Purpose of pre-filter fuel pump

[bill209]

Hi all, I am confused about how to ensure I don’t have air in my lines when I change the filters with what appears to be a nifty addition to the boat by the previous owner.

Pre-filter fuel pump

My boat has something which I feel could be helpful, but not exactly sure how it should be used; you can direct the fuel flow from the fuel tank through a fuel pump before it goes through the fuel filter. The fuel bypasses this pump during normal operations.

fuel tank —> (fuel pump/fuel pump bypass) —> fuel filter —> engine

I was wondering if this could be used during filter changes to prevent issues with air in the lines, and if so what would be the proper procedure? Or is there another use for this pump?

Fuel filter case pump

The fuel filter case I have is similar to the stock image contained below and I found out that the black screw on top of the fuel filter is actually a pump built into the casing. I did loosen the screw and turn on the fuel pump, but no fuel came out, so the fuel pump does not seem to be useful for filling up the fuel filter with fuel and pushing out any air that may have gotten in. I also don’t really understand the use of this pump, it certainly doesn’t seem to be able to clear air from the top of the air filter, as when I pumped it no fuel came out.

So is the Pre-filter fuel pump and the Fuel filter case pump mainly useful for moving air bubbles down the line so they can be cleared out by undoing a bleed plug?

[NOTE] switching over to a new filter really scares me as the last time I did it caused an airlock in the injector pump which required servicing to clear up. ouch.

 

[Delta Riverat]

Yeah. I have them on my boat and they are switchable with valves and also electric. You can use them to transfer fuel between tanks, polish or prime after filter changes.

 

[Bmarler]

The electric pump was most likely installed for doing filter changes. Really makes it easy.
The little pump on the racor housing can also be used, but I’d prefer the electric. be sure the valve is in the bypass position, as it may have a tough time pulling fuel through the electric pump. It’s not a very speedy pump, but it’s better than nothing. I think they push fuel better than pull. Would be good for venting the secondary filter.
I’m at a loss as to why you’re not getting fuel out of the vent screw when using the electric pump. I presume that you have the supply valve to the pump open, the other valve to the pump position, loosen the vent, turn on the pump till clear fuel escapes. Close the vent and turn off the pump.
You can also vent air using the filters output fitting if nothing else seems to work. I wouldn’t be afraid to change filters, just be sure you vent properly after doing so, including the injector pump if you change the secondary filter.

 

[jgwinks]

I have electric priming pumps on my Perkins 6.354 engines. These things can be a bear to bleed, there are 3 different fittings that need to be loosened on the injector pump and the mechanical lift pump with it's hand lever is on the opposite side if the engine. Virtually impossible for one person to do alone. With the electric pump, easy peasy. Turn on the pump, crack and re tighten the 3 fittings, start the engine. Done.

 

[bill209]

awesome information everyone - thank you!

First let me acknowledge I missed something on the air filter itself that clarified one of my questions - why I could not purge air from the filter. Turns out the knob on top, which I understood to be the pump handle, was not doubling up as the air bleed plug. The air bleed plug was located on the opposite side of the filter which I could not see from the access location from which I was attempting to perform this task. I was both excited and dismayed (at myself!) when I moved over and saw the actual air bleed plug.

I checked the air in the fuel filter as well as the fuel lines and all looked good. I then started the engine and she ran flawlessly for 20 minutes.. I’m so happy!

Because of your information, I now understand that the pump can be used to purge air not only from the filter, but also from the fuel line, and it is sooo much easier to use the electric motor than the tiny little hand pump located on the engine. : )

Thanks again!

 

[rgano]

Shortly after I bought my twin-engine trawler back in 1986, I had an electric "priming" installed in the same relative position as your electric pump because the three Racor 500 filters (each engine and the genny had one) were mounted about mid-height of the four fuel tanks, and I was afraid of losing prime in the Racors when changing filters if the fuel levels were low. It was great and worked just as Bmarler describes. Years and years later, my port engine developed an irritating habit of suddenly stopping at odd intervals. I'd go down and shut the bypass valve at the priming pump, fire it up, and then open the engine's injector pump bleed valve and watch a bunch of bubbles come out for a short time until clean fuel exited. Then after shutting off the pump and reopening its bypass vaves, I was underway again, until the next time this obvious air ingestion problem reared its ugly head. Until I finally found the air ingection point in that engine's fuel supply, I took to leaving the priming pump on to prevent unannounced engine stoppages. In the end, the source of the air was a crimped o-ring under the cover plate tee handle of the port engine's Racor 500. Oddly, fuel would not get pumped out of it with the priming pump running making it really hard to find - took months.

 

[bill209]

Nice job on hunting down that leak! And thanks for the input.

I do want to report back that I was successfully able to change filters using the pre-filter priming pump. I was more afraid of the unknown and now it all makes so much sense! : )

Thanks to everyone!
bill

 

[promariner]

Hi all, I am confused about how to ensure I don’t have air in my lines when I change the filters with what appears to be a nifty addition to the boat by the previous owner.

Pre-filter fuel pump

My boat has something which I feel could be helpful, but not exactly sure how it should be used; you can direct the fuel flow from the fuel tank through a fuel pump before it goes through the fuel filter. The fuel bypasses this pump during normal operations.

fuel tank —> (fuel pump/fuel pump bypass) —> fuel filter —> engine

I was wondering if this could be used during filter changes to prevent issues with air in the lines, and if so what would be the proper procedure? Or is there another use for this pump?

Fuel filter case pump

The fuel filter case I have is similar to the stock image contained below and I found out that the black screw on top of the fuel filter is actually a pump built into the casing. I did loosen the screw and turn on the fuel pump, but no fuel came out, so the fuel pump does not seem to be useful for filling up the fuel filter with fuel and pushing out any air that may have gotten in. I also don’t really understand the use of this pump, it certainly doesn’t seem to be able to clear air from the top of the air filter, as when I pumped it no fuel came out.

So is the Pre-filter fuel pump and the Fuel filter case pump mainly useful for moving air bubbles down the line so they can be cleared out by undoing a bleed plug?

[NOTE] switching over to a new filter really scares me as the last time I did it caused an airlock in the injector pump which required servicing to clear up. ouch.

Use a Fuel Pump Primer Bulb right before the engine mounted filter

 

[Irish Rambler]

Hi all, I am confused about how to ensure I don’t have air in my lines when I change the filters with what appears to be a nifty addition to the boat by the previous owner.

Pre-filter fuel pump

My boat has something which I feel could be helpful, but not exactly sure how it should be used; you can direct the fuel flow from the fuel tank through a fuel pump before it goes through the fuel filter. The fuel bypasses this pump during normal operations.

fuel tank —> (fuel pump/fuel pump bypass) —> fuel filter —> engine

I was wondering if this could be used during filter changes to prevent issues with air in the lines, and if so what would be the proper procedure? Or is there another use for this pump?

Fuel filter case pump

The fuel filter case I have is similar to the stock image contained below and I found out that the black screw on top of the fuel filter is actually a pump built into the casing. I did loosen the screw and turn on the fuel pump, but no fuel came out, so the fuel pump does not seem to be useful for filling up the fuel filter with fuel and pushing out any air that may have gotten in. I also don’t really understand the use of this pump, it certainly doesn’t seem to be able to clear air from the top of the air filter, as when I pumped it no fuel came out.

So is the Pre-filter fuel pump and the Fuel filter case pump mainly useful for moving air bubbles down the line so they can be cleared out by undoing a bleed plug?

[NOTE] switching over to a new filter really scares me as the last time I did it caused an airlock in the injector pump which required servicing to clear up. ouch.

When you loosen the top screw, use the heel of your hand to pump it and it pushes the fuel and any air through your fuel system and back through the return lines to your fuel tank.
When I change fuel filters I start the engine, run it until its warm, stop the engine, remove you old fuel filter, fill your new filter to the top with clean fuel before refitting. Then start your engine just slightly above tickover you generally won't need to bleed the engine. If it doesn't start, just crack open a couple of the fuel pipes at the injector, turn the key until if fires and as soon as its running close the injectors again.