Actual water expansion

[sparke]

My tank hold 700-750 gallons. I changed my lid arrangement. Instead of a piece of liner silicon-ed to the top of the tank, I installed 2" polyisocyanurate foam board in the tank.

I left 2" from the water line to the bottom of the foam to allow for expansion. That was not enough. The water is pushing up the foam. How do I figure out the proper distance from the waterline to the foam. I am going to have to siphon some out. I want to siphon out an exact amount of gallons as opposed to lowering the waterline say 1". I guess the real question is - What is the formula to figure out expansion of 725 gallons? I found a formula on line. The math said water expands approx. 2% at that temp. Does that sound right?


Thanks!

 

[free75degrees]

At 20*C (68*F) water has a density of 0.9982 g/cm3. At 80*C (176*F) it has a density of 0.9718 g/cm3. Therefore the denisty at 80* is 0.9718 / 0.9982 = 97.355% of the density at 20*. The volume change is the inverse so the volume at 80* will be 1 / 0.97355 = 102.72% of the volume at 20*. In other words the volume goes up by 2.72% between 20* and 80*. If the tank cross section is uniform from bottom to top then the water depth also goes up by 2.72% over this temp range.

So if you want the depth to be 5 feet at 176*F then the depth at 68*F should be 5 / 1.0272 = 4.867 ' = 4' 10.4".

Just take your desired water depth and divide by 1.0272. Also, please check my math.

 

[sparke]

Perfect, just what I was looking for. Thanks!!

 

[chuck172]

free75degrees- Holy cow, I wish I were sitting by you in High School.

 

[jebatty]

Don't forget about the water in the system being fed by the tank, if any is being fed by the open system tank. That water expands too and you will need to leave room.