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Backflow Training

Learn about backflow, cross connections, hydraulics, and backflow preventers in irrigation systems, including product selection and installations.

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Backflow Training

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  1. Backflow Training Introduction to Backflow For Irrigation Systems

  2. Agenda • Backflow definitions • Hydraulics • Degree of Hazard • Types of Backflow Preventers • Product Selection • Approvals • Installations

  3. 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.

  4. Normal Flow

  5. 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.

  6. 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

  7. Hydraulics • Back-pressure • Back-siphonage • Head • Barometric loop • Continuous vs. non-continuous pressure

  8. 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

  9. Back-Pressure

  10. Back-Pressure

  11. 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

  12. Back-Siphonage

  13. Back-Siphonage

  14. 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.

  15. Head 27 3/4” of water generates a pressure of one pound per square inch (psi) 27 3/4” 1 psi

  16. 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.

  17. Pressure • Non-continuous • System cannot realize more than 12 hours of continuous pressure per 24 hour period. • Continuous • Anything that is not non-continuous!

  18. Low Hazard Non-Health Hazard Pollution High Hazard Health Hazard Contamination Degree of Hazard

  19. Types of Backflow Preventers used in Irrigation Systems • Atmospheric Vacuum Breaker • Pressure Vacuum Breaker • Double Check Assembly • Reduced Pressure Principal Assembly

  20. 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.

  21. Air-Gap

  22. 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.

  23. 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 AVB

  24. Atmospheric Vacuum Breaker

  25. Anti-Siphon Valves • Non-Testable • Not USC Approved • Usually not inspected

  26. 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.

  27. 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. PVB

  28. Pressure Vacuum Breaker

  29. Pressure Vacuum Breaker

  30. Double Check Valve Assembly (DC) • Contains two independently-acting approved check valves. • Four resilient-seated test cocks. • Two resilient-seated isolation valves.

  31. Double Check Valve Assembly • Protects against a non-health hazard. • Back-pressure condition. • Back-siphonage condition. • Continuous pressure applications. DC

  32. Double Check Assembly - Small

  33. Double Check Assembly - Large

  34. 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.

  35. Reduced Pressure Principal Backflow Preventer • Protects against a health hazard. • Back-pressure condition. • Back-siphonage condition. • Continuous pressure applications. • The Ultimate in mechanical protection. RP Rules

  36. Reduced Pressure Assembly - Small

  37. Reduced Pressure Assembly - Large

  38. Operation of an RP Device

  39. No-Flow Condition

  40. Normal Flow

  41. Backpressure with 2nd Check Fouled

  42. Backsiphonage with 2nd Check Fouled

  43. Troubleshooting an RP Assembly • Turn off number 2 shutoff valve • If discharge stops, problem is in 2nd Check

  44. Troubleshooting an RP Assembly • If discharge continues, induce flow by opening number four testcock • If discharge stops or slows dramatically, problem is in first check

  45. Troubleshooting an RP Assembly • If discharge continues with no change, problem is in relief valve

  46. Product Selection Guide

  47. 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.

  48. Approvals FCCC&HR@USC FM Listings ASSE UPC UL CSA AWWA (Voluntary Standard - Certified to) Approvals and Listings

  49. Installation Requirements • Hydraulics • Accessibility for testing and repair • Indoor vs. Outdoor • Freeze protection • Vandal protection • Relief valve discharge

  50. Pressure Vacuum Breaker Installations

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