How to Replace an Irrigation System’s Pressure-Vacuum Breaker

Replacing a pressure-vacuum breaker on an irrigation system is an important maintenance task that ensures the system functions properly and safely. A pressure-vacuum breaker is a safety device designed to prevent backflow of contaminated water into the drinking water supply. Over time, the spring and seals inside the device can wear out or fail, requiring replacement of the entire unit. By following some key steps, you can remove your old pressure-vacuum breaker and install a new one correctly.

Understanding Pressure-Vacuum Breakers

What is a pressure-vacuum breaker?

A pressure-vacuum breaker, also known as an atmospheric vacuum breaker or backflow prevention device, is a safety component installed on irrigation systems that are connected to a potable water supply. It is designed to prevent backflow, which is when water flows in the opposite direction of its intended flow. This can allow contaminated water to enter the clean water supply, posing a health risk.

The pressure-vacuum breaker contains a disc or float that gets pushed up to block water flow when pressure is lost or reversed. This stops backflow from occurring. It also contains an air inlet valve that allows air to enter the water line when pressure drops, preventing backsiphonage.

Where are they installed?

Pressure-vacuum breakers are commonly installed:

  • On the main water line supplying an irrigation system.
  • On zone control valves.
  • Near sprinkler heads.
  • At least 6 inches above the highest outlet or sprinkler head in the system.

This placement protects the potable water supply from potential contamination.

When do they need to be replaced?

Pressure-vacuum breakers contain seals and a spring that allow the device to operate properly. Over time, these components wear out through normal use and exposure to weather. As they deteriorate, the device becomes prone to leaking and failure.

You should replace your pressure-vacuum breaker every 5-10 years as part of routine maintenance. It should also be replaced immediately if you observe any of the following:

  • Leaking from the top of the device.
  • Improper opening and closing of internal seals.
  • Damage from freezing temperatures, UV exposure, or mechanical stress.
  • Failure to stop water flow when system is shut off.

Replacing old or faulty pressure-vacuum breakers ensures maximum protection against backflow events. Consult a professional irrigation specialist if you are unsure about replacing your device.

Shutting Off the Water

The first step in replacing a pressure-vacuum breaker is to locate the main water shut-off valve for the irrigation system and turn it to the closed position. This is usually an in-line valve on the main water supply line.

Locating the shut-off:

  • Trace the main irrigation line back from the sprinklers or zone valves to find the shut-off valve.
  • It is often near an exterior hose bib or the main water meter.
  • The shut-off valve may be underground in a valve box. Use a valve key to operate it.
  • If you cannot find the valve, shut off water supply to entire property at main house valve.

Closing the valve:

  • Turn the valve clockwise to the closed position.
  • Confirm water is shut off by operating a zone valve and checking that no water flows.
  • Open a low point drain or sprinkler head to relieve pressure.

With the water supply shut-off and pressure relieved, you can now work safely on replacing the pressure-vacuum breaker.

Removing the Old Pressure-Vacuum Breaker

With the water supply off, follow these steps to remove the old pressure-vacuum breaker:

1. Unthread the pressure-vacuum breaker from the piping:

  • The PVB likely has either threaded or grooved end connections.
  • For threaded, use the proper sized wrench to loosen and unthread the pipes.
  • For grooved, loosen the coupling and unseat from grooves.

2. Inspect and clean mounting surface:

  • Check the mounting area for any dirt, debris, or defects.
  • Clean and smooth surface to ensure proper sealing for new device.

3. Remove old plumber’s tape and pipe dope:

  • Use a wire brush and emery cloth to remove all old thread sealant.
  • This allows new tape and dope to adhere properly.

The pressure-vacuum breaker is now removed. Inspect it and note any deficiencies that may have led to its failure. Dispose of the old device appropriately.

Thoroughly clean the irrigation piping to prepare for installation of the new PVB. Flush lines to remove any debris.

Installing the New Pressure-Vacuum Breaker

Follow these key steps to install the replacement pressure-vacuum breaker correctly:

1. Apply plumber’s tape:

  • Wrap fresh plumber’s tape around the pipe threads in a clockwise direction.
  • Apply tape to the male threaded ends.
  • Ensure at least 3-5 tight wraps for a complete seal.

2. Add pipe dope:

  • Use a thread sealant paste compatible with your piping.
  • Apply a thin layer over the tape to fully seal the joint.

3. Thread on new pressure-vacuum breaker:

  • Hand tighten the new device initially.
  • Finish tightening with a wrench to proper torque level.
  • Take care not to overtighten.

4. Position device properly:

  • Install vertically on main line or horizontally on zone valves.
  • Position at least 6 inches above highest sprinkler outlet.
  • Ensure air inlet port faces down.

5. Open isolation valves:

  • Gradually open upstream isolation valve if one was closed.
  • Open slowly to allow air to escape and fill device properly.

6. Open main supply valve:

  • When installation is complete, open main shut-off valve.
  • Check for leaks during system pressurization.

The new pressure-vacuum breaker is now installed! It will provide maximum protection against backflow events into the potable water supply.

Testing the New Pressure-Vacuum Breaker

It is important to test a newly installed pressure-vacuum breaker to ensure it is functioning correctly before returning the system to regular use. Here are the recommended testing steps:

Check for leaks:

  • With water pressure restored, check entire device for any leaks.
  • Look for water dripping or spraying from seals or threaded joints.
  • Repair any leaks before continuing.

Test air inlet valve:

  • Open the highest zone valve to pressurize system downstream of PVB.
  • Close the main supply valve to simulate pressure loss.
  • The air inlet valve should open to allow air entry.
  • A hissing sound should be heard as air enters.

Test check valve closing:

  • Reopen the main supply valve to repressurize the system.
  • The air inlet valve should snap closed immediately upon repressurization.
  • No water leakage should occur from the air inlet after closing.

Test vacuum relief:

  • Shut off highest zone valve while leaving main valve open.
  • This will create a vacuum condition downstream.
  • Air should discharge through vent port, relieving the vacuum.

If the pressure-vacuum breaker passes all tests, normal system operation can resume. Flush zones to purge any debris or air. The PVB will now protect the potable water supply from backflow contamination.

Troubleshooting Common Pressure-Vacuum Breaker Problems

Sometimes issues can arise when installing or testing a new pressure-vacuum breaker. Here are some common problems and solutions:

PVB leaks water:

  • Ensure threads have sufficient tape and paste.
  • Check for cracks in device housing.
  • Examine internal seals for damage or wear.
  • Debris may be obstructing seal. Flush system.

Air inlet valve does not open:

  • Dirty or damaged seal preventing operation.
  • Check spring for breakage or loss of tension.
  • Crimping of piping connection affecting movement.

Fails vacuum relief test:

  • Blockage in vent port due to debris.
  • Sticking air inlet valve not relieving vacuum.
  • Downstream zone valve not closing fully.

Does not prevent water flow when off:

  • Worn-out or leaking check valve seals.
  • Insufficient spring tension to close check valve.
  • Air inlet not closing fully.

If any malfunction persists, replace the pressure-vacuum breaker with a new unit. Never override or bypass a PVB that is not functioning correctly. This compromises backflow prevention.

Maintaining and Replacing Pressure-Vacuum Breakers

To get continued optimal performance from pressure-vacuum breakers and avoid unexpected failures, follow these maintenance best practices:

Conduct annual inspections:

  • Visually inspect device for damage, leaks, or wear.
  • Test air inlet, check valve, and vacuum relief operation.
  • Ensure proper vertical or horizontal orientation.

Flush debris regularly:

  • Debris buildup can prevent proper sealing.
  • Isolate PVB and flush lines to remove sediment and organic material.

Check downstream strainers:

  • Dirty system strainers can allow debris into PVB.
  • Clean strainer screens and flush lines regularly.

Replace every 5-10 years:

  • Internal seals and springs age and wear over time.
  • Even if operating fine, replace PVB after 10 years maximum as preventive maintenance.

Replace damaged or faulty units immediately:

  • Do not delay replacing non-functioning pressure-vacuum breakers.
  • Loss of backflow protection poses serious health risks.

Following these guidelines will maintain the safety of your drinking water by keeping pressure-vacuum breakers in optimum operating condition.

Frequently Asked Questions

What are the risks of not replacing a faulty PVB?

Neglecting to replace a malfunctioning pressure-vacuum beaker poses serious health risks. It fails to prevent backflow of contaminated irrigation water into the drinking water supply. This can cause sickness from bacteria, chemicals, or other pollutants entering the potable water system.

Where should the PVB be positioned on the main line?

Install the pressure-vacuum breaker vertically on the main supply line at least 6 inches above the highest sprinkler head or outlet. This positioning maintains proper operation and backflow prevention.

How soon after installation should the PVB be tested?

It is important to test the operation of a newly installed pressure-vacuum breaker before putting the irrigation system back into normal usage. This ensures it is functioning correctly from the start to prevent backflow.

Can I isolate the PVB when making repairs?

It is not recommended to isolate the pressure-vacuum breaker without installing a temporary backflow preventer in its place. This provides continuous protection when the PVB is removed for maintenance or repairs.

How do I know if the internal seals need replacement?

Signs like leaking from the air inlet, improper opening or closing of the check valve, and inability to prevent water flow when off indicate worn seals. Preventive replacement is recommended every 5-10 years.


Maintaining functional pressure-vacuum breakers is essential for irrigation system safety. Following the steps covered in this article will allow you to remove and replace old pressure-vacuum breakers with new ones properly. Be sure to confirm proper installation by testing for leaks, verifying air inlet operation, and checking vacuum relief performance before returning the system to service. Periodic replacement every 5-10 years and diligent maintenance helps ensure these critical backflow prevention devices continue working reliably to keep water supplies pathogen-free. Taking the time to correctly replace pressure-vacuum breakers ultimately protects the health and safety of your building’s occupants or irrigation system users.