Quick Answer
Gravity plays a vital role in cistern water flow by facilitating the movement of water from the storage tank to the distribution system, typically through a combination of gravity-fed and pump-assisted methods.
Water Head Pressure
When a cistern is buried in concrete, water pressure is determined by the head of water (in feet) and the friction loss (in PSI) through the piping. A general rule of thumb is that every 10 feet of vertical rise requires an additional 0.433 PSI to overcome gravity. For example, a 20-foot vertical rise would require 8.67 PSI of pump pressure to maintain water flow.
Pipe Sizing and Slope
To ensure efficient water flow, it’s essential to size pipes correctly and maintain a gentle slope to minimize friction loss. A good starting point is to use a pipe diameter of 1.5 to 2 times the diameter of the water supply line. A slope of 1/4 inch per foot is also recommended to prevent sediment buildup and facilitate easy cleaning.
Distribution System Design
A well-designed distribution system should incorporate features such as check valves to prevent backflow, air release valves to eliminate air pockets, and gate valves to control water flow. It’s also crucial to maintain a consistent water pressure throughout the system to prevent siphoning and ensure reliable water supply to all faucets and appliances.
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