A reduced pressure principle must be installed at what height above grade?

• A. 6 inches above grade
• B. 3 inches above grade
• C. 12 inches above grade
• D. 24 inches above grade

Answer: (C)

The key idea here is that backflow prevention devices must sit above ground level to stay protected from surface conditions and to be easily tested and serviced. A reduced pressure principle backflow preventer needs enough clearance so that its relief valve can discharge safely and won’t be blocked by soil, mulch, or mower blades, and so that the test cocks remain accessible for annual testing. Twelve inches above grade provides this necessary clearance without being excessively tall. Installing it closer to the ground, like a few inches high, risks flooding or obstruction during rain, irrigation, or snow, while going well above twelve inches isn’t required by standard practice and can complicate installation. Hence, twelve inches above grade is the correct height.