Which Plumbing Device Helps Prevent a Backflow?


Backflow occurs when dirty water flows backward into clean water lines, introducing contaminants and pollutants into our drinking supply. Specialized devices exist to guard against this risk.

Find out which plumbing device will best help your family avoid backflow and stay healthy. Articles cover pressure vacuum breakers, reduced pressure zone assemblies, double-check valve assemblies, and air gaps as possible solutions.

Pressure Vacuum Breakers

Pressure vacuum breakers (PVBs) are backflow prevention devices designed to safeguard water systems against contamination. Installed on supply lines before equipment, PVBs act like one-way air valves that only open when there is negative pressure in the system and only let air in when there’s negative pressure present.

Water pressure drops can create a siphoning effect that pulls water from sprinkler lines into home plumbing, potentially polluting household fixtures. PVBs prevent this by constantly flowing in the opposite direction so they cannot be siphoned backward into irrigation systems or household plumbing.

PVBs provide an affordable backflow solution for residential irrigation systems. Their testing and maintenance requirements may be slightly more complicated than those for other devices; local codes will determine whether homeowners can test them themselves or a certified tester must come out.

Installation is pretty straightforward: using pipe sealant compound, tighten the first Slip X MIP adapter at the inlet of the PVB assembly to its second one at its outflow and secure four inches of pipe to it before gluing the PVB assembly inlet shutoff valve to its riser and cutting at mark three of assembly. Before returning the system into service, open the isolation valve and flush out the PVB using the open isolation valve. Open the isolation valve again to make sure the system is transparent.

Reduced Pressure Zone Assemblies

Backflow Prevention Devices are essential in protecting our water supply from contaminants like hard metals, pesticides, and toxic chemicals. These devices ensure that water from the city only flows in one direction towards our homes and businesses and stays pure; additionally, they prevent any contaminants from mixing into it unknowingly.

Backflow prevention devices must undergo testing to ensure they can withstand back pressure and back siphonage conditions. There are various kinds of backflow preventers, with two of the most popular being Reduced Pressure Zone Assemblies (RPZs) and Double Check Valve Assemblies (DCVAs).

RPZs use two independently operating spring-loaded check valves separated by a hydraulically operated differential pressure relief valve to maintain reduced pressure zones at a lower pressure than upstream water pressure by using tension from #1 Check spring tensioning; should pressure in this zone increase beyond its limits, its relief valve automatically discharges, preventing backflow.

RPZs are effective fail-safe systems designed to safeguard low and high-hazard backflow conditions under both back siphonage and backpressure conditions. Unlike DCVA, which only includes two check valves without relief valve capability, the RPZ provides for proper testing and monitoring of its system through features like its test cock and water meter connection allowing good system evaluation and maintenance.

Double Check Valve Assemblies

Backflow poses multiple risks to equipment and systems, including equipment damage and system shutdowns. But the most significant threat from backflow is the contamination of public water supplies with pollutants that look, smell, or taste foul – potentially leading to illness or even death if consumed directly.

Double Check Valve Assemblies (DCA devices) are an increasingly popular backflow preventer option. Also referred to as DCA devices, these backflow preventers feature two inline independent positive seating check valves with captured springs and replaceable seat discs – typically lead-free with NPT end connections featuring quarter turn ball valve shut-offs – in addition to test cocks and easy top entry design for maintenance purposes.

Operating this device works on the principle that when downstream pressure exceeds upstream pressure, spring force forces will push the clapper against the rubber seat, creating a watertight seal and stopping any backflow. A second check valve acts as a backup should either of them fail; should backflow persist, both valves close immediately, controlling all flow directly – making this device virtually fail-safe! Additionally, its assembly contains a hydraulically operated differential relief valve beneath its first check valve that activates when both close – thus protecting its surrounding environment against overflow.

Air Gap

An air gap is a physical separation between a faucet and its drain that prevents wastewater from returning up the faucet, helping protect individuals from potentially hazardous bacteria and contaminants that would otherwise contaminate our water supply system.

An air gap refers to the space between a bathroom sink faucet and the bottom of a drain basin or between your washing machine’s standpipe and its p-trap, where water drains in from your drains and washing machine, thus protecting your potable water supply line from potentially polluted drain water entering via your drainage pipes and entering back up again as potable drinking water supply line contaminant, thus creating severe health hazards in your home.

If an air gap is unavailable, mechanical backflow prevention devices are an alternative method for protecting water supplies from contamination from non-potable sources. Such devices use mechanisms like check valves, double check valves, reduced pressure zone assemblies, or atmospheric vacuum breaker valves to keep out contaminants entering potable supplies from non-potable sources. They should be installed directly onto water supply lines for best performance, and regular testing should ensure optimal functioning.

An atmospheric vacuum breaker (AVB) is one of the simplest mechanical backflow prevention devices and works by creating an air gap in a water supply line whenever pressure in it drops below its threshold level. A special valve opens automatically upon this event, thus creating an air pocket between it and the sink or appliance being supplied by water.