Kenworth T2000 with Dual tanks and no cross over tube, need to connect generator

[Driveshaft Shop]

im building a Kenworth Show hauler and have to hook up the 12500kw generator, like the truck its Diesel but what im a little confused on is this. i have dual tanks and no switch it pulls from the top of both tanks, on the top of each tank there is both a feed and return. there is no tube on the bottom of the tank to equalize the tanks. so my question is what happens if you were to run one tank out. or the real question if i pull fuel from one tank for the Generator how will the system know one tank is lower and could even empty ? the two feed and return lines seem to go to a distribution box in the middle of the frame and leave in one line to the Engine ?

 

[bushpilot-TC]

Im following this closely (for selfish reasons).

My gen pulls from the passenger side tank (not certain if/where the generator return goes, but now ill look).

On the drivers side (on top of the tanks) I have two levers which "shut off" (engine?) fuel from each tank.

Ive noticed some UNEVEN consumption when driving (long distances between fuel stops).
when driven more than 700 miles between re-fueling one tank (i don't recall which) will only have 5 gallons or so remaining, while the other tank will have 20 gallons remaining.

 

[Driveshaft Shop]

what i was told is the tanks leave and go into a pump, there is one they lead to in the middles of the frame and then go forward with single feed and return. Its supposed to transfer from one side to the other by this pump but im kinda old school and used to a hose between them. mine has no valves and only one gas gauge so it must equalize some how. just looking for a little insight

 

[superbird03]

Any updates on this? I have the same truck and want to go down to one tank. Not sure how that will work. Can you block off one set of lines?

 

[Driveshaft Shop]

I Actually found out that there is a pump that the lines on the top of the tank go to, when the truck idles this pump will equalize the fuel in the tanks with in 10% of of each, i took the truck to the station put more in one tank and took a ride for a bit and then let it run for 15 minutes after i got back, both tanks were about the same (had allot more in the pass side) im going to just run a bulkhead style fitting like they use in Fuel cell's for a race car on the top back of the tank, running a tube inside the feed to about 12" off the bottom on the drivers tank for both the feed and return.

i would ask more about using one tank but im guessing running the lines direct from the output of the tank and bypassing the pump would do it, just not sure about the flow.

 

[superbird03]

Thanks for the response and info! Very cool idea with putting the stacker trailer on! How did you make the frame rails work? Are they on top of our truck ones or?

 

[Driveshaft Shop]

The Trailer rails are allot wider then the truck, a friend of mine made a grid at the right height to hold the trailer on the truck frame and create the floor, were getting there. sure is allot more work than i thought.

 

[CumminsFan]

Your twin tanks are connected together under the rear of the cab with a tee, just in front of the cab air suspension. The tee fitting allows one line to feed the engine fuel filter and engine mounted fuel pump. The fuel feed line draws a vacuum on the fuel tanks to feed the engine. The smaller fuel return line goes from the engine to the rear of the cab where another tee splits the return into two lines that return to the tank. Your fuel gauge actually reads the fuel level in the drivers side tank, since the draw/return is approximately the same, the fuel gauge reads approximately correct for each tank. Since the fuel/return lines on the tanks are the same length and size, the flow to/from each tank is roughly the same. If you alter this relationship, one tank will tend to be higher or lower depending on the flow change you induce with your modifications.

If you are going to feed your generator from your tank directly, then you might want to put your additional generator feed/return on the drivers side tank. At least you will have some idea of how much fuel your generator is using. Running the truck will eventually balance out the fuel level in each tank depending on how far you have drawn down the tank with the generator.

You might consider taping the fuel feed/returns ahead of the factory tank tees. Doing this way should keep the flows to/from each tank roughly equal. This would enable you to draw/return to both tanks similar to the way the factory design works. This would potentially avoid the problem with uneven fuel tank levels. You might consider some one way check valves in your generator fuel lines to prevent issues between the engine fuel supply and the generator.

 

[bushpilot-TC]

all of the systems I've seen pull from only one tank (in a duel/multi tank system).

mine pulls & returns from the passenger side tank (via fittings in the top of the passenger side tank) - and i ASSUME the feed line does not extend completely to the bottom of the tank, to prevent complete consumption of all the fuel in the passenger side tank.

question: since I've notices some un-even consumption (especially on long/road trips), what would happen if i consumed all the fuel from one tank ? won't i be sucking air or inducing air into the line (even if i still have plenty of fuel from the other tank) ?

this past weekend i topped up our tanks after several "local" camping trips and 650 miles of driving (which included a fair amount of generator run time)....my tanks are 60gal each....i put 55 gallons in the drivers side tank and only 20 gallons in the passenger side tank

 

[Bob86ZZ4]

Don, was the engine running during filling? or between filling the one tank before you filled the other tank? I ask because I think the truck tries to equalize the tanks when it's running somehow. I almost always fuel both tanks at the same time. But once I needed fuel real bad and could only find a station with a single pump. I filled up the one tank and then started up and had to do quite a bit of maneuvering to get to fill the other tank. When I filled that it took much less than the first tank. I'm thinking it was equalizing the tanks somehow?

 

[bushpilot-TC]

Engine was off during filling, i cant think of a single time when i have filled the tanks w/ the engine running.

This last time (this past sunday) i did have to move the coach to fill the other tank.
Doesnt take me long to turn the coach around at my local filling stations / grocery store, so i don't think the pump could have turned over 20 or 30 gallons into the other side/tank.

I've seen similar results when I've NOT had to move the coach (using master/slave pumps at the same time).

is there a gravity equalization going on here ? w/ 60gal tanks even on a master/slave (think truck stop) pump set up i don't like to let one run while I'm at the other tank filling...ONCE i had a nozzle jump out and spill a few bucks on the ground (now i use bungie cords to hold the nozzle down but still don't trust it too much).

When I've filled one tank at a time (even at master/slaves) I've never seen one side drop (after I've filled it to the brim...and i do fill to the brim every time).

 

[Driveshaft Shop]

Thanks for the info, i actually did end up putting in the drivers side tank, i was told there was a pump (there one that the lines go to in the center) that will equalize the
tanks, i was low on fuel so i went and filled one side and not much on the other. took
the truck for a ride and let it sit running for about 20 minutes. the tanks were almost equal after that, say with in 10% so im hoping this will not be an issue. thanks for info.

 

[CumminsFan]

Main fuel feed line to the engine is typically 1/2" id tube, return line is typically 3/8" id. The lift pump is typically relies on vacuum to pull fuel forward to the engine. The lift pump typically has a return pressure is a couple of PSI. Assuming a single 3/8" return line split by a tee into equal length 3/8" tank return line, if equalization occurs, it is going to take many, many hours of operation to see any significant difference. You are not likely to see any significant equalization in an hour or less of operation using the OEM design. You may be able to alter these dynamics and line pressures by using an aftermarket FASS or Air Dog fuel filter/pump system.

The fuel return on a multi tank system is designed on equal pressure (i.e. equal pressure loss) to the tanks to more or less split the returning fuel volume evenly between both tanks at the tee. This design does not lend itself to equalization. However in the real world, the return line pressures are never quite equal. Return lines with reduced cross section, tight bends, different flow fittings, etc. cause different flows. This leads to the returning fuel flow tending to be higher to the tank that has lower return line pressure loss. Generally this imbalance is small and is not a problem.

To truly get equalization between the two tanks, you are going to need to install a large diameter connection between the bottoms of each tank. Manufacturers moved away from this bottom of the tank connection due to fuel spills caused during accidents or road debris penetrating the equalization line. The operator doesn't need to manage fuel levels between tanks with this approach. Alternatively, you could install a fuel pump to move fuel between the two tanks but the operator would have to be on top of fuel levels in the tanks to prevent overfilling a tank. Either approach sounds like a problem waiting to happen for different reasons.

If one tank is run dry and the tank pick up is pulling air, an engine non-run condition will most likely occur. Fuel flow to the engine will stop (due to the air being introduced into the fuel system by the empty tank and the loss of vacuum) even though the other side tank may have plenty of fuel. To return engine operation, the empty tank will require additional fuel, and the fuel system will have to be purged of air.

Hope this helps

 

[porky69]

On my Haulmark ( Freightliner) if I fill one side right full by the time I slide the hose underneath to fill the other side (my favorite station is only single side) the first tank will have dropped a couple of inches, even with the engine off. All of the big trucks (Peterbilt, Kenworth, Western Star, IH) I have driven were the same.

There are no pumps just a Tee fitting with equal length hoses (very important) and it works on the siphon principle.

 

[Driveshaft Shop]

Main fuel feed line to the engine is typically 1/2" id tube, return line is typically 3/8" id. The lift pump is typically relies on vacuum to pull fuel forward to the engine. The lift pump typically has a return pressure is a couple of PSI. Assuming a single 3/8" return line split by a tee into equal length 3/8" tank return line, if equalization occurs, it is going to take many, many hours of operation to see any significant difference. You are not likely to see any significant equalization in an hour or less of operation using the OEM design. You may be able to alter these dynamics and line pressures by using an aftermarket FASS or Air Dog fuel filter/pump system.

The fuel return on a multi tank system is designed on equal pressure (i.e. equal pressure loss) to the tanks to more or less split the returning fuel volume evenly between both tanks at the tee. This design does not lend itself to equalization. However in the real world, the return line pressures are never quite equal. Return lines with reduced cross section, tight bends, different flow fittings, etc. cause different flows. This leads to the returning fuel flow tending to be higher to the tank that has lower return line pressure loss. Generally this imbalance is small and is not a problem.

To truly get equalization between the two tanks, you are going to need to install a large diameter connection between the bottoms of each tank. Manufacturers moved away from this bottom of the tank connection due to fuel spills caused during accidents or road debris penetrating the equalization line. The operator doesn't need to manage fuel levels between tanks with this approach. Alternatively, you could install a fuel pump to move fuel between the two tanks but the operator would have to be on top of fuel levels in the tanks to prevent overfilling a tank. Either approach sounds like a problem waiting to happen for different reasons.

If one tank is run dry and the tank pick up is pulling air, an engine non-run condition will most likely occur. Fuel flow to the engine will stop (due to the air being introduced into the fuel system by the empty tank and the loss of vacuum) even though the other side tank may have plenty of fuel. To return engine operation, the empty tank will require additional fuel, and the fuel system will have to be purged of air.

Hope this helps

well now im confused, i did the test to see what happened and it seem to have worked out, i drove on the Hwy for a bit but not that long.

 

[bushpilot-TC]

On my Haulmark ( Freightliner) if I fill one side right full by the time I slide the hose underneath to fill the other side (my favorite station is only single side) the first tank will have dropped a couple of inches, even with the engine off. All of the big trucks (Peterbilt, Kenworth, Western Star, IH) I have driven were the same.

There are no pumps just a Tee fitting with equal length hoses (very important) and it works on the siphon principle.

porky our coach (also a Haulmark) is a Columbia cab/chassis ('04).

if tank balancing works as you say (and i don't doubt yours does) - i haven't seen that in our coach....in fact i would expect balancing to happen ALL the time - including when running down the road...which doesnt explain why my drivers side tank can get so low while the passenger side isn't (so low).

IN FACT...if balance occurs as you say, then wouldnt a generator (which is only getting its supply and return on from the passenger side) potentially drawl from BOTH (balanced) tanks ???

Ive run the generator (after topping my tanks up) pretty constant on/off while tailgating for 3 or 4 days and only saw my passenger side level drop.

 

[porky69]

In a perfect world, yes but the world is not. Fluids follow the path of least resistance and therefore draws and returns may not be equal. On my Peterbilt the only way I could get the tanks close to the same level was to close, ever so slightly, the shut off valve on the return line at one tank (the one that is fuller), over eeveral tanks until they stay even.

In my opinion, and I have no solid facts to back it up, but with fluids following the path of least resistance, when you are travelling down most highways the main (right hand) driving lane is crowned to the right (ie your coach is leaning slightly to the passenger side), therefore the fuel on the uphill side would be the easiest to draw (suck "downhill" by the pump) and the return fuel would flow "downhill" easier to the passenger side, resulting in your scenario of passenger side fuller than the drivers.

Another possible source of imbalance is plugged/partially plugged tank breathers (may be separate or built into the caps) and if there are extension hoses on the vents they need to be equal length as well. This may explain why the generator only draws one side. Here is a link to a guy with an extreme case of fuel imbalance
Fuel tank problems 2004 century freightliner

I have experienced this as well. If this is the case the breather on the full tank would be the plugged one, it would be like trying to suck liquid out of a glass bottle with your lips tightly wrapped around the opening, you will get a little out but not much.

Here is a technical paper on dual draw fuel systems http://www.google.ca/url?q=http://www.ideationtriz.com/new/materials/FuelTanksImbalanceProblem.pdf&sa=U&ei=C3hhVOnIIIWpNuSNgtAO&ved=0CCYQFjAC&usg=AFQjCNHP5tEb7eJkldJS21nkRsOckSERkQ