Plumbing: Backflow Preventers

SKU: RVI-11511Duration: 20 Minutes

Backflow is an often unknown or misunderstood phenomena. Even less understood is the purpose of backflow preventers and how they operate. Backflow is a condition in which water in a building or facility will flow backwards, creating a potential hazard to the domestic water system. Without a properly selected, installed, maintained and tested backflow device, hazard conditions resulting in illness or even death can occur. In this course you will be introduced to what backflow is, under what conditions backflow can occur and the provisions to prevent backflow from occurring. Several key definitions will be presented and the operation of each type of backflow preventer is briefly explained. At the end of this training you will have a workable understanding of backflow devices and how to troubleshoot breakdowns.

Course Details


Training Time: 20 minutes

Compatibility: Desktop, Tablet, Phone

Based on: Industry Standards and Best Practices

Languages: English

Learning Objectives

  • State the purpose of backflow preventers
  • Identify who is permitted to perform the annual backflow preventer test
  • List the steps to diagnose a leaking RPBP
  • Recognize the correct backflow preventer to use in a given situation
  • Select the correct air gap size for relief openings on backflow preventers
  • State the frequency in which backflow devices are required to be tested

Key Questions

The following key questions are answered in this module:

What are the two types of hazards associated with contamination of potable water?
A low hazard is when potential backflow can pollute the drinking water. A high hazard application is one where the potential backflow can contaminate the water supply.

What is an atmospheric vacuum breaker (AVB)?
A device made to prevent only backsiphonage. The AVB is installed after the control valve and for each irrigation zone. This type of system should not be used in areas where chemicals or fertilizers are used.

What is a requirement with air gap systems?
A gap is a type of system that keeps a physical barrier between the potable water and non-potable water systems. One of the requirements is to maintain a minimum distance based on the diameter of the water source. In general, the minimum air gap distance is 2-inch.

What are the three pressure zones in the Reduced Pressure Backflow Preventer?
There are three pressure zones in the RPBP assembly: the upstream pressure, the reduced pressure zone between the check valves and the downstream zone.

What are the four questions to answer when selecting a backflow device?
1. Is it a high hazard or low hazard? 2. What are the backsiphonage conditions? 3. What are the backpressure conditions? 4. Is it continuous or intermittent pressure?

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

The double check valve assembly (DCVA) is a big step up in terms of sizes available and the number of applications. As the name implies, DCVA's are simply two high-quality checks valves in series. If one of the check valves becomes inoperative due to fouling or a mechanical failure, the other check valve will still provide backflow protection. However, if both check valves fail, all backflow protection is lost. The is the reason double check valves are listed for low hazard applications only. Like the PVB, the double check valve assemblies are testable and need to be tested by an approved testing agency regularly. Large gate valves are shown on each side of the DCVA. While not part of the backflow assembly, these shut-off valves are required for maintenance or replacement of the assembly. These valves do need to be provided by the manufacturer as after-market valves do not meet code. Often, a full-size loop around the DCVA is provided to ensure water service is not interrupted during repairs. On fire sprinkler systems, the shut-off valves are often secured with locks, chains or removal of the handles to ensure the valves are not shut inadvertently. One of the maintenance and inspection tasks should be periodically inspecting the DCVA's to confirm the shut-off valves are open. A specialized version of the double check valve assembly is the double detector check valve assembly. A DDCVA consists of two double check valve assemblies. DDCVA is often used in fire sprinkler system applications. A small loop is installed around the check valve assembly. A small water meter is installed in this loop. In a properly functioning fire sprinkler system, there should never be flow through this loop. If the meter detects water usage, there may be a water leak or water is being used for something other than for fire sprinklers. This metered bypass also provides a path for backflow unless provisions are made.
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