Which injection method relies solely on pressure difference?

The unassisted Venturi method relies solely on the pressure difference created by the flow of water through a constricted area of the system. In this method, the water's velocity increases as it passes through the narrowed section of the Venturi tube, resulting in a decrease in pressure according to Bernoulli's principle. This pressure drop is what draws in the chemical from the injection point into the water stream.

This method is particularly effective in situations where the system does not have the ability to apply additional force or pressure to introduce fluids, making it ideal for certain applications in water treatment where minimal intervention is desired. The unassisted Venturi effect is advantageous for its simplicity and cost-effectiveness since it does not require external pumps or mechanical devices to create the necessary pressure differential for injection.

In contrast, other methods like assisted Venturi rely on additional mechanical pressure or pumps, gravity injection depends on the natural force of gravity to assist in fluid flow, and pressure injection requires an external source to generate the pressure needed for injection.