TYPES OF BACKFLOW PREVENTION DEVICES
Complete Guide to RPZ, DCVA, PVB & Other Backflow Devices
OVERVIEW OF BACKFLOW DEVICES
Backflow prevention devices are mechanical valves that prevent contaminated water from flowing backward into the clean water supply. Different device types provide different levels of protection for different applications.
Four Main Types for Residential & Commercial Use:
1. RPZ - Reduced Pressure Zone Assembly (Maximum Protection)
2. DCVA - Double Check Valve Assembly (High Protection)
3. PVB - Pressure Vacuum Breaker (Moderate Protection)
4. AVB - Atmospheric Vacuum Breaker (Basic Protection)
RPZ - REDUCED PRESSURE ZONE ASSEMBLY
Description:
The most sophisticated and reliable backflow prevention device. Contains two independent check valves with a pressure-monitored zone between them and a relief valve that opens if the zone pressure drops.
How It Works:
• First check valve prevents backflow
• Second check valve is backup
• Relief valve in middle zone monitors pressure
• If either check valve fails, relief valve opens and discharges water
• This alerts owner to problem
• Provides continuous monitoring
Common Application - High-Hazard Situations:
• Fire suppression/sprinkler systems
• Irrigation systems with chemical injection
• Boiler systems with additives
• Commercial buildings
• Industrial processes
• Medical facilities
• Restaurants and food service
• Any system with toxic chemicals
Typical Locations:
• Fire system rooms
• Mechanical rooms
• Exterior walls (commercial)
• Underground vaults
• Basement installations
Size Range:
• Residential: 3/4" to 2"
• Commercial: 2" to 12"+
• Most common residential: 1" to 2"
Appearance:
• Bronze or stainless steel body
• Four test cocks (small valves for testing)
• Relief valve port in middle
• Requires shutoff valves both sides
• Larger and heavier than other types
Installation Requirements:
• Must be installed above ground (drainage needed)
• Relief valve must drain freely
• Horizontal installation typically
• Accessible for testing
• Protection from freezing required
• 12" minimum above floor drain or outside drainage
Annual Testing: Required by law
Typical Repairs Needed:
• Check valve seals (every 5-10 years)
• Relief valve rebuild (every 7-12 years)
• Complete rebuild (every 10-15 years)
Device Lifespan: 15-25 years with proper maintenance
Cost Range:
• Device cost: $300-$2,000
• Installation: $800-$3,000
• Annual testing: $125-$200
• Typical repairs: $200-$600
Advantages:
• Maximum protection
• Continuous monitoring via relief valve
• Testable
• Acceptable for all hazard levels
• Most reliable
Disadvantages:
• Most expensive
• Requires drain location
• More complex maintenance
• Relief valve may drip occasionally (normal)
• Larger physical size
DCVA - DOUBLE CHECK VALVE ASSEMBLY
Description:
Contains two independent check valves in series that provide redundant protection. Simpler than RPZ but still provides excellent protection.
How It Works:
• First check valve stops backflow
• If first valve fails, second valve provides backup
• No relief valve (unlike RPZ)
• No continuous monitoring
• Only discovered during testing if failed
Common Application - Moderate-Hazard Situations:
• Residential irrigation systems
• Commercial irrigation without chemicals
• Building supply protection
• Fire protection (residential)
• Non-toxic commercial applications
• Auxiliary water supplies
Typical Locations:
• Underground pits/vaults
• Basements
• Crawl spaces
• Exterior locations
• Mechanical rooms
Physical Characteristics:
Size Range:
• Residential: 3/4" to 2"
• Commercial: 2" to 10"
• Most common residential: 1"
Appearance:
• Bronze or iron body
• Four test cocks
• No relief valve
• Simpler than RPZ
• Compact design
Installation Requirements:
• Can be installed underground
• No drainage required
• Horizontal installation preferred
• Must be accessible for testing
• Freeze protection if above ground
Maintenance & Lifespan
Annual Testing: Required by law
Typical Repairs Needed:
• Check valve seals (every 7-12 years)
• Complete rebuild (every 12-18 years)
Device Lifespan: 15-20 years
Cost Range:
• Device cost: $200-$800
• Installation: $600-$2,000
• Annual testing: $125-$150
• Typical repairs: $150-$400
Advantages:
• Less expensive than RPZ
• Can be installed below grade
• No drainage needed
• Reliable protection
• Lower maintenance
• Compact size
Disadvantages:
• No continuous monitoring
• Failure only detected during testing
• Not acceptable for high-hazard applications
• Must be tested to verify operation
PVB - PRESSURE VACUUM BREAKER
Description:
A simpler device that opens an air inlet when water pressure drops, preventing backsiphonage. Most common for residential irrigation.
How It Works:
• Check valve prevents backflow
• Air inlet valve opens when pressure drops
• Admits air to break siphon
• Prevents vacuum condition
• Only protects against backsiphonage (not back pressure)
Common Application - Low-Pressure Irrigation:
• Residential lawn sprinklers
• Garden irrigation
• Landscape watering
• Residential applications only
Typical Locations:
• Near house connection
• Beginning of irrigation system
• Above ground installations
• Accessible outdoor locations
Size Range:
• Residential: 1/2" to 2"
• Most common: 3/4" to 1"
Appearance:
• Brass or plastic body
• Two test cocks
• Air inlet on top
• Bonnet cover
• Smaller than RPZ or DCVA
Installation Requirements:
• MUST be installed minimum 12" above highest sprinkler head
• This is non-negotiable
• If not, cannot function properly
• Will fail testing
• Must be installed vertically
• Must be above ground
• Accessible for testing
• Protection from freezing needed
• Cannot be under continuous pressure
Annual Testing: Required by law
Typical Repairs Needed:
• Air inlet diaphragm (every 5-8 years)
• Check valve poppet (every 7-12 years)
• Complete rebuild (every 10-15 years)
Device Lifespan: 10-15 years
Cost Range:
• Device cost: $75-$400
• Installation: $400-$1,200
• Annual testing: $125
• Typical repairs: $100-$300
Advantages:
• Simple design
• Easy to maintain
• Less expensive
• Lightweight
• Perfect for residential irrigation
Disadvantages:
• Must be 12" above highest outlet
• Cannot protect against back pressure
• Above ground only
• Not suitable for commercial use
• Seasonal use only (irrigation)
AVB - ATMOSPHERIC VACUUM BREAKER
Description:
The simplest backflow prevention device. Admits air when water flow stops, preventing backsiphonage.
How It Works:
• Check disc closes when water flows
• Air inlet opens when flow stops
• Simple mechanical operation
• No spring-loaded components
• Cannot be under continuous pressure
Common Application - Individual Fixture Protection:
• Outdoor hose bibs
• Utility sinks
• Individual sprinkler connections
• Garden hose connections
• Non-critical applications
Typical Locations:
• Individual faucets
• Hose connections
• Outdoor spigots
Size Range:
• Typically 1/2" to 3/4"
• Small device
Appearance:
• Brass body
• Very simple design
• No test cocks
• Bonnet with air inlet
• Smallest backflow device
Installation Requirements:
• Must be 6" above highest outlet
• Must be downstream of shutoff valve
• Cannot be under continuous pressure
• Cannot have shutoff valve downstream
Testing: Not typically tested (non-testable)
Repairs: Usually replaced rather than repaired
Device Lifespan: 5-10 years
Cost Range:
• Device cost: $15-$75
• Installation: $100-$300
• Not testable (no annual test requirement)
• Usually replaced when problems occur
Advantages:
• Very inexpensive
• Simple design
• Easy to install
• Good for individual fixtures
• Widely available
Disadvantages:
• Not testable
• Limited protection
• Cannot be under continuous pressure
• Not suitable for most applications requiring testing
• No redundancy
SPECIALTY DEVICES
Other Backflow Devices
Dual Check Valve:
• Two check valves (non-testable)
• Minimal protection
• Often used for internal building protection
• Not accepted by most water authorities for required testing
Barometric Loop:
• Physical loop of pipe 35+ feet high
• No mechanical device
• Rarely used
• Impractical for most applications
Air Gap:
• Physical separation between supply and outlet
• Most effective method (100% protection)
• Not always practical
• Expensive to install
CHOOSING THE RIGHT DEVICE
Selection Criteria:
Based on Hazard Level:
High Hazard (requires RPZ):
• Chemicals or toxins present
• Fire suppression systems
• Medical/industrial facilities
• Sewage or waste
• Radioactive materials
Moderate Hazard (requires DCVA or RPZ):
• Irrigation without chemicals
• Building supply protection
• Swimming pools
• Food processing
Low Hazard (allows PVB or DCVA):
• Residential irrigation
• Landscape watering
• Non-toxic applications
Need Underground Installation:
• DCVA only
• RPZ requires drainage
Limited Space:
• PVB (smallest for testable devices)
• DCVA (compact)
Must Be Above Outlets:
• PVB requires 12" above outlets
• Affects irrigation system design
Most Economical:
• PVB for appropriate applications
• Lowest initial cost
• Simple maintenance
Best Value:
• DCVA for moderate hazard
• Reliable, lower maintenance
• Can go underground
Maximum Protection:
• RPZ regardless of cost
• Required for high hazard
• Most reliable but most expensive
BACKFLOW DEVICE TYPE - FREQUENTLY ASKED QUESTIONS
Q: Which device is best for my residential irrigation system?
A: PVB is most common and economical if you can install it 12" above the highest sprinkler. Otherwise, DCVA underground.
Q: Can I use a PVB for my fire sprinkler system?
A: No. Fire systems require RPZ for maximum protection.
Q: Why does my RPZ leak water occasionally?
A: Small drips from the relief valve are normal. It's monitoring pressure. Heavy or constant flow indicates a problem.
Q: Can I replace an RPZ with a less expensive DCVA?
A: Not if your application requires RPZ-level protection. Check with your water authority.
Q: How long do backflow devices last?
A: 10-25 years depending on type, water quality, and maintenance. Regular testing extends life.
Q: Do all devices require annual testing?
A: All testable devices (RPZ, DCVA, PVB) require annual testing by law in NY. AVB is not testable.
PROFESSIONAL GUIDANCE
J&J Backflow Device Testers Inc. Expert Advice on All Device Types
We Can Help You:
• Choose the right device for your application
• Test all device types
• Repair or replace any device
• Upgrade to appropriate device
• Meet regulatory requirements
Our Experience:
• 30+ years with all device types
• Thousands of devices tested
• Installation expertise
• Honest recommendations
Services:
• Annual testing: $99*
• Device installation: $400-$3,000
• Repairs: $100-$600
• Consultations: FREE
Call: 914-403-0181
Email: jandjbackflow@gmail.com
*introductory offer for new residential customers