A pressure vacuum breaker is an important device used in plumbing and sprinkler systems to prevent backflow contamination. We will provide an in-depth overview of what a pressure vacuum breaker is, how it works, its components, installation, and maintenance.
What is a Pressure Vacuum Breaker?
A pressure vacuum breaker (PVB) is a type of backflow prevention device that is designed to prevent backflow in water supply systems. It consists of an independently acting check valve and an independently operating air inlet valve located on the downstream side of the check valve.
The PVB allows water to flow in only one direction – from the supply to the system. It prevents backflow by closing off the check valve if either back-siphonage or back pressure occurs. This stops contaminated water from being sucked or pushed back into the clean water supply.
PVBs are commonly installed on lawn irrigation systems, chemical injection systems, and other applications where there is a risk of downstream contamination siphoning back into the potable water system. They provide an important barrier to backflow and are mandated by plumbing codes in many jurisdictions.
How Does a Pressure Vacuum Breaker Work?
A PVB uses a simple but clever design to prevent backflow. Here is how it works:
- Normal Flow: During normal operation, the check valve is open and water flows freely from the supply through the PVB to the system. The air inlet valve remains closed.
- Back-Siphonage: If a negative pressure occurs in the downstream system, it will siphon water backwards. This backflow is stopped by the check valve immediately closing to block reverse flow.
- Back Pressure: If downstream pressure becomes higher than the supply pressure, backflow could also occur. However, the air inlet valve senses this pressure differential and opens to allow air to enter the chamber. This equalizes the pressure and stops backflow from occurring.
Once the pressure equalizes, the air inlet valve closes again and prevents any contaminated water from entering the supply line. The check valve also remains closed until normal pressure resumes.
This dual-valve operation reliably prevents backflow events, keeping the water supply protected.
Main Components of a PVB
A pressure vacuum breaker consists of just a few main parts:
- Check Valve – The spring-loaded check valve only allows one-way flow from supply to system. It closes tightly when pressure reverses.
- Air Inlet Valve – This valve vents air into the body to relieve back pressure. It is sensitive and opens with just a slight pressure differential.
- Test Cocks – Test cocks are installed to allow field testing and verification of proper check valve and air inlet operation.
- Shutoff Valves – Shutoff valves allow isolation of the PVB for testing or maintenance. Ball valves are commonly used.
- Body – The main body houses the check valve, air inlet, and test cocks. It is constructed of brass, stainless steel, or durable plastic.
Proper installation and maintenance of these core PVB components is essential for them to provide effective backflow prevention over time.
Where are PVBs Installed?
Pressure vacuum breakers are an important backflow prevention device mandated by plumbing codes in many applications, including:
- Irrigation systems – Commonly installed on the main line to prevent backflow from chemical injectors, low sprinkler heads, etc.
- Chemical lines – Used in pure water systems, boilers, cooling towers to protect potable water supplies.
- Laboratory benches and sinks – Prevent dangerous chemicals from contaminating supply lines.
- Fire sprinkler systems – Where antifreeze, fire retardants, or other agents are used.
- Hose bibs – Installation at hose connections prevents garden chemicals from backsiphoning.
- Dental operatories – Protects water systems from contaminants used in dental work.
PVBs provide reliable protection against backflow when properly installed in these and other applications. Their unique dual-valve design makes them highly effective at stopping both back-siphonage and back pressure.
Proper Installation of Pressure Vacuum Breakers
To work effectively, pressure vacuum breakers must be installed properly according to the manufacturer’s specifications and plumbing codes. Here are some key installation guidelines:
- Install vertically upright +/- 5 degrees. Never horizontally.
- Allow sufficient room for testing and maintenance.
- Install above highest downstream piping point. Must have at least 12 inches clearance.
- Install insulation sleeves if piping is prone to freezing.
- Use lukewarm water or heat packs when winterizing. Avoid damaging frangible valve parts.
- Install shutoff valves before and after the PVB for isolation during testing or repair.
- May need to install a strainer upstream to prevent debris fouling the check valve seat.
- Support the device appropriately to prevent side-load stress on the body.
Proper PVB selection, installation location, orientation, and clearance are all critical factors for it to function as intended. Follow manufacturer guidance and plumbing codes.
Testing and Maintenance of PVBs
Routine testing and maintenance is necessary to ensure pressure vacuum breakers continue providing effective backflow prevention over time. Testing validates both check valve and air inlet valve operation.
Testing PVBs
PVB testing involves:
- Isolating the PVB using the shutoff valves.
- Opening test cocks to bleed pressure.
- Confirming the check valve holds tightly against backflow. No water discharge should occur.
- Observing the air inlet valve opens when supply pressure is reduced, allowing air to enter body.
PVBs must be tested annually and after any repairs by qualified personnel. Make any needed repairs immediately if issues are found during testing.
Maintaining PVBs
To keep PVBs working properly:
- Inspect PVBs regularly for signs of wear, corrosion, leakage, freezing damage, etc.
- Repair or replace damaged or deteriorated components. Kits are often available.
- Keep the device clean and free of debris. Flush if necessary.
- Winterize as needed in freezing climates.
- Confirm adequate upstream pressure and unrestricted supply flow.
Proper installation combined with routine testing and maintenance will maximize the useful service life of a pressure vacuum breaker. This ensures ongoing backflow prevention.
Pressure Vacuum Breaker Advantages
Pressure vacuum breakers offer some excellent benefits:
- Reliable protection against both back-siphonage and back pressure.
- No risk of fouling like spring checks or RPAs.
- Independent air inlet minimizes spills if check fails.
- Relatively compact, simple design.
- Approved for use against health hazards.
- Allows easy in-line testing and maintenance.
- Available in a range of sizes and materials.
- Often a cost-effective backflow solution.
For these reasons, PVBs are trusted and widely used to prevent dangerous cross-connections from contaminating potable water supplies in many systems.
When are PVBs Not Suitable?
While very useful, pressure vacuum breakers do have some limitations:
- Cannot have downstream shutoff valves or restrictions.
- Installation orientation is critical – only upright.
- Requires minimum 12 inches of clearance below PVB.
- Can spill water if check valve fails.
- Components are somewhat delicate and require care in winter.
- Only moderate maximum pressure – around 150 psi.
- Will not work against constant pressure like RPAs.
In applications with downstream valves, very high pressure, chemical hazards, or constant pressure, an RPA may be more suitable than a PVB.
Conclusion
Pressure vacuum breakers provide reliable protection against backflow in water supply systems where there is risk of downstream contamination. They use a simple but clever dual-valve design to prevent back-siphonage and back pressure from allowing contaminants to enter potable water lines.
Proper installation, testing, and maintenance are essential for PVBs to work effectively over many years of service. When applied appropriately, pressure vacuum breakers offer a great solution to prevent dangerous cross-connections and keep water supplies safe.
FAQs
What is a pressure vacuum breaker?
A pressure vacuum breaker (PVB) is a backflow prevention device consisting of a check valve and air inlet valve. It allows water to flow in only one direction and prevents backflow contamination.
Where are PVBs installed?
PVBs are commonly installed on irrigation systems, chemical lines, hose bibs, fire systems, laboratory benches, and other locations prone to backflow.
How does a PVB stop backflow?
The check valve closes when back pressure or back-siphonage occurs. The air inlet valve then opens to prevent contaminated water from entering the supply line.
What are the main parts of a PVB?
A PVB consists of a check valve, air inlet valve, test cocks, shutoff valves, and a main body. These components allow it to stop backflow.
How often should you test a PVB?
PVBs should be tested at least annually and after any repairs to ensure check valve and air inlet valve proper operation.
How do you maintain PVBs?
Inspect for damage, clean debris, repair components, confirm adequate pressure, and properly winterize PVBs. This maximizes service life.
When can’t you use a PVB?
PVBs cannot have downstream valves or restrictions. Very high pressure, chemical hazards, and constant pressure may require an RPA instead.