Researching Walbro fuel pumps (diy polishing)

[svselkie]

I'm intent on building a recirculating fuel polishing system for my 35-gal tank and I've read all the posts I can find on this board. Walbro seems to be the fuel pump of choice, but I've gotten mixed input re the continuous versus the on-demand types of pump. Rich H, who seems to know the stuff pretty well, somewhere suggested the FRB-13, an on-demand pump. Fuelpumps.net, an online supplier, advises the FRA's--continuous duty pumps. It would seem to me you'd want the pump to run continuously--how will it sense demand on a recirculating system? Is the distinction important? Or am I missing something? I'm pretty new to this stuff.
Thanks for any help.
John V.

 

[Herrick18911]

I don't think you are missing anything. A pump used in that configuration; hose out from tank to pump, to Racor, back to tank would run continuously until switched off. So I would evaluate accordingly.

Tod

 

[Roger Long]

Rich H, who seems to know the stuff pretty well, somewhere suggested the FRB-13, an on-demand pump.

I don't know anyone I would trust more on something like this than Rich who helped me design my system.

http://www.cruisingonstrider.us/FOpolishing.htm

http://www.cruisingonstrider.us/StriderFuelSystem.htm

I started with an unregulated Walbro FRA pump in 2008 since it is an open circuit system as you point out. It died after three seasons for unknown reasons. I don't believe this is typical.

I replaced it 15 months ago with a FRA1-1 4.5-7.0 PSI, 20 GPH pump since I couldn't get an unregulated one quickly enough. Since it's an open circuit, the on demand feature is just simply along for the ride. If you look at my schematics, you'll see I have a valve to force fuel to the engine if I'm trying to squeeze a little more running out of it in event of clogging of the engine mounted filter or similar failure. The pressure stop on the pump is some insurance against starting a fuel leak with the unregulated pump.

I've run the new pump, cruising full time, mostly under power, and probably have close to 1500 hours on it now.

My tank is 20 gallons and the nominal GPH should be about the same as your tank so you probably do want to go to the larger pump.

Note my 3 way switch. One setting turns the pump on and off with the engine and the other sets it to a panel switch.

I never got my web site fully updated but I did later install this reserve tank in the system:

It serves primarily as an automatically refilling (whenever the engine is running) gravity supply for my cabin heater but is also about an hour of reserve fuel.

A Forespar Marlon MF 841 Vent/Duck Bill replacement kit for their anti-siphon vent loops fits a 1/4" compression fitting like it was made for it. Another compression fitting goes on the tank and the copper tube is run as high as possible. Air trapped in the tank top and tube will keep fuel from reaching the valve.

Here is the full schematic for my system. It violates several points of gospel you will encounter about the subject on the net but has performed flawlessly for about 15,000 miles.

Note also that I can turn one valve and the polishing system becomes a back up fuel supply while I change the main Racor filter. Running time in this mode is unlimited so no need to change the filter underway.

Oh yes, don't use a Racor for your polishing filter. See my site for the details on the Shelco. If you can fit the standard 10" elements, do so. I didn't have room and it is harder to obtain the half length filter elements. There is almost no difference in cost between the 10" and 5" element units. The 5" elements can actually cost more since they have to be cut in half.

 

[RichH]

My name is RichH and I endorse Roger's message. ;-)

For a recirc. polisher to work, you want to constantly 'turnover' (filter, refilter, refilter) as much and as fast as possible. A good 'turnover rate' will be somewhere about 1-3 gallons per MINUTE per 100 gallon tank. You want a the largest filter for the least amount of pressure loss through the filter to ensure that 'turnover rate' ... and low amps draw on the pump. A continuous duty pump is the best choice for long service life. The Shellco is a common industrial configuration for 2.5 -2.75" diameter X 9.75 - 10" long filters ... so you can use 'any' common industrial standard filter cartridge; plus, you dont get locked into using proprietary configurations from just one manufacturer. Any time the engine is on, the polisher is running. Set up a fuel recirc. polisher to 'push' oil through the filter, not 'suck' the oil through .... pump can develop much higher pressure when pushing than pulling - the pump should be protected by an (inbuilt) screen/strainer; use double flared tubing connections if possible, not 'compression' fittings as they can 'relax' and then leak .

The benefits of an onboard polisher:
• removes the 'seed' particles and 'nucleation sites' upon which larger particles grow/agglomerate, including fungal spores - one of the most common contaminants in diesel fuel .... for less need to 'clean out' an already cleaned out tank.
• if a large amount of 'sludge' breaks loose from the tank walls or you pick up BAD fuel, very quick recovery of the particle distribution in the tank back to 'normal' ... 'several minutes'.
• Virtually NO particle challenge to the "Racor System" ... (but still change the Racor(s) @ 1 year).
• Common Industrial style filter cartridges are one hell of a lot cheaper than costly 'proprietary' filters from a single manufacturer
• you can use whats known as 'graded pore density' depth filters, a filter that has successively finer and finer retention as the fluid moves through the filter material .... good for removing gels and 'soft' particles -- the most common particle species in fuel oil.
• less need to clean out your exhaust system, the hard-to-burn 'soft' particles are removed from the fuel - are the probable largest cause of 'coke' formation in the exhaust system.
• will quickly remove water from the tank, especially if the filter is run empty without any filter cartridge inside it. Do this after every long term boat lay-up if you inadvertently 'topped off the fuel tank' before long term layup ... an empty tank doesnt uptake water from the atmosphere.

Target filter rate: 1 - 3 gallons per MINUTE per 100 gallon tank.
Retention size: 5-10µM ... (constant recirculation will yield essentially the removal of all submicronic particles - 'crystal clear' fuel ..... but wont remove 'black' if the fuel is heavily bio-contaminated, as those particles can be 'submicronic' down into 'nano-sized'.

 

[Roger Long]

Set up a fuel recirc. polisher to 'push' oil through the filter, not 'suck' the oil through .... pump can develop much higher pressure when pushing than pulling - the pump should be protected by an (inbuilt) screen/strainer;..

I gave that a lot of thought when we talked about it and then did it the other way. My polishing system serves as my emergency supply. I figured that if something really gross happened, like a slug of crud from a marina hose, the polishing filter would be the best thing for it to first encounter without introducing other screens or filters into the system that I might have to take apart and check or clean under adverse circumstances. Not getting optimal filtration on the big filter seemed a good trade off to me.

I did set up my Racor in push mode. This makes also makes it a lot easier to bleed and fill after changing elements as well as providing optimum filtration.

A sudden slug of crud or other debris could disable my electric fuel pump but I then have the well protected polishing pump to fall back on.

I haven't changed the polishing filter element in a long time. Once the system gets very clean with the constant filtering, it pretty much stays that way. I'm on the move nearly constantly though so the mileage of a weekend boater may vary.

I've had no significant problems with a system based on nipples, fuel hose, and clamps. All my weep points are at valves around the ball valve stems, even using valves rated for FO service. You do have to take up the hose clamps occasionally.

 

[RichH]

Roger, not a problem.
As anyway you do any recic. polishing, even inefficient polishing, is a BIG plus.

The ONLY downside of a pressure fed oil filter system is, if you spring a leak you can possibly fill a bilge or the USCG/EPA coffers and that why with a Pressure feed you need bombproof connections, etc. A vacuum motive system, simply sucks air then stops .... often.
;-)

 

[svselkie]

Thank you all for your replies—they are very helpful.
Tod, that’s just what I was wondering about.
RichH, I see that a Walbro FRB is rated for 18000 hrs continuous duty, whereas the FRA’s are rated for only 5000 hours. So I guess that spells out the advantage in going with the ‘on-demand’ FRB vs the 'continuously-running' FRA—have I got that right? There are so many of them, I don’t want to get the wrong one. An FRB-22 would be the best way to go (43 gpm for my 35 gal tank), you think?
Also, Rich, I saw in one of your posts elsewhere that a “hardware store” polypropylene pump housing is OK to use. That was an epiphany. It’s a huge cost saving (lacks a picture of a boat on it), but is it sufficiently bombproof, as opposed to a metal housing? Intuition suggests that it should be fine—it’s in a protected location. Boat dogma says buy bronze and stainless. Are there any downsides to polypro that would warrant spending 4-5 times more for a metal one? If not, I’m on my way to Home Depot.
Roger, thanks for the diagrams and description—and that’s a really great website. Wife and I are planning to move to mid-coast Maine—maybe we’ll cross paths someday.
John V.

 

[MWybo]

Hi,
Will the Shelco filter housing with the standard Buna-N seals be sufficient for diesel fuel?

Also, the Walbro pumps have NPTF threads and the Shelco filters have NPT threads. Will normal teflon tape suffice on the NPT threads or do you recommend something else?

Finally, any recommendations on three way valves? Will the big box store brass valves with stainless balls be sufficient?

Thanks

Mike