Introduction & Instructions
for
Friction Loss Calculator
Reference Tip
RT5010
Technical Bulletin Series

Go to Instructions ☀

Introduction
Within Drip Irrigation, emitter flow rate, locations, quantities and scheduled run-times all need to be calculated. There are usually 2 to 4 or more valves (or zones) which require this calculation. Each zone needs it's own calculation due to the differences in the quantity and frequency of water required by various plants or turf.

When determining run-time desired on a particular zone, the actual quantity of water delivered by the emitters at the end depend on the pressure available at that point and the quantity and rating of the drip emitters.

Whether your current project is a New Zone Additrion - or - modifying an existing zone; understanding the water pressure at each of the significant points along the way [P1] to [P6] - [Image 2] is vital in order to deliver enough water to provide adequate depth of moisture. This is also vital toward making sure that the application of too much water is avoided.

Whether the end of the system [feeder section] uses dripperline (or individual emitters), flow rates 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 sections can be significant. The GG-Friction Loss 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 entire dripline.

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.

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.


Common Designs 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 secondary; ½" Black/Brown Poly tubing.

The terminating emitters are located in the Feeder Section and can either be Dripperline or Individual autonomous emitters.

Dripperline has the emitters built into; either a ¼ or ½" diameter dripline. The emitters are then spaced (6", 12", 18") between. With sandy (fast draining soil) or smaller plants the chioce is usually ¼" tubing with 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 installation.

If autonomous emitters are used, these generally run with flow 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. Due to the complexity of utilizing many extra connectors, and selecting proper emitter location to assure good distribution, Dripperline has become very popular.

The GG-Friction Loss Calculator will analyze one (1) Feeder Section, and it's Supply Lines "A" & "B1" at a time. This analysis will provide an accurate calculation for all similarly designed sections within that group.
If other feeder sections have significantly different demand and design - only the data in section 5 need be reviszed in order to provide analysis on these differing sections.
In the likely event that the sections in a group are dissimilar, or the groups are dissimilar within the same Supply combination; there are instructions to guide you through the process.

These instructions include details for more complex irrigation designs. Such as:
    A) Multiple secondary supply lines. B2, B3, etc.
    B) High Flow Rate (over 150 gph) demand
      on the Primary or Secondary supply lines.
    C) Feeder sections with dissimilar emitter types

Instructions

Section 1
1) Note: Regulated Supply pressure [psi) [P1]
      1.1) This is set by the pressure regulator used.
2) Estimating total Feeder Demand
      2.1) When multiple secondary supply lines
      are connected to the same primary line;
      an additional analysis will be needed for each.
      Example (refer to Image 1)
        2.11) The closest secondary supply is "B1"
        2.12) This supply will be used for
           initial analysis
        2.13) Determine the total Feeder Sections
           demand as supplied from secondary
           supply lines "B2, B3" etc. (not B1)
        2.14) Note the emitter qty & avg. flow rate
           2.141) This total demand will be entered at step (2.17)
           If the current design for Supply "A" is large & complex an
           estimated summary will suffice.
           Good Drip designs feed at approx. (0.35 to 1.75 gph)
           1.0 gph per sq. ft. avg » depending on soil composition.
           Set gph at 1.0 gph & set Qty at 1 times area sq.ft.

        2.15) Information for multiple
         secondary supplies (B2..)
            Note: though these will be evaluated in subsequent
            analyses, their total demand must be estimated here.
            as this will impact PSI drop on supply "A"
        2.16) Total the Feeder Sections demand for
        subsequant secondary supply line; "B2, B3"
        2.17) The 4th row of Groups (Section 1)
             provides the option to input demand from the multiple
             secondary supplies (see 4.1). This demand will not
             be applied to supply line "B1" in (Sec. 3 1st analysis).

Estimating Combined Feeder Demand
Looking at Calculator Data Input Section 1
      2.2) "Output PSI" from Valve @ regulator [P1]
           This pressure will be input to section 1.
      2.3) Feeder Demand from "B1"
           » Determine Feeder demand for each section.
           » Demand is Emitter gph and Qty'
           » Total the (emitter qty & flow rate)
           for all sections in each group.
           » Data Entry - Use Drop-Down box
           2.31) This may require more than one group
      2.4) Information for different groups
           Feeder Sections with similar demand
           should be assigned to the same group
           Those Feeders with significantly higher
           or lower demand put into another group
        2.41) Sections with similar demand - 1 group
              » Count the number of groups.
              » Note the Emitter Qty & Rate within each group.
        2.43) A max of 4 groups is provided
        2.44) Data Entry Analysis #1, section 1.
              » Input Emitter Demand 1st group
                Enter Gph - Qty - # of Groups (similar demand)
              » Input Emitter Demand 2nd, (3rd) groups
                Enter Gph - Qty - # of Groups (similar demand)
        2.45) If design has more than 3 groups:
              total the demand from all other Sections,
              Avg. flow rate & total quantity 3rd group.
              Data Enty - into 3rd Group put rate & qty
              Use Drop-Down boxes

              The 4th group for multi-secondary only.

        2.5) Data Entry Analysis #1 section 1
              Input total flow demand from secondary supply
              See (2.16) for details.

Estimating Line "A" PSI Loss
    [section 2]
Look at Calculator Data Input Section 2
      3.1) Select the type of Supply Piping used.
         from drop-down box
      3.2) Determine the length of this Supply Line
         use drop-down box to enter data.
      3.3) If the end of this line is elevated, estimate
         use drop-down box - enter feet up + or -
      3.4) Press Calculate-A & analysis will report
         Input & Output PSI
      3.5) Supply line "B2, etc." were used for
         pressure loss through this supply line "A"


Estimating Line "B" PSI Loss
    [section 3]
Look at Calculator Data Input Section 3
      4.1) Select the type of Secondary Supply Line.
         from drop-down box
      4.2) Determine the length of this Supply Line
         use drop-down box to enter data.
      4.3) If the end of this line is elevated, estimate
         use drop-down box - enter feet up + or -
      4.4) Press Calculate-B & analysis will report
         Input & Output PSI
          Note: Supply lines "B2, etc." are NOT used to
          determine pressure loss across B1 supply line

Termination Feeder Section Data
    [sections 4 & 5]
Look at Calculator Data Input Section 4
      5.1) Determine if type of emitters used
           are "Dripperline" or Individual Emitters
      5.2) Select the type of Feeder Emitters used.
          from drop-down box
      5.3) When using Dripperline
              » When using ½" dripline, no ¼" connecting feeder is used.
              » When using ¼" dripline, a ¼" connecting feeder is used.
              » Determine the length of ¼" connecting feeder
              » Data Entry (¼" feeder length)
              » use drop-down box to enter data.
        5.33) Determine the length of the Dripperline
              » Data Entry (dripperline length)
              » use drop-down box to enter data.
        5.34) Press Calculate-C to perform analysis.

      5.4) When using Individual Emitters
Look at Calculator Data Input Section 5
        5.41) Data Input Analysis #1, section 5
              » Data Entry (¼" feeder length)
              » use drop-down box to enter data.
              5.411) When using ½" dripline, no
                  ¼" connecting feeder is used.
        5.42) Data Input Analysis #1, section 5
              » Data Entry Qty of individual emitters
              » Data Entry emitter flow rate
              » use drop-down box to enter data.
              there can be multiple connectors & feeder lines
              leading to the end of an individual emitter.
              » Data Entry Qty of "tees" used to connect
              » Data Entry length of 2nd feeder line
              » Use the lower 2 drop down boxes

       5.5) Press Calculate-C to perform analysis.

A separate Reference document is available to help understand the Friction Loss Report in addition to Summary and Warnings