Anyone know what the native state of the Tank Change Over Return Valves beside the rear wheels is? without power are they in an 'open' or 'closed' state? what does the provision of power to these valves do, essentially, open or closed.

 

Selecting 'right tank' sends voltage to all three valves (left return, right return, changeover). This opens the right return valve and closes the left return valve. The changeover valve opens to the right tank.

Selecting 'left tank' removes voltage form all three valves....with exactly opposite results

Cheers
DD

 

boy, that's not as simple as I had hoped.
series2 body adding series3efi engine, original car had two pumps for carbs so wires in boot go live with change tank switch on dash, i was planning to run an earth and 'all hot' or 'ignition wire' (whatever term is) to power the efi's single 'always on' pump and connect the orphaned wires from the return change over valves that emerge in the boot with no destination to the fuel switches in hope i could power the change over valves off the old pump lines, relying on their on/off state. but its not like that at all from what you say then.

 

Simple and Jaguar , there's two words you dont see used together too often.

Not sure what it is in Dougs description that makes it more difficult. One way or another you have voltage arriving in the boot that commands left /right , supply /return. Not saying its simple but all the ingredients seem to be there.

 

i have a skill for making simple become difficult complex very easily

i guess its just the matter of how one valve knows that the other has come on, or is it more that denying power to one and transferring it to the other is the 'signal'?

hope that makes sense.

.i.e. pressing the tank change button switches power from left valve and left tank to right valve and right tank in one hit..?

 

With the button set for the right tank all the valves receive voltage. With the button is set for the left tank, none of them receive voltage. They don't 'know' anything.

The return valves (which have a solenoid inside) are "handed"....a specific one for right side and a different one for left. They look the same but are different internally. The right side return valve is closed at rest (no voltage applied) and opens when power is applied. The left side return valve is open at rest (no voltage applied) and closed when power is applied. There is no neutral position, so to speak. Whenever one valve is open and the other will be closed.

Cheers
DD

 

[QUOTE=Doug;Whenever one valve is open and the other will be closed.

Cheers
DD[/QUOTE]

Assuming all parts are in good nick!🙏

 

cheers-
i think it was the individual behaviors of the solenoids i was trying to get my head around, makes more sense now.

 

What repercussions would there be if both tanks had the return valves removed, along with feed valves too? making it all just one system.


Would the returning fuel favour filling one side more than the other?


Would the fuel pump drain one tank before the other?


I would think gravity would play a big part in it and keep both tanks on roughly the same fuel level

 

Some guys do just that. Remove the changeover valve and 'tee' the 3 hose together and remove the return valves . Both tank should drain equally. Return fuel might go to the closest tank first but the levels should equalize.





Right! Unless the car is parked on an uneven surface, of course. In that case fuel flows to the lower tank, possibly overflowing it. Gotta be careful. This is the rub in joining the tanks together.

Cheers
DD

 

True true, damn gravity

 

interesting points!
so now getting head around the tank switch valve in the boot. does it have an on/off default .. only appears to have one power connector and an earth.. does it snap (say) left without power and right with power on the fuel change over circuit?

 

saw this, so its a case of no volts or volts? I assume
"The dashboard switch applies or removes voltage from all three valves simultaneously. The changeover valve dictates from which tank fuel is drawn when the fuel pump is operated. The left and right return valves dictate to which tank unused fuel is returned to. When the left tank is selected there is no voltage applied and fuel is drawn from, and returns to, the left tank. When the right tank is selected, voltage is applied to all valves and reverses the flow. The left and right valves are identical except their mounting brackets which orient them in opposite directions. A single electronic event (application of 12 volts) effectively "closes" the left valve but "opens" the right. Actually, the same mechanical action takes place in both valves....only their orientation is different."

 

"Changeover valve"


Right. As mentioned above........

Selecting 'right tank' sends voltage to all three valves (left return, right return, changeover). This opens the right return valve and closes the left return valve. The changeover valve opens to the right tank.

Selecting 'left tank' removes voltage form all three valves....with exactly opposite results


Cheers
DD

 

Exactly right, as mentioned earlier......

"With the button set for the right tank all the valves receive voltage. With the button is set for the left tank, none of them receive voltage."






Right!

Go back and look who wrote it


Cheers
DD

 

~ thanks, i think i have the changeover valves configured electrically now.

 

AHA!! That explains why my Right gauge doesn't work when I select the Right tank! They're Tee'd together and have no valves, but I thought the gauge should still work.

Thank you, Doug, that crosses one Dreaded item off my list!
(';')

 

I probably haven't helped you at all, sorry to say.

The fuel gauge circuit is separate from the changeover circuit. And unless your Ser II is a 1978/79 with fuel injection the changeover system is different anyway!

Cheers
DD

 

Aw Dang! Here I thought I had the answer!
It's MY '76; Carbed OE. (sigh)
I've still crossed it off my list!
(';')

 

Synopsis:


1. Right, yes, left, no! as to voltage to the change over valve.


2. Elinor, better than you think. *** your tanks are T'eed together, it merely takes some interpolation. If the car is on level ground the reading on the guage is the same for either tank. If on a slant, not so much. Then, extrapolation required!!!


3. Fall back, if in doubt, off to the gas station!!!


Carl