Quick Answer
Using pressure tanks with gravity systems is not always necessary, but it can be beneficial in certain situations, such as maintaining a steady water pressure and preventing low-flow conditions in distant locations.
Gravity Systems and Pressure Tanks
Gravity-fed systems that rely on natural elevation can be efficient for serving small to medium-sized households or communities. These systems typically consist of a spring or source, a collection tank, and a distribution network that utilizes gravity to deliver water to users. Pressure tanks are not essential components in these systems, but they can be used to improve water pressure in certain locations.
When to Use Pressure Tanks
Pressure tanks can be beneficial in gravity-fed systems where users are located at a significant distance from the spring or collection tank. In such cases, a pressure tank can help maintain a steady water pressure by storing excess water during periods of high flow and releasing it during periods of low flow. For example, a 75-gallon pressure tank can effectively serve a household with a flow rate of up to 10 gallons per minute (GPM) and a pressure drop of up to 20 feet.
System Design Considerations
When designing a gravity-fed system that incorporates a pressure tank, it’s essential to consider the system’s total head, pipe sizing, and flow requirements. A general rule of thumb is to size the pressure tank based on the system’s peak demand and the desired pressure at the point of use. For instance, a system with a peak demand of 10 GPM and a pressure drop of 20 feet may require a 75-gallon pressure tank with a minimum pressure of 30 pounds per square inch (PSI).
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