Dmax fuel system ? on quick disconnect fittings

[mdrag]

SoCalDmax made a comment in another thread when explaining the PSD cackle to another forum member, and I did not want to side track that discussion with my question:

http://forum.62-65-dieselpage.com/ubb/ultimatebb.php?ubb=get_topic&f=3&t=003900&p=2

Quote:

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"Another issue they're having is the use of quick disconnect fittings on the fuel system. They're designed for pressurized use, not vacuum as found on a diesel. The O-rings leak air into the fuel system...."

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I installed the 56 gal TFI tank in my truck, and I have to report that quick disconnect fittings are used on the Dmax fuel system.

Are the Dmax quick disconnect fuel fittings different in design than the PSD?

IIRC, the tool I bought to disconnect the fuel lines was marked to work on Chevy, Ford, and Chrysler fuel lines...

[SoCalDMAX]

Hi Mittie,

I'm no expert on fuel systems, but if you recall, a member called Doc Dyno was answering lot of my "air in the fuel system" questions. I met him in person, and he is far more knowledgeable about fuel systems than he alluded to (modesty, I guess). His co. performs fuel system engineering/consulting for a number of different clients, including marine mfrs.

I asked him this same question and he did tell me that they are slightly different fittings between GM and Ford, but when I asked point blank if he thought the Dmax fittings were leaking, IIRC he said that it would need to be investigated and quantified.

This is what I've gathered from other forums: The fuel already has a certain amount of air entrained in it, and more air is trapped in it from sloshing. Whenever a vacuum is pulled on the fuel, it can release this entrained air, and it can be exacerbated by rough edges in the tubing, sharp bends or higher vacuum or temp. This can show up especially in the fuel filter, where there is a differential already just from the way a filter works and it gets worse as the filter gets dirty. This results in a partially full fuel filter, the rest is air released from the fuel.

I'm still convinced a pressurized system from a pump near the tank is better than a vacuum draw system. But I'm not an engineer. Enough of my opinion. Perhaps Doc Dyno will swing by.

Regards, Steve