Fuel supply/return lines query

[Dave64]

Hi All, 

                 Sorting out the fuel system (or attempting to, anyway) on this 200TD 12L engine into project vehicle.

Looks pretty basic, about a 5/16" main supply nylon line from tank to lift pump, (had to make bracket to re-position fuel filter housing), and about a 1/4" return excess fuel line back to the tank. Pretty straight forward. NOT using a standard fuel tank though, rather an 18 gallon diesel tank off some early Mazda cabover diesel, 3 litre , roughly mid 80's.

Came across this device inserted in what I take to be the return line (on tank, NOT engine), one of THREE steel lines going in/coming out of tank.Main line , pretty self explanatory, return line could be either of other two, wouldn't have worried me except for this little nylon device pictured, was in the nylon return line just before where it joined the steel line back into the tank itself. Some sort of restrictor or check valve (although you can blow air in either end). Approx 30mm long, 5/16" OD and inner passage will take a 7/64" drill bit. has two tiny metal balls in it on some sort of slide. Only thing I can think it's purpose is, is to either stop or restrict the amount of fuel allowed back to the tank, beats me why though.

The tank also has another line which I think is some sort of breather. The filler cap is a screw on type with a rubber gasket under the lid, so the tank itself would have to breathe otherwise it would either pressurise or create a vacuum. Where this line went or was originally hooked up to is a mystery to me, bloke who gave me the tank didn't know either, he inherited it off someone else.

 Had a look through the Land Rover book I have here, no mention of any restrictor and only has reference to main supply and return excess fuel lines. I take it that this engine when in a Discovery (or whatever), vented the tank to the atmosphere via the filler cap, much the same as in just about any other early petrol engined car.

Must be a moral here somewhere:- "Thou shalt not tinker OR modify!"

Anyway, here's the little jigger I dug out of the return line. 

Any thoughts would be appreciated , Dave64

[Bowie69]

I believe... That is a breather, and the balls shut the pipe under pressure of diesel in the event of a rollover.

 

[Dave64]

Bowie69

Ah! That makes sense.

Does the 12L engine run anything similar?

Probably wouldn't hurt to reinstall it, got another line I can run from the engine excess fuel back to the tank, so can bypass that little valve if the 12L doesn't need, or like any sort of restriction as per standard L/R setup.

Thanks, Dave64 

[Bowie69]

No idea on the 12L, though I do recall some other posts about a similar device, albeit on later trucks.

[missingsid]

I have seen topics that suggest that this is a legal requirement for vehicles after a certain manufacture year?

[Bowie69]

Yup I believe so, wrapped up in the C&U regs I think.