## Calculations

Working on the water aspects of the project. Helpful things to know when working with water, pressure and volume: ’head’ is the amount of vertical water space in a tube or container from the top of the column of water to the release point, valve or pump. There is 5′ of head in a 5′ tube of water, when vertical.

1 gallon = 8.43 lbs
1 cubic foot = 7.47 gallons
1 cubic foot (7.47g) = 62.38 lbs
1 foot of head = 0.433 psi (pounds per square inch, of water pressure in a vertical chamber)

To fill an 8′ x 6’5″ x 6′ volume with water:

8′ x 6’5″ = 51.36 sq/ft x 0.5 ft/depth = 25.68 cu/ft
25.68 cu/ft = 191.83 Gallons
25.68 cu/ft x 62.38 lbs = 1601 lbs

(oy vey)

The cistern at the top of the structure, where the water will sit until draining into the chamber, will have the volumetric measurements of 4′ x 4.2′ x 1.5′ (depth) = 25.68 cu/ft

The cistern will be visible to whoever ventures up the slope to the top, and the bottom will be transparent, like a glass bottomed boat, creating a threshold where the body builder and rats are visible, albeit through 1.5′ of water and 1/2″ thick polycarbonate. If I want the cistern to not be a box shape, I’ll take a few inches off the bottom extents and add them to the top.

Bottom: 3’9″ x 3’11″
Top: 4’3″ x 4’5″
Depth: still 1’6″

Since I’m using gravity, there is only head, vertical pressure. To drain the chamber, I’m using an electronic solenoid valve (EchoTech 1/2″ Gravity Feed Electric Solenoid Valve DDT-CD-12VDC, \$16 on ebay), or more than one of them. It didn’t work. Too much head– the valve doesn’t like more than 7 feet. Or because I was pumping the valve with 18A when it wants 500mA. The valve works continuously, or can be opened and closed repeatedly within 1 second. I can use that feature to slow down the flow of water. I’ll have to program it to respond to switches, or to analog values in.

Surprisingly difficult to find cheap parts to step down the 1/2″ bore to 3/8″ to 1/4″. The foam store on Canal was not the right place for this. Maybe Home Depot, or something. I like to support the little guy though!

The transistor circuit controlled by Arduino, powered by a liberated PC power supply. 5v for Arduino and 12v and for the valve. I’ll also use the 12v to power ventilation fans, and the Arduino will also control the transistors that allow AC current to flow to the incandescent light bulbs in the chamber.

More testing needed. And I have to mirror this system at the bottom of the chamber to drain the 6″ of water into a sub-chamber. The sub-chamber will be drained to the street using a submersible pump. Work ahead of me.

Some helpful sites to have open for speed, cause you can easily change one number and not the others:

Right triangle calculations

http://www.csgnetwork.com/righttricalc.html

Volume calculations

http://www.dep.state.pa.us/dep/deputate/waterops/redesign/calculators/volcalchtm.htm

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