Adding a fuel primer pump

I am looking at adding a fuel primer pump to facilitate priming the racor filters and fuel system after a fuel filter change. At the same time I would like to be able to use the new primer pump to polish the fuel and/or transfer fuel in-between the 2 fuel tanks. The new primer pump could also serve as a back up fuel pump in an emergency. I have attached a reference drawing of what I am thinking about. Items in black are existing while items in red are new.

The fuel polishing and fuel transfer are not the most efficient due to the fuel having to cycle through the fuel rail but I think this is the easiest way without re-doing the fuel system completely and having a bunch more valves.

What do you think? Would this circuit be able to prime the main racors and secondary fuel filters upon a filter change, polish the fuel, allow for fuel transfer, and provide fuel pump backup? Do you see any issues?

Thank You for your input and advice. Thanks also for the snide comments I will probably get as well. LOL

KevinAttachment 72892

That s not how I ve done mines. You want the priming pump to not only prime the Racors but the secondary as well.

The way I’ve set up my priming pump is using two 3 way valves between the fuel selector and the racor

To prime, the first 3 way valve sends the fuel to a an additional filter (to protect the pump) then to the priming pump and to the second 3 way valve

In normal operation, the fuel goes from the first 3 way valve directly to the second valve, bypassing the filter and priming pump and into the racor

I didn’t include a fuel polishing feature but that would be easily done with another 3 way valve at the racor outlet to either send the fuel to the engine or back to the return tank selector

Let me see if I have picture.

Here it is

A is from the fuel selector valve
B goes to the prefilter and priming pump
C is the priming pump output

When both valves are vertical as in the picture the fuel bypasses the priming valve pump. Flip both valves and fuel goes to the priming pump

Priming pumps are low pressure Walbros

The priming aspect of your design looks good.

IMO, the best fuel polisher on your boat is the engines. I have 671's and they circulate about 90 gal/hr when running at standard cruise. If you want to polish your fuel, either go out for nice cruise or idle your engines at the slip.

I have updated the drawing to be able to prime the engine mounted secondary filter as well as the Racor primary filter.

If my drawing is correct the fuel line schematic should be able to provide the following functions:
1) Prime Racor primary and secondary engine fuel filters
2) Polish fuel through both the primary and secondary filters
3) Transfer and polish by default fuel from one fuel tank to another.
4) If the primer pump has enough fuel flow capacity it can be used as a backup fuel pump in case of the engine mounted fuel pump failure.



I do have some questions for the more experienced.
1) Do you agree that my fuel circuit schematic will accomplish the 4 tasks listed above? I realize there are some other more efficient designs for fuel transfer and polishing but I wanted to limit the number of valves. Want to keep the primer and other functions as simple as possible and not need an engineering degree to operate the boat.

2) Assuming air is introduced into the Racor and/or secondary filter due to a filter change, will the air need to be bled off at the systems highest point? Most likely engine fuel rail? Or will the air be pushed through the return line back to the tank?

3) The priming pump being self priming should be able to draw air out of the fuel system on the pump suction side, correct? Or does it need to be on the pump discharge side of the primer pump?

Thanks for your input and helpful information.
Kevin

Thought;
Engines move some fuel to run.
Good gear driven pumps can move more if not pushing thru the engine.

My polishing pump draws thru the mud filters (Racors) and returns to the tank.
Not drawing thru the secondary filter or thru the motor.
It moves A LOT of fuel for polishing in this config.
It draws and primes the mud filters very well when needed.

My secondary filters have another primer that has dust on it. Used maybe once 20 years ago when we purchased the boat.
When I change the spin on secondary filters, I fill them up a bit with fresh fuel and never touch them till their next service.

It is usually the primary filters that get changes in a hurry, here you need dual filters and/or fast priming.

I feel your diagram is to complicated for what is needed.

Yes pumps like the walbros are self priming but pulling fuel thru both the primary and secondary will take longer than if it is pushing the fuel thru. As mentioned I prefer to have the pump closer to the tank and push fuel thru both filters.

Also if you have a small air leak somewhere at the racor or at a connection, the priming pump will not prime itself whereas if you push the fuel thru, you will see the leak instead of spending hours chasing it

That’s how every factory installed priming pump I have seen is set up

finally, in order to put the pump past the secondary you re going to have to make the plumbing modifications on the engine and run longer hoses to where you can mount the electric pump and valve. More complex installation

The Racor instructions say to pull fuel through them, not push it through. So the pump has to be after the Racor.

Just make sure you pay very close attention to the thread type. Not only size but type. Had to replace one after decades and also put a new section of hose in and I remember it being unique but also close to a common size.

Quote:

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Originally Posted by SKYCHENEY

The Racor instructions say to pull fuel through them, not push it through. So the pump has to be after the Racor.

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Low pressure is fine. Many boats are set up that way and it works very well. As I said if you ever get an issue with the racor, it will make it easy to troubleshoot. That happened to me last year with my gen which was hunting and not putting up with a load. I wasted hours and hours checking everything until I finally put a small pump at the tank. I immediately noticed a drip from the water sensor plug on the racor bowl.

Yea the Racors are not designed to be installed past the fuel pump but for priming and troubleshooting it works better

Normalization of risk. Just because you've gotten away with bad practice doesn't make it safe.

Quote:

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Originally Posted by Avenger

Normalization of risk. Just because you've gotten away with bad practice doesn't make it safe.

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I and thousands of factory installed priming pumps on quality boats “have gotten” away with it…. They re only under light pressure while priming not running

Another reason to not do it that way is that pumps emulsify water which hinders filter performance when they are installed before the filter. If you are trying to polish fuel, you'll want to pull the fuel through the filter, not push it through. That's why the water separator is always on the primary. I've never seen a water separator after a fuel pump for a reason.

Maybe that's not as big of a deal on Detroits, but if you have a common rail engine then you definitely don't want to take a chance of getting any water to the injection system.