If your property has a backflow prevention device, you may have heard terms like RPZ, DCVA, or PVB without knowing exactly what they mean. These are different types of backflow prevention assemblies, and each is designed for specific applications and levels of contamination risk.
The main difference is how each device prevents contaminated or non-potable water from flowing backward into the drinking water supply. An RPZ provides the highest level of protection of the three, while a DCVA and PVB are designed for specific applications where the level and type of risk are different.
Understanding which device your property has can help you know what kind of testing, maintenance, and compliance requirements may apply.
What Is a Backflow Preventer?
A backflow preventer is a plumbing device designed to keep contaminated or non-potable water from flowing backward into a potable water supply.
Normally, water flows in one direction—from the public water system toward a property. However, changes in water pressure can cause the flow to reverse. This is known as backflow.
Backflow can occur through two primary conditions:
- Backpressure: Pressure on the property side becomes greater than the pressure in the potable water supply.
- Backsiphonage: A drop in the potable water supply creates a siphoning effect that can pull water from a connected system back toward the drinking water supply.
Backflow prevention assemblies are designed to stop that reversal before contaminated water reaches the potable supply.
New Jersey identifies cross connections between potable and non-potable water systems as a public health concern and requires appropriate backflow prevention in applicable situations.
What Is an RPZ Backflow Preventer?
RPZ stands for Reduced Pressure Zone.
An RPZ assembly uses two check valves and a pressure-monitored zone between them. The design allows the assembly to protect against both backpressure and backsiphonage.
One of the major advantages of an RPZ is its ability to provide protection against high-hazard or potentially health-threatening contamination.
If the device detects a problem with the pressure relationship inside the assembly, the relief valve can discharge water rather than allowing contaminated water to move back into the potable supply.
RPZ assemblies are commonly used when a higher level of protection is necessary.
Where Are RPZ Assemblies Used?
Depending on the specific installation and local requirements, RPZ assemblies may be found in applications involving:
- Irrigation systems
- Commercial plumbing systems
- Industrial facilities
- Chemical systems
- Boiler systems
- Certain fire protection applications
- Other connections where the potential contamination hazard requires higher protection
RPZ assemblies are also among the devices covered by New Jersey’s physical connection permitting and testing requirements in applicable facilities.
What Is a DCVA?
DCVA stands for Double Check Valve Assembly.
A DCVA uses two independently operating check valves to prevent water from flowing backward.
Unlike an RPZ, a DCVA does not have the same relief-valve design. It is generally used where the potential hazard is considered lower than the situations requiring reduced-pressure protection.
A DCVA can protect against both backsiphonage and backpressure when properly installed and maintained.
Where Are DCVAs Used?
DCVA assemblies can be used in a variety of applications, including certain:
- Commercial plumbing systems
- Irrigation systems
- Fire protection systems
- Other connections where a double-check assembly is appropriate
The correct device depends on the application, the potential hazard, the plumbing configuration, and applicable requirements.
What Is a PVB?
PVB stands for Pressure Vacuum Breaker.
A PVB is designed primarily to protect against backsiphonage.
It uses a check valve and an air inlet valve to prevent contaminated water from being siphoned backward into the potable water supply.
Unlike an RPZ, a PVB is not designed to provide the same type of protection against backpressure.
Where Are PVBs Used?
PVBs are commonly associated with irrigation systems and other applications where backsiphonage is the primary concern.
You may see a PVB installed above ground near an irrigation system or in another location where the assembly can be properly installed and maintained.
RPZ vs. DCVA vs. PVB: What’s the Difference?
The easiest way to understand the three devices is to compare what they are designed to protect against.
| Device | Primary Protection | Common Applications |
|---|---|---|
| RPZ | Backpressure and backsiphonage | Higher-hazard applications, irrigation, commercial and industrial systems |
| DCVA | Backpressure and backsiphonage | Lower-hazard applications, irrigation, commercial and fire systems |
| PVB | Primarily backsiphonage | Irrigation and other approved applications |
The correct device is not simply a matter of choosing whichever option is cheapest or easiest to install.
The required level of protection depends on the potential hazard and the specific plumbing application.
Does the Type of Backflow Preventer Affect Testing?
Yes.
Different backflow assemblies have different testing procedures. Testable devices must be evaluated using appropriate procedures and calibrated equipment by a qualified tester.
New Jersey requires applicable field-testable backflow preventers to be tested by qualified or certified testers. NJDEP also maintains information on certified backflow prevention device testers.
During a professional appointment, the technician can identify the device, inspect its condition, perform the appropriate test, and document the results.
For example, New Jersey’s testing documentation for RPZ and DCVA assemblies includes identifying the manufacturer, type, size, model, serial number, flow direction, shut-off valves, and test cocks before testing.
Can You Replace One Type of Backflow Preventer With Another?
Not necessarily.
A property owner should not assume that an RPZ, DCVA, or PVB can simply be swapped for another type.
The appropriate backflow assembly depends on the specific application and level of hazard. Changing the device without confirming the requirements could result in inadequate protection or a failed inspection.
If you are replacing an existing device, have a qualified professional evaluate the installation first.
What Happens If a Backflow Preventer Fails?
A failed test does not necessarily mean the entire system needs to be replaced.
Depending on the condition of the assembly, the problem may be related to:
- Worn check valves
- Debris
- Corrosion
- Damaged internal components
- Leaking seals
- Improper installation
- Freeze damage
- Other mechanical issues
A professional can determine whether the device can be repaired or whether replacement is necessary.
Which Backflow Preventer Does My Property Need?
There is no single backflow preventer that is right for every property.
The appropriate device depends on factors such as:
- What is connected to the water supply
- The type of potential contaminant
- Whether backpressure is possible
- Whether backsiphonage is possible
- The property’s plumbing configuration
- Applicable local requirements
- The requirements of the water supplier or enforcing authority
That is why identifying the device is only the first step. The more important question is whether the device provides the appropriate protection for the connection.
Frequently Asked Questions
Is an RPZ better than a DCVA?
An RPZ provides a higher level of protection than a DCVA in applications where reduced-pressure protection is required. That does not mean an RPZ is automatically the correct choice for every property.
Is a PVB the same as an RPZ?
No. A PVB and RPZ use different mechanisms and provide different types of protection. A PVB is primarily designed to protect against backsiphonage, while an RPZ provides protection against both backpressure and backsiphonage.
Which backflow preventer is used for irrigation?
Irrigation systems may use PVBs, DCVAs, RPZs, or other approved assemblies depending on the installation and applicable requirements. The correct device should be determined based on the specific system.
Do all backflow preventers need to be tested?
Testing requirements depend on the type of device, property, application, and applicable regulations. New Jersey requires applicable testable backflow preventers to be tested according to state and local requirements.
What should I do if I don’t know what type of backflow preventer I have?
A qualified backflow professional can identify the assembly and determine what type of testing or maintenance it requires.
Keep Your Backflow Prevention System Working Properly
RPZs, DCVAs, and PVBs all serve an important purpose, but they are not interchangeable. Knowing which assembly is installed on your property can help you understand your testing and maintenance responsibilities.
If you are unsure which type of backflow preventer you have, or your device has failed a test, a professional inspection can help determine what needs to be done next.
WXFX provides backflow testing, inspection, certification, and repair services throughout New Jersey.