Figure 4 - Venturi injection diagram showing two pressure gauges on the high side and the low side when the flow is constricted. The vacuum port is placed in that constricted throat and the pressure differential allows for uptake (Source: Shutterstock).
Figure 5 - Venturi injection diagram showing how that narrowing of the flow can allow for chemical injection into the water stream and allow for mixing in the downstream pipe (Source: Faith Critzer, Washington State University).
A second type of injection technology is the positive displacement piston. These can be water powered, which means their piston movement operates with the water that is flowing through the device. Water pressure at the inlet side pushes an internal piston up. This piston action draws sanitizer into the mixing chamber. As water flows through the mixing chamber a vacuum is drawn by water flow at the outlet and the piston is drawn back down, clearing the mixing chamber. This action is repeated as long as the water is flowing through the device.
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