Overfill valve in vent line ?

[zkx14]

Planning to replace my fuel and vent line on 75 Duster and I noticed a bulge in the end of the steel line going to the canister. After a bit of thread searching I figured out it is my 'overfill limiting valve' Do any repop lines include this? Anybody know where to get them?

 

[67Dart273]

Boy I don't but "back then" the service replacement was a short length of tube that you just spliced in it's place.

 

[zkx14]

I saw that ... and tried searching for the replacement piece. Not finding anything that would splice in. Looks like some do a valve at the tank. Seems kinda backward, but I could cut the end off the old tube and use it with new lines. The inner piece moves inside the tube, but the old pics show what looks like a ball in center. I don't see any way I am going to be able to check if it works. I might just soak it in gas to clean it inside. I'd re-use that front section of tube back to the passenger floor area, but it has a spot in it that was bent and crimped pretty bad - actually think it was installed that way.

 

[zkx14]

Here is a pic of what I am talking about. The thick part of the tube contains the valve. This is normally covered by the hose from the canister.
So, is this thing even important? Why was it there? Apparently there are a lot of cars running without them.
I got my new lines Friday at Carlisle from Fine Lines. They said they used to include it in theirs, but have recently discontinued it. He referred to it as the check valve, but could not tell me anything more about it. He did not know of any alternative. The guy from Inline did not know anything about it....

 

[67Dart273]

Unless someone has completely changed the plumbing for your fuel tank, that IS th fuel vent. Some guys plumb them to the air filter outer bonnet.

There are some threads on this. Some years-----72, Ma used external vapor separators. I believe some, up around 73? 74? later? used a vapor separator built into the tank. That line originally tied in with the carbon canister.

As I said, it IS the tank vent

Some of these threads are not entirely correct because of the year, but this is the idea...........

http://www.forabodiesonly.com/mopar/showthread.php?t=183956

http://www.forabodiesonly.com/mopar/showthread.php?t=210314

http://www.forabodiesonly.com/mopar/showthread.php?t=236298

http://www.forabodiesonly.com/mopar/showthread.php?t=217628

http://www.forabodiesonly.com/mopar/showthread.php?t=192792&highlight=273+evaporative

http://www.forabodiesonly.com/mopar/showthread.php?p=1787178

http://www.forabodiesonly.com/mopar/showthread.php?t=222929

 

[zkx14]

Unless someone has completely changed the plumbing for your fuel tank, that IS th fuel vent. Some guys plumb them to the air filter outer bonnet.

There are some threads on this. Some years-----72, Ma used external vapor separators. I believe some, up around 73? 74? later? used a vapor separator built into the tank. That line originally tied in with the carbon canister.

As I said, it IS the tank vent

Some of these threads are not entirely correct because of the year, but this is the idea...........

http://www.forabodiesonly.com/mopar/showthread.php?t=183956

Yes this is the vent line. It was, and will remain plumbed directly from the tank (2 line system, no external separator or other lines) to the canister as original, just that I am puting in new lines that don't include the valve. The pic I posted is the original tube with the valve in it that is shown in the drawing in first thread you referenced, I'm just trying to understand the purpose/importance of the valve. How did it work? What happens if it is not ther? What would happen if the valve was stuck? Mostly want to know because no replacement seams to be available. Even on that drawing it says not required on all models.

 

[67Dart273]

I don't have a 75 shop manual, so I don't know the specific plumbing / hardware differences in the system, l but the basics are in most any shop manual after 70 or so. You can download a 72 here

[ame]http://www.abodyjoe.com/pictures/Misc.%20car%20info/1972%20Plymouth%20Chassis%20Serv%20Man.pdf[/ame]

You have to read both the fuel section and the emissions section

Basically, the tank either has a separate or built in vapor separator. The only place "out of" the tank for vent is the line in question.

The filler caps have never been vented, and if you look at those threads, you'll see how the older cars (pre 70) had a vent welded into the upper filler tube. The caps have a "pressure vaccuum" relief.

That line comes up front and ties into the carbon can system. The ball valve in the end of that line is supposed to keep liquid surges of fuel at bay during filling, etc.

The MAIN purpose of the line is what I've been trying to convey. It IS the tank vent. The reason it is there and the reason it ties into the carbon can is to recover fuel vapors instead of venting them overboard.

 

[zkx14]

I don't have a 75 shop manual, so I don't know the specific plumbing / hardware differences in the system, l but the basics are in most any shop manual after 70 or so. You can download a 72 here

http://www.abodyjoe.com/pictures/Misc. car info/1972 Plymouth Chassis Serv Man.pdf

You have to read both the fuel section and the emissions section

Basically, the tank either has a separate or built in vapor separator. The only place "out of" the tank for vent is the line in question.

The filler caps have never been vented, and if you look at those threads, you'll see how the older cars (pre 70) had a vent welded into the upper filler tube. The caps have a "pressure vaccuum" relief.

That line comes up front and ties into the carbon can system. The ball valve in the end of that line is supposed to keep liquid surges of fuel at bay during filling, etc.

The MAIN purpose of the line is what I've been trying to convey. It IS the tank vent. The reason it is there and the reason it ties into the carbon can is to recover fuel vapors instead of venting them overboard.

Thanks for the input, I think I am finaly making sense out of this ....
I understand the vent line allows recovery of pressure let-off or fuel vapor could push out the cap. I do have a 74 manual as well as a Chiltons. been studying these as well as the pic from your post. It looks like the 'valve' has a small tube in the center, which must be the part that according to the manual - open at 1/2 PSI differential to allow vapor escape. Chilton's includes this under the "vapor saver system" so I guess it's supposed to conserve fuel by limiting free evaporation with a very slight backpressure. That small slider is enclosed in another larger slider that will close off the end of the tube when it lifts. I guess that is what would stop a liquid surge as you mentioned in last post.
So, that pretty much covers how it works. I guess the answer to my real question of what happens without it is - not much. I suppose since the lines go to the canister the fuel is recirculated anyway and it's not a big loss?
As long as I can keep it in a vertical position; I think I will just cut the valve off the old tube and shove it up the hose ahead of the new tube end. Should work as it was intended.

 

[805moparkid]

i just went thru this on my 73. i deleted the canister, cut that little guy off. now i use a fram filter with a bypass that is plumbed into that as a return. i yarded a 68 vent line and tube so the vent is on the tube.