CSLB C-27 Landscaping ContractorIrrigation SystemsMedium
A C-27 contractor is preparing to connect a new irrigation system to a potable water supply. The design specifies a Reduced Pressure Principle (RPZ) backflow preventer. What is the minimum required clearance between the lowest point of the RPZ assembly and the finished grade or potential flood level?
- A18 inches
- B24 inches
- C6 inches
- D12 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 12 inches
According to Uniform Plumbing Code (UPC) standards, which are widely adopted in California, a Reduced Pressure Principle (RPZ) backflow preventer must have its relief valve (the lowest point) installed at least 12 inches above the finished grade or potential flood level. This ensures that discharged water can drain freely and prevent backpressure.
Why the other options are wrong
- A. 18 inches is a more conservative installation height but not the minimum requirement.
- B. 24 inches is an excessive minimum requirement, though sometimes specified in very unique situations.
- C. 6 inches is the minimum for some Atmospheric Vacuum Breakers (AVBs) above the highest outlet, but not for the much more protective RPZ clearance to grade.
RPZ Backflow Preventer Clearance
The minimum vertical distance required between the lowest point (relief valve) of a Reduced Pressure Principle (RPZ) backflow preventer and the surrounding grade or potential flood level.
- Ensures proper drainage of relieved water
- Prevents submergence and failure of the relief valve
- Typically 12 inches according to UPC
- Critical for maintaining potable water safety
Memory trick: RPZ, relief valve clear, a foot from the ground, no fear.