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Boat Forum / Building / November 2006Fuel Polishing, in general
As part of my trying to get smarter than I am (not hard!) about fuel and oil issues, in the course of searching for info about the oil-change-into-fuel-tank issue, I stumbled on discussions of fuel polishing. Our setup is now such that the pump is the last thing before it returns - it sucks through the two filters in series, with the vacuum gauge in between the pump and the filter line, drawing the fuel from the same supply point as the engine. We have two honking big 30 and 10 (in series) micron filters driven by a 3.5gpm Walbro pump, and monitored with a gauge, for the polisher. I've run that enough, now (at the slip, so no slosh, yet) to have circulated the fuel several hundred times. No change in the vac gauge, yet. I debated doing a separate feed, but decided that getting the fuel from the same point as the engine in the tank would have the best likelihood of making sure that what the engine pulled would have first been polished. That's because - as above - I'll have run the polisher excessively, as well as all the time the engine is running, plus any time the batteries are charged and we're sailing, as the wind generator will more than take care of that load (.8A), and it's pulling from the same point, at least somewhat assuring that that point will get lots of fuel flow, and by extrapolation, said fuel will have been through the filters many times. However, I'm scratching my head a bit about filter sizes. In one of the threads I read, it was observed that a 30 micron filter will also catch many smaller particles, and ditto the 10. After enough passes, effectively, it appears that the fuel will be down to something on the order of 2 microns, perhaps even less. One of the assertions I've recalled seeing in the past (not that it showed up in this recent search) was that multiple passes, as the filters eventually started filling with catch product, yielded finer filtration as time went on. That makes sense to me - I suspect the only problem would be how fast the filter got so full as to inhibit transfer through it. In my case, the filters are very big - the cases are 3.5x11 inches - so I expect it will take a very long time to cause the vacuum to rise enough to warrant a change. So, I'm wondering if that postulate is right - that lots of running will make my tank have a net particulate of only tiny (relative, of course!) size? Other commentary in the past showed very extended standard filter changes with this sort of arrangement, apparently as a product of this polishing. I have this dual Racor setup, as well. I have only the filter which came in the new one (10), and some spares of the original on the boat (30), plus a spare of the engine filter (2). I'm about to buy spares for all of these as part of our provisioning. So, more head scratching, from a very long-ago thread in this space, someone suggested 2 was appropriate. Certainly, with the dual setup I have now, swapping over and doing a filter change is easy - much easier than changing the engine filter (2) and repriming, etc. I had been going to do 10s in the Racors, on the presumption that the polishing had reduced it to that level, and likely I'd never have to change them, anyway. However, if all the above is right, perhaps I'd be better off with 2s, on the likelihood that even those would not likely need changing very often, having had the fuel polished to that or better levels, already, by the time it got there. So, two questions from all this. 1) Is my polishing setup appropriate - is the 30 followed by the 10 a good practice? 2) For those who have done it, or if there's still a professional filtration person looking into this group who can give empirical commentary vs usage experience, will I be changing 2s in the dual Racor setup often, or will the polishing likely reduce the particulate to that or below? And, doing a Columbo, thinking of something I forgot... I also have an electric priming pump, operated by a momentary push switch. However, when we bought the boat, it was next to the engine, after, not before, the Racor. Logic suggests it should be in front of the Racor, to refill it, before priming, rather than sucking all that air into the system. Or, is that not a problem? I've never changed a Racor, so I don't know what's really involved, but I can say for sure I'm not enthusiastic about having to pour fuel into the body as is suggested in the instructions. My apologies for asking what might be stupid newbie questions - but I've had the good fortune never to have to deal with a stopped diesel engine, and would like to keep it that way. A very well equipped tool kit is just fine with me if it never leaves the locker... Thanks for putting up with me - likely there will be a flurry of this sort of thing as we approach, and then do, our sea trials... L8R Skip, installing and filling more engine stuff so we can fire it up and service it soon... Morgan 461 #2 SV Flying Pig KI4MPC See our galleries at www.justpickone.org/skip/gallery! Follow us at http://groups.google.com/group/flyingpiglog and/or http://groups.yahoo.com/group/TheFlyingPigLog "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain >So, two questions from all this. > >1) Is my polishing setup appropriate - is the 30 followed by the 10 a >good practice? It can't hurt but is probably overkill. I polish through my regular Racors with 10 micron elements. It seems to work OK, no hard data but I've had no fuel issues since I started doing this. >2) For those who have done it, or if there's still a professional >filtration person looking into this group who can give empirical >commentary vs usage experience, will I be changing 2s in the dual Racor >setup often, or will the polishing likely reduce the particulate to >that or below? There has been a big ongoing debate on one of the trawler lists regarding this question. Most engine manufacturers, including Cummings and Cat, are recommending 10 micron elements in the Racors followed by a 2 micron engine mounted filter. Since the engine mounted filter is frequently much more difficult to change, some have advocated 2 micron elements in the Racors on the assumption that the engine mounted filters would then last more or less indefinitely. The manufacturers have countered that the engine mounted filter should be changed on its recommended schedule regardless. I have come full circle and gone back to 10 micron elements in the Racors. Although you sound like you've done all the right things, I'd offer one word of caution. Fuel problems often do not occur until the boat starts moving around and stirs up sediment accumulated in the bottom of the tank. This is almost impossible to address with dock side polishing so I'd recommend extra filter and vacuum guage vigilance the first few times you go out, especially in rough conditions. If you can run your polishing system while underway in rough conditions, that should speed the cleaning process. Don't forget to use a good fuel conditioner in the recommended quantities. I've been using mostly Biobor and it seems to work. Regarding your other question on filter changes and filling the Racor cannister with fuel; it depends on the boat. If your tanks are below the level of the Racors, then you will need some way of topping off the filters after you change out the element. On my boat the tanks are higher so it is not a problem. I just crack open the inlet valve while watching the fuel level in the cannister. Hi, Wayne, and thanks for the lengthy response. > There has been a big ongoing debate on one of the trawler lists > regarding this question. Most engine manufacturers, including [quoted text clipped - 17 lines] > conditioner in the recommended quantities. I've been using mostly > Biobor and it seems to work. I'd commented many times privately, but forgot to include it in my note here, that I was hoping for some really snotty sailing in our sea trials, during which time the polisher would be running all the time, for just that reason. As little as it draws, likely I'll be running it non-stop during nearly any of our sailing. Unlike another poster in one of the threads I researched, I'll not have it connected to the ignition but rather maintain the ability to control it separately, but expect to have it operating any time the engine's turning, as the alternator will keep up with whatever draw is happening. > Regarding your other question on filter changes and filling the Racor > cannister with fuel; it depends on the boat. If your tanks are below > the level of the Racors, then you will need some way of topping off > the filters after you change out the element. On my boat the tanks > are higher so it is not a problem. I just crack open the inlet valve > while watching the fuel level in the cannister. My filters are about 2' above the tank, unfortunately. Thus the question about using the priming pump as filler. Certainly, it would suck the fuel, if the top was closed - but I don't know if that would just leave some air in the top, or if that air would be sucked into the system. With the priming pump before the filters, I could fill the canisters before closing them, and *then* do the prime sequence if needed. Of course, if I'm changing by just shutting/changing the valve, going to the other filter, the lines would stay full, and the only thing I'd be dealing with would be the racors. I *do* have the polishing filters equipped with drain valves, so could draw fuel from those to fill the Racor in question. However, I'd have to hope I got the right amount, so I wouldn't have to deal with any excess or shortage. Hm. Looks like I'll be re-mounting the pump upstream of the Racors... Or, any reason not to?? More "hmmm..." - perhaps I could put a line on the end of the 10micron polishing filter valve, mounted above the Racors (see the November gallery) and use that as my fill medium. That might solve both problems... Thanks... L8R Skip, back to the engine room in the cold rainy weather (had to put on jeans, today!) Morgan 461 #2 SV Flying Pig KI4MPC See our galleries at www.justpickone.org/skip/gallery! Follow us at http://groups.google.com/group/flyingpiglog and/or http://groups.yahoo.com/group/TheFlyingPigLog "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain > My filters are about 2' above the tank, unfortunately. Thus the > question about using the priming pump as filler. If the polishing system is totally seperate from the engine fuel feed, you can't. But you could connect the discharge of the polishing pump to the upstream side of the engine filters and use that to prime the system. Put in a needle valve so you can throttle the flow. This could also be a big help spotting air leaks in your fuel feed line. Happens often and can be very frustrating. DSK I'd do the separate feeds. A friend of mine had one feed going to his heater and engine and somehow that got air in the engine line. Would you believe a Hans Christian? moral of this story was separate feeds and check your anchor for easy deployment before shoving off. an electric fuel pump plumbed in for bleeding would have sped up the job too. he won't even sail with me now unless I check the anchor before we leave the dock. I'd err on the side of caution. >I debated doing a separate feed, but decided that getting the fuel from >the same point as the engine in the tank would have the best likelihood >of making sure that what the engine pulled would have first been >polished. I can add nothing to the debate on filter size, but I run two fuel tanks and a seperate day tank in the engine room. I have a high volume fuel transfer system with an inlet and outlet manifold. Each manifold has 3 ball valves. Between the manifolds I use two RACORs with a strainer and a ten micron filter.This allows transfer from and to any tank. Additionally, the day tank is slightly higher than the engine and generator, which allows self priming. Steve > As part of my trying to get smarter than I am (not hard!) about fuel > and oil issues, in the course of searching for info about the [quoted text clipped - 106 lines] > Explore. > Dream. Discover." - Mark Twain A 'DAY' tank is probably the BEST insurance for any fuel system. If all hell breaks loose upstream (plugged filters, tank violently 'particulating', etc. ... all you have to do is open the vent on the day tank lock out or isolate the 'trouble' and simply run for several hours solely on the day tank .... until you can 'sort out' the problem. My day tank is mounted well above th engine plane so I can still get fuel oil by gravity feed even if the mechanical lift pump craps out. So, two questions from all this. > 1) Is my polishing setup appropriate - is the 30 followed by the 10 a > good practice? This is probable great overkill and will reduce the overall efficiency of the 'turnover' of the recirculation system. A recirculation polisher is effective because it can 'turn-over' or pass a LOT of fluid through the filter set - depending on capture by all the capture sites in the filter media that are much smaller that the 'rating'. Adding 'sequential' filters will drastically reduce the recirculation volume .... and the system will take MUCH LONGER to turnover and down to 'acceptable' resident particles in the tank (a 'mathematical anomoly' of recirculation filtration). In a high turnover recirculation system, adding additional filters will add flow resistance which will slow down the 'turnover'. A nominally rated 10uM filter is probably closer to 30uM on an absolute basis, plus the 10uM filter will have smaller diameter cellulosic fibers than a 30uM nominal. I'd go with the 10uM nominally rated filter even though a 10uM filter will have approximately 1/3 the flow capacity of a 30uM. (Cavaeat: if the system is fouled or if you havent cleaned the tank in some time ----- indications are: repetetive plugging of the main line racors, etc. and you're too lazy or cant clean the tank--- then use a 30uM to 'hog' the system down to low particle levels THEN use the 10uM to clean-up further. If you use a 30 immediately followed by a 10 it will probably take 10 times as long to do the same job as when you use 'single' filters in a recirc. loop. .... unless you have a 'humongous' pump to do all the 'work'. Id also do this in an independent loop being careful to discharge the recirculation loop near the bottom of the fuel tank or directly onto a side wall to minimize 'whipping up a froth' of air-oil bubbles. Obviously air bubbles being entraned into the main fuel line will eventually separate into large bubbles and eventually 'stall' the engine or fuel system .... 'flooded discharge' from a recirculation system is a 'necessity' or you may have to put in a 'air bubble trap' on the main fuel line. Keep it simple and be sure of a flooded discharge or alternatively discharging onto the tank wall. Filter 'ratings' in such 'fuel' filters are extremely 'arbitrary' and usually NO realistic connection to the 'actual' removal of the filter !!!!! Even the technically superior Racors are probably no more than 95% efficient at their 'rating'. .... meaning they can pass a 'basketball sized' particle and still be honestly rated at whatever you but ..... the rating is '% weight removal' at the designated particle size. Recirculation filters should be set up as PRESSURE FEED not vacuum feed where the pump is at the END of the circuit ..... the filters will be vastly more efficient versus on-stream service life due to the better deposition of particles ON the filter surface than IN the filter when in vacuum feed mode. The Walbro has an integral screen of about 100-200uM so you dont have to worry of large particles harming the pump; although, you must remember to clean the integral pump inlet screen occasionally. Do NOT use compression fittings on a pressure feed system single or double flared connection (or better) only .... in fact you should probably replace ALL compression fittings ANYWHERE in a fuel system as they ALWAYS eventually leak (air gets sucked INTO the system on a leaky compression fitting when the system is in vacuum mode) over time. > 2) For those who have done it, or if there's still a professional > filtration person looking into this group who can give empirical > commentary vs usage experience, will I be changing 2s in the dual Racor > setup often, or will the polishing likely reduce the particulate to > that or below? If the recirculation system is well designed and maintained you probably NEVER will encounter ANY challenge of particles to the racors. The recirculation system (if ON often or anytime the engine is running) will keep the particle background in the tank to well below submicronic levels thus no challenge to the Racors. Racors however willl eventually fail due to being soaked by free or emulsified water (causing 'digestion' of the cellulosic component of the filter media) and 'flexure fatigue' of the pleats due to pulsations coming from the mechanical lift pump on the engine. Whats NICE about a recirculation system is that you can remove the majority of 'crud' in very 'inexpensive' filters and keep a single racor (and engine mounted 'last chance' or 'guard' filter) from plugging. You dont need prefilters (primary) in a system that has an adequate recirculation filtration system. In such a system you can even run a 'hard line' bypass (no filter) when changing a plugged racor as the fuel tank will have essentially ultra filtered oil and you can run for sseveral minutes with this clean already filtered oil as you change out the racor. The dip tube of the recirculation should pick up the fuel at the VERY bottom of the tank to ensure that youre down into the crud and water thats usually in the bottom. The water can be removed in the recirculation loop by simply adding and 'empty' filter housing and letting the water 'settle out by gravity' in the empty housing, etc. .... a clear plastic 'tail' tube with a valve on the bottom of the empty filter housing will show when there is water in the empty 'knock-out' pot. The better you filter the tank contents removes the submicronic particles that are the nucleation sites upon which larger and large particles 'grow'/aggloerate. Stands to reason if you continually remove these very small particles ... then you will have infinitely less particles growing. The caveat here is that you still have to get inside the tank every few years and clean out all the crap thats stuck to the walls .... but not as often as if didnt have a recirculation filtration system. The best reason for having a high turnover recirculations system is when due to degrading oil (cracked oil, or oil thats becoming fouled with microorganism growth) and the crap has formed on the walls ..... even if the crap does break loose from the walls during a heavy sea state the reciruclation will QUICKLY restore the tank back to low particle levels. STill need to clean the tank occasionally. The BEST way to operate the fuel system is to continuously MONITOR the main fuel system filters with a vacuum or pressure gauge (measured as pressure drop across the filter versus maximum engine rpm) ... so you know WHEN to change the filters. Ditto on the recirculation system. ALL filters should have an operational 'recommendation' of liters per minute versus 'differential pressure' .... when the operating flow to the engine is getting close (flow through the filter vs. what the gagte is telling you - then its time to change the filter ---- READ the technical specification that come with the filter or go to the filter manufacturers website for the 'tech' / flow data. Be aware that the tech data for flow vs. 'delta P' should be for *fuel oil* and NOT for water --- big difference in flow/pressure requirements. If the tech info is in 'water flow' contact the filter manufacturer and get the 'fuel oil' flow rating. Change the filters when the pressure/vac. gage shows (versus the performance curve of the filter) that the flow rate 'could be' 200-150% of flow of the engine demand at full throttle .... look at the engine fuel consumption vs. horsepower curve and then compare to the fuel filter(s) performance (flow vs. differential pressure) curve. Size the filters based on the 'performance flow rate vs. operational differential pressure curve .... NOT the maximum flow rate on the 'box' .... when filters get dirty their flow begins to shut down .... plan on it and know the gage pressure when you should change the filter. Not all the particles that a filter 'captures' are 'hard' particles; many of the particles retained will be 'soft' particles and will begine to 'extrude' through a filter if the differential pressure across the filter becomes 'high'. Best is to maintain your own 'history' of operation (make notes, etc.) and then stick to the maintenance & filter changeout depending on YOUR operational history, etc.. No sense having ANY filter installed and not knowing WHEN to change it ..... other than having a stalled engine !!!!!!!!! Otherwise, you're just throwing away good filters or risk stalling the engine (usually at the worst possible time). Before you add a recirculations system .... better to get inside the tank and scrub out and mechanically remove all the crap .... then you wont NEED all those expensive 'filters'. Filters only remove 'symptoms', the cause is usually a dirty tank or taking onboard extremely dirty fuel. When to NOT buy fuel: before pumping into the tank, take a clear glass, pour some fuel into to it and hold the full glass between you and a strong light. If there is any 'haze' to the fuel .... get your fuel somewhere else. When to clean out the tank .... ditto with the glass in front of strong light. Hope this make 'sense'. ;-) Wow, Rich! What a detailed response - I scarcely know where to begin... > So, two questions from all this. > > [quoted text clipped - 9 lines] > 'acceptable' resident particles in the tank (a 'mathematical anomoly' > of recirculation filtration). Is this the effective equivalent of what happens with resistors vs capacitors in series and parallel? Putting these in parallel would more than double the effectiveness, whereas in series diminishes the effectiveness? > In a high turnover recirculation system, adding additional filters will > add flow resistance which will slow down the 'turnover'. A nominally [quoted text clipped - 10 lines] > 'single' filters in a recirc. loop. .... unless you have a 'humongous' > pump to do all the 'work'. Hm. I've never cleaned the tank - and nothing I got in the otherwise pretty complete records suggests it's been done in the last 15 years. For whatever it's worth, however, we had a very rough trip over when we took possession and brought it 500 miles through the nasty conditions in the Gulf, and had no issues whatever; the filter, while dirty, shows no lumps or identifiable spots. About the length of time to accomplish, I'm not sure I understand why that should be so. I'm operating on the presumption, despite the previous, that I have a lousy tank condition. The point of the 30 followed by the 10 is the presumption that I'll have crud which we'll dislodge pretty quickly. The suction gauge shows a very low level of suction, so I presume there's little obstruction. I don't know about "humongous" as a pump, but it seems to be doing reasonably well so far with the 30 followed by 10. I've not put a bucket under the output to test what the actual volume is, but opening a small unused port on the tank to see what's going on shows theres a notable amount of fuel being moved. > Id also do this in an independent loop being careful to discharge the > recirculation loop near the bottom of the fuel tank or directly onto a [quoted text clipped - 5 lines] > on the main fuel line. Keep it simple and be sure of a flooded > discharge or alternatively discharging onto the tank wall. Hm, again. I don't have an easy means of doing the discharge you suggest. Currently, the discharge is straight down - no tube, no directional difference. The pickup is the same as the Racors, however far down that is. We've never experienced (yet, of course -and all this is in an effort to make sure we don't get the first) a clog in the old (very rotted by the time I tore it out) fuel lines. However, an inspection of the tank through that small port above showed no bubbles evident. Dunno why, as it seems it should be happening, after many hours of running the fuel through. The pump is evidently a diaphragm variety, as initially it was very fast and noisy, but that was only until it sucked up the fuel in the line and filled the filters, whereupon it settled down very quickly to a very quiet pulsing sound - so, perhaps that's why no froth? > Filter 'ratings' in such 'fuel' filters are extremely 'arbitrary' and > usually NO realistic connection to the 'actual' removal of the filter [quoted text clipped - 3 lines] > but ..... the rating is '% weight removal' at the designated particle > size. Hm. Makes the toilet paper and paper towel type filter seem more effective, doesn't it? > Recirculation filters should be set up as PRESSURE FEED not vacuum feed > where the pump is at the END of the circuit ..... the filters will be > vastly more efficient versus on-stream service life due to the better > deposition of particles ON the filter surface than IN the filter when > in vacuum feed mode. I admit to being entirely unknowledgeable about all this, other than what I thought I remembered from discussions on filtration over the many years I've been looking at it, before having a real life application of my own. What I *thought* I remembered was that you absolutely didn't want to have pressure on the filters, but suction. And, I presume there's some explanation in fluid dynamics or some such of which I am likewise totally unaware, but I don't know why it should be one way or the other. Is it that particles are being sucked *in*, vs pushed *on*, the filter? And, in the case of Racors, why is it that they have to be suction? The Walbro has an integral screen of about > 100-200uM so you dont have to worry of large particles harming the > pump; although, you must remember to clean the integral pump inlet [quoted text clipped - 4 lines] > system on a leaky compression fitting when the system is in vacuum > mode) over time. I'm pretty sure that's what I have - the nut is free to rotate after it's loose but the nipple stays in place. Looking at it before putting it on, the male is somewhat pointed, and the female is like the bell of a horn, with the nut pushing it down on tightening. That's that I have in all the connections of the hoses.. > > 2) For those who have done it, or if there's still a professional > > filtration person looking into this group who can give empirical > > commentary vs usage experience, will I be changing 2s in the dual Racor > > setup often, or will the polishing likely reduce the particulate to > > that or below? > If the recirculation system is well designed and maintained you Heh. Well, so far, it appears that it's not well designed - though it meets all the various inputs I'd stored over many years while getting ready for this point. I even had a couple of what looked like professional designs in pdf. However, my recollection has you with umpteen years in the filtration biz (recalling some of the endless threads with jax and and perhaps some others), so my presumption is you come from an industry perspective, rather than conjecture... So, if I understand you correctly, I should either completely disassemble my currently installed unit and start over, or, at a minimum, reverse the flow, change the suction gauge for a pressure gauge, and leave one of the canisters empty and, after lots of 30 filter hours, go to only 10 filter and replacements?? > probably NEVER will encounter ANY challenge of particles to the racors. That's encouraging, at least - the rest, so far, is very disappointing (because I'll have to start over, and I have no easy means of cleaning the tank)... > The recirculation system (if ON often or anytime the engine is running) My intent and expectation is that it will be on any time the engine is running, as well as any time we're sailing with full batteries (the wind generator should more than keep up with the load, if there's enough wind to be sailing). I'd assumed that would provide the very best opportunities for clean fuel other than to have it running nonstop (never mind how it's powered in that case...). > will keep the particle background in the tank to well below submicronic > levels thus no challenge to the Racors. Racors however willl [quoted text clipped - 11 lines] > run for sseveral minutes with this clean already filtered oil as you > change out the racor. Well, that's comforting to know - though, having already made the investment, and installed, a dual racor (change on the fly), I expect I'll keep it. However, I'll also keep a very close eye on the bowls for water. Currently there's the flame-arrest bowls with not only the spin-off-the-bowl, but a plug in the bottom. I believe I'll trade the plugs for a valved nipple so I can drain and check what's there without the flood which would result in removing the flame arrestor, or even just the plug... > The dip tube of the recirculation should pick up the fuel at the VERY > bottom of the tank to ensure that youre down into the crud and water [quoted text clipped - 4 lines] > empty filter housing will show when there is water in the empty > 'knock-out' pot. So, as to the above, if I were to reverse this, the second, very large, container could be the water accumulator? Wouldn't the other also have the same properties? That the water would accumulate at the bottom? In any case, should the empty, if that's what I do, be before or after the filter in the train? FWIW, both of these have valves at the bottom; I'd thought I might put a nipple in one of them to use to refill the Racor space when I changed a filter, but I'd pretty much decided to put my priming pump, left next to the engine where I found it, in front of the Racors, to make that easier. Though, I don't know about the pressure vs suction, any more, nor, as this one has been for the presumed 15 years before we bought it, in line all the time, rather than on a separate circuit, which reality was disparaged by a diesel guy in the yard yesterday (he said it absolutely could not be an inline pump, despite any prior history)... > The better you filter the tank contents removes the submicronic > particles that are the nucleation sites upon which larger and large [quoted text clipped - 4 lines] > to the walls .... but not as often as if didnt have a recirculation > filtration system. In our particular installation, that's a bit challenging, as the only access is in the top (bow) deep corner, 1.5", other than some major disassembly. It's my presumption that it's never been done in this boat... > The best reason for having a high turnover recirculations system is > when due to degrading oil (cracked oil, or oil thats becoming fouled [quoted text clipped - 6 lines] > main fuel system filters with a vacuum or pressure gauge (measured as > pressure drop across the filter versus maximum engine rpm) ... so you My Racor setup has the same (make, model, not literally the same) vacuum gauge as the polishing system. I expected to use that as my guide - but it's vacuum... > know WHEN to change the filters. Ditto on the recirculation system. > ALL filters should have an operational 'recommendation' of liters per [quoted text clipped - 3 lines] > technical specification that come with the filter or go to the filter > manufacturers website for the 'tech' / flow data. Be aware that the Interesting - neither the Racors nor the other have any such data with the documentation. IN the case of Racor, I have not had any luck trying to get information about them, at all. However, the others are rather more mainstream, so I might be able to discover something about them... > tech data for flow vs. 'delta P' should be for *fuel oil* and NOT for > water --- big difference in flow/pressure requirements. If the tech [quoted text clipped - 9 lines] > down .... plan on it and know the gage pressure when you should change > the filter. Phew! I only *thought* I thought like an engineer. I'm in way over my head, here. I'm not sure there's much info on our 30 year old engine WRT consumption/HP/pressure/vac. I'm pretty sure I'll have to go by the seat of my pants for the first several changes, after which I can have the baseline to use... > Not all the particles that a filter 'captures' are 'hard' particles; > many of the particles retained will be 'soft' particles and will begine [quoted text clipped - 6 lines] > just throwing away good filters or risk stalling the engine (usually at > the worst possible time). Heh. No kidding. However, I'm wondering if what I'll have to do isn't a bit like Edison's running a machine until it broke, to see what it would do, then running the rest of them at 90%... > Before you add a recirculations system .... better to get inside the > tank and scrub out and mechanically remove all the crap .... then you > wont NEED all those expensive 'filters'. Filters only remove > 'symptoms', the cause is usually a dirty tank or taking onboard > extremely dirty fuel. Heh. Fortunately, the polishing system filters aren't all that expensive, and are huge by the Racor 500 standards of what will follow all that polishing. And, of course, it was the symptoms, of which I've had none, yet, that I was looking to address. > When to NOT buy fuel: before pumping into the tank, take a clear > glass, pour some fuel into to it and hold the full glass between you > and a strong light. If there is any 'haze' to the fuel .... get your > fuel somewhere else. When to clean out the tank .... ditto with the > glass in front of strong light. Gotcha. With any luck what I pull out of the bottom of the polishing units won't even look like that... > Hope this make 'sense'. > ;-) :{)) More, or less, as per the above. Elucidation/expansion, please? Thanks L8R Skip, up again way too late > Is this the effective equivalent of what happens with resistors vs > capacitors in series and parallel? Putting these in parallel would > more than double the effectiveness, whereas in series diminishes the > effectiveness? No not at all. Has to do with the laws of exponential decay .... the decay of the absolute amount of particles in the tank. The reason is that the faster that you 'dilute' the residence of particles the faster the decay to some finite level of particulate; the slower the filter, the slower the recovery .... a 1 uM filter will have approx. 1/15-1/20th the flow rate of a 15uM ; plus the 15uM filter will have capture sites (at a low efficiency of 1uM). Reciruclation filtration takes the advantaage of using inexpensive very high flow rate filters to arrive a MUCH lower retention ratings as if you'd filter in a 'series' mode. > Hm. I've never cleaned the tank - and nothing I got in the otherwise > pretty complete records suggests it's been done in the last 15 years. > For whatever it's worth, however, we had a very rough trip over when we > took possession and brought it 500 miles through the nasty conditions > in the Gulf, and had no issues whatever; the filter, while dirty, shows > no lumps or identifiable spots. Fuel begins to degrade at the interface between the fuel and water layers by fungi and bacteria using the oil (and the tanks walls) as a nutrient source. If the fuel is produced as distillate it will be more stable from breakdown than a 'cracked' fuel. There's lots of opinions from API engineers ab out what is happening versus decomposition but Im one who considers that cracked fuel (the most common i n the USA readily breaks down in heavy alkene fractions, etc. .... which do not burn well in the combustion chamber and usually settle downstream in the exhaust section as coke which can block the exhaust .... these are probably the large 'liquid particles' that extrude through filters or block them. > About the length of time to accomplish, I'm not sure I understand why > that should be so. I'm operating on the presumption, despite the [quoted text clipped - 7 lines] > tank to see what's going on shows theres a notable amount of fuel being > moved. When using two filters in series the purpose the first stage is to protect the second stage and give life extension to the second stage .... in a properly designed two stage system you want to aim so that the particle distribution is such that both filters plug almost simultaneously. You need some fancy instrumentation to determine the actual weight - particle size distribution. > Hm, again. I don't have an easy means of doing the discharge you > suggest. Currently, the discharge is straight down - no tube, no [quoted text clipped - 9 lines] > whereupon it settled down very quickly to a very quiet pulsing sound - > so, perhaps that's why no froth? If you 'drop' oil onto itself you will most assuredly mix up air into the tank oil. When the engine is running this air will eventually separate from the oil and form bubbles in the most elevated sections of the piping. Depending on how and how much air comes out and is trapped these collected large bubbles can 'accumulate' and eventually stall the injector pump, etc. Not a good practice to 'drop' oil into a tank, especially if you're pumpin about *3 gallons per minute* back to the tank from a Walbro transfer pump. Flodded discharge from the recirculation system is proper. > Hm. Makes the toilet paper and paper towel type filter seem more > effective, doesn't it? No, Not al all as paper towels and especially toilet paper has no or VERY little resin binder to hold the filbers together. This makes TWO problems: 1. upon increasing differential pressure a non-resinated 'paper' will unload particles as the cellulose fibers flex. 2. Cellulosic fibers that arent resin bound are easily attacked and digested by water - toilet paper is *made* to fall apart after its in water for a short time - if your ever have the chance to go to a sewqage treatment plant you will find that there is very little 'visible' toilet paper in such plants .... by the time the toilet paper gets to such plants its all essentially broken down into individual fibers or is essentially dissolved. There is ALWAYS water (emulsions and free water) in fuel oil that is stored long term - it gets in there by chemical equilibrium (not condensation). > I admit to being entirely unknowledgeable about all this, other than > what I thought I remembered from discussions on filtration over the [quoted text clipped - 6 lines] > vs pushed *on*, the filter? And, in the case of Racors, why is it that > they have to be suction? With vacuum feed there is little tendancy of the particles to form a 'cake' of debris on the upper surface of the filter, so the cake forms more INSIDE the filter taking up space and closing down the flow paths. With pressure filtration the cake more readily forms on the upstream surface ... and then for quite a while the 'cake' becomes the filter media - ie.: the dirt is now filtering out more dirt. This is all velocity dependent so the lower the flow rate (face velocity) the more apt the dirt will form on the upper surface as a 'cake'. With higher velocities (or with vacuum feed) the dirt gets driven deeply into the filter media and quickly plugs it. > ed you > [quoted text clipped - 5 lines] > threads with jax and and perhaps some others), so my presumption is you > come from an industry perspective, rather than conjecture... Disagree .... as ANY mode of recirculation filtration is VASTLY superior to 'in-line' filtration when it comes to keep low particles in a tank. Hell, a pressure pot filled with pubic hair or shredded kotex can be effective. > > So, if I understand you correctly, I should either completely > disassemble my currently installed unit and start over, or, at a > minimum, reverse the flow, change the suction gauge for a pressure > gauge, and leave one of the canisters empty and, after lots of 30 > filter hours, go to only 10 filter and replacements?? Nah, leave it alone. Next time you build a system do it the other way. As I state ANY recirculation is a far superior approach. > > probably NEVER will encounter ANY challenge of particles to the racors. > [quoted text clipped - 4 lines] > best opportunities for clean fuel other than to have it running nonstop > (never mind how it's powered in that case...). Dont do this 'stuff' blindly ..... use the glass and strong light. Then you know what you are about. > Well, that's comforting to know - though, having already made the > investment, and installed, a dual racor (change on the fly), I expect [quoted text clipped - 4 lines] > the flood which would result in removing the flame arrestor, or even > just the plug... Those clear bottom racors will show you when to drain out any water that gets trapped in them. IT sometimes takes a bit of time for any emulsion and mixed-up large amounts of free water to settle out. > > The better you filter the tank contents removes the submicronic > > particles that are the nucleation sites upon which larger and large [quoted text clipped - 13 lines] > vacuum gauge as the polishing system. I expected to use that as my > guide - but it's vacuum... Vacuum feed is OK for filtration, just *not as good* as pressure feed. Vacuum feed on boats has been driven by the boat builders being cheap and dirty ..... the engine comes with the lift pump and its just so cheap and easy to add the filters and fuel lines to the 'other side' of the pump. With a pressure feed system you need a (lift) pump at the tank and bombproof tubes and fitting so that you dont inadvertently fill the bilge with oil. With a vacuum feed system if you have a leak the system sucks air and the whole system automatically shuts down .... good for EPA and Coast Guard but not for a boat operator who needs to keep moving. > > know WHEN to change the filters. Ditto on the recirculation system. > > ALL filters should have an operational 'recommendation' of liters per [quoted text clipped - 9 lines] > rather more mainstream, so I might be able to discover something about > them... Go to the Paker .com website (www.parker.com) then ---->"marine" then ultimately to the Racor Division... its all there in the 'technical data' section .... or at least is was the last time I looked. Dont get lost in the 'european' sub-website stay in the USA dcata sections of the site. If you dont find the data, call Racor ask for an Application engineer and have them send you the *flow vs. delta-P* curves for your filters. > Phew! I only *thought* I thought like an engineer. I'm in way over my > head, here. I'm not sure there's much info on our 30 year old engine > WRT consumption/HP/pressure/vac. I'm pretty sure I'll have to go by > the seat of my pants for the first several changes, after which I can > have the baseline to use... Get the data from Parker Racor ... or keep records and build an operational history of your set-up. > > Before you add a recirculations system .... better to get inside the > > tank and scrub out and mechanically remove all the crap .... then you [quoted text clipped - 6 lines] > all that polishing. And, of course, it was the symptoms, of which I've > had none, yet, that I was looking to address. The RAcor 500 has huge comparative surface area .... that will allow LONG term service life, especially if you engine is only drawing 1 gallons per minute at WOT. ;-) >Recirculation filters should be set up as PRESSURE FEED not vacuum feed >where the pump is at the END of the circuit ..... the filters will be >vastly more efficient versus on-stream service life due to the better >deposition of particles ON the filter surface than IN the filter when >in vacuum feed mode. The Walbro has an integral screen of about When the filter media sees a pressure differential, how does it know whether it's caused by sucking on one side or pushing on the other? Does the filter media actually get compressed by the slightly (tiny) higher pressure inside the filter housing when it's in pressure feed vs. vacuum feed? Since the fibers are surrounded by the fluid, the pressure on each fiber is pretty much equal all around. The only difference being the difference between the front of the fiber and the back, which only depends on the differential not the absolute pressure. So the only way I can see pressure vs. vacuum makin a difference is if the actual fibers get compressed and get smaller in diameter by the higher pressure in the canister. But now I have to understand how only a few PSI difference can cause any significant deformation/compression of the media fibers. The only other thing I can think of is maybe the fluid flow rate is faster for pressure fed vs. vacuum because the pump may be operating more efficiently that way. But then, assuming the flow rate is different, the opposite situation would occur. I.e., particles would be deposited IN the filter for the faster flow rate (pressure) vs. ON the surface for the slower flow rate (vacuum) Anyway, enough of my rambling. I'd just like to understand why particles get deposited ON the filter surface for pressure fed and IN the filter for vacuum fed. Steve Well first of all filters are not screen doors. The filter media in fuel oil filters is a 'felt' made of microfibers bound together with a waterproof resin. Pressure feed and correct flow rate will establish that the flow is very slow asw it crosses the face of the filter media. If designed correctly the dirt will form a 'cake' ON the surface of the media ... and the dirt will begin to filter out other dirt. If the velocities are too great the cake will collapse and become very dense .... and the filter will shut down/plug. With vacuum filtration the cake forms IN the filter media, and there is less space - because the filbers of the filter media are also found there. Once the filter gets dirt IN the filter the fluid velocities become higher and higher thus driving the dirt deeper into the media due to the increased fluid velocity and quickly shuts down the fluid flow because there are few flow paths still open. In all filtration the larger the upstream surface area, the slower the fluid velocity, the lower the viscosity of the fluid .... all make for 'happy' long lasting filters. When selecting a filter always choose the LARGEST you can fit or afford .... it will save you $$$$$$$ in the long term. >Well first of all filters are not screen doors. The filter media in >fuel oil filters is a 'felt' made of microfibers bound together with a [quoted text clipped - 16 lines] >When selecting a filter always choose the LARGEST you can fit or afford >.... it will save you $$$$$$$ in the long term. That didn't really answer the question, which is WHY does the "cake" form IN the filter media for vacuum fed but ON the surface for pressure fed? I would think that, all else being equal, it would work the other way because the pump is operating more efficiently with pressure fed, so the velocity would be higher, driving the dirt deeper in the media. Other than that, I don't understand how the felt media knows whether the pressure differential across it is caused by pressure on one side or vacuum on the other. Theoretically, it shouldn't matter. So I'm just trying to understand the physical "real world" process that causes it not to behave according to theory. Steve > That didn't really answer the question, which is WHY does the "cake" > form IN the filter media for vacuum fed but ON the surface for [quoted text clipped - 8 lines] > > Steve Possibly the Vac system is more constant, whereas the pumped system pulsates, this may affect the level of turbulence causing the crap to lie long ways across the filter, but with a more smooth flow (vac system)the crap will align with the flow and penetrate deeper into the filter media. This is a blind guess, but may prompt someone who knows about these things. I Retention of particulate in/on a filter is an extremely complex entity due to simultaneous and varied 'capture mechanisms'. that 'hold' the particles in place: seiving - where the statistical pores of the filter structure are smaller than the particle; inertial impaction - where the particles leave the flow stream when the flow stream takes sharp bends; aDsorption - where the particles are held to the filter media subtrate by weak electronic bonding (van der waals forces); the formation of a "cake" on the upper surface and into the upper 10-15% of the depth of filter medium; Polarization of gel-forms, etc. All filtration is 'particle specific' .... and depends exactly which mechanism of capture 'predominates' for which type of particle you want to remove. For fuel oil, etc. filtration where probably there are more 'deformable' particles or particles that can change shape under increasing differential pressure and then are subject to extrusion either through or partly through the media (settling deeper into the media) thus 'blinding it' ..... vacuum filtration has historically shown the least efficacy of on-stream service life versus pressure filtration. Apparently vacuum feed filtration allows the deformables and smaller than 'seiving' size particles to partly extrude more deeply into the matrix, partly closees off the statistical pores which increases the face velocity of the fluid in the cross sections of the filter matrix. The increasing face velocity of the fluid through the sections creates an untowards physical event (as per the standard D'Arcys equation) derived to be: On stream life (T1/T2) being a function of the ratio of face velocities to the 'n-th' power where 'n' - approximately approaches to the 2/3 power). My 'guess' (after 35 years of observation, etc.) is that in vacuum filtration the capture involves an *accelerating* particle; while pressure feed involves a *decelerating* particle. Simplistically and historically, vacuum draws the deformables and smaller than the target 'seiving sized' particles deeper into the matrix, shuts down the open flow paths quicker than in pressure feed --- all apparently internal velocity dependent. Filtration hydrodynamics is probably very similar to aerodynamics where intuition and simple logic will always produce the wrong answer. I've been deeply involved in ultra-purity filtration and 'separations' engineering (and the physical chemistry of) for almost 35 years and still dont know all the answers .... although I do know that vacuum feed filtration will *always* have comparatively shorter service life than pressure feed (for just about ALL filtrations) ... and for that reason alone is good enough for me and most others to stay away from vacuum feed filtration. There's probably a doctoral discertation waiting for someone who can correctly figure this one out - many have tried but none have ever been successful. Like I posted earlier, filtration has nothing to do with 'screen doors' and is an extremely variable complex entity at below the macroscopic level. Dont attempt to 'rationalize' it as you will ultimately always wind up with the wrong solution. It's really an 'art-form'. Not to mention that vacuum filtration is intrinsically less robust from a purely mechanical perspective. Under vacuum filtration, you have, at most, atmospheric pressure and tank head pressure available to generate filter DP (which, even with 10' of head - very unlikely in a boat - amounts to <20psi). Under pressure filtration, you're limited only by pump size/flow curve, and filter specifications. If you have a filter rated for 65psid, why would you want to toss it when the DP is 15psi (at which point the resulting flow rate, using vacuum, would likely be negligible)? Vacuum filtration, using any realistic type of circulation pump, results in a low discharge pressure (i.e. open tank return line) and very low suction pressure (increasing with filter load), which is a recipe for cavitation and low/no flow conditions. Pressure filtration, on the other hand, maintains pressure (typical installation with sufficient head on the pump) on the suction side, and a higher discharge pressure (increasing with filter load). Thus filter loading decreases the chances of pump cavitation for pressure filtration, versus increasing chances under vacuum filtration. So, whether you agree with Rich's observations or not, there are sound hydraulic reasons for pressure filtration instead of vacuum filtration. Keith Hughes > I > Retention of particulate in/on a filter is an extremely complex entity [quoted text clipped - 48 lines] > level. Dont attempt to 'rationalize' it as you will ultimately always > wind up with the wrong solution. It's really an 'art-form'. |
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