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How to Calculate for a Hydrostatic Water Pressure Tank Conduit

Hydrostatic water pressure is the pressure exerted by a column of water. The pressure is a function of the density of the water (or other liquid) and the height of the column of water. This pressure is not dependent on the volume of water and can be transferred to associated piping and equipment. In a water tank, the discharge pipe or conduit must be designed to withstand the hydrostatic water pressure. Pipe or conduit has certain pressure ratings based on the service. For instance, a 150 class pipe has a nominal pressure rating of 150 pounds per square inch (PSI) and a 300 class pipe has a nominal pressure rating at 60 degrees Fahrenheit up to 350 PSI.

Things You'll Need

Calculator

Instructions

- 1
  Determine the size of the water tank and the density of the water. This can be assumed to be a large storage tank that is 25 feet tall. The diameter of the tank is irrelevant for this calculation. The density (mass/volume) of water is dependent upon the temperature. If this storage tank is at 60 degrees Fahrenheit, then the standard density is 62.37 pounds per cubic foot.
- 2
  Determine the total hydrostatic water pressure using the formula P = rho x g x h where P is the hydrostatic water pressure in PSI, rho is the water density in pounds per cubic foot, g is the constant of acceleration due to gravity which is 32.2 feet per second squared and h is the height of the tank in feet. This calculates to be 62.37 x 32.2 x 25 which equals 50,208 pounds per square foot. This is converted to PSI using 1 pound per square foot = 0.0069 PSI and is approximately 346 PSI.
- 3
  Determine the class of pipe based on the hydrostatic water pressure. The calculated hydrostatic water pressure is 346 PSI so the pipe or conduit to be used should be at least class 300 (350 PSI rating).

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