Page 309 - Water Engineering Hydraulics, Distribution and Treatment

9.5 Reduced Pressure Principle Backflow Preventer
Reduced pressure zone backflow
3
preventer ( / 4 inch thru 2 inches)
95 psi
94 psi
100 psi
1 / 4 1 / 4 287
Supply 60 psi Out 47 psi
50 psi

1 / 4

(a)

Reduced pressure zone backflow
1
preventer (2 / 2 inches thru 10 inches)

Reduced pressure zone
First check valve Second check valve

94 psi 93 psi
100 psi

Relief valve (rotated 90° for clarity)

(b)
Figure 9.27 Types of reduced pressure zone backflow preventers. Conversion factors:
1inch = 25.4mm; 1psi = 6.94 kPa.