How to Drain Sprinkler Backflow? Safe Backflow Drainage Tips

Introduction

If you have an irrigation system, you have likely encountered the term backflow at some point. Backflow is a critical safety mechanism that prevents contaminated water from flowing backward into your clean water supply. However, when it comes time to perform maintenance, winterize your system, or repair components, knowing how to drain sprinkler backflow becomes essential. Draining backflow devices properly protects your system from freeze damage, ensures safe operation, and extends the lifespan of your irrigation components.

This guide walks you through everything you need to know about safely and effectively draining your sprinkler backflow preventer. Whether you are preparing for winter, performing routine maintenance, or troubleshooting a problem, understanding the correct drainage process will save you money and prevent costly repairs.

Table of Contents

• Understanding Backflow Preventers
• Why Drain a Backflow Preventer
• Types of Backflow Preventers
• Tools You Will Need
• Step-by-Step Draining Process
• Draining Specific Preventer Types
• Comparison Table of Preventer Types
• Common Mistakes to Avoid
• Tips and Best Practices
• Troubleshooting
• When to Call a Professional
• Frequently Asked Questions
• Conclusion

Understanding Backflow Preventers

A backflow preventer is a mechanical device installed in your sprinkler system to ensure water flows in only one direction. Its primary function is to stop potentially contaminated water from reversing direction and entering your home’s potable water supply. This is especially important in irrigation systems, where water may sit in pipes and contain fertilizers, pesticides, or other chemicals that pose health risks if they enter drinking water.

Backflow preventers come in various designs, but they all operate on the same basic principle. They use check valves, pressure differentials, and sometimes relief valves to detect and stop reverse water flow. When water pressure drops or reverses, these internal mechanisms activate to seal off the pathway back to your main water supply.

Understanding how your specific backflow preventer works is crucial before attempting any maintenance or drainage procedures. Each type has unique components and requires different approaches for safe and effective draining.

Why Drain a Backflow Preventer

There are several compelling reasons to learn how to drain sprinkler backflow systems properly:

• Winterization: Leaving water in your backflow preventer during freezing temperatures can cause the device to crack or burst, leading to expensive repairs or full replacement.
• Maintenance: Draining allows you to inspect internal components, clean debris, and perform routine checks without water pressure interfering.
• Repairs: If your system has a leak or malfunction, draining the area provides a safe workspace for repairs.
• System Longevity: Regular draining prevents mineral buildup, corrosion, and water stagnation that can degrade internal seals and valves over time.
• Code Compliance: Many local water authorities require annual inspections and proper maintenance, including drainage, to maintain compliance.

Failing to drain your backflow preventer when necessary can result in frozen pipes, contaminated water, system failure, and potential legal issues if your property violates local ordinances.

Types of Backflow Preventers

Before diving into the draining process, it is important to identify which type of backflow preventer your system uses. The four most common types include:

Atmospheric Vacuum Breaker (AVB)

AVBs are the simplest and most commonly used backflow preventers in residential irrigation systems. They rely on a rubber diaphragm and spring-loaded plunger that seals when water pressure drops. These devices are typically installed after each zone valve and must be positioned at least six inches above the highest sprinkler head.

Pressure Vacuum Breaker (PVB)

PVBs offer more robust protection than AVBs and are usually installed at the main water line entering your property. They use a spring-loaded check valve and an atmosphere open port that activates when pressure drops. Unlike AVBs, PVBs can handle higher pressures and are suitable for systems with multiple zones.

Double Check Valve Assembly (DCVA)

DCVAs contain two independently acting check valves and are often used where there is no significant health hazard but cross-connection control is still required. They are more complex than AVBs or PVBs and typically require professional servicing, though draining can often be done by homeowners.

Reduced Pressure Principle Assembly (RPZ)

RPZs are the most sophisticated and safest backflow preventers available. They feature two check valves separated by a reduced pressure zone with a relief valve. These devices are used in high-risk applications and usually require professional installation, maintenance, and drainage due to their complexity.

Tools You Will Need

Having the right tools on hand makes the draining process much smoother and safer. Gather these items before you begin:

• Adjustable wrench or channel-lock pliers
• Garden hose or bucket for catching water
• Towels or rags for drying
• Safety gloves and goggles
• Screwdriver set (flathead and Phillips)
• Flashlight or headlamp for visibility
• Plumber’s tape (Teflon tape) for reassembly
• Freeze-proof silicone lubricant (for reassembly)

Ensure all tools are clean and in good working condition. Damaged tools can make the job more difficult and potentially harm the backflow preventer components.

Step-by-Step Draining Process

Follow these general steps when learning how to drain sprinkler backflow systems. Always consult your device’s manual for model-specific instructions, as procedures can vary slightly between manufacturers and types.

1. Turn Off the Water Supply: Locate the main shut-off valve for your irrigation system and turn it clockwise to stop water flow. This is usually found near your water meter or where the irrigation line branches off from your main water supply.
2. Open the Downstream Valves: Turn on the lowest sprinkler zone in your system. This allows gravity to help drain water from the lines and backflow preventer. Let it run for several minutes to ensure most water has exited the system.
3. Relieve Remaining Pressure: Even after shutting off the main supply, pressure may remain in the system. Open a few sprinkler heads manually to release this pressure safely.
4. Locate the Drain Points: Identify all drain valves, test cocks, and low-point drains on your backflow preventer. Most devices have small brass or plastic screws or valves specifically designed for draining.
5. Open All Drain Points: Using an adjustable wrench or screwdriver, carefully open each drain point. Place a bucket or garden hose beneath each opening to catch runoff. Turn counterclockwise for threaded drains or push in and turn for quarter-turn drains.
6. Allow Complete Drainage: Let the water drain completely. This may take several minutes depending on how much water is trapped in the system. Tilting the device slightly can help remove stubborn pockets of water.
7. Inspect Internal Components: Once drained, inspect the interior of the device for debris, mineral buildup, or signs of wear. Clean any visible dirt or sediment with a soft brush or cloth.
8. Close All Drain Points: After inspection, securely close all drain valves and test cocks. Hand-tighten first, then give a quarter turn with a wrench. Avoid over-tightening, which can damage threads or seals.
9. Restore Water Supply: Slowly turn the main water supply back on. Watch for leaks around drain points and connections. If you notice any dripping, tighten the fitting slightly or reapply plumber’s tape.
10. Test the System: Activate each zone of your sprinkler system to ensure proper operation. Check that the backflow preventer is functioning correctly and that no water is leaking from any joints or seals.

Following these steps ensures that your backflow preventer is properly drained, inspected, and restored to working condition.

Draining Specific Preventer Types

While the general process outlined above applies to most backflow preventers, each type has specific considerations. Here is how to drain sprinkler backflow devices based on their design:

Draining an Atmospheric Vacuum Breaker

AVBs are relatively simple to drain. Locate the small drain screw on the side or top of the unit. Turn it counterclockwise to open. Water should flow out freely. Because AVBs are installed vertically, ensure the unit remains upright during drainage. Once drained, close the screw tightly. If your AVB has a test cock, open it as well to ensure complete drainage.

Draining a Pressure Vacuum Breaker

PVBs have a drain outlet at the base of the device and a test port on the side. Open both to allow water to escape. The drain outlet is usually a quarter-turn valve that you push in and rotate. The test port requires removing a small cap or opening a valve. Because PVBs sit horizontally, water may pool in low spots. Tilt the assembly slightly or use a wet/dry vacuum to remove residual water if necessary.

Draining a Double Check Valve Assembly

DCVAs have two check valves housed in a single body. Locate the drain valves on either end of the assembly. These are typically brass ball valves or gate valves. Open both completely to allow water to drain from both chambers. Some DCVAs also have test cocks between the check valves. Open these as well for thorough drainage. Because DCVAs are more complex, consider marking the orientation of valve positions before disassembly for easier reassembly.

Draining a Reduced Pressure Principle Assembly

RPZs are the most complex devices and often require professional attention. However, basic drainage can be performed by homeowners. Locate the four test cocks on the assembly—two on each side of the intermediate chamber. Open all four test cocks along with any drain valves. The relief valve at the center should also be opened. Because RPZs contain springs and small parts under pressure, handle them with care and avoid forcing any components.

Comparison Table of Preventer Types

This table helps you understand the relative complexity and requirements for each type of backflow preventer, making it easier to decide whether you can handle the draining process yourself or should seek professional assistance.

Common Mistakes to Avoid

Even experienced homeowners can make errors when draining backflow preventers. Avoiding these common pitfalls will save you time, money, and potential damage to your system:

• Draining Without Shutting Off Water: Attempting to drain while water is still flowing can lead to flooding, injury, or incomplete drainage. Always turn off the main supply first.
• Over-Tightening Drain Valves: Using excessive force when closing drain points can strip threads, crack plastic components, or damage O-rings. Hand-tighten first, then use a wrench for only a quarter turn.
• Ignoring Test Cocks: Many people forget to open test cocks, which can trap water in critical areas. Always open all available drain points for complete water removal.
• Rushing the Process: Draining too quickly can leave water pockets behind, especially in horizontal assemblies. Take your time and ensure thorough drainage.
• Using Incorrect Tools: Using the wrong size wrench or screwdriver can damage valve stems or screw heads. Always use properly sized tools.
• Skipping Inspection: Failing to inspect internal components during drainage means you might miss signs of wear, corrosion, or debris buildup that could cause future failures.
• Improper Reassembly: Forgetting to apply plumber’s tape, misaligning O-rings, or assembling components in the wrong order can lead to leaks and system failure.
• Not Testing After Reassembly: Skipping the final system test means you might not discover leaks or malfunctions until they cause damage.

Tips and Best Practices

Implementing these best practices will make your backflow draining experience safer, more efficient, and more effective:

• Schedule Regular Draining: Drain your backflow preventer at least twice per year—once in the fall for winterization and once in the spring for system startup. Regular draining prevents stagnant water buildup and extends device life.
• Keep a Maintenance Log: Record the date, weather conditions, and any observations during each draining session. This helps track patterns and identify potential issues early.
• Use Proper Lighting: Work in daylight or use a bright flashlight. Many components are small and difficult to see, and good lighting prevents mistakes and injuries.
• Have Replacement Parts Ready: Keep common replacement parts such as O-rings, gaskets, and washers on hand. These inexpensive items can prevent emergency calls when a seal fails.
• Label Components: Before disassembly, label or photograph the orientation of parts. This makes reassembly much easier, especially on complex devices like DCVAs and RPZs.
• Store Tools Properly: Keep your wrench set and screwdrivers organized and clean. Rusty or damaged tools can contaminate the device or slip during use.
• Check Local Codes: Some municipalities require certified professionals to perform backflow testing and maintenance. Verify local regulations before beginning any work.
• Use a Wet/Dry Vacuum: For horizontal assemblies that retain water in low spots, a wet/dry vacuum can remove residual water that gravity alone cannot drain.
• Apply Silicone Lubricant: When reassembling, apply a thin layer of food-grade silicone lubricant to O-rings and threads. This ensures smooth operation and prevents premature wear.
• Monitor Weather Conditions: Avoid draining during freezing weather if you plan to refill immediately. Cold temperatures can cause newly introduced water to freeze before it drains.

Troubleshooting

If you encounter problems during the draining process, these troubleshooting tips can help you resolve common issues:

Water Keeps Flowing After Shut-Off: This usually indicates a faulty shut-off valve or that you have not located the correct main supply valve. Double-check all valves in the system and ensure they are fully closed. If the problem persists, the valve itself may need replacement.

Drain Valves Are Stuck: Corrosion and mineral buildup can seize drain valves. Apply penetrating oil and let it sit for several minutes before attempting to turn the valve again. Gently tap the valve with a hammer to break up deposits. If it remains stuck, do not force it—replace the valve rather than risk damaging the entire assembly.

Water Leaks During Refilling: Leaks after reassembly typically indicate loose fittings, damaged O-rings, or improper assembly. Shut off the water, disassemble the leaking joint, inspect the O-ring for cuts or deformation, apply plumber’s tape, and reassemble carefully. If the leak continues, the component itself may be cracked and require replacement.

No Water Drains: If opening drain points produces no flow, the system may already be drained, or there could be a blockage. Check upstream valves to ensure they are open and that water can reach the drain point. In some cases, air locks prevent drainage—try opening additional points to break the vacuum.

Device Won’t Refill Properly: After draining and reassembly, if the backflow preventer does not refill or function correctly, internal components may be misaligned. Disassemble and check that check valves, springs, and diaphragms are installed in the correct order according to the manufacturer’s diagram.

When to Call a Professional

While many homeowners can successfully drain their own backflow preventers, certain situations warrant professional assistance:

• Complex Assemblies: RPZ assemblies are highly complex and often require certified technicians for proper servicing. Attempting to drain or repair these devices yourself can violate local codes and create safety hazards.
• Commercial Systems: Larger commercial irrigation systems may have multiple backflow preventers and extensive piping networks that require specialized equipment and knowledge.
• Repeated Failures: If you experience frequent leaks, pressure drops, or component failures, a professional can diagnose underlying issues such as water quality problems or system design flaws.
• Code Compliance: Some jurisdictions require annual certified inspections and maintenance. Hiring a licensed professional ensures compliance and protects you from liability.
• High Water Pressure: Extremely high water pressure can make draining dangerous and increase the risk of component failure. Professionals have the tools and expertise to manage high-pressure systems safely.
• Hard-to-Reach Locations: If your backflow preventer is in a difficult-to-access location, such as a buried vault or high rooftop, professional assistance may be safer and more efficient.

When in doubt, consulting a professional plumber or irrigation specialist is always the safest choice. They can drain your system correctly, identify potential problems, and ensure everything meets local codes and standards.

Frequently Asked Questions

Can You Drain a Backflow Preventer Yourself?

Yes, you can drain many types of backflow preventers yourself, particularly atmospheric vacuum breakers and pressure vacuum breakers. However, more complex devices like double check valve assemblies and reduced pressure principle assemblies may require professional assistance. Always assess your skill level and the complexity of your device before proceeding. If you are unsure, it is safer to call a certified technician.

How Often Should You Drain a Backflow Preventer?

You should drain your backflow preventer at least twice per year. The first draining should occur in the fall to prepare for winterization and prevent freeze damage. The second draining should happen in the spring during system startup to remove any water that accumulated over winter. If your system experiences heavy use or you notice signs of stagnation, additional drainings may be beneficial.

What Happens If You Don’t Drain Your Backflow Preventer?

Failing to drain your backflow preventer can lead to several serious problems. In freezing climates, trapped water will expand when it freezes, potentially cracking or bursting the device. Even in warmer climates, stagnant water promotes bacterial growth, mineral buildup, and corrosion that can degrade seals and valves. Over time, this can result in system failure, contaminated water, and costly repairs or replacements.

Do You Need to Turn Off Water to Drain a Backflow Preventer?

Yes, you must turn off the main water supply before draining a backflow preventer. Draining while water is still flowing can cause flooding, make the process ineffective, and create unsafe working conditions. After shutting off the water, open downstream valves to relieve pressure and allow gravity to assist with drainage.

How Long Does It Take to Drain a Backflow Preventer?

The time required varies depending on the size of your system and the type of backflow preventer. Simple atmospheric vacuum breakers may drain in just a few minutes. Larger assemblies with multiple chambers, such as double check valve assemblies, can take 10 to 20 minutes to fully drain and inspect. Allow additional time for cleanup and reassembly.

Can a Backflow Preventer Freeze with Water in It?

Absolutely. Any water left inside a backflow preventer during freezing temperatures will expand as it turns to ice. This expansion creates pressure that can crack plastic components, split brass fittings, or rupture internal seals. The damage is often severe enough to require complete replacement of the device. Proper draining before the first freeze is essential to prevent this costly problem.

Is It Illegal to Drain a Backflow Preventer Yourself?

Depending on your location, it may be illegal to perform backflow testing or maintenance yourself. Many municipalities require certified professionals to handle backflow preventers, especially commercial systems or those connected to potable water supplies. Check with your local water authority to determine if DIY draining is permitted in your area. Violating local codes can result in fines and liability issues.

What Tools Do You Need to Drain a Backflow Preventer?

The essential tools include an adjustable wrench or channel-lock pliers, a screwdriver set, a garden hose or bucket for catching water, safety gloves and goggles, and plumber’s tape for reassembly. Having a flashlight for visibility and a wet/dry vacuum for stubborn water pockets can also be helpful. Always use properly sized tools to avoid damaging valve stems or screw heads.

Conclusion

Learning how to drain sprinkler backflow systems is an essential skill for any homeowner with an irrigation system. By following the proper procedures outlined in this guide, you can protect your backflow preventer from freeze damage, maintain optimal system performance, and extend the lifespan of your entire irrigation setup. Remember to always shut off the main water supply, open all drain points and test cocks, inspect internal components, and test your system after reassembly.

While many types of backflow preventers can be safely drained by homeowners, more complex assemblies like reduced pressure principle devices may require professional attention. Regular maintenance, including seasonal draining, is the best way to prevent costly repairs and ensure your irrigation system operates efficiently for years to come. When in doubt, do not hesitate to contact a certified plumber or irrigation specialist who can provide expert service and ensure compliance with local regulations.