Preventing Backflow of Chemicals:
1. water pressure is suddenly reduced from the water supply side.
2. the supply side water wants to return to the lower pressure; the air gap ensures that the incoming stream is broken and will begin sucking air into the supply line (depending on amount of back-fault pressure).
3. the chemical mixture may want to flow backward from some small static pressure from the output side; the back-flow is limited by the air gap; the attempt to flow past the second venturi in the reverse direction also lowers its venting pressure. The small amount of chemical mixture that may back-flow is vented to the open side of the air gap and does not contaminate the water supply.

return to technology page.