Final answer:
Gravity tanks should be at least x feet above the highest line of sprinkler heads. This ensures proper pressure for the water to reach all the sprinkler heads in the building.
Step-by-step explanation:
Gravity tanks should be at least x feet above the highest line of sprinkler heads.
This is because the pressure of the water in the tank depends on its height, and this pressure needs to be sufficient to ensure that the water can reach all the sprinkler heads in the building.
For example, if the sprinkler heads require a minimum pressure of 10 psi to work properly, and each foot of elevation adds 0.43 psi of pressure, then the tank should be at least x feet above the highest sprinkler head, where x is the minimum pressure requirement divided by 0.43.