These are the four most common types of backflow prevention methods/devices:
1. Air Gap Separation (AG)
An AG is a physical separation between the supply pipe (or faucet) and the flood level rim of its receptacle.
2. Pressure Vacuum Breaker (PVB)
The components of a PVB valve are: two independently acting valves (check valve & air valve); test cocks & 2 shutoff valves. This valve is commonly used for irrigation systems.
3. Double Check (DC) Valve
The components of a DC valve are: 2 single check valves, test cocks & 2 shut-off valves. This valve is commonly used to protect against low to medium hazard installations such as firefighting systems which does not use toxic additives.
4. Reduce Pressure (RP) Valve
The components of a RP valve are: 2 single check valves, 1 relief valve, test cocks & 2 shut-off valves. This valve is commonly used to protect against high hazard installations such irrigation systems that use chemical additives; or firefighting systems that use toxic additives (antifreeze).