Install Instructions

Guidelines

1. Most field problems occur because dirt and debris present in

the system at the time of installation becomes trapped in the

#1 check. The system should be flushed before the back-

flow valve is installed. If the system is not flushed until after

the backflow valve is installed, remove both check modules

from the valve and open the inlet shutoff to allow water to

flow for a sufficient time to flush debris from the water line. If

debris in the water system continues to cause fouling, a

strainer can be installed upstream of the backflow assembly.

2. Watts models 957 and 957RPDA may be installed in either

horizontal, “N” pattern, or “Z” pattern position as long as the

backflow assembly is installed in accordance with the direc-

tion of the flow arrow on the assembly and the local water

authority approves the installation.

3. The assembly should be installed with adequate clearance

around the valve to allow for inspection, testing and servic-

ing. 12" (305mm) should be the minimum clearance

between the lower portion of the assembly and the floor or

grade. The valve should be protected from freezing.

4. Installing a backflow preventer in a pit or vault is not recom-

mended.

5. Normal discharge and nuisance spitting are accommodated

by the use of a Watts air gap fitting and a fabricated indirect

waste line. Floor drains of the same size must be provided in

case of excessive discharge.

6. The 957 and 957RPDA backflow preventer should be tested

by a certified tester at the time of installation.

NOTE: Assembly body should not be painted.

Horizontal Installation

N Pattern

Z Pattern

Basic Installation Instructions

Relief Valve Discharge Rates

⁄2" – 10" (65 - 250mm) 957 and 957RPDA

lpm gpm

1330 350

1140 300

950 250

760 200

570 150

380 100

190 50

0 20 40 60 80 psi

0 138 276 413 551 kPa

Rate of Flow

Pressure