Water Supply Backflow Preventers

The backflow preventers shown below are the most common types used to protect water distribution systems from cross connections caused by backflow, backpressure or backsiphonage.

Swing check valve
These simple backflow preventers have a single disc type check that swings open under flow and closes under no flow or backflow conditions. They are typically used for commercial / industrial applications but may also be found in residential heating systems.		 Swing check valve
Inline check valve
Typically used in well systems, these single check valves have a spring actuated disc that is only open under flow conditions. 		Inline check valve
Dual check valve
These backflow preventers are typically used in low health risk applications, such as to protect the municipal system from a residential potable system. They are non testable, have two spring loaded check valves and are typically installed immediately downstream of the water meter.		 Dual check valve
Double check valve assembly (DCA)
These backflow preventers do not provide any additional protection over a dual check valve except that they are testable and incorporate isolation valves that permit easy servicing. DCA's are typically used to prevent cross connections in scenario's that don't pose a significant health risk. 		 DCVA
Double check valve with atmospheric port (DCAP)
These backflow preventers are used in low health risk systems, such as a boiler feed. They have two spring loaded check valves with an intermediate opening that will allow water to discharge if the second check fails to properly seat under backflow conditions.		 Dcap
Reduced pressure zone assembly (RPZ)
The ultimate in backflow prevention, these devices provide three layers of protection that can be used in high health risk hazards. RPZ's have two check valves and an intermediate chamber that diverts water out of the system if backpressure or backsiphonage occurs. It is a testable device and incorporates upstream and downstream stops for servicing.		 RPZ
Anti-Siphon vacuum breaker
As the name suggests, these devices will prevent siphonic action from introducing possible contamination into the potable water system by allowing air into the pipe and breaking the siphon.		 Anti-Siphon Vacuum Breaker
Spill resistant anti-siphon vacuum breaker
Same as above but is testable and also includes a spill resistant cap that is better suited for some indoor applications.		 Spill resistant anti-siphon vacuum breaker
Hose bib vacuum breaker
Your home garden hose poses the single greatest backflow risk to your potable water system as they are often left filling up pools, ponds and other chemical concoctions. They prevent backsiphonage by allowing air into the system.		 Hose bib vacuum breaker

Thanks to Watts Canada for the use of the photographs.