crud. Some doesnt move without mechanical intervention. After lots of design attempts to scour the bottom of a tank we came to the conclusion that it would only ever be partially effective. We ran the fuel polishing pumps 24/7/365 and accepted that we would bring in external contractors to do an annual fuel polishing. This involved very much larger pumps and mechanical vacuuming of the tank bottom.
The fuel polishing we did was only really fuel filtering to remove any debris in suspension and water.
With my boat, we have an electric fuel pump. This pump moves 500% of the fuel needed for the injection pump so actually provides filtration of the fuel without needing a seperate system. The engine has two large capacity fuel filters as part of the engine installation. Annual or 6 monthly vacuuming of the bottom of the tank is all I do. I always get a little debris out when I do this and the main filters seem to stay pretty clean

 

[rogerthebodger]

I have worked on designs for very large fuel polishing systems for standy generator tanks for data centres. We found it was very hard to create enough scouring of the bottom of a tank. There are always spots that see very little velocity from fuel wash. It takes a lot of velocity to dislodge some of the crud. Some doesnt move without mechanical intervention. After lots of design attempts to scour the bottom of a tank we came to the conclusion that it would only ever be partially effective. We ran the fuel polishing pumps 24/7/365 and accepted that we would bring in external contractors to do an annual fuel polishing. This involved very much larger pumps and mechanical vacuuming of the tank bottom.
The fuel polishing we did was only really fuel filtering to remove any debris in suspension and water.
With my boat, we have an electric fuel pump. This pump moves 500% of the fuel needed for the injection pump so actually provides filtration of the fuel without needing a seperate system. The engine has two large capacity fuel filters as part of the engine installation. Annual or 6 monthly vacuuming of the bottom of the tank is all I do. I always get a little debris out when I do this and the main filters seem to stay pretty clean

Ok I not saying my system is prefect, but I do have a rigid tube that allows me to get into the corners to try to blast and stubborn crud.

I use this on the steel tanks built into my steel boat works for me

 

[thinwater]

In my day job, I've built fuel polishing systems from 250-150,000 gallons per day. I've built industrial water treatment systems from 10-5,000,000 gallons per day. As an engineer, the first question is always "what are we trying to remove?" Obviously, the answers are all over the place. The fluid may be pretty clean or right bad. The requirement is usually related to a standard or permit.

What are we trying to do?

• Remove a large amount of water? Pump it out using and oil change pump first. This is not a job for filters. Easy.
• Remove water from filler leaks? Fix the leak.
• Remove water from fuel we bought. Very unlikely in the UK or US. But if so, I probably don't want a slow polish through a depth media, I want higher rate through a separating media. And I don't want to pull off the engine suction, I want to draw lower. And I probably don't want this fuel going to the engine dirrectly, because it was right off the bottom.
• Remove solids from bug, avoid the problem by keeping the fuel dry (filler cap) and treating preventative with Biobor JF or similar. Filtering out bugs is very difficult because they slime everything. Best to shock treat (kills and loosens them up), pump the tank, clean it, shock treat again, and start over.
• Remove solids from other sources. (a) They are probably from bugs unless the boat is quite old. Diesel in the US and UK is quite clean, or cars wouldn't run. Delivery pumps have 40 micron filters by law. (b) Stuff you stirred up underway. Better be a high rate pump, separate from the fuel system, able to turn the tank over in 20 minutes. See Nolex. If you want to filter going into the engine, be prepared to change filters a lot at the worst time. Having them in parallel is not always enough. (c) Polishing the fuel at the dock does not really help with (b) because the tanks is not stirred up then. Really, this is probably a 20-40 year accumulation and cleaning the tanks is better. It's not that hard, just a skill most owners don't have.
• Water from condensation. Install a silica gel vent filter. But unless you don't move the boat much, this is not typically enough to cause trouble. The water actually came in through the filler or splash into the vent.

But mostly I think we just guess at the source of the dirt and water.

Me, I would:

• Inspect the filler regularly and every season. I would move it if it is in a watercourse or flat/puddled area. Number one cause.
• Check the BOTTOM of the tank regularly for free water if I have been getting ANYTHING in the engine Raycor. There is indicating paste or you can just pump a little with the oil change pump. Easy.
• Install a separate system that pulled a loop from the lowest point and back into the tanks at the opposite end. I want to run this when sailing in lumpy seas without the motor on. It would not be connected to the engine fuel system; that system should be stand-alone IMO. I don't want to feed the engine right off the bottom for several reasons. So a separate system. See Nolex. By the time all of the extra valves are considered to rig some sort of by-pass system off the main fuel system, no money is saved.
• A fuel additive with corrosion inhibitors/metal deactivator. Startron is one. I have not tested many UK brands. One of the leading sources of solids is catalytic polymerization, and it happens right inside you fuel system, particularly if you don't burn enough to turn your tank over every year. Copper and zinc ions generate sludge. You should also consider minimizing copper fuel system components, such as long runs of tubing (not engine fittings). Copper, zinc, and sludge
• I might add a Raycor or similar, but I would hesitate to modify the engine fuel system unless the filters are clearly inadequate. For example, going up a size or placing two in parallel is safe.
• Install a cleaning port of one does not exist. Size depends on the tank and geometry, but 4-6 inches.

I have also been involved in the cleaning and inspection of literally thousands of vessels, from 5-10,000,000 gallons. Many tricks, but anything can be cleaned.

 

[NormanS]

I don't think that anyone has so far mentioned the best and simplest. Have relatively tall narrow tank(s), tapering towards the bottom, and at the bottom have a dirt/water trap fitted with a drain valve. That way, any dirt or water automatically gravitates into the sump, which can then be drained off. I check mine regularly and particularly after rough passages. I appreciate that not every boat can be thus equipped.

 

[rogerthebodger]

My Fuel Tanks and steel and welded in as part of the hull so the bottom and outside of the tank is also the part of the tank. As they are towards the aft of the boat the forward part of the tanks is lower than the aft section. There is a drain point at this lower forward part so I can draw off from that point if required and feed back into the tank to further clean the fuel.

This drain has a ball valve and a plug on the outlet

 

[noelex]

After lots of design attempts to scour the bottom of a tank we came to the conclusion that it would only ever be partially effective.

I can understand that polishing would only be "partially effective" on a stationary tank on land. You really need the agitation of sailing or perhaps a rolly anchorage for debris to be picked up. This is why boat engines typically stop on rough passages. A polishing system on a stationary tank would pick up and eliminate water (this is still helpful), but probably not much else.

This pump moves 500% of the fuel needed for the injection pump so actually provides filtration of the fuel without needing a seperate system. The engine has two large capacity fuel filters as part of the engine installation. Annual or 6 monthly vacuuming of the bottom of the tank is all I do. I always get a little debris out when I do this and the main filters seem to stay pretty clean

This should provide a slight polishing effect, but the volume of fuel is much smaller. Even our modest polishing system filters an average amount of perhaps two thousand litres per week. This high volume means any water or deposits are likely to be caught before it has a chance to feed the diesel bug.

A polishing system is not essential and it does not eliminate the need for other steps such as using biocide, but it does help ensure the engine receives clean fuel. In my experience it completely eliminates the need to periodically clean the tank (providing it starts reasonably clean).

This is our primary engine filter after about three years of full time cruising. It was virtually indistinguishable from new.

 

[geem]

I don't think that anyone has so far mentioned the best and simplest. Have relatively tall narrow tank(s), tapering towards the bottom, and at the bottom have a dirt/water trap fitted with a drain valve. That way, any dirt or water automatically gravitates into the sump, which can then be drained off. I check mine regularly and particularly after rough passages. I appreciate that not every boat can be thus equipped.

My fuel tank is 500 litres and built as part of the boat. The tank goes into the keel so there is a natural sump. The only problem is there is no way to draw off the lowest point to remove crud and water. This is why I do a periodic vacuuming of the bottom of the tank. The last time I cleaned is manually was 12 years ago. I checked the bottom recently with an endoscope and it all looks clean. The periodic vacuuming does work

 

[Fr J Hackett]

checking ones bottom with an endoscope is something best left to the professionals, you never know what's down there or what you might find.

 

[thinwater]

I don't think that anyone has so far mentioned the best and simplest. Have relatively tall narrow tank(s), tapering towards the bottom, and at the bottom have a dirt/water trap fitted with a drain valve. That way, any dirt or water automatically gravitates into the sump, which can then be drained off. I check mine regularly and particularly after rough passages. I appreciate that not every boat can be thus equipped.

This is why I suggested pumping the bottom with an oil change vacuum. If you have a stiff tube of the correct diameter, it can fit in through a small opening, sometimes even the filler pipe. If not, I would probably install something as simple as a small (~ 1/2-inch NPT, which is about 21 mm) pipe flange (no chance of leaks if done properly) with a plug I could screw out.

But a drain is very nice. Note that neither drains nor side suctions are permitted in petrol tanks on boats. Slightly off topic, but worth mentioning.