Fuel Check Valve

[Len Silva]

We have often had discussions about the fuel check valve and loss of prime.  It just occurred to me that if the fuel return line was run to the bottom of the fuel tank so that it was always submerged, there would be no need for a check valve. 

It's so simple that there must be a flaw in my thinking.  What say you?

[Busted Knuckle]

Len the only flaw I can see right now is that the returning fuel flowing at the bottom will stir the settled "trash" and sediment!

But trust me some wiser folks will chime in with "what we don't see!"

I like the idea, but if it were that easy it'd been done before. Would'n it?   BK 

[zubzub]

My guess is more resistance to fuel flow ie even back pressure   if you were on a hill

[Len Silva]

I know that this is the simplest of fluid dynamics issues.  Thinking about it begs the question:  Why would a bad check valve in an otherwise tight fuel system cause it to lose prime?  It seems to me that air must get in from somewhere for the fuel to flow back to the tank and that the only real purpose of the check valve is to preserve prime when the system is opened (like for filter replacement).

[TomC]

ALL return lines return to free air at the top of the tank.  You don't want any restriction on the return line.  As to "stirring" up the bottom dirt, everytime you drive down the road, the fuel in the tank is being violently churned up-so that's not an issue.  Find out why you are loosing your prime-replace your fuel lines, fittings,etc.  Good Luck, TomC

[bobofthenorth]

I dunno either Len - I went through the same thought process a couple of years ago.  I had an intermittent no start exactly like John is experiencing.  I looked for leaks, tightened lines and generally fought with it for a year before I finally just gave up and changed the check valve.  The problem went away immediately and hasn't recurred. 

My guess, and that's all it is, is that you simply can't get our systems perfectly air tight.  Over time those of us with air suspensions leak down and similarly over time some of the fuel connections must leak a little air.  The check valve would then serve to hold the fuel so that the pump doesn't lose its prime despite those small vacuum leaks.

[compedgemarine]

actually not all return to the air space in the tank. on my Eagle the return line runs to the bottom of the tank. I pulled both the pickup and returns out of my tanks while the floor was up. the pickup had a spot where it was near the baffle that was worn almost through which would have caused it to run out of fuel at 1/3 rd. of a tank. my return line did not have a check valve in it any where. so far it has never had a prime issue.
steve

[gus]

Len,

My check valve is on the supply line just before the primary filter.

If there is one on the return line I don't know about it and don't see what purpose it would serve?

[bobofthenorth]

My check valve is on the supply line just before the primary filter.

Mine too.