Flow Sensors - Weathermatic SLFSI-T10 Design Manual

FLOW SENSOR
The Weathermatic SmartWire™ Controller can utilize a flow sensor provided the controller is connected
to a SmartLink Aircard. Due to the need for accuracy in the flow measurement, flow sensors must be
wired back to the Aircard using a double-jacketed, shielded, twisted pair, direct bury PE type cable
FLOW SENSOR SIZING
Flow sensors should be sized to accommodate the range of flows they will measure, rather than match
the size of the pipeline. Generally accepted design practices recommend that the maximum velocity of
water in PVC piping systems does not exceed velocities of 5 feet per second (f/s). Keeping the velocity
below this level helps minimize the effects of water hammer and protects the pipe. In addition, pipe size
may be oversized to reduce pressure drop caused by friction losses.
Irrigation systems don't operate at a fixed flow rates; there are always variations in the size of flow
zones or differences in the types of sprinkler heads or emitters used. Often times the velocity in the
pipeline is far less than the maximum flow and can be so low that it can't be detected. No flow sensor
can measure down to zero flow. There is always a minimum flow rate or velocity below which there is
not enough energy in the water to turn the impeller and generate a flow signal. WEATHERMATIC flow
sensors have a wide measurement range from ¼ foot per second to 15 feet per second. This means that
a 2-inch flow sensor can easily handle the design flow rate of a 3-inch pipeline without exceeding its
maximum velocity. More often, the lower limit of the flow range is far more important. With the new
water conserving technology of stream rotors, micro-sprays and low volume drip emitters, it is easy to
reduce irrigation zone flow rates below minimum velocity ranges of line-sized sensors. Check the
irrigation program or flow zones to determine minimum and maximum flow rates. Then use this table to
select the flow sensor size with the best fit between these ranges.
FLOW SENSOR FLOW RANGE
SmartLink Flow
Sensor Model
Feet/Sec
Minimum Flow 0.25
1
2
3
5
7
10
12
Maximum Flow 15
Friction Loss at Max Flow
FLOW SENSOR WIRING
Wiring may be extended up to 2,000 feet with SLFLOW-WIRE-193 cable. Size of the conductors is not as
important as the twisting and shielding because flow sensor signals are more subject to interference
from outside sources than from line losses. Outside interference may be generated by electrical wiring
for motors, lights or signals that cross or pass close by the flow sensor cable. Interference may result in
momentary loss of flow signal or an increase in signal frequency resulting in flow measurement errors.
16 | P a g e
SLFSI-T10 SLFSI-T15 SLFSI-T20
1" 1 1/2"
GPM GPM
0.86 1.8
3.5 7.24
7 14.5
10.4 22
17 36
24 51
35 72
42 97
52 108
.025 psi .018 psi 0.15 psi
SLFSI-S30 SLFSI-S40
2" 3"
GPM GPM GPM
2.8 6
11.3 25
23 50
34 75 120
57 125 200
79 175 280
113 250 400
136 300 490
170
0.15 psi 0.15 psi
SLFSI-S60
SLFSI-B15
6"
4" 1 1/2"
GPM
GPM
23
10
90
40 5.5
180
90 11
270
16.5
450
27.5
630
38.5
900
55
66
83
0.07 psi
0.18 psi