Tank Gauging Project on ELIXIR
By Joran Gendell (10/17/05)
(Posted 1/06.06)

I was tired of guessing the volume in my tanks and although I have dipsticks for all four, they just aren't convenient to use.  There are commercially available systems to pneumatically read the level in your tanks, but a four tank unit lists for something ridiculous like $600. (Check out www.thetanktender.com).  So I decided to make one.  The method used is a dip tube descending to the bottom of the tank.  This is connected to a pressure gauge.  Between the two, an air pump is teed into the line.  To read the level in the tank, air is pumped into the tubing until it bubbles into the tank.  At this point, the air pressure is equal to the water height.  The gauge displays the liquid level in the tank. 

The following items were employed.

-  A pressure gauge:  I found one on eBay for about $10.  Mine is 0-60 inches water column (WC).  A 40" span might have been a slightly better choice.

-  A means to pump air:  From www.AllHeart.com , I ordered a blood pressure cuff replacement bulb and valve.  About $16 with shipping.

-  A four valve manifold:  This allows the one gauge/bulb combo to read any of the four tanks.  I spent a long time searching for an affordable solution to this.  I hit pay dirt in the aquarium air accessories section of the local pet store.  $8.

-  Tubing:  Quarter inch polyethylene tubing at any hardware store is incredibly inexpensive.

-  Dip tubes:  I used 1/4" copper tubing, mounted via nylon 1/4" tube to 3/8" MPT adapter fittings.  Nylon for two reasons:  First, it avoids any electrolysis issue between the copper and the aluminum tank.  Second, it was easy to drill out the back side of the fitting so that the tube could pass right through the fitting and into the tank.  Last item at each tank was a 90 degree compression elbow to attach the poly tubing to the copper dip tubes.  As an alternate design, I think the dip tubes could have been 3/8" plastic. 

I built a small wood frame to hold the gauge, bulb, and manifold.  This I fastened down inside the forward locker over the port settee.  This keeps the components high and dry. Four tubes pass through holes drilled in the locker bottom and are routed forward to the head, down under the cabin sole, and there they split to the four tanks.  See the three pictures attached.

   

 I made a conversion table (inches to gallons) for each tank.  Starting with empty tanks and a five gallon jug, I made a gauge reading for every five gallons added.  For the fuel tank, I just transcribed the dipstick readings and did the math for Imperial gallons to US gallons and allowed for the (low) specific gravity of diesel.

 Open the valve for the tank to be measured, squeeze the bulb once or twice until the gauge stops rising, and read the tank's liquid level on the gauge.  Look at the nearby laminated table to convert to gallons.

 Joran Gendell