DIY tank vent?

[GREASE FIRE]

i have an aluminum fuel tank in the bed that i bought used off CL. It had a tank vent fitting on the top and i assumed it worked at first but then realized it did not because there was a lot of pressure in the tank when i removed the fill cap (non-vented type). So i took it off just now and need to rig up something in a hurry that works. I do have some check valves around here.

The problem is that i am feeling a bit "mentally challenged" right now because i can't figure out which direction the check valve should be going.
on the one hand, i know the tank needs something to prevent pressure from building up so that makes me think the arrow on the check valve should be pointing away from the tank.
But, it seems the tank is also subject to vacuum because the lift pump is sucking fuel out of it so there needs to be some air coming in as well - right?

this makes me think i would either need to use two check valves, or else find a vented fuel tank cap with 2" female threads that would screw onto the fill neck of this tank, and the cap would have to be vented ways (rather than a check-valve style vent).

could anyone please set me straight on this? it was a hard day with my truck (i will spare you all the rest of the details!)

thanks,
Paul

 

[Rollin Coal]

I won't lie at first I thought you were an idiot but then you made a great point hahaha I'm in for seeing how this should work too. While we are on the subject with tank vents. Is there anything that can be done to our truck's tanks to vent them? My TDI Golf had a "switch" inside the neck that you could vent the tank with to get more fuel in.

 

[MIDNIGHT RIDER]

i have an aluminum fuel tank in the bed that i bought used off CL. It had a tank vent fitting on the top and i assumed it worked at first but then realized it did not because there was a lot of pressure in the tank when i removed the fill cap (non-vented type). So i took it off just now and need to rig up something in a hurry that works. I do have some check valves around here.

The problem is that i am feeling a bit "mentally challenged" right now because i can't figure out which direction the check valve should be going.
on the one hand, i know the tank needs something to prevent pressure from building up so that makes me think the arrow on the check valve should be pointing away from the tank.
But, it seems the tank is also subject to vacuum because the lift pump is sucking fuel out of it so there needs to be some air coming in as well - right?

this makes me think i would either need to use two check valves, or else find a vented fuel tank cap with 2" female threads that would screw onto the fill neck of this tank, and the cap would have to be vented ways (rather than a check-valve style vent).

could anyone please set me straight on this? it was a hard day with my truck (i will spare you all the rest of the details!)

thanks,
Paul

Forget about check-valves on a tank vent; no way can it vent with a check-valve.

Without actually seeing what you have to work with, I will make a few stabs at some possible means of venting the tank.

The vent needs to be at least 1/2" I.D.; bigger is better.

Is your filler-cap or neck threaded NPT ??

If so, by using a couple nipples and a TEE, plus maybe some elbows, you can make a port to thread in a 1/2" hose-barb to clamp the vent-hose to.

This will be plenty good enough for driving, but not the best when fueling.


Best is to cut/drill an access in the very top of the tank and install a bulk-head fitting, to which you can either add a hose-barb, or simply add a rigid hi-rise "U"-shaped vent made by fitting two street-ells together.



Or, you could just screw out the vent fitting that is already on there and fix it.


For venting the factory tanks, lubricate the twenty-plus-year-old grommets in the top of the tanks and pull out the factory 7/16 vent-hoses.

Throw away the old hoses and roll-over valves.

Lubricate and install new 1/2-inch hoses through the grommets.

TEE the two individual vent-hoses together into one main vent-hose.

Route this up high and dry, terminating in a down-ward pointing "U".

Done thus, you can use the high-volume pumps that the big boys use, instead of dribbling around with the baby hose at the car islands.

 

[MIDNIGHT RIDER]

or else find a vented fuel tank cap with 2" female threads that would screw onto the fill neck of this tank,

If the cap you have is a plain old pipe-cap, you can drill it and either weld in, epoxy, or install a bulk-head fitting directly into the top of the cap and thread an inverted "U" into this.

The inverted/upside-down "U" is to prevent rain from entering the tank.

 

[jim x 3]

GF: You can't use check valves. If the existing tank vent opening is closed off, then buy a vented tank cap. Otherwise, attach a fuel-rated rubber hose to the top-of-tank vent and loop it up as high as possible, with a downturn (as midnight suggested) or with a cap with a small vent hole drilled in the side.

Regards,

 

[GREASE FIRE]

thanks for the replies!

just curious as to why check valves won't work? is it because they don't allow enough air flow or because they won't crack open with the pressures found in fuel tanks?
the one i was thinking to use is an "extra low cracking pressure" check valve - i can open it with my breath, both on the pressure and suction side.
Reason i ask is that my impression, about the vent that came with the tank and is no longer working, had some kind of spring-loaded valve inside. It got blocked with crud, then i cleaned it out and it is now basically just a hose barb that will not preven fuel from spilling out of the tank.


BTW, just for the record - i am in fact an idiot....but this tank is slightly different because it has a coolant-heated fuel pick up in it for wvo so it builds up a lot more pressure than a diesel tank as the fuel heats up. ALSO - my wvo setups do not return fuel to the tank but rather back to the inlet of the lift pump (when on wvo only) for numerous reasons (that would be the topic of a new thread). So, this tank had no return line or vent. For some reason it was working fine for several thousand miles and then suddenly stopped working......

thanks!
paul

 

[GREASE FIRE]

also...

Also, just FYI, here is a picture of the non-working tank vent my tank came with:

http://www.gtdev.com/products/tankvents.asp

it is the one in the top left corner. I thought for sure this had some kind of check valve/pressure release valve built in.

 

[MIDNIGHT RIDER]

thanks for the replies!

just curious as to why check valves won't work? is it because they don't allow enough air flow or because they won't crack open with the pressures found in fuel tanks?
the one i was thinking to use is an "extra low cracking pressure" check valve - i can open it with my breath, both on the pressure and suction side.
Reason i ask is that my impression, about the vent that came with the tank and is no longer working, had some kind of spring-loaded valve inside. It got blocked with crud, then i cleaned it out and it is now basically just a hose barb that will not preven fuel from spilling out of the tank.


BTW, just for the record - i am in fact an idiot....but this tank is slightly different because it has a coolant-heated fuel pick up in it for wvo so it builds up a lot more pressure than a diesel tank as the fuel heats up. ALSO - my wvo setups do not return fuel to the tank but rather back to the inlet of the lift pump (when on wvo only) for numerous reasons (that would be the topic of a new thread). So, this tank had no return line or vent. For some reason it was working fine for several thousand miles and then suddenly stopped working......

thanks!
paul

The valve shown in the pictured vents is a roll-over protection valve that is supposed to shut off the vent in the event of a roll-over or an over-fill situation.

Roll-over valves never work as intended, usually just preventing proper tank venting, as in your situation.



A check-valve is an entirely different animal.

A check-valve permits passage in only one direction.

Think about the job of a fuel-tank vent for a minute.

When you are adding fuel, the air you are displacing has to have somewhere to go, so the vent must be open in the OUT direction to permit the tank to vent; otherwise, the fuel would "puke" back out the filler-neck, instead of going in the tank.


On the other hand, when the engine is drawing fuel out of the tank, the vent must be un-restricted in the IN direction, allowing air to replace the fuel that is sucked out; otherwise, the tank would collapse.

In the summer-time, when heat expands the fuel, the displaced air exits the vent; then, that night, as the fuel cools, it shrinks, thus air must re-enter the vent to prevent a vacuum situation within the tank.


A check-valve would only permit passage either IN or OUT, but NOT both ways.




Were it myself, I would remove that fancy valved vent and replace it with a plain old hose-barb; connect a 1/2" hose and route it high and dry, un-hampered by any troublesome "anti-siphon" valve.

 

[MIDNIGHT RIDER]

BTW, just for the record - i am in fact an idiot....

ALSO - my wvo setups do not return fuel to the tank but rather back to the inlet of the lift pump

I cannot see the wisdom of routing the return to the lift-pump inlet.

The return fuel system is there to both LUBE and COOL the injection-pump.

On a properly operating system, there is at least ten-gallons of fuel cycled through the return-lines to every single gallon actually burned.

Routing the return to the lift-pump inlet, for one, will over-work the lift-pump.

For another, on a normal system, the returned fuel enters the tank, where it can transfer accumulated heat from the injection-pump, while much cooler fuel is being drawn off the bottom of the tank.

By cycling the hot fuel straight back through the system, the injection-pump loses the cooling benefits.


Please enlighten me.

 

[GREASE FIRE]

Were it myself, I would remove that fancy valved vent and replace it with a plain old hose-barb; connect a 1/2" hose and route it high and dry, un-hampered by any troublesome "anti-siphon" valve.

i ended up doing just that tonight - i found a 1/2 street and realized there was just enough room for it. hopefully that will solve the problem. thanks!
Paul

 

[GREASE FIRE]

I cannot see the wisdom of routing the return to the lift-pump inlet.

The return fuel system is there to both LUBE and COOL the injection-pump.

On a properly operating system, there is at least ten-gallons of fuel cycled through the return-lines to every single gallon actually burned.

Routing the return to the lift-pump inlet, for one, will over-work the lift-pump.

For another, on a normal system, the returned fuel enters the tank, where it can transfer accumulated heat from the injection-pump, while much cooler fuel is being drawn off the bottom of the tank.

By cycling the hot fuel straight back through the system, the injection-pump loses the cooling benefits.


Please enlighten me.

my system ONLY does the looped return with wvo - not with diesel. I understand that all the points you make are established facts, for diesel.
Looping the wvo return line is common for most two-tank kits these days and also most home-built systems like mine are designed that way. It sends the hottest oil back to the engine where you want it and it prevents polymerization of the fuel in the wvo tank, which causes the wvo fuel filter to get clogged prematurely. It also makes the wvo fuel filter last longer for another reason, which is that you are not constantly re-running fuel through it.
my 6.2 step van has about 50K wvo miles on a looped-return system with no apparent problems caused by it.

thanks again!
paul

 

[jwalterus]

i have an aluminum fuel tank in the bed that i bought used off CL. It had a tank vent fitting on the top and i assumed it worked at first but then realized it did not because there was a lot of pressure in the tank when i removed the fill cap (non-vented type). So i took it off just now and need to rig up something in a hurry that works. I do have some check valves around here.

The problem is that i am feeling a bit "mentally challenged" right now because i can't figure out which direction the check valve should be going.
on the one hand, i know the tank needs something to prevent pressure from building up so that makes me think the arrow on the check valve should be pointing away from the tank.
But, it seems the tank is also subject to vacuum because the lift pump is sucking fuel out of it so there needs to be some air coming in as well - right?

this makes me think i would either need to use two check valves, or else find a vented fuel tank cap with 2" female threads that would screw onto the fill neck of this tank, and the cap would have to be vented ways (rather than a check-valve style vent).

could anyone please set me straight on this? it was a hard day with my truck (i will spare you all the rest of the details!)

thanks,
Paul

might I make a suggestion???

it's seems a LOT easier way to go (since you need a 2" female cap with a vent) would be to go to wally world, Scheels, or a boat place and buy a new cap for a plastic boat tank......

they are a 2" female thread, and they have the little brass vent screw right in the center of them, and it would only cost you a couple of bucks.......