Weathermatic SLFSI-T10 Design Manual page 17

The chance for interference increases with the increase in distance between the flow sensor and the
receiving device. Use good installation practices when installing communication cables. Also avoid
splices in the flow sensor cable if possible. If splices are required, make sure they are mechanically tight,
waterproofed and shielded. In longer runs, over 500 feet, it is always a good practice to connect one end
(only) of the cable shield to a properly installed 8-foot copper ground rod.
NOTE: Using 14 gauge, two wire cable or irrigation "multi-strand" wire for flow sensor wire will increase
potential interference of the flow sensor signal and create poor flow sensor readings.
FLOW SENSOR INSTALLATION
A straight section of pipe is required to eliminate distortions in the water flow that cause inaccurate
measurements. When water moves through a pipeline at the rates associated with pressurized irrigation
systems, it moves at about the same velocity all across the pipe. It moves a little faster in the center of
the pipe and a little slower closer to the inside wall in a predictable shape called a ballistic profile. When
water is forced to bend around an elbow, the water takes a longer path around the outside than the
inside changing the local velocity and distorting the profile. Other distortions may be caused by valves or
fittings that produce eddy currents (swirls in the flow) as they change the path of the water. If these
profile distortions are close to the sensor impeller they will change its speed and produce inaccurate
measurements.
The minimum length of straight pipe needed to correct these distortions is generally given as 10 times
the diameter of the pipe before (upstream of) the flow sensor and 5 times the diameter of the pipe after
(downstream of) the sensor. If possible, provide more than these minimum lengths.
HOW TO SPECIFY:
Flow Sensor ONLY
SLFSI-T10 – 1" PVC Tee Mounted Flow Sensor
SLFSI-T15 – 1 ½" PVC Tee Mounted Flow Sensor
SLFSI-T20 – 2" PVC Tee Mounted Flow Sensor
SLFSI-S30 – 3" PVC Saddle Mounted Flow Sensor
SLFSI-S40 – 4" PVC Saddle Mounted Flow Sensor
SLFSI-S60 – 6" PVC Saddle Mounted Flow Sensor
SLFSI-B15 – 1 ½" Brass Tee Mounted Flow Sensor
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