Multiple fuel tank draining query

[cardboard]

Hi guys,

I am studing automotive engineering at loughborough university and to cut a long story short we have had to design an amphibious vehicle, this vehicle will have two tanks one on each side. they need to drain simultaneously but be independant of each other, i.e. fuel cannot flow betweem them but the level in each must remain the same.

can anyone help, any ideas how this can be achieved?

thanks

[Kay9]

Y connection with a check valve in each line just before the Y.

K9

[cardboard]

apparently according to my lecturers this wont work effectively enough???

[Ratch]

What about using the differential pressure of the fuel in each tank to control a valve on each line so the higher pressure line opens and/or the lower pressure side closes. You could do this proportionately so the greater the difference in tank levels the greater the differences in valve positions. This can be done mechanically or electronically using diaphragms measuring the hydraulic pressure directly or pneumatically through a tube in each tank.

The other way could be to use strain gauges on the tank mounts to measure the weight of each tank. You could only measure while going straight and at a constant speed or you would need to measure acceleration and centrifugal force to compensate.

[Fanie]

A hose from the bottom of one tank out and to the bottom of the other tank will keep the level in both tanks the same. Once the air in the hose is forced out by lightly pressurising or vacuuming the one tank the level will stay the same for both tanks. The principle is called gravity.

[masalai]

And, following on from Fanie, since flow is not allowed between tanks, use that potential flow to open and close the respective fuel lines so the "fuller" tank gets used.... A problem may arise when making a turn so placement of the measuring tube needs to be near the fore/aft centreline of each tank (assuming the tanks are symmetrical and adequately baffeled)...

[safewalrus]

This is an amphibious vehicle right? you drain both tanks at the same time right? this gives rise to large areas of something known as "free surface"! As the vehicle rolls the liquid in the tanks sloshes from side to side and increases the roll (I don't intend to get too technical)! This effect has sunk many a vessel and caused loss of life!! During the rolling the liquid rushes from one tank to another thus increasing the roll effect! ONLY Kay9's check valves would stop this! What works on land doesn't always work afloat!!

Why would you want to risk the stability of your amphibian and possibility the life of the crew? Check it out with the car mechanics who are supposedly teaching you (presuming they know about such things!)

[Fanie]

Solution is simple, really. Two fuel tanks, two fuel pumps, two fuel level sensors, one controller. When a tank has supplied X % fuel the controller switches over to the next tank. The user is not even aware that this is done. The controller can also output the fuel level and if you log the rate the level sensors indication drop you could predict fuel time usage remaining.

Shallower flat tanks are more desirable since less pressure is experienced in shallow tanks than deep tanks. A 1m deep tank 100mm x 100mm has the same pressure at the bottom as a 1m x 1m x 1m tank !

Wide flat tanks such as Wally talks about should have slosh barriers in that allows limited fuel flow from one section to another. They even put them in car fuel tanks. When you fill up fuel runs over the top of the barriers, but gets blocked when cornering. Duel fuel tanks are used either for weight distribution or because of space restrictions.

Since you're a student, Cardboard, if you're going to build a project PLEASE do not attempt to cut open an old or empty fuel tank, you fill it completely with water after you rinsed it out before switching power to the grinder on. You could imagine the gossip if the newspaper heading says "Student goes to moon in a fuel tank..."

[Kay9]

You lecturer is wrong. Anything else is going to either give way to, too much surface effect or be way to complex to expect to work for long in a marine enviroment.

The check valve with a Y connection has been used for years and years in the marine enviroment and it WORKS. No matter how educated you get, it will still work.

K9

[safewalrus]

Originally Posted by Fanie

Since you're a student, Cardboard, if you're going to build a project PLEASE do not attempt to cut open an old or empty fuel tank, you fill it completely with water after you rinsed it out before switching power to the grinder on.

Which of course is perfectly true, but hell it's more fun (for everybody else!!) if you just go at it with the "old gas axe" (oxy-acetylene burner) the fireworks can be quite spectacular! Your dead of course, but you will be remembered for many a year after!!