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11. How to Calculate Station Flow Rates
There are two methods to determine station flow rates if a Calsense flow meter is not installed on the system. The following
describes each method.
Using Manufacturers Published Data:
With this method you use a manufacturers catalog which has the flow rates listed for the type heads, and nozzle sizes on the system
you are calculating. Simply total the flow rates for all the nozzles on the station.
Example:
A station has 8 half-circle pop-ups with a flow rate of 2 gpm each, 3 full-circle pop-ups at 4 gpm each and 4 quarter-circle pop-ups
at 1 gpm each. The station’s flow rate would be calculated as follows.
8 heads x 2 gpm =
16 gpm
3 heads x 4 gpm =
12 gpm
2 heads x 1 gpm =
2 gpm
Total flow =
30 gpm
Measuring Station Flow Rates:
The second method is a little more complicated, but the results are more accurate. You will use the irrigation system’s water meter
to calculate flow rates. Use the following procedure :
1. Determine the units used by the water meter (gallons, cubic feet, etc.). Make sure no other water will be flowing while you are
measuring flow rates. Also, if there is more that one water meter connected to the mainline, all of them must be turned-off except
the one you are using to measure flow with.
2. Before beginning, turn on each station to make sure there are no broken heads or pipe and no plugged heads. Breaks or
plugged heads will cause incorrect flow readings.
3. Begin by turning on a station, let it run long enough to purge all the air out of the system. Then simultaneously, make note of the
meter reading and start timing using a stopwatch. After 3 minutes has elapsed make note of the meter reading again. Subtract
the starting meter reading from the ending meter reading, this will give you the amount of water used by the station in 3 minutes.
Continue this procedure until all stations have been measured.
4. To calculate the flow rate, divide the amount of water the station used (measured in gallons) by 3 minutes, this will give you the
station’s flow rate measured in GPM’s (gallons per minute).
Example #1 (if water meter units are in gallons) :
The starting meter reading is 312,121. After 3 minutes the ending meter reading is 312,378 gallons, the flow rate would be calculated
as follows:
312,378 gallons - 312,121 gallons = 257 gallons
257 gallons ÷ 3 minutes = 85.6 gpm
station flow rate = 85.6 gpm
Example #2 (if water meter units are in cubic feet or CF) :
The starting meter reading is 9,975 CF After 3 minutes the ending meter reading is 10,003 CF, the flow rate would be calculated as
follows:
10,003 CF - 9,975 CF = 28 CF
28 CF x 7.48 gallons = 209.4 gallons
(1 CF = 7.48 gallons)
209.4 gallons ÷ 3 minutes = 69.8 gpm
station flow rate = 69.8 gpm
Example #3 (if water meter units are in hundreds of cubic feet or CCF) :
The starting meter reading is 12,321 CCF After 3 minutes the ending meter reading is 12,321.25 CCF, the flow rate would be
calculated as follows:
12,321.25 CCF - 12,321 CCF = .25 CCF
.25 CCF x 748 gallons = 187 gallons
(1 CCF = 748 gallons)
187 gallons ÷ 3 minutes = 62.3 gpm
station flow rate = 62.3 gpm
NOTE : In examples #2 and #3 above, there is one extra step in the calculation, this is to convert the cubic feet into gallons before
dividing by 3 minutes.
