posted 12-04-2008 07:01 PM ET (US)        

Still, I had been quoted for a custom tank with 10" high by 18" long by 13" wide to hold near 10 gallons.

I appreciate the all replies.

posted 12-04-2008 07:40 PM ET (US)            

Their measurements are: 14-1/4 L x 10 W x 20-1/4 H

cf: http://www.shipstore.com/SS/HTML/TEM/TEM630014.html

Regardless, it is important to note that Tempo is no longer in the marine fuel tank business.

posted 12-04-2008 08:12 PM ET (US)            

I've done some considerable research via GOOGLE and I've found all kinds of discrepancies with regards to the actual capacity of the subject fuel tank. I've seen the site that states it is a 9-gallon tank, for example.

I've read BB material from folks that the subject tank is really a 7.5 and Tempo finally changed the capacity after many bought it thinking it was 9 gal.

So, I don't know what to believe. Therefore, I posted asking for first hand owner experiences.

Thanks again for the reply and providing the site.

posted 12-04-2008 08:14 PM ET (US)            

To determine the number of gallons in a rectangular aquarium:

posted 12-05-2008 02:50 AM ET (US)            

On the 9GAS model, the height is listed at 10.25 inches, however, the cap is recessed so I surmise the safe fill line is about 9 inches above the bottom of the tank.

So, even if I deduct a little bit off the overall measurements, to be conservative, this tank should hold about 9 to 10 gals.

Perfect.

posted 12-05-2008 08:43 AM ET (US)            

I tried searching for the info again but can not find anything to link to for a reference - most sites are listing this model as a 7.5 gallon tank, but soem have it listed as 9 gal or simply "discontinued."

posted 12-05-2008 10:11 AM ET (US)            

Question though - since the formula as performed by Jeff shows that the tank could hold in excess of the "rated" storage of 7.5-9 gals is this because of the properties of gasoline transitioning between liquid and gaseous form, therefore leaving room (volume) for the fuel to safely expand and contract as it transition between gas and liquid?

posted 12-06-2008 09:52 AM ET (US)            

"the widely accepted coefficient of expansion for gasoline is 0.00069/°F"

Cf.: http://ts.nist.gov/WeightsAndMeasures/upload/B-015.pdf
Note that this is a volume coefficient.

If a fuel tank is filled with 9-gallons of gasoline at a temperature of 60-degrees, and the temperature rises to 90-degrees, the volume of the fuel will increase by

30 x 0..00069 = 0.0207

And the 9-gallons of volume will become

9 + (9 x .0207) = 9.1863 gallons.

One should also consider that the fuel tank is also made of a material which likely expands with temperature, and therefore the volume of the fuel tank will also increase slightly as the temperature increases.

We assume the tank is made from polypropylene; it has a coefficient of linear expansion of 4.8 x 10^-5 inch/inch/°F

Cf.: http://www.edl-inc.com/Plastic%20expansion%20rates.htm

A 9-gallon fuel tank will have a volume of

9 x 231 = 2079 cubic-inches

If we assume the tank is a cube, each side will therefore be

Cube Root of 2079 = 12.76-inches

Each side will expand by

30 x 12.76 x 4.8 x 10^-5 = 0.01837 inch

and the volume of the tank will increase to 2,088-cubic-inches, or 9.039-gallons.

New gasoline volume = 9.1863 gallons
New tank volulme = 9.039-gallons
Difference in volume = 0.1473-gallons

The rate of volume increase of the gasoline is higher than the polypropylene, so the tank must have some additional space for the product to expand.

If the tank has additional room to accommodate the expansion of the liquid, and if the tank is vented to the atmosphere, the fuel expands and fills more of the tank. If the tank has room but it is sealed, the fuel expands, but it has to compress the gaseous material in the tank. Gases are compressible, but there will be an increase in pressure exerted on the tank walls.

If we assume that there was 0.5-gallons of space left in the tank at 60-degrees, and the fuel expanded faster than the tank by 0.1473-gallons, the difference in volume of the space in the tank above the liquid changes from

V1 = 0.5
V2= (0.5 - 0.1473) = 0.3527

From Boyle's Law we know that

P1 x V1 = P2 x V2

Cf.: http://www.indiana.edu/~geog109/topics/10_Forces&Winds/GasPressWeb/ PressGasLaws.html

The pressure in the tank will therefore increase by a factor of

V1 / V2 = (0.5 / 0.3527) = 1.418

If the pressure were at atmospheric pressure (29.9-PSI) before the expansion, it will rise to

29.92 x 1.418 = 42.4-PSI absolute

and

42.4 -29.92 = 12.5-PSI relative to atmosphere

posted 12-06-2008 10:04 AM ET (US)            

231 x 0.3527 = 81.4737 cubic-inches

If we again assume this is a cube, each side will have a length of

Cube Root of 81.4737 = 4.335-inch

The surface area of a cube is

6 x L^2, where L is the length of one side

so the surface area of the remaining space will be

6 X 4.335^2 = 112.76 square-inches

The pressure exerted by the gas is 12.5-PSI, so the total force acting on the walls of the tank will be

12.5 x 112.76 = 1,409.5-lbs

Calculation of whether or not the polypropylene has enough material strength to withstand this force is left as an exercise to the reader.

posted 12-06-2008 07:00 PM ET (US)            

Well, at least it didn't come with a homework assignment.
Ouch!!

posted 12-07-2008 07:56 AM ET (US)            

That is, if you are trying to figure out how much USABLE fuel you have from a full tank.