Backflow Training
Introduction to Backflow For Irrigation Systems
Agenda
Backflow definitions Hydraulics Degree of Hazard Types of Backflow Preventers Product Selection Approvals Installations
What is Backflow?
The undesirable reversal of flow of water or mixtures of water and other liquids, gases, or other substances into the potable water supply from any source or sources.
Normal Flow
What is a Cross Connection?
Any unprotected actual or potential connection between a public or a consumer’s potable water system and any other source or system through which it is possible to introduce into any part of the potable water system any used water, industrial fluid, gas, or substance other than the intended potable water with which the system is supplied.
What is a Cross Connection?
A direct cross connection is subject to both back-siphonage and back-pressure. Usually a hard piped connection
An in-direct cross connection is subject to back-siphonage only. Can be a potential cross connection
Hydraulics
Back-pressure Back-siphonage Head Barometric loop Continuous vs. non-continuous pressure
Back-Pressure
Any elevation of pressure in the downstream piping system above the supply pressure at the point of consideration which would cause a reversal of the normal direction of flow.
Causes Change in elevation of the downstream piping. High pressure piping interconnect
Back-Pressure
Back-Pressure
Back-Siphonage Any decrease of pressure that causes a
negative or sub-atmospheric pressure to exist in the upstream piping ahead of the point of consideration which would cause a reversal of the normal direction of flow.
Causes Undersize piping Line breaks High water withdrawal rates
Back-Siphonage
Back-Siphonage
Head
The term “head” is used to describe pressure.
One foot of head equals .433 pounds per square inch.
In the backflow industry, the pressure loss through the valve is called “head loss”.
All manufacturers express the head loss of their valves in units of pounds per square inch.
Head27 3/4” of water
generates a pressure of one pound per square inch (psi)
27 3/4”1 psi
Barometric Loop
A barometric loop is a horseshoe-shaped loop in a water line, that has a height greater than 33.9 ft.
A very effective means of preventing backflow due to back-siphonage.
Impractical due to physical size.
Pressure
Non-continuous System cannot realize more than 12 hours
of continuous pressure per 24 hour period. Continuous
Anything that is not non-continuous!
Degree of Hazard
Low Hazard
Non-Health Hazard
Pollution
High Hazard
Health Hazard
Contamination
Types of Backflow Preventers used in Irrigation Systems
Atmospheric Vacuum Breaker Pressure Vacuum Breaker Double Check Assembly Reduced Pressure Principal Assembly
Types of Non-Mechanical Backflow Preventers
Air Gap A physical separation between the free flowing
discharge end of a potable water supply pipeline and an open or non-pressure receiving vessel.
An “approved air gap” shall be at least double the diameter of the supply pipe measured vertically above the overflow rim of the vessel.
Never less than 1 inch.
Air-Gap
Atmospheric Vacuum Breaker
Contains a float-check, a check seat, and an air inlet port.
Water flow causes the float to close the air inlet port.
When the flow of water stops... The float falls and forms a check valve against
back-siphonage The air inlet port opens to allow air to enter and
satisfy the vacuum.
Atmospheric Vacuum Breaker (AVB)
Protects against a health hazard Back-siphonage condition only. Non-continuous pressure application.
No more than 12 hours of pressure per 24 hour period
Atmospheric Vacuum Breaker
Anti-Siphon Valves
Non-Testable Not USC Approved Usually not inspected
Pressure Vacuum Breaker (PVB)
Contains... Independently-acting, internally-loaded
check valve. Independently-acting, loaded air inlet valve
located on the discharge side of the check valve.
Two resilient-seated test cocks. Two resilient-seated isolation valves.
Pressure Vacuum Breaker
Protects against a health hazard. Back-siphonage condition only. Continuous pressure application.
Can realize pressure for 12 hours or more per 24 hour period.
Pressure Vacuum Breaker
Pressure Vacuum Breaker
Double Check Valve Assembly (DC)
Contains two independently-acting approved check valves.
Four resilient-seated test cocks. Two resilient-seated isolation valves.
Double Check Valve Assembly
Protects against a non-health hazard. Back-pressure condition. Back-siphonage condition. Continuous pressure applications.
Double Check Assembly - Small
Double Check Assembly - Large
Reduced Pressure Principal Backflow Preventer (RP)
Contains two independently-acting approved check valves.
A hydraulically-operating, mechanically independent differential pressure relief valve located between the two check valves.
Four resilient-seated test cocks. Two resilient-seated isolation valves.
Reduced Pressure Principal Backflow Preventer
Protects against a health hazard. Back-pressure condition. Back-siphonage condition. Continuous pressure applications. The Ultimate in mechanical protection.
Reduced Pressure Assembly - Small
Reduced Pressure Assembly - Large
Operation of an RP Device
No-Flow Condition
Normal Flow
Backpressure with 2nd Check Fouled
Backsiphonage with 2nd Check Fouled
Troubleshooting an RP Assembly
1. Turn off number 2 shutoff valve2. If discharge stops, problem is in 2nd
Check
Troubleshooting an RP Assembly
3. If discharge continues, induce flow by opening number four testcock
4. If discharge stops or slows dramatically, problem is in first check
Troubleshooting an RP Assembly
5. If discharge continues with no change, problem is in relief valve
Product Selection Guide
APPLICATION
MODEL TYPE BACK BACK CONTINUOUS POLLUTANT CONTAMINANT
SIPHONAGE PRESSURE PRESSURE
975XL RPZ *** *** *** *** ***
375 RPZ *** *** *** *** ***
950XL DCV *** *** *** ***
350 DCV *** *** *** ***
420 PVB *** *** *** ***
35 AVB *** *** ***
Specify the Proper Device for the Application
We can communicate industry standards for degree of hazard, hydraulic and backflow conditions.
Up to authority having jurisdiction to make the final decision.
Approvals and Listings Approvals
FCCC&HR@USC FM
Listings ASSE UPC UL CSA
AWWA (Voluntary Standard - Certified to)
Installation Requirements
Hydraulics Accessibility for testing and repair Indoor vs. Outdoor Freeze protection Vandal protection Relief valve discharge
Pressure Vacuum Breaker Installations
Double Check Assembly Installations
Below Grade
Above Grade
RP Assembly Installations
Irrigation Systems Issues
Quick closing solenoid valves Create water hammer Cause RP to discharge
Soft seated check valve between solenoid and RP
Cause noise Install water hammer arrestor
Water Hammer Devices Soft Seated Check Water Hammer
Arrestor
Key Terms Accessible Approved Assembly Approved Check
Valve Isolation Backflow program
Administrative Authority
Annual test Certified Tester Containment Point of use
Thank You
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