What is a Pressure Vacuum Breaker Valve?

What is a Pressure Vacuum Breaker Valve?

Jun 19th 2024

A pressure vacuum breaker (PVB) valve is a type of backflow prevention device used to stop contaminated (non-potable) water from entering the home's drinking water supply. It is a safety component of irrigation systems and protects water supplies from pollution or contamination.

In this article, we will explore how a PVB valve works, why it is essential for your irrigation system, how to maintain it, and more about this backflow prevention device.

What is a PVB Valve?

A PVB valve is a backflow preventer that prevents dirty water from flowing into the potable water supply. PVB valve consists of the spring-loaded check valve and an air inlet valve that operates independently. The check valve and air inlet have a minimum load of 1 PSI. This device is made of durable and sturdy bronze or stainless-steel material. PVBs also have two test cocks and two shutoff valves at the end of the device. A PVB is like an AVB (atmospheric vacuum breaker) except that a PVB valve contains a spring-loaded poppet, which makes it suitable for applications where valves are downstream.

Why is Pressure Vacuum Breaker Essential for Your Water System?

A PVB valve protects against mixing contaminated water from your sprinkler system with your household water. It keeps your drinking water safe from cross-contamination with irrigation water. Pesticides, fertilizers, and other products applied to lawns can enter your irrigation water. A PVB ensures this water does not flow back into your household water.

Most municipal codes require a backflow prevention device on irrigation systems. Since a home has only one water system for drinking and all household uses, there is a risk of cross-contamination from backflow. Backflow may occur if the water pressure in the home's main supply suddenly drops, causing the water to flow back into the pipes.

What are the Parts of a Pressure Vacuum Breaker Valve?

Here are the key components of the PVB valve.

Valve Body: A main body that contains the components of PVB.

Check Valve: Prevents the reverse water flow when the water system is pressurized.

Air Inlet Valve: It opens when the water pressure drops, allows air to enter the system and stops vacuum formation.

2 Test Cocks and Shutoff Valves: Make PVB testing and maintenance easier.

How a Pressure Vacuum Breaker Works?

A PVB consists of a check valve and an air inlet valve that is vented into the atmosphere. During normal conditions, the check valve allows the water to pass smoothly and keeps the inlet valve closed. When the PVB device is pressurized with water, the check valve goes up in the open position. This means the input pressure is more than one psi. Then, the water pushes the air inlet valve upward into the closed position. When both conditions are met, the water smoothly flows through the device for its intended use.

The check valve prevents water from flowing in the reverse direction in case of backflow. It always tries to remain close unless there is a flow downstream. The air inlet valve opens when the device pressure is reduced to let air in, separating the dirty water from the clean water when backflow occurs.

How many Check Valves does the PVB device have?

A pressure vacuum breaker has one check valve that prevents backflow occurrence and one air inlet valve. The check valve in PVB is designed to hold one psi in the flow direction. When a check valve opens, water flows past it, causing an air inlet valve to travel up to compress an air inlet loading, which is supposed to generate at least one psi. The air inlet valve is closed at normal water pressure and opens when the force from the air inlet exceeds the water pressure in the area downstream of the check valve.

PVB check valves are simple systems that respond promptly to minor pressure changes. Their quick action can keep the water system safe by preventing backflow and reducing the risk of pipe collapse.

How to Close Test Cocks of PVB Valve?

If you have turned on your sprinkler system in the summer after a long break and test cocks of the PVB valve have been left open at a 45-degree angle all winter, now it's time to close them before starting your irrigation system. Take the flat-tip screwdriver and insert it into the slot of the test cock and close them tightly. The slot should be perpendicular to the test cock. Now, turn on the water to check the connection. If there's water dripping out of test cocks, they're still open. Give the slot another slight twist until it shuts off completely.

Where is the Pressure Vacuum Breaker Valve Located?

The PVB valve assembly is installed close to a water source. It is usually located outside the home or in the basement near the sprinkler system's shutoff valve and the home's main water pipe. A PVB valve should be installed where you can fully drain the device and piping before freezing weather. Freezing conditions can damage the valve if it is not properly winterized.

Pressure Vacuum Breaker Installation

Here are some key considerations when installing PVB valve assembly.

  • Before installation, see the manufacturer's instructions for temperature ranges. A PVB should be protected from freezing temperatures.
  • The PVB should be installed at least 12 inches above the downstream pipe and the highest point of water use.
  • Install the PVB valve vertically with enough space to facilitate testing and maintenance.
  • A PVB device should be installed where water spillage from the vacuum relief valve is not an issue.
  • Don't install the PVB in an area where toxic or hazardous fumes could contaminate drinking water piping.

Pressure Vacuum Breaker Valve Maintenance

A PVB valve requires minimal maintenance. The components may need replacement every 4-5 years. However, whenever you inspect your irrigation system, check the PVB, too. O-rings that seal against the inner walls of the device may become weak and crack over time. In addition, the plastic bonnet that protects the body from freeze damage can also wear out. When these parts break down, water can leak from under the cap.

  • Inspect the breaker frequently for leaks.
  • Check sealing tape or putty at connection points. The connection might leak if the tape is worn, missing, or improperly installed.
  • Closely check the connections, and if needed, replace the seals.


The pressure vacuum breaker is designed to provide protection against back siphonage of contaminants into your drinking water. It is a vital component of irrigation systems. Install PVB valves on your irrigation system and keep your potable water safe from cross-contamination with sprinkler water.

DripWorks carries a variety of irrigation backflow prevention devices and valves to provide you with an easy, affordable backflow preventer. Experience greater protection for your water systems with our premium collection of backflow preventers, vacuum breakers, check valves, air bleed valves, and brass double-check valves.