fuel tank question

[fishmagnet]

the best way to pull from both tanks is to have a 1gallon or so "sump" tank that both saddle fill.. However this only works if your pickups are on the bottom of the tank

[Destroyer]

Originally Posted by fishmagnet

the best way to pull from both tanks is to have a 1gallon or so "sump" tank that both saddle fill.. However this only works if your pickups are on the bottom of the tank

Respectfully, wouldn't that be just adding another layer of something to break onto the system? What's the benefit of it?

[reelapeelin]

Originally Posted by Destroyer

You know... actually, there IS a way to make it work.. It's one of those simple things that stare you in the face and it's so easy you don't see it...

The answer is simply to cross connect them... plumb the bottom of tank one over to the bottom of tank two. Then, on a second line, plumb tank two to the engine. Do not connect the line running from tank one to tank two with the line running to the engine.

Gas, like water, will always seek it's own level. So, since both tanks are connected together at the bottom, and as long as both tanks are vented so atmospheric pressure is the same inside each tank, and both tanks are sitting at about the same height inside the hull, what will happen is that as tank two is drawn down tank one will replenish it in an effort to stay level with it. The result will be both tanks will be drawn down at the same time!!!

That'll certainly work as far as draining each at the same rate...sounds like a good idea, as long as you can deal w/all the crud that sinks to the bottom of the tank(including water)...aren't conventional fuel pick-ups mounted just above the tank bottom?

[Destroyer]

Originally Posted by reelapeelin

That'll certainly work as far as draining each at the same rate...sounds like a good idea, as long as you can deal w/all the crud that sinks to the bottom of the tank(including water)...aren't conventional fuel pick-ups mounted just above the tank bottom?

You're right on the money Reelapeelin. Fuel pick-ups are typically mounted an inch or two above the bottom, and some of them even have a screen over them just to avoid the crud, water, etc that can accumulate in the bottom.

My answer to you would be to follow the leader. Use the factory line from the tank to your engine that is already above the bottom level, and when you plumb the tanks for the cross connect mount the new lines about an inch or so above the bottom, for the same reasons already discussed. Take extra care to make sure the new lines don't leak where you insert them into the tanks. As a matter of fact, I'd probably put in a JIC (Joint Industrial Council) 37 degree flare fitting at each tank so that I could remove or replace the line as necessary. Use a 37 degree flare instead of the normal 45 degree so there is less chance of leakage. In fact, I'd even be tempted to make a double flair in the line, such as is used in brake lines, just for the additional safety it provides.

Note* Most flare tools are set up to make 45 degree flares for fuel lines and household applications but a 37 degree flare is the proper angle for AN (Army-Navy)automotive fittings. Those 8 degrees can be the difference between a dangerous leak and a perfect seal.

[reelapeelin]

Originally Posted by Destroyer

You're right on the money Reelapeelin. Fuel pick-ups are typically mounted an inch or two above the bottom, and some of them even have a screen over them just to avoid the crud, water, etc that can accumulate in the bottom.

My answer to you would be to follow the leader. Use the factory line from the tank to your engine that is already above the bottom level, and when you plumb the tanks for the cross connect mount the new lines about an inch or so above the bottom, for the same reasons already discussed. Take extra care to make sure the new lines don't leak where you insert them into the tanks. As a matter of fact, I'd probably put in a JIC (Joint Industrial Council) 37 degree flare fitting at each tank so that I could remove or replace the line as necessary. Use a 37 degree flare instead of the normal 45 degree so there is less chance of leakage. In fact, I'd even be tempted to make a double flair in the line, such as is used in brake lines, just for the additional safety it provides.

Note* Most flare tools are set up to make 45 degree flares for fuel lines and household applications but a 37 degree flare is the proper angle for AN (Army-Navy)automotive fittings. Those 8 degrees can be the difference between a dangerous leak and a perfect seal.

I gotta feelin the reason fuel pickups started coming from the top was to ELIMINATE possibility of bottom leakage (also makes servicing from the top easier too)...what I was thinking is a "J" shaped pic-up tube...long end welded to a hole in the bottom, short end turns down and has filter screen 1-2" above the bottom..what the heck...there's a thousand ways to skin the same cat...here kitty, kitty...

[Destroyer]

Originally Posted by reelapeelin

I gotta feelin the reason fuel pickups started coming from the top was to ELIMINATE possibility of bottom leakage (also makes servicing from the top easier too)...what I was thinking is a "J" shaped pic-up tube...long end welded to a hole in the bottom, short end turns down and has filter screen 1-2" above the bottom..what the heck...there's a thousand ways to skin the same cat...here kitty, kitty...

Ya... I like that... sounds like it could work. You know, I've got two 18 gal side Alum tanks that are pulls from another boat. I may have to start playing around with this in the garage over the winter. That extra 36 gals would be a hell of a range extension. The rod holders in the sides of my boat broke into tiny pieces long ago, so putting the tanks there would not be a problem.. Hmmmm....this is getting interesting.

[Steplift 72']

Connecting tanks below the deck could also drain BOTH tanks to the bilge. Then any leak on either tank would drop to the level of the hole. Also a slight list would probably let a bit of gas vent overboard as the tanks sought their level side to side. I am a fan of the 20 gallon saddle tanks, above the floor and it keeps any leakage obvious.