Reduced Pressure Detector Assembly
This page lists the various types of backflow prevention assemblies that are available. Some assemblies can be tested to ensure that they are working while others cannot. Typically, each assembly is designed to be used for a specific process hazard level application: low, medium or high hazard level.
Residential Irrigation
Backflow preventers installed in residential irrigation systems are required to be tested tri-annually (once every three years). All other backflow preventers installed in or at a residential property must be tested annually.
The Reduced Pressure Backflow Assembly (RPBA) incorporates the use of two independently-acting spring-loaded check valves separated by a spring-loaded differential pressure relief valve, two resilient seated shutoff valves and four properly located test cocks.
During normal operation the pressure between the two check valves (referred to as the zone of reduced pressure) is maintained at a lower pressure than the supply pressure. If either check valve should leak, the relief valve is designed to open and discharge water to the outside.
A properly functioning RPBA will periodically discharge small amounts of water due to fluctuation in line pressure up or downstream of the assembly. For this reason the RPBA should be installed in an area that is not subject to water damage and should be provided with adequate drainage. During a backflow condition, the RBPA can and will discharge a large volume of water, how much is dependent upon the size of the assembly.
The Reduced Pressure Backflow Assembly is designed to prevent backflow caused either by back-pressure or back-siphonage and may be installed on either low or high hazard connections.
The Reduced Pressure Detector Assembly (RPDA) is an outgrowth of the Double Check Detector Assembly and is typically only used on fire line applications. However, this assembly is intended to protect the potable water supply from fire sprinkler systems that contain chemical additives or can be connected to an auxiliary non-potable water source. This assembly is comprised of a mainline reduced pressure backflow assembly equipped with OS&Y gate valves, a bypass arrangement containing a smaller reduced pressure backflow assembly and water meter. The RPDA must be installed at least 12" above finished grade or the 100 year flood plain which ever is greater.
No diagram available at this time.
An Air Gap is a physical separation between the free flowing discharge end of a potable water supply pipeline and an open or non-pressure receiving vessel. An approved air gap shall be at least double the diameter of the supply pipe measured vertically above the overflow rim of the vessel and in no case should be less than 1 inch.
Unlike other backflow prevention assemblies, an air gap is a totaly non-mechanical means of backflow prevention.
An Air Gap is considered the maximum protection available against back pressure backflow or back-siphonage, but unfortunately is not always practical and can easily be bypassed.
The general configuration of an approved Air Gap is illustrated here:
he Double Check Valve Assembly (DCVA) is essentially two single check valves assembled within one body and furnished with four test cocks and two shut-off valves. Double check valve assemblies are commonly used to protect against medium hazard installations such as lawn sprinkler systems. They may be used under continuous pressure and protect against both back-siphonage and back-pressure conditions.
A diagram of a Double Check Valve Assembly is provided at right.
A dual check valve is similar to a double check valve in that it is a mechanical backflow preventer consisting of two independently acting, spring-loaded check valves. However, it usually does not include shutoff valves, may or may not be equipped with test cocks or ports, and is generally less reliable than a DC.
A dual check valve is effective against back-pressure backflow and back-siphonage but should be used to isolate only non-health hazards and is used primarily at water service connections to single-family homes.
A picture of a Dual Check Valve is provided below:
A Hose Bibb Vacuum Breaker consists of a spring-loaded check valve that seals against an atmospheric outlet when the water supply is turned on. When the supply is turned off, the device vents to atmosphere, thus protecting against backsiphonage conditions.
A diagram of a Hose Bibb Vacuum Breaker is provided below along with a typical installation:
The Pressure Vacuum Breaker Assembly (PVBA) is an outgrowth of the atmospheric vacuum breaker and evolved in response to a need to have an atmospheric vacuum breaker that could be utilized under constant pressure and was testable. These assemblies may be used under constant pressure but do not protect against back-pressure conditions. The assembly must be at least 12 inches higher than any downstream piping.
A diagram of a Pressure Vacuum Breaker is illustrated below along with typical installation drawings:
