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Marine Fuel Polishing System using Walbro Fuel Pumps

By Chris Myer

Lately we've been receiving quite a few emails regarding fuel polishing systems. We've learned a lot from not only our customers but from some independent testing. This article will attempt to convey what we've learned and what other's have provided us about fuel polishing systems used in marine applications.

Why Use A Fuel Polishing System?

Diesel fuel can become contaminated not only in your fuel tank but on its way from the refinery. Impurities, rust, and even tar build up can cause a wide range of issues with marine engine injection systems. Even "pure" diesel fuel in a clean tank can become contaminated as it oxidizes, resulting in paraffin and asphalt. Intermittent engine stumbling and even complete engine failure can be a direct result of diesel fuel contamination.

There are many companies who can pump your fuel out, polish and pump the diesel back into your tank. This can be time consuming and worst of all, expensive. This problem is so common that new boat manufacturers offer fuel polishing systems as a purchase option. So what do you do if you don't have a new boat with a new system and you don't want to rely on professional fuel polishers? Consider installing your own onboard fuel polishing system.

Fuel Polishing Process and System Components

What is fuel polishing system and how does it work? Very simply, it is the process of circulating fuel from your tank through fuel filters and back into your tank. The concept of the system is very easy to understand. Determining what components you will need can be difficult since every fuel system will have its own set of requirements.

To determine what is needed for your particular fuel polishing system you must determine how fuel is utilized in your boat. Do you have one or two fuel tanks? Do you have a separate fuel system for an onboard generator? Do you have any other components installed that utilize your fuel system? There are a few "universal" kits available by various manufacturers. The pricing seems costly, and the universal fitments leave a lot to be desired. No one knows a vessel like its owner. Call us crazy or maybe it's a pride thing but all of us enjoy doing our own work and the satisfaction the finished product provides.

A few basic components are needed in any custom fuel polishing system. Every system will need a fuel filter and a high quality fuel pump like the Walbro Marine Fuel Pump.

Fuel Filters

It's common to use filters from SIERRA and another company called RACOR. We've also talked to some of our customers and they have opted to use filters from commercial farming & construction equipment. It's important when considering fuel filters that you choose the correct micron rating. The smaller the micron rating, the more filtration you can expect. You will have to frequently check and or replace a low micron filter; however, you will also filter more of the impurities out of your diesel fuel. Or, for a more advanced system, use a two-stage filter system, with the first filter being a larger micron rating. We recommend using a final filter with approximately a 10 micron range. (Please do your own research or weigh your options as this is only an opinion for our typical customer's application).

Fuel Pumps

Our company's focus is on the Walbro fuel pump line. You don't have to take our word for it when it comes to the quality of these pumps. We encourage you to research other pumps. We're confident you will come to realize that the Walbro FR series of pumps to be the best for marine fuel polishing systems. Walbro maintains U.S. Coast Guard standards and draw less than 2 amps at 12 volts. Walbro pumps have a reverse-polarity safeguard and can run dry continuously for up to 4 hours! There are many configurations to choose from in Walbro's FR series. The paragraph below will help you select the right Walbro Fuel Pump for your fuel polishing system.

Fuel Pump Selection: Continuous or On-Demand Operation?

For fuel polishing a continuous operation pump is preferable. On-demand is only required in very low-volume operations where demand is intermittent. When the fuel polishing system is on, you want the pump moving fuel so continuous operation is the correct choice. The Walbro FRA and FRC pumps are the best choice.

Fuel Pump Selection: Built-In Filter?

The Walbro FRC fuel pumps have a built-in filter screen. It comes from the factory with a 70-micron screen, or a much larger 420-micron screen is also available. Even the 70-micron screen is inadequate for fuel polishing. However, as we mentioned above, a two-stage system can be beneficial and for a low-volume fuel polishing system the FRC pump might be adequate. If you are polishing a large volume of fuel, however, you should utilize a much larger first-stage filter, and select the FRA pump without a built-in filter.

Fuel Pump Selection: Volume and Pressure?

Now that you've narrowed your selection to either an FRA or an FRC pump, you need to choose your pressure and flow requirements. In general, fuel polishing systems are low pressure, high volume systems. However, volume is the more important factor, since the amount of pressure generated is nominal in most cases. When looking at the Walbro FR-Series Industrial and Marine Fuel Pump Table, keep in mind that the flow rates are minimum based on pressure restrictions consistent with the "Max PSI" column. Since you will not generally have significant restrictions to create this amount of pressure, your flow will be much higher. Here is a basic formula for estimate purposes only: Diesel or kerosene fuel systems: Gallons per Hour is Engine Horsepower (maximum) multiplied by 18% or GPH = HP X 0.18.

Fuel Pump Selection: Marine or Industrial?

Now that we've explained that the FRA or FRC is probably the best choice for your fuel polishing application, we should point out that only the FRB pump is available in the 1000 hour salt-spray marine corrosion rating. Now, if your fuel polishing system is well protected from salt spray, the FRA or FRC pump is more than adequate. However, if your environment is particularly harsh, you may want to back up and select one of the FRB on-demand pumps. This won't hurt you in any way, it's just not necessary.

  • Click here for a list of FR Series Walbro Pumps.

  • Fuel Pump Selection: Other Fuel Pump Factors and Options

    As you are browsing through the selection of Walbro FR series fuel pumps to select the proper pump for your fuel polishing system, you will note that some are sized with 1/8-inch, 27 thread per inch (TPI) inlets and outlets, while a few have 1/4-inch, 18 TPI inlets and outlets. Either works well, but if you have a preference you may want to check that in the pumps you are viewing. Some have an outlet check valve and others do not. Again, either will work but it might be something that sways you to choose one over the other based on your particular requirements.

    Additional Parts

    You will need U.S. Coast Guard certified Fuel hosing (just check the labels before buying as this is regularly available from most boat stores). Various valves will be needed depending on how you route your fuel. Some of our customers have even used timers so that their fuel polishing system can operate while they're away from their vessel. If you have multiple fuel tanks make sure you consider what other items you may need.

    Multiple Fuel Tanks

    Single fuel tanks are relatively easy to configure. When you have two or more tanks it's important to isolate your filtration system to each tank. If you were to neglect this step and attempt to filter the full volume of fuel, you may run into issues of returning too much fuel to one of the tanks if they are not auto-balancing. If you are polishing tow auto-balancing tanks, be sure to pull from one and return to the other to ensure that the entire volume of fuel is polished.

    Design & Install Your New Fuel Polishing System

    It's important to plan out your fuel line route in advance. This will help you select the correct Walbro FR Series pump. Determining the size of the pump will require knowing your lengths and applying the appropriate math. Make sure your filter system is installed where you can get back to it for servicing. Filters installed in your engine room need to have metal bowl guards to remain compliant with U.S. Coast Guard standards. Mount all of your components firmly to fixed objects. Make sure your fuel lines are routed away from heat and areas that may rub the lines. Finally, make sure you label everything so you and future users understand your custom configuration.

    Utilizing the System

    How often should you use the fuel polishing system? During the warmer months it's advised to cycle your fuel through the filtration system at least twice a week. If you let your boat sit for extended periods of time then you may want to consider timers to handle this for you.

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