How Do Rainwater First Flush Diverters Function?

What is a First Flush Diverter?

A first flush diverter is a simple device that attaches to the downspout of a roof gutter system and is designed to divert the first flow of water from the roof, known as the “first flush,” away from the storage tank. This initial flush typically makes up around 10% of the total rainfall and contains the highest concentration of contaminants, such as debris, leaves, and roof granules. The first flush diverter is usually a simple valve that allows water to flow through it until a certain volume (typically 10-20 gallons) has passed, after which the valve closes, diverting the clean water into the storage tank.

How Do First Flush Diverters Work?

The typical design of a first flush diverter involves a float valve that controls the flow of water. The float rises as water flows through the system, and once a certain volume has been reached, the float drops, closing the valve and diverting the water into the storage tank. Some first flush diverters also use a timer or a flow meter to control the flow of water, allowing for more precise control over the first flush volume. Proper installation and calibration of the first flush diverter are crucial to ensure that it functions correctly and effectively protects the storage tank from contaminants.

Design and Installation Considerations

When designing and installing a first flush diverter, it’s essential to consider factors such as roof size, gutter size, and storage tank capacity. A general rule of thumb is to use a first flush diverter that can handle at least 10 gallons of water for every 1,000 square feet of roof surface. Additionally, the device should be installed at a slight angle to ensure that water flows through it easily and that debris is flushed out properly. Regular maintenance and inspections are also necessary to ensure that the first flush diverter continues to function correctly and effectively.