After posting my attempt at a Hutch mod (I'll get around to responding to questions there, thanks for all the replies) https://www.ford-trucks.com/forums/585717-i-tried-for-a-hutch-but-got-harpooned-have-questions.html , I did some Googling and came up with the following from David Hodgkins, a Racor employee with 40 years in diesel fuel system engineering http://www.parker.com/racor/ProductCatalog/Side%20Bar%20Links/Air%20Sep/Air%20Separation.pdf I consolidated his key points below.

My interpretation of them is that:

1) Diesel has much air in it already when you buy it to fill up, and while the truck is underway the fuel is sloshing around in the tank creating more entrained air. A Hutch mod would only seem to eliminate any additional air due to the disconnects?

2) A (simple?) modification to my newly installed Racor 645, will allow it to act as an "air separator" in a manner similar to a FASS. This only requires the addition of an orifice fitting from an output port on the Racor which goes to the return (or maybe overflow) line to the tank?

Please read below, and comment if such a mod is feasible, and just how to do it. If a true "air/fuel separator" is really this simple, it seems that every one would be doing their own, and FASS/Air Dog wouldn't be doing much business!


Depending on how much air is present in molecular form, more or less will separate from fuel as it moves through any torturous path, such as a fuel filter, and collects in any high point in its path. This can allow air to pass into the outlet line as significant size bubbles.

The simplest and best solution is to use a filter head that has the outlet line exiting directly from the top,with no place for air bubbles to collect. In this solution, air is not stopped from coming out of fuel, but as each minute bubble forms, or coalesces on the downstream side of the filter media and passes to the top side of the element, it will pass out of the filter as a very tiny bubble.

Racor has a filter assembly available that will solve the problem. The 600 Series has an outlet directly on top that, when connected with an orifice fitting, will send any air directly to the return system. An air vent must be fitted with an orifice between 0.020 to 0.040 inches (0.5 to 1.0 mm).

 

Are you going to install this "air vent" orifice on your setup? It has to be pressurized or it will just suck more air in.

 

Keep reading ernest! You will find that most of the modified fuel return systems people have done either DIY or the through kits purchased from sponsors provide some type of orifice for air to entrailed air to escape. Take a look at Kwiks set up.

http://rides.webshots.com/album/32614313yLKyrS?start=12

I haven't done this yet, but I'm getting ready too. I also read about Raycor's air escape filter and thought that was a great idea.

 

Oops, I just had fish (brain food) for lunch, and realized that any bleed orifice has to be on the pressure side, so I'd have to install a second Racor there to use for air separation!

 

After reading some of info above, just wondering if you could put a fitting in the top of the fuel bowl cap with a orfice to bleed the air back to the fuel return line? I bet there is alot of air just under the cap, being this is the highest point the fuel reaches after the rail fuel pump. I remember seeing a fuel bowl cap with a fitting in it somewhere on this forum awhile back.. maybe you can buy a cap just for this purpose.

 

That is a good idea, if you had a lift pump. I do not know if it will work better with a lift pump pressurizing the filter at 5-7psi, or in the fuel filter cap, at 55ish psi. With more pressure, it would certainly benefit from a smaller orifice, but on the flipside, you could use a larger orifice so air could pass easier if it was only under 5psi of pressure. Also there would be less piping back to the tank/return line, if the seperator was frame-mounted. As far as the fuel filter cap, the way to go would buy a billet aluminum fuel filter cap, that way it will not crack, break, or need to be replaced. I think DieselInnovations has them.

 

Good thoughts, Kris and Clint. I'm getting ready to do the "trial" thing with FN74 on the fuel system mods, so I will already be getting one air bleed opportunity there. When I get the in-tank mods done, that will become step 1 in a 2-step air removal effort, with the on-engine bleed off being the second step. I bet the "law of diminishing returns probably starts kicking in at about the second or third bleed-off effort, so I might not be able to realize much benefit from tapping into a billet fuel cap on my truck.

 

I was just looking at my fuel bowl during filter change and it looks like the return fuel line from the engine actually starts near the top of the fuel bowl and goes directly back to the tank. Why couldn't a guy just get a aluminum cap and re-connect this line using the proper orfice to the top of the cap to bleed off any air collecting there, which is the highest point in the fuel system? I am still trying to learn how all of this works so excuse me if this sounds silly... To me the engineers kinda had this in mind but did not go to the highest point, which is where the air bubbles are..