Process 2: Basic Precipitation Rate Calculation
1.
Measure the row spacing for each zone. Measure the head
spacing for each zone.
2.
Measure the pressure at a head closest to the valve and a head
furthest from the valve. Calculate the average pressure.
3.
Look up the flow rate for a full head for the sprinkler type,
nozzle size and pressure of the heads on each zone. If the
manufacturer’s information is not available, HPDS has charts for
many different types of sprinkler heads available and general
information that will get you information sufficient to complete
this step.
4.
If the measured pressure is above or below the manufacturers
chart, a rework of the system may be required before continuing
this process.
5.
Calculate the PR with this formula:
PR = (96.3 * Full head flow (gpm)) / (row spacing * head
spacing (in feet))
6.
Enter the data on the PR gathering sheet and in the
WeatherTRAK ET plus controller.
7.
Note:
This process assumes the sprinklers are installed in a
matched precipitation rate arrangement. If the zone is not
installed as a matched precipitation rate zone, a rework of the
irrigation system may be necessary.
Process 3: Station Catch Can Audit
1.
Obtain a Landscape Irrigation Audit Kit.
2.
Perform an audit of each representative station on the controller.
3.
Calculate the PR and Efficiency using the formulas below:
PR = (CV avg * 3.66) / (TR * CDA)
Where:
CV avg = the average catch can
amount in milliliters
TR = the test run time in minutes
CDA = the throat area in square
inches
Site Data Gathering
99
Compare Site Information to Criteria
1.
Do the heads have head-to-head coverage? (Does
one head spray all the way to the next head? i.e. it does not spray
less than or greater than the spacing between heads) If YES, go
to next step. If NO, go to step 2.
2.
Do you have access to the manufacturers sprinkler nozzle data?
If YES, go to Process 1. If NO, go to next step.
3.
Do the heads produce a lot of misting spray? If YES, go to
Process 3. If NO, go to next step.
4.
Is the system less than 10 years old? If YES, go to Process 2. If
NO, go to Process 3.
Process 1: Manufacturer’s Charts
1.
Look up the sprinkler head data in the manufacturers catalog for
the sprinkler head, nozzle size, pressure and spacing that you
found for each zone.
2.
If the pressure at the heads appear to be too high or too low,
measure the pressure at a head closest to the valve and a head
furthest from the valve. Calculate the average pressure.
3.
Identify on the manufacturers chart, the precipitation rate (PR)
for each head at the average or measured pressure in each zone.
If the measured pressure is above or below the manufacturers
chart for the head, a rework of the system may be required
before continuing with this process.
4.
Enter the data on the PR gathering sheet and in the
WeatherTRAK ET plus controller.
Site Data Gathering
98
