Fuel tank vent line thingamabob?

snal · Posted: Mon Oct 08, 2007 6:46 pm Post subject: Fuel tank vent line thingamabob?

My boat has 2 plastic "thingamabobs" in the fuel tank vent lines (both of which I discovered to be broken)...at first I thought these might be some sort of water stop, just in case water got in thru the vent, but after seeing the "guts"...they are simply an expansion chamber with a center plate (washer-like) and necked down at both ends to match the hose diameter.
These are plastic, and I can duplicate the part out of stainless, but what does it do? I can't see as how it would stop any water.

tsturm · Last edited by tsturm on Mon Oct 08, 2007 7:39 pm; edited 1 time in total

snal · Posted: Mon Oct 08, 2007 7:37 pm Post subject:

Hmmm...that makes sense! They broke just below the "washer" so I'll check to see if there's anything that'll "rattle" up above.

Dreamer · Posted: Mon Oct 08, 2007 8:03 pm Post subject:

The new ones I have, that I never installed, don't have a ball, only the hole in the 'washer' shaped disc. It acts as a whistle until a drop of fuel gets in there, then it stops whistling. You're full!

Sea Wolf · Posted: Mon Oct 08, 2007 8:31 pm Post subject:

Another related problem with the fuel vents over the years has been water intake into the tanks, particularly when the little screened openings in the vent fitting were turned forward and took on spray water when underway, or were turned upward and took on runoff rainwater.

The solution has been to add a gooseneck type of fitting in the vent line, placing it above the vent outlet to prevent water intrusion.

The original anti-siphon valave was a Perko, but here is one by Attwood.

Here is the surge protector you currently have, also by Attwood.

Joe.

oldgrowth · Posted: Sat Oct 13, 2007 2:30 pm Post subject:

When I went to the Sequim CBGT, I filled both tanks prior to leaving home. Had about 21 gallons in each 22-gal tank. If I made just a moderately hard stop I noticed fuel coming out of the vents and going down a steep hill, anything over a gentle coasting stop caused fuel to come out of the vents. With 18 gallons in each tank, I do not have this problem.

I had been thinking about how to solve this problem and it looks like the surge protector Joe shows should do the trick. My vent is a couple of feet forward of my fuel tank and about 16 inches higher than the top of tank. You can see it in the photo, between the side cleat and the C in C-Voyager.

Anybody have any other ideas?

________
Dave