This calculator is designed to assist you in determining the
water pressure [psi] available at various points
throughout the irrigation system.
This webpage and the source code
were developed solely by Frank Rauscher & Garden Galaxy and are
subject to Copyright. If it desired to reproduce any portion
of this webpage, written approval by F. Rauscher or GardenGalaxy.xyz is
When determining run-time desired on a particular zone,
the actual quantity of water delivered by the emitters at the end
depend greatly on the pressure available at that point.
Whether the current project is a New Zone - or adding to or
modifying an existing zone; understanding the water pressure
at each of the significant points along the way [P1 to P6]
is vital in order to deliver enough water to provide adequate
depth of moisture. Also this is vital in making sure that the
application of too much water is avoided.
Whether the end of the system [feeder section] uses dripperline (or autonomous emitters), remember;
flow rate varies with pressure. Even with pressure compensating emitters this variance
only diminishes volitility by 50%.
Emitters are standard rated at a full 30 psi. A 20% reduction
(even with pressure compensation) results in a 10% reduction in water flow.
Avoiding high PSI line loss is a very important part of a good irrigation system design.
Operating the terminating emitters more than 18% below the regulated input pressure
will make any future modifications that may be needed nearly impossible.
Depending on the landscape size and slope, and feeder sections demand, losing pressure along the
Supply Line sctions can be significant. This calculator takes all of these into consideration.
With Dripperline a little pressure is lost at each emitter outlet along the line.
This calculator will report the pressure and flow at each section along the delivery line.
The final outlet pressure and the average across the
With autonomous emitters psi is calculated at feeder input and emitter output
(including pressure drop from feed line and connectors.)
With this information you can determine the runtime
required in order to get the volume of water (gallons) the specific plant needs.
Typically a [½ or ¾"] PVC line is connected to
a pressure regulator following the valve and filter for a particular zone.
This supply line is often followed by a ¼" Black/Brown Poly
tubing. This tubing is easily pierced by the hole punch tool
and seals effectively following insertion of the "barb" that
will then be connected to the Feeder line and subsequent emitters.
The feeding emitters can either be Dripperline or Autonomous & separate.
With Dripperline the options are either [¼ or ½]" diameter dripline; then
the space (6", 12", 18") between emitters on the line is the second option.
With sandy (fast draining soil) or smaller plants the chioce is usually ¼"-6" spacing.
Sometimes due to resticted runtime options, this condensed line is selected in order
to apply more water in less time. Larger irrigation areas will do best with 12" or even 18" spacings.
½" diameter dripline is more durable for higher traffic areas or for sub-surface
If autonomous emitters are used, these generally run with flowe rates from
0.5 to 15 gph (depending on the type). If more than a single autonomous emitter is
used, there will be a "Tee" and a second feeder line used prior
to the terminating emitters.
This calculator will analyze one (1) feeder section at a time.
This analysis will be accurate for all sections within a group, as
all groups are basically equal.
Where there are multiple groups, then the analysis should be carried out
on at least one section in each group.
When the number of irrigation zones to run in a single day is minimal (4 to 6)
Scheduling Long Run Times provides superior depth of moisture and enables
the option to supply more plants from a single zone. Water expense
is not increased simply due to long run-times. Slow flow emitters help with
deeper watering and hence reduced evaporation. "Water Savings"
Visit Garden Galaxy Irrigation Design Strategies webpage for
more ideas and considerations.
Instructions In order to discover the friction loss across the supply and feeder lines, you will need to
1) the Regulated Supply pressure [psi)
2) Estimating the water flow demand of the combined feeders
supplied by this zone.
2.1) Observe each plant's (or plant-bed) feeder line.
2.2) A single feeder line taping into the ½" Polytubing
specifies a Single Group. From that feeder there
will either be a number of autonomous emitters or a length of
2.3) When estimating demand
- Minimize the number of groups (simply)
by including groups with emitter counts within 10% of each other.
2.4) When designing a new system
Try to use emitters with
a standard flow rate throughout each zone. Slow flow is best.
If more water is needed, use more emitters. Distributing
water evenly throughout the planting area is superior.
Evaluating the Supply Sections
3) The diameter, length and slope of the PVC run
3.1) Use drop down boxes to select
3.2) Estimate elevation change from beginning to end.
3.3) Review psi out for possible entry errors
4) The length & slope of the Polytubing run
4.1) use drop down box to select
4.2) Estimate elevation change from beginning to end.
4.3) Review psi out for possible entry errors
Evaluating the Feeder Section
5) Select the type of Emitters or Emitterline
6) The length (in feet) of the ¼" diameter feeder line.
6.1) When using ½" dripline, no ¼" connecting feeder is used.
7a) the length of Dripperline (if used)
- or -
8a) the # of autonomous emitters (if used)
8b) the flow rate for those emitters
8c) the number of "tees" used to interconnect
8d) the length of 2nd feeder line
There are 8 boxes of data reporting the results of
this analysis. If data is missing the first box
will notify you that this is so, in order to correct.