Most products use venturi technology (the vacuum created by manipulating the speed of a stream of water) to mix chemicals with water. ( Run simulation) The incoming water stream is restricted by a nozzle, while the speed of the outgoing water is decreased by the inverted funnel shape at the bottom of the venturi. The result is a vacuum in the middle, where the chemical is sucked into the water stream. The amount of chemical introduced is regulated by interchangeable metering tips that restrict chemical flow into the water stream. The device does not require external electricity, batteries, pumps, or air pressure; it works from ordinary line pressure available in most buildings (15psi).

HYDROGAP II AIR GAP EDUCTORS

Air gap eductors function just like the standard eductor described above. However, before reaching the point of chemical injection, the water must pass through a 1" gap. ( Run simulation) Should the pressure in the incoming water supply drop while the air gap eductor is in operation, the mixed solution would be drawn backward into the gap, but chemical could not cross the air gap to contaminate the water supply. (Run safety simulation)
This type of backflow protection is required in several areas. (See air gap approval status page) 

EGAP EDUCTORS

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. (Run Simulation)