Dripper Lines Length & Friction Loss of Pressure & Flow
Bulletin #TP1022	Horticultural Observations for Healthier Landscapes

Often a homeowner is trying to make some additions to their landscape or perhaps trying to correct a flow problem. It is important to have an idea regarding the maximum number of emitters (drippers) that can be used from a single ¼ inch feeder tubing.

Due to the occasional complexity of many irrigation designs, simple charts showing how many feet you can run ¼" feeder line with emitters at various spacing may (or may not) not be useful.

    ◊ Color Codes definition chart

    ◊ Maximum ½ & ¾ inch Supply line run chart

    ◊ Maximum ¼ inch Feeder line run chart

    ◊ Maximum ¼ & ½ inch Dripperline run charts

    ◊ Miscellaneous PSI loss

    ◊ Drip System Design - Maintaining Pressure

    ◊ Pressure loss Calculator

Pressure Loss & Run charts - Introduction

Larger diameter non-emitter lines are
refered to as Supply lines.
While smaller lines that do not have
terminating emitters are referred to as Feeder lines.

Dripperlines have emitters built into the line.

Pressure loss due to friction for Driplines
is a bit more complex, as emitter psi drops
to some degree at each emitter location.

The charts below are provided to give a quick estimate of pressure loss to be experienced when using either ½" or ¼ inch [OD] dripperline, but do not reflect this complexity. The Friction-Loss Calculator, however does report the diminishing emitter pressure across the dripline.

Loss of pressure creates loss of flow. If this is not taken into account when designing the drip irrigation layout, some of the plants will be getting less than their share of water. This frequently causes some plants to do well while others are not. Just "looking" at the water coming out of the emitter will not reveal how much water is being emitted. The pressure loss factors are critical towards achieving an irrigation design that neither wastes water nor under waters the landscape.

These charts are only intended to present a "Big-View Picture" of the relationship between tubing or pipe size, water volume flow and the loss of water pressure at the output. Your intended flow rate (determined by output emitter flow & count) and length of run (in feet) is likely very different from these charts!

There is a link to our Friction Loss Calculator [below] where you can input your current design parameters, and see what the line losses are for those specs.

Following are charts: for color code reference, and various supply or feeder lines.

Color Codes for the following Charts

Pale Blue background indicates the Friction-Loss is
very safe

Pale Green background indicates the Friction-Loss is
safe & normal

Lavender background indicates the Friction-Loss is
notable - operate at 30# pressure

Orange background indicates the Friction-Loss is
high - CAUTION - operate at 30# pressure

Red background indicates the Friction-Loss is
excessive - WARNING - change design

½ inch Supply [no emitters] line

½ inch PVC [#40] Drip Irrigation Supply line
no emitters - .60" ID.

Flow Rate gph	Tubing Length	Pressure Loss	% Loss at 20 psi	% Loss at 30 psi
75 gph	75 feet	0.6 psi	2.9 %	1.9 %
100 gph	100 feet	1.3 psi	6.6 %	4.4 %
150 gph	75 feet	2.1 psi	10.4 %	7.0 %
200 gph	75 feet	3.6 psi	17.8 %	11.9 %
250 gph	125 feet	7.6 psi	38.2 %	25.5 %

½ inch Poly Tubing Drip Irrigation Supply line
no emitters - .62" ID.

Flow Rate gph	Tubing Length	Pressure Loss	% Loss at 20 psi	% Loss at 30 psi
75 gph	75 feet	0.49 psi	2.5 %	1.6 %
100 gph	100 feet	1.1 psi	5.5 %	3.7 %
150 gph	75 feet	1.8 psi	8.9 %	5.9 %
200 gph	75 feet	3.0 psi	15.2 %	10.1 %
250 gph	75 feet	4.6 psi	22.9 %	15.3 %

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¾ inch PVC [#40] Drip Irrigation Supply line
no emitters - .82" ID.

Flow Rate gph	PVC Length	Pressure Loss	% Loss at 20 psi	% Loss at 30 psi
150 gph	100 feet	0.61 psi	3.0 %	2.0 %
150 gph	200 feet	1.2 psi	6.1 %	4.1 %
200 gph	200 feet	2.1 psi	10.4 %	6.9 %
350 gph	100 feet	2.9 psi	14.6 %	9.7 %
350 gph	200 feet	5.8 psi	29.2 %	19.5 %

Feeder line {without emitters] run chart
(¼ inch diameter)

¼ inch feeder lines provide the connection between the ½ inch Poly Supply Lines and the Emitters (or dripperline). This Feeder run chart is provided to give a quick estimate of the pressure loss to be experienced when using various combinations of combined emitter flow, being used - in combination with the length of the feeder line being used.

Loss of pressure in the feeder creates loss of flow. If this is not taken into account when designing the drip irrigation layout, the plant(s) being supplied from this feeder will be getting less than their share of water.
Visual appearance of water flow will not provide the answer as to how much water is being given to the plant. The pressure loss factors are critical towards achieving an irrigation design that neither wastes water nor under waters the landscape.

If your intended flow rate (determined by emitter count) and length of run (in feet) is significantly different from these charts - there is a link to our Friction Loss Calculator [below] where you can input your current design parameters, and see what the line losses are for those specs.

¼ inch Feeder line
no emitters - .17" ID.

Flow Rate gph	Tubing Length	Pressure Loss	% Loss at 20 psi	% Loss at 30 psi
8.0 gph	5.0 feet	0.28 psi	1.4 %	1.0 %
8.0 gph	15.0 feet	0.85 psi	4.3 %	2.8 %
8.0 gph	30.0 feet	1.7 psi	8.5 %	5.7 %
12.0 gph	20.0 feet	2.4 psi	12.0 %	8.0 %
18.0 gph	10.0 feet	2.5 psi	12.7 %	8.5 %
22.0 gph	10.0 feet	3.7 psi	18.4 %	12.3 %

¼" Feeder & Dripper lines

¼ inch Dripperline with 6 inch spacings
flow per emitter = 0.50 gph [20 psi]

Run Length emitters	Total Flow gph	Pressure End-Loss	% Loss at 20 psi	% Loss at 30 psi
8.0 [16]	10.4 gph	0.70 psi	3.7 %	2.5 %
10.0 [20]	13.0 gph	1.4 psi	7.0 %	4.7 %
15.0 [30]	19.5 gph	4.4 psi	22.2 %	14.8 %
18.0 [36]	23.4 gph	7.5 psi	37.3 %	24.8 %

¼ inch Dripperline with 12 inch spacings
flow per emitter = 0.50 gph [20 psi]

Run Length emitters	Total Flow gph	Pressure End-Loss	% Loss at 20 psi	% Loss at 30 psi
8.0 [8]	5.2 gph	0.2 psi	1.0 %	0.7 %
10.0 [10]	6.5 gph	0.4 psi	1.9 %	1.3 %
15.0 [15]	9.8 gph	1.2 psi	6.2 %	4.1 %
20.0 [20]	13.0 gph	2.8 psi	13.9 %	9.3 %
25.0 [25]	16.3 gph	5.3 psi	26.4 %	17.6 %

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½" Dripperline

½ inch Dripperline with 12 inch spacings
flow per emitter = 0.90 gph

Run Length emitters	Total Flow gph	Pressure End-Loss	% Loss at 20 psi	% Loss at 30 psi
50 [50]	45.0 gph	0.15 psi	0.8 %	0.5 %
100 [100]	90.0 gph	1.1 psi	5.4 %	3.6 %
130 [130]	117 gph	2.3 psi	11.4 %	7.6 %
150 [150]	135 gph	3.4 psi	17.2 %	11.5 %
180 [175]	162 gph	5.8 psi	29.0 %	19.2 %

Pressure loss due to PVC Fittings & Couplings
in your irrigation supply line

½ or ¾ inch pipe There are Other sources for loss of pressure which are encountered where PVC has elbows, couplings or adapters.
Because the "drip" zones generally have much slower flow rates than zones intended for Lawns; Pressure loss from various fitting is not usually a concern. If supplying water at a rate of about 120 gph (2 gpm) - one 90° Elbow (½" PVC Std.) will cause approximately 0.2% additional pressure loss. Most PVC fittings or couplings are larger than the pipes connected, but still cause water turbulence which creates PSI loss. Count 0.1% loss for typical fitting.
¼ inch tubing
In ¼" feeder line; elbows and stright barb connectors cause a bit higher percent of pressure loss. Loss in pressure will be approximately 0.3% for each in-line fitting.

Drip System Design
Planning & Maintaining even Pressure
throughout your Drip System

When making decisions about how many drips (emitters) you can have in one zone, and how to lay these drips out for each plant, you need to take into consideration "loss of pressure" across the supply and feeder lines. Always use a pressure regulator following the valve in order to assure water pressure does not exceed that recommended for drip fittings (usually no morfe than 30 psi).

When either investigating an existing system or zone, or planning a new one - You should be considering all of the following:

1) What % PSI loss prior to outlet emitter?
 add all line and connector losses [in percent]
2) Based on final PSI & emitter count - how many gallons?
 Most ¼" emitters are rated at 0.65 gph
 when supplied by 30 psi.
 The initial regulated pressure will be considerably
 less by the time water flow reaches the emitters.
3) Are enough gallons being delivered to each plant?
4) Is this water being properly distributed?
  throughout the intended root zone?
5) Note if any "Feeder" is at "CAUTION".
6) Note if any "Supply" is at "CAUTION".
 If any feeder or supply is at caution
  - do not add to this run in the future.

The amount of water provided needs to adequate to assure a depth of moisture sufficient to permeate 8 inches or more.
Plants, as they mature - grow and subsequently will need a wider area of moisture to keep them healthy.

Planning a system that barely meets the needs of the plants to begin with, all but assures trouble down the road.

The factors presented above; will be considered by a skilled irrigation designer during the process of creating a system design.

Trying to skimp on design costs doesn't pay!

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