Plumbing (C-36) · Lesson 7 of 8

Backflow Prevention Types

"Backflow Prevention Types" is lesson 7 of 8 in the Plumbing (C-36) Learning Hub. It opens with "What Backflow Actually Is" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What Backflow Actually Is
  2. Air Gap - the Simplest, Most Reliable Method
  3. AVB and PVB - Vacuum Breakers, for Backsiphonage Only
  4. DCVA and RPZ - for Higher Hazard, Including Backpressure
  5. Testing Requirement

The worked example in the course applies this lesson to a realistic job in 3 steps, moving through "Identify the hazard type", "Check whether a downstream shutoff exists", and "Select PVB and apply its installation rule".

What you'll be able to do

  • Explain the main idea of "Backflow Prevention Types" in plain language you can use on the exam.
  • Apply this step with confidence: "DCVA and RPZ - for Higher Hazard, Including Backpressure".
  • Apply this step with confidence: "Testing Requirement".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
BACKFLOW PREVENTION TYPES Five devices, ranked by protection level (CPC 603) AIR GAP Physical open space - no mechanical part to fail. Highest-hazard connections. RPZ Reduced Pressure Zone - actively relieves on failure. High-hazard, backpressure + backsiphonage. DCVA Double Check Valve Assembly - two checks in series. Low-to-moderate hazard. PVB Pressure Vacuum Breaker - check + air inlet, 12" above highest outlet. Backsiphonage only. AVB Atmospheric Vacuum Breaker - simplest. No downstream shutoff allowed. Backsiphonage only. less more TWO RULES THAT DECIDE WHICH ONE TO USE 1. Is there a downstream shutoff valve? If yes, AVB is disqualified - use PVB or better. 2. Is the hazard backpressure, not just backsiphonage? If yes, only DCVA/RPZ/air gap protect against it. CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What Backflow Actually Is

Backflow is the reversal of normal flow - contaminated water, gas, or suspended solids traveling backward into the clean potable water supply, instead of forward out to where it's supposed to go. It typically happens from either backpressure (something downstream pushes harder than the supply) or backsiphonage (a drop in supply pressure creates suction, pulling water backward). Every backflow device exists to stop one or both of those.

Step 2: Air Gap - the Simplest, Most Reliable Method

An air gap is a physical, open vertical space between a supply outlet and the flood-level rim of a fixture - there's no mechanical part to fail because there's simply no direct connection at all. It's the gold-standard protection for the highest-hazard cross-connections, alongside the RPZ assembly below.

Step 3: AVB and PVB - Vacuum Breakers, for Backsiphonage Only

An Atmospheric Vacuum Breaker (AVB) is the simplest mechanical device - it's approved only where there's no downstream shutoff valve, and it cannot be used under continuous pressure. A Pressure Vacuum Breaker (PVB) improves on that: a single check valve plus an air inlet valve, commonly used for irrigation, and it must be installed at least 12 inches above the highest downstream outlet per CPC 603. Neither AVB nor PVB protects against backpressure - only backsiphonage.

The remaining 2 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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