1/4 check valve

[jim]

Hey, Jurjen,
I believe you were the one to discover that our Eagles had the check valve in the return line, so maybe you can answer a couple of questions about it.

Which way does it flow? 

What is the purpose?

Thanks
Jim

[vangremlin]

Jim, here is what I found in the 1981 TSM about the check valve.  Hope everyone can read this.

[carnuck]

rollover valve

[BenM]

Not mentioned, it reduces the chance of fuel draining out of the supply lines which reduces cranking after the car has sat for a few days.

[jim]

Not mentioned, it reduces the chance of fuel draining out of the supply lines which reduces cranking after the car has sat for a few days.

This is what I was looking for. I had hoped this was the case.  If the 88 sits up for a couple of months, it is very difficult to get gas back to the carb.
So, even though I have the Motorcraft carb, I reinstalled the dual outlet filter and connected the top outlet to the return line.
BUT - now I have a major gas leak from the top right front of the tank.  I suspect that the rubber hose deteriorated from being out of use so long.
I have not replaced the check valve.  Since the valve was inside the gas line most of us did not know it was there.  I'm sure almost all were lost when hoses were replaced.

[BenM]

The cracked and rotting hoses are probably the cause. Air is smaller and less dense than gas and will go through those hoses much easier.

Even with the check valve you're going to be lucky to have a whole week before it drains back to the tank or (especially) evaporates. I don't want to lead you astray on how much it may help with bad lines, which is probably not at all.

[macdude443]

I've been looking into re-connecting the return lines in mine.  The vent (smaller metal line) was plugged when I bought it and the return line was wide open.  I filled the tank a week ago and after driving for ten minutes I noticed gas running out of the open return line under the hood.  I plugged it and have been driving it like that for a while.  I've decided to reconnect it to something, so I bought the 3 way filter and a check valve.  I no longer have a charcoal canister (po removed it).  I suppose it's ok to use this in-line valve from BMW, PN#16 14 9 068 988?  Was going to run the top hole of the filter to the check valve and then to the open return line.   I haven't had any issues with starting, though.

[BenM]

I've been looking into re-connecting the return lines in mine.  The vent (smaller metal line) was plugged when I bought it and the return line was wide open.  I filled the tank a week ago and after driving for ten minutes I noticed gas running out of the open return line under the hood.  I plugged it and have been driving it like that for a while.  I've decided to reconnect it to something, so I bought the 3 way filter and a check valve.  I no longer have a charcoal canister (po removed it).  I suppose it's ok to use this in-line valve from BMW, PN#16 14 9 068 988?  Was going to run the top hole of the filter to the check valve and then to the open return line.   I haven't had any issues with starting, though.

The plugged vent is why the gas came out of the return line.

Gas in an underground tank is a constant temperature, within a few degrees of the mean yearly temperature of wherever you live.

In a normal mid-latitude area where the ground is 58* the cold gas gets pumped into your tank and absorbs heat and expands as it reaches ambient temperature. (The vapor expands more than the liquid.) Without the vent line the pressure is forced out somewhere else, at a lower connection in the tank than the vent line, a connection in the liquid gas.

Sometimes the gas cap leaks enough to allow air in, sometimes it doesn't, but even a basic mechanical fuel pump can create enough suction to collapse a fuel tank.

Plugging up the vent is just a problem waiting to happen.

I haven't a clue why someone would remove a charcoal canister. It provides no performance gain to remove it and makes your car smell like gas on a hot day. It allows moisture, dirt, and insects a direct route into the tank. It creates the possibility that liquid fuel may drip onto a hot exhaust.

Even without the vacuum purge working it does most of its intended functions.

[macdude443]

Makes a lot of sense.  I was speaking to my brother tonight and he reminded me that he picked up a spare charcoal canister for me.  I'll just put it back in.  Would the check valve on the return line still be necessary?

Sorry if I'm hi-jacking the thread!

[BenM]

Definitely put a check valve in the return line. It's not necessary, but it helps with a number of little things.

[macdude443]

My mistake.  The vent and return lines were wide open under the hood.  No sure why it leaked.