Phil B. - Aux / Main tank venting

[BigRedDMaxx]

Phil,
I am in the process of installing a bed mounted aux tank much like your set-up with the fuel being pumped from the aux tank into the main tank thru a fitting tapped into the upper metal part of the fill line.
The question I have is do you have any problems with the main tank not being able to vent out air (pressure builds up)as the main tank fills ? The fuel cap vents in so that a vacumn does not form when the main tank level drops, but it seems like a vent would have to be added to allow it to fill. Not a problem during a regular station fill-up as the cap is removed. My pump rate is only 46 gal per hour. The aux tank is vented both in and out with a roll-over valve.
Thanks,
Big Red

[Paintdude]

Put a T in the fill line. One side to the OEM tank and the other back to the Aux tank. you will use the vent in the Aux tank.

[Phil B.]

Big Red - No, I have no problems with venting. My pump is very slow (35 gal/hr.). I only transfer fuel when I'm just below 1/4 tank and that allows all of the 20 gals. from the aux. tank to fit into the main tank (no overflows this way). I love the set-up. When I want to haul stuff, it takes about five mins. to remove the box and tank from the bed.


Good luck,

Phil B.

[poorloser]

Big Red
What kind of roll-over valve did you use? Where did you get it?

Thanks
Poorloser

[letsgo]

since I'm going to install an aux. tank, I need clarification. would you not put 2 tee fitings in the existing vent tub the lower one used for the fuel being pumped into the lower tank and the upper tee used for venting and overflow back to the aux. tank???

thanks for any input.

[Paintdude]

The tanks I use have a pickup line ,return line and a vent. 3 holes in the top of the tank. I think that is what is confusing you. My guess is yours only has 2. I am using Utilimater saddle tanks off of Fedex units that get replaced for rust under the inspection plate. I weld up the area with a patch,POR 15 the tank and we are good to go. I just did one today. I cant get enough of these tanks. :( The rollover vales have been coming on the tanks. My guess is you could get one from Utilimaster. The tank could be Freightliner also, that is what the chassis is on the Diesel fedex units.
The reaqson I use the T fitting is incase the operator forgets to turn the pump off. It will just go back into the aux tank. If you have the fuel cap tight on the truck..
My guess is you could weld a fitting into the fill cap of the Aux tank for a vent tube. But you really need a rollover valve. that would make the cap kind of bulky..Just an idea.

[ 11-11-2003, 04:35 PM: Message edited by: Paintdude ]

[Applecore]

I had a 35 gal tank constructed of 'diamond aluminum' for the box of the pickup. There was a L fitting put in the top of the tank with a rubber hose pointed towards the front of the box as a vent. The tank drains from a hole in the bottom of the box through a 3/8" rubber hose to an electric valve that is mounted to the rear of the cab below the box level that in turn is plumbed to the filler neck. I did have the filler neck replaced with the one sold by TransferFlow ( it has a larger neck for filling at the BIG TRUCK pumps.) The valve is wired to a switch on the dash in the cab. It is wired so that the valve can be active only if the ignition switch is on. If you don't know, the OEM filler on the tank has a 4 foot (approx) tube that goes down into the tank - I guess to prevent 'splash out' during filling. That was removed when I installed the replacement filler. I too wait until I'm about 1/4 on the gauge before doing the transfer - it is all by gravity, so filling can take quite a while. Works for Me

[Phil B.]

I'd think the stock tank would have to have the ability to vent out. Temperature changes alone are going to cause an increase in pressure. I have absolutely no problem with with pressurizing the stock tank. The aux. tank is of course vented with a one way check valve.

In addition to a roll-over valve, you may want to consider a transfer valve. I used a six port valve from a ford. I have to throw two switches to start the fuel flow: 1 to open the transfer valve and 1 to start the pump. When I'm done, I shut down the pump and close the valve. This prevents any siphon from continuing to drain the fuel through the de-energized pump.


Phil B.

[Paintdude]

Phil I set them up the same way. They make a 3 way valve for 1984 Chevy with dual tanks. Might be cheaper than the Ford one.List price is like 62 bucks.

[MAV]

My main tank has no problem venting either. My aux tank is 60 gals. I use a 1/2 inch ball valve to transfer fuel via gravity.
http://pic8.picturetrail.com/VOL227/437876/777914/37263484.jpg
http://pic8.picturetrail.com/VOL227/437876/777914/25620696.jpg
http://pic8.picturetrail.com/VOL227/437876/777914/24919801.jpg

[BigRedDMaxx]

Poorloser:
The rollover valve came with the tank. The valve is stamped "Temco 90-00945" if that helps at all.

Everything is all hooked up and seems to work fine without any need to vent the main tank. I'll take some pictures of the setup and post later.