2
• Most field problems occur because dirt and debris are present
in the system at the time of installation and becomes trapped
in check #1. 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.
• Series 957-FS, 957RPDA-FS, and LF957RPDA-FS can be
installed in either horizontal, “N” pattern, or “Z” pattern position
as long as the backflow assembly is installed in accordance
with the direction of the flow arrow on the assembly and the
local water authority approves the installation.
• The assembly should be installed with adequate clearance
around the valve to allow for inspection, testing, and servicing.
A minimum clearance of 12" should be between the lower
portion of the assembly and the floor or grade. The valve
should be protected from freezing.
• Installing a backflow preventer in a pit or vault is not
recommended.
• Normal discharge and nuisance spitting are accommodated
by the use of a Watts air gap fitting and a fabricated indirect
waste line. A floor drain appropriately sized for the discharge
must be provided in case of excessive discharge. For more
information, download ES-RVD for relief valve discharge rates.
• When installing an air gap, attach the air gap brackets directly
onto the flood sensor.
• Series 957-FS, 957RPDA-FS, and LF957RPDA-FS backflow
preventers should be tested by a certified tester at the time
of installation.
NOTICE
Assembly body should not be painted.
Relief Valve Discharge Rates 2
1
⁄
2
" – 10"
lpm gpm
1330 350
1140 300
950 250
760 200
570 150
380 100
190 50
0 0
0
20
40
60
80 psi
0
138
276
413
551 kPa
Rate of Flow
Pressure
Horizontal Installation
N Pattern
Z Pattern
Installation Guidelines
