Syncro gravity (rollover) valves

Bassyaks · Posted: Sun Oct 11, 2015 2:28 pm Post subject: Syncro gravity (rollover) valves

What are the functions of the gravity valves?

candyman · Posted: Sun Oct 11, 2015 3:26 pm Post subject:

In the event of a roll over, they shut off the fuel flow from tank

Bassyaks · Posted: Sun Oct 11, 2015 3:37 pm Post subject:

No, they have no direct contact to the fuel supply ,The main vent line is at the top of the tank and is vented to the filler area and will spill everything if rolled , so that makes the gravity valves useless .
I think they have more to do with vapors, directing them to the canister, but if there is a main vent line, what's the use of the valves

syncrodoka · Posted: Sun Oct 11, 2015 8:58 pm Post subject:

The main vent line is to equalize the pressure when filling the tank. That vent line ties back to the filler port and as long as there is a cap with a decent seal it is still a closed system in the event of a rollover.
The rollover valves are to keep gas from getting out of the fuel tank as they are routed outside of the closed tank system and into the charcoal canister and finally to the atmosphere.

I have been in a rollover in 2 carbureted vehicles and a bunch of fuel is spilled everywhere from the float bowl that wouldn't be a issue with a FI motor as long as no hoses are lacerated during the maneuver.

BillM · Posted: Mon Oct 12, 2015 4:28 am Post subject:

The valves if you turn one upside down will close. If I recall correctly Bentley makes a mention of the valves purpose and how to test.
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Bill M
87 Westy

insyncro · Posted: Mon Oct 12, 2015 5:30 am Post subject:

The title should be changed to "rollover" valves, the more common name, so more people can find it in a search.

candyman · Posted: Mon Oct 12, 2015 5:55 am Post subject:

insyncro · Posted: Mon Oct 12, 2015 6:28 am Post subject:

kamzcab86 · Posted: Mon Oct 12, 2015 10:05 am Post subject:

insyncro · Posted: Mon Oct 12, 2015 4:16 pm Post subject:

Syncros have a vent line for filling that runs along the filler tube and allows most of the air out while filling.
It is part of the metal portion that you put the nozzle into.

The rollover valves are in the top of the tank, in direct contact with gasoline and provide additional venting and act as a safety features when the vehicle ends up on its side or roof.

The vent line and the rollover valves are directly related to slow filling and when you can not get 18+ gallons into the tank.

The hose and tank diagram has been posted in other Syncro gas tank threads and should be viewed and understood before tackling Syncro gas tank work/rehabs.

Bassyaks · Posted: Mon Oct 12, 2015 5:02 pm Post subject:

I disassembled one to understand how they work , but are they use primarily for venting of the fuel tank? When would the valves interfere with the filling if the main vent line was clear, pressure from the inside shuts the valve off.
Insyncro had mentioned that he hard lines them to the intake manifold, is he bypassing the charcoal canister?

insyncro · Posted: Mon Oct 12, 2015 5:16 pm Post subject:

Bassyaks · Posted: Tue Oct 13, 2015 9:15 am Post subject:

So the main purpose of these valves is to vent (the top of) the fuel tank, and the "rollover" aspect was added as a secondary feature so the primary could be achieved in the event of a rollover the fuel would not leak from the vents.
Why are there 2 valves when other vehicles have only one?
If the main vent line was not at the highest point of the fuel tank would air become trapped at the top of the tank because the pressure couldn't be released through the valves
So in that case, would leaving the engine running (bad idea, and illegal ) allow the tank to fill to 100%

MsTaboo · Posted: Tue Oct 13, 2015 9:44 am Post subject:

insyncro · Posted: Tue Oct 13, 2015 10:18 am Post subject:

Every single part of the fuel system that is in contact with gasoline is breaking down.
The rollover valves and vent line are not the only parts that effect filling, didn't say that.

Each of the hoses should be checked once every two years, the submerged line, every 5 for preventative maintenance sake.

New hoses are not holding up as well in smaller sizes as of late.
Buy the best quality products as you can.

I would not want the job of the parts that hold and deliver gasoline, no thanks.

All4You

Hello all,

I wonder if my rollover valves have failed. 86 syncro with completely redone fuel tank and EJ25 conversion 4 years back. In the last 1-2 years i have noticed that the tank pressurizes every time I’m stuck in traffic, going slow or idling. If I’m cruising it may or may not pressurize. At the worst, when I open the gas cap there’s a loud woosh with gas boiling over from gas to liquid at the filler. Charcoal canister replaced twice. Canister and outflow hose at bottom of canister move air with minimal resistance. If I push air in to the tank vent line (thank connects at the top of the charcoal canister) air pushes out of the filler. I tried pushing air in from vent line at the filler neck while plugging the filler itself and gas poured out of the filler (even though it was duct taped shut) and I didn’t feel any flow at charcoal canister line.
Does anyone have ideas on where the failure is and if the roll over valves could be the culprit?
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86' Syncro, EJ25
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http://www.thesamba.com/vw/forum/viewtopic.php?t=647477&postdays=0&postorder=asc&start=0

MarkWard

dobryan

MarkWard

I read it was building pressure.
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dobryan


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