If you have done any research on backflow prevention prior to locating this article, you’ve no doubt run into more acronyms than you know what to do with, they are particularly ubiquitous when it comes to backflow prevention. In this article, I will try to use the popular/accepted acronyms for each type and hope to include as many alternatives as possible.

A double check valve assembly (DCVA) is another common choice for backflow prevention in both indoor and outdoor plumbing systems. It is the most common type of backflow preventer for underground or in-line usage.

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The chart below covers the primary features of each type of backflow preventer. Note, that "Hazardous Systems" does not necessarily include irrigation systems. Hazardous in this context is generally referred to applications such as car washes, launderers, and others that use caustic chemicals.

Backflow occurs when water reverses course and begins to flow in the wrong direction. Serious contamination can result, leading to illnesses and even fatalities. For this reason, it’s important to test for backflow and address any problems immediately.

A PVB assembly also has an air inlet valve that opens when the internal system pressure is higher than the external pressure, thereby preventing backsiphonage.

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Technically, these two types should not be grouped together, any irrigation professional can (and will!)  tell you that. Although they are extraordinarily similar, they are not the same thing. For the DIY’er, however, I’ve grouped them together for convenience. Essentially, a double-check valve is the better option (when approved for use in an area) out of the two for irrigation purposes.

The pressure vacuum breaker (PVB) assembly is one of the most common types of backflow preventers. Its design is straightforward and intuitive, and it is relatively economical to purchase and use, as well as easy to maintain and repair. A PVB assembly consists of a couple of different parts:

Unlike PVBs, DCVAs can protect against both backsiphonage and backpressure, but they typically cannot safeguard against chemigation backflow. They are designed for use only in low-hazard scenarios.

Several other limitations impede the efficacy of atmospheric vacuum breaker assemblies. For instance, these assemblies cannot protect against chemigation backflow — that is, the application of chemical pesticides or fertilizers via irrigation water. They also cannot be used in systems where they will be under constant pressure, such as in plumbing systems with downstream shutoff valves. For this same reason, though they protect against backsiphonage, they cannot protect against backpressure. Atmospheric vacuum breakers must also be installed at least 6 inches above any downstream piping.

There are two types of backflow we concern ourselves with: back-siphonage and backpressure. Backsiphonage is a reversal of flow caused by negative pressure in the supply line. Backpressure is a reversal of flow caused by downstream pressure exceeding system pressure. Both types can occur in residential water systems, however, not all backflow devices protect from both types of backflow.

These assemblies are typically installed vertically, at least a foot above the highest downstream point in the plumbing system.

Ready & Able is family owned and operated, and our licensed, experienced technicians provide friendly, reliable, professional service every time. We can test your backflow preventers and give you the peace of mind of knowing everything is working as it should be. We can also repair any issues we discover with precise workmanship you can depend on to keep your family safe. We offer a two-year warranty on all our work, so you’re covered just in case any further issues come up.

Backflow prevention assemblies, on the other hand, contain all the requisite valves and shutoffs for testing, so they can and should undergo regular testing to ensure their effective function. Below are a few common types of backflow prevention assemblies:

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Similar to a double check valve is a dual check valve. Dual check valves should not be used in potentially toxic or hazardous systems, meaning they are not recommended for use in irrigation systems. Double-check valves are often recommended in irrigation systems and can be used in hazardous systems (note, what qualifies as hazardous can vary significantly from location to location, check with local regulatory officials). The biggest difference between a double and dual check valve is in testing capabilities. Double-check valves have test ports, dual check valves do not.

With that said, irrigation systems can be considered hazardous depending on the chemicals (fertilizers, water treatments) that are used with that irrigation system. Some municipalities will classify a simple sprinkler system as hazardous. Like other variables when it comes to backflow prevention, many of the specifics will vary significantly from location to location. Accept no final word of authority other than local officials in these regards -- what one location considers non-hazardous, another very well may consider a high hazard.

These are sometimes referred to as Double Check Assembly (DCA), or just DC. A double-check valve is a backflow preventer that features a second check valve. The second one acts as a backup should the first fail or otherwise get stuck open. The two check valves in these assemblies operate independently.

A double check valve typically contains an inlet shutoff valve and a valve body with two spring-loaded, independently operating check valves, four test valves and an outlet shutoff valve. A DCVA can be installed either horizontally or vertically — an in-line installation means that the valve will be installed parallel to the piping, whichever way the piping runs. Unlike with a PVB installation, a DCVA does not need to be installed at least a foot above the highest downstream point in the plumbing system. It does, however, require a foot of clearance underneath for maintenance purposes.

Backflow testing is vital for mitigating the harmful effects of backflow. Some backflow testing benefits include the following:

Constant pressure, also referred to as static pressure, is a situation in which a unit, be it a filter, a backflow preventer, or even a pressure regulator, is not relieved of pressure when the system is not in use. Typically this will be anything that comes before the zone or timer valve. Think about when you turn off the water at the hose bib; the internal valve inside the hose bib is now under constant pressure, as the water continues to push against it until the valve is opened again.

constant pressureconstant pressureWith non-constant pressure backflow preventers, one is needed for each and every zone; with constant-pressure backflow preventers, a single unit can prevent backflow for all zones. All hose-end backflow preventers are not rated for constant pressure.

Cost may be a factor when consumers are considering an atmospheric vacuum breaker. Instead of being installed in one central location, atmospheric vacuum breakers are installed after every control valve on a pipe or on each zone of a sprinkler system. So for complex plumbing systems with many valves, atmospheric vacuum breaker assemblies are not typically economical solutions.

Backflow prevention is perhaps the second most important component of an irrigation system after the water itself. Backflow prevention’s primary goal is to protect the potable water supply from harmful contaminants that can be found in the soil. Bacteria, fungus, fertilizers and other treatments are often present in the soil and these can all be harmful if ingested. Backflow prevention prevents these harmful contaminants from flowing back into the potable water supply, protecting not only yourself and your family, but your neighbors and community as well. In the article below, I will cover several different types of backflow prevention that are commonly found in use.

None of the backflow preventers mentioned in this article should be submerged, including those that can be installed below grade. Regarding minimum install height, note that like others, the minimum installation height is likely to differ from location to location. The recurring theme of "check with local officials" applies here again.

Essentially, if you have not, you will need to look into local regulations and requirements. Installing the proper system now can save significant money down the road, re-doing an installation can be a very costly endeavor.

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Sometimes also referred to as RP or RP Units or RPZA. These offer the highest level of protection available out of any backflow prevention device (except perhaps air gap systems) and are the go-to in high-hazard conditions. Due to this, commercial projects use these exclusively, however, they are not limited to commercial uses. Residential use, though not as common as the other options, is not uncommon. Homeowners wanting the strongest protection possible for their potable water supply will often opt for RPZ backflow protection.

Out of the two types, a residential system is most likely to encounter back-siphonage, however, backpressure is still a concern, particularly in water systems utilizing a pump, such as a well or similar.

A reduced pressure principle (RP) backflow assembly, also known as a reduced pressure zone assembly, is one of the safest and most dependable backflow preventers on the market. It is also one of the most expensive and one of the most complex to install and maintain, so consumers will need to weigh these pros and cons carefully.

Backflow preventers are often located in the cross-connections that link clean water to the applications in which it is used. For example, backflow preventers are often present in equipment such as sprinkler irrigation systems to prevent chemical fertilizer or manure from backflowing into the water supply and contaminating the drinking water. They are mandatory on plumbing systems that may contain hazardous chemicals, industrial fluids, fertilizers or additional sources of water. But they are vital for home protection as well.

If you’ve ever purchased, or looked into purchasing, a drip irrigation kit you’ve probably used or seen one of these. When we think backflow prevention, these are usually the default that we turn to in the residential side of the drip irrigation industry. Common acronyms for these types of backflow preventers are AVB, HEVB, and HBVB. They are not acceptable for use in sub-surface applications and should be elevated above the highest point emitters when possible as this allows the unit to break the vacuum that can lead to conditions favorable to backflow. They are among the most affordable of all backflow prevention options but also amongst the most limited. For a residential drip system running from a hose bib they work great, but you won’t find many in use in lawn irrigation systems.  among

What are backflow preventers, and what can they do for your home? This article answers these questions, explains how to prevent backflow and discusses the importance of backflow testing to keep your household’s water safe.

Pressure vacuum breakers are generally not recommended for irrigation applications, however, they can be used under constant pressure and contain a test port for annual testing.

An RP assembly typically consists of an inlet shutoff valve, a pressure differential release valve that separates two independent spring-loaded check valves, four test valves and an outlet shutoff valve. It also contains a mechanically independent relief valve to maintain a low-pressure zone between the check valves.

If the valves are working correctly, you’ll be all set — if not, the plumber can most likely do some quick repairs to keep your home’s water safe and clean.

An atmospheric vacuum breaker, also known as an atmospheric antisiphon, is one type of backflow prevention device. Two common examples are household hose bib vacuum breakers and frostproof wall hydrant faucets. An atmospheric vacuum breaker is generally a less reliable and effective backflow preventer than the backflow prevention assemblies we will discuss below.

Investing in backflow preventers to prevent that scenario from happening is an excellent idea. You should also invest in regular backflow testing to make sure your first lines of defense against contaminated water are working properly.

It is important to note that different municipalities will require different types of backflow prevention when it comes to lawn irrigation. Whether it be ASV, PVB, DCV, or RPZ (acronyms will be explained below), every town and city can be expected to have their own requirements when it comes to backflow prevention and you will want to reach out to them to find out what is approved for use in your area. The one common exception to this is hose-end backflow preventers, the type you thread on to an outdoor spigot. Almost universally, hose-threaded AVB units (Atmospheric Vacuum Breaker) are acceptable (and required) for use on residential irrigation systems operating from an outdoor hose bib. The system still needs to be within specification for the unit used in regards to flow and pressure, but they are recognized across the states as sufficient backflow when running from a hose bib. Again, and this cannot be emphasized enough, check local regulations before purchasing and installing any type of backflow prevention.

One of the main disadvantages of PVB assemblies is that they are not typically suitable as a defense against backpressure — they protect against backsiphonage only. So consumers should not use these models where the likelihood of backpressure in the plumbing system is high. PVB assemblies also cannot protect against backflow of chemigation. They are, however, designed for use in both low- and high-hazard scenarios.

During backflow testing, a certified plumber will open and close the valves of the backflow prevention device or assembly to make sure it is functioning as it should. The plumber will assess the valves for leakage, gauge movement and other telltale indicators of a malfunction.

These assemblies can be installed in a range of different configurations. Underground installation typically calls for straight, in-line installation, whereas above-ground installation allows for a more compact installation to conserve space. Ordinarily, the installation must be horizontal, though some assemblies can be specially configured for vertical installation. As with DCVAs, RP assemblies require a foot of clearance underneath for maintenance purposes.

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Though they need to be installed above-grade, they do not have to be higher than emitters on the system. They must never be installed in a location where they may become submerged underwater. Due to their efficacy, many professional irrigation designers will only design for systems that will use an RPZ unit. Their thought is that other than cost, there is no detriment in over-protecting a water source but there can be in under-protecting one. Note, when functioning properly these can leak a lot of water, thus it will be necessary to plan for proper drainage.

Think of the waste you flush down the toilet or the dirty water that flows out of your dishwasher or laundry machine. Imagine if that dirty water got into your home’s clean water supply — the water you drink and bathe in. Even though the United States has some of the safest public water in the world, the country sees up to 32 million cases of acute gastrointestinal illness every year, and backflow from contaminated water is one reason why. The Centers for Disease Control and Prevention (CDC) recorded 57 waterborne disease outbreaks between 1981 and 1998 that resulted from cross-connections that led to backflow. These outbreaks caused more than 9,700 illnesses.

It will always be worth checking with local water regulatory officials. Each municipality has its own regulations; some regulate what you can not use, and some regulate what you must use in regard to backflow prevention. Some municipalities will even require the installation be done by a licensed professional, or by the homeowner after receiving training and/or certification. Some municipalities will require different backflow protection for sprinkler systems than they require for drip irrigation systems.

Backflow is a concern at any cross-connection. A cross connection in this context is defined as any direct connection between potable and non-potable water, such as an irrigation system. It does not matter if this cross-connection is temporary or permanent, backflow prevention will be needed.

These are quite similar to atmospheric vacuum breakers, however, they can withstand static pressure and are typically placed before the zone valves. Like AVB units these need to be installed higher than the highest point emitter on the zone and must be above grade. These are notorious for leaking some when backflow occurs, so be sure in its installation you account for this in regards to drainage as they should not be submerged in water.

The 3/4 Inch thread outlet is compatible with most of standard hose and end valves including sillcocks, wall faucets and garden hose.

PVBs may sometimes leak water, but consumers can look for spillproof models for indoor plumbing installations to help prevent water leakage. Spill-resistant vacuum breakers (SVBs) solve the problem of leaky assemblies. They are similar in construction to PVBs, but they have additional diaphragm seals to keep water from spilling out of the air inlet when the assembly becomes pressurized.

Water that flows into your home should flow in only one direction. Clean water enters, and dirty water exits. And usually, that’s how it works. Sometimes, though, the flow of water changes direction so the dirty water flows back toward the clean. When that happens, you have backflow on your hands.

Unlike other types of backflow preventers, RP assemblies can protect against chemigation backflow. They can also protect against backsiphonage and backpressure and are designed for use in both low-hazard and high-hazard scenarios.

So what is backflow testing? Backflow testing evaluates a plumbing system to see if backflow is occurring. Fortunately, the process is relatively fast and easy.

Anti-Siphon valves can be handy in that they are both a control valve and a backflow preventer in one. These are the most common types seen in residential irrigation systems. Like the two above, the backflow prevention portion of it is an atmospheric vacuum breaker, meaning they also need to be installed above the highest point emitters on the system and cannot be installed below-grade, even if the sprinklers or drip are below the valves. Anti-siphon valves must be downstream of the zone valves in order to provide protection from backflow. When used for backflow prevention, every zone on the system must also use an anti-siphon valve.

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An atmospheric vacuum breaker relies on air pressure to function rather than water pressure. It contains an air inlet valve that remains closed if water flows in the proper direction. If the flow of water reverses, the air inlet valve opens to prevent backsiphonage.

Backflow preventers generally come in two different types: backflow prevention devices and backflow prevention assemblies.

Our listings of Atmospheric Vacuum Breakers and Hose End Vacuum Breakers can be browsed here: Backflow Preventers (AVB and HEVB).

In backflow testing, a plumber assesses how well backflow preventers are working. Backflow preventers are devices within the plumbing system that keep the flow of water moving in the proper direction. They act as barriers to prevent harmful contaminants from entering a community’s potable water supply.

Backflow prevention devices can stop the reversal of flow in a plumbing system. Once installed, however, they are impossible to test because they lack inlet valve shutoffs, outlet valve shutoffs and test valves.