Rule
of 4’s & 9’s as pertaining to pipe
sizing in an irrigation system
This is a good rule of thumb system for sizing
mainline & lateral pipe in a residential irrigation
system
With PVC pipe as flows increase, so does velocity
in the lines. Most irrigation applications use 5
feet per second as the maximum velocity allowable
(velocities in excess of 5 fps are generally not
used due to increased friction loss as well as increased
chance of water hammer.) Using the below system
you will always be at an acceptable velocity.
Sch 40 PVC Pipe (Rule of 4’s)
1/2” 4 Gallons Per Minute Maximum
3/4” 8 Gallons Per Minute Maximum
1” 12 Gallons Per Minute Maximum
As you can see each time the flow increases by 4
Gallons per minute a change of pipe size is necessary.
If the flow decreases by 4 GPM a change of pipe
size can be done, but it is not always necessary
as the velocity in the pipeline decreases with flow
reductions. Pipe is generally sized down due to
economics.
Class 200 PVC Pipe (Rule of 9’s)
3/4” 9 Gallons Per Minute Maximum
1” 18 Gallons Per Minute Maximum
1 1/4” 27 Gallons Per Minute Maximum
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Troubleshooting
controller/valve issues #1
Your controller seems to work fine, but none
of the valves come on:
The probable cause is a short in a solenoid or a
broken common wire. The most likely cause, is a
short in a solenoid. This will short out and blow
the fuse in the controller and nothing will come
on. Simply replacing the fuse will not fix the problem,
you will need to determine which valve is causing
the problem. I suggest running the clock through
it’s cycle, then when the fuse blows on the
problem station, that is the valve that needs to
have the solenoid replaced. Replace the solenoid,
and install new fuse, and your problem should be
solved.
To test for a broken common wire:
A simple troubleshooting technique is to run a temporary
wire on top of the ground to the first valve. Connect
it to the clock and tie it in to the valve. Then
run the controller, the valve should operate normally.
If it doesn’t then it is not a broken wire,
it is another problem.
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Irrigation
comes on at different times of the day.
First: Check the current
clock time, because there may have been a power
failure, and reset. Install new batteries, because
they should have kept the current time.
Other possibilities are:
•Phantom programs due to a glitch in the program.
If this is the case remove the battery, and turn
off the power supply. Reprogram as needed, and test
the program to make sure it functions properly.
Add new battery, and you are ready to go.
•Check for days on, and start times for all programs.
Sometimes you may find that program B or C has accidentally
been programmed when you only wanted program A to
run.
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