An inline check valve is a mechanism on your backflow prevention device that regulates the flow of water.  In particular this backflow preventer it keeps the water moving in the right direction.  It is designed to be installed in-between joints where you want water to flow through but not backward. To better understand the function

Aqua backflow is a phrase that refers to the reversal of flow of water in a home’s water system, basically meaning that contaminated water will flow back into the potable water supply, a contamination problem which must be avoided at all costs for public safety. Aqua backflow is prevented by the use of backflow preventers,

The FEBCO 860 is a reduced pressure zone assembly (RPZ) used to protect against high hazard fluids reversing flow in the water supply.  The 860 is generally used in industrial plants, hospitals, morgues, mortuaries, and chemical plants, but can also be used in irrigation systems, boiler feeds, water lines and other installations which require maximum