GCO 2431
Irrigation
1
BASIC HYDRAULICS &
IRRIGATION
SYSTEM DESIGN
INSTRUCTOR
Doug Callison
Area Specifications Manager
1/4/98
DESIGN TERMINOLOGY
 Scale = mechanical or engineering
measurements.
 Plan view = flat view of the
site from a particular height.
 PSI = pounds per square inch
(water pressure).
 GPM = gallons per minute (flow rate).
 Elevation = height difference in feet.
3
DESIGN TERMINOLOGY
 Friction Loss = pressure lost by water
flowing through system components
(pipe, valves, etc...) measured in psi.
 Velocity = speed of the water moving
through system components measured
in feet per second (fps).
 Water hammer = surge pressures created by
combinations of high velocity, fast closing
valves, long pipe runs & high psi.
4
BASIC HYDRAULICS
 Relationship between pressure & elevation:
 1 foot of elevation = .433 psi
 1 psi = 2.31 feet of elevation (head)
 Static (hydrostatic) pressure = water
at rest / experiencing no friction or
pressure losses.
 Dynamic (hydrodynamic or working)
pressure = water in motion / experiencing
friction or pressure losses.
5
BASIC HYDRAULICS
Feet of elevation x .433 = psi
2 feet of elevation x .433 = .866 psi
or
20 feet of elevation x .433 = 8.66 psi
6
STATIC PSI EXERCISE
Calculate the static pressure at the following points:
60 PSI
Outlet of control valve __________
Pressure gauge A
60 PSI
__________
Pressure gauge B
55.67 PSI
__________
Pressure gauge C
C
20
10’
51.34 PSI
__________
10
10’
1-1/4” Class
200 PVC Pipe
6
0
30
40
50
60
A
20
100’
10
0
30
40
50
60
0
40
50
60
B
20
100-PEB valve
Inlet 60 PSI Static
10
30
3/4” Class
200 PVC Pipe
1” Class
200 PVC Pipe
50’
50’
DYNAMIC PSI EXERCISE
Calculate the dynamic pressure at the following points:
55 PSI
Outlet of control valve __________
Inlet of sprinkler A
51.8 PSI
__________
Inlet of sprinkler B
45.1 PSI
__________
Inlet of sprinkler C
38.6 PSI
__________
Falcon Rotor
10 GPM each
10’
100-PEB valve
Inlet 60 PSI Static
1-1/4” Class
200 PVC Pipe
7
100’
10’
C
B
3/4” Class
200 PVC Pipe
A
1” Class
200 PVC Pipe
50’
50’
OBTAINING SITE INFORMATION
 Plot plan = scaled drawing
of the site including:
 all structures and hardscapes.
 water source (water meter size,
service main size, gpm & psi).
 landscape (type & location of plant
material / lawn shrub borders).
 exposures to sun, wind & rain (direction north).
 soil & slope conditions.
9
CALCULATING SYSTEM
REQUIREMENTS
 ET = evapotranspiration (water
lost to the plants use by
evaporation & transpiration)
in inches for a certain time period.
 PET = potential highest ET
(maximum
inches of ET based
on historical
records and site conditions.
 Irrigation design should be based on the site
PET or the worst case scenario.
10
CALCULATING SYSTEM
REQUIREMENTS
11
 Soil infiltration rate = maximum inches of
water that can be absorbed by a particular
type of soil in one hours time.
 Soil holding capacity = inches of water
available to the plant in different soils.
 Rooting depth = average depth of a
plants root system in different soils.
 This information is used to determine the
frequency of irrigation.
CALCULATING WATER
SOURCE CAPACITY & PSI
 Collect the following water source info:
 Water meter size (5/8”, 3/4”, 1”, etc...).
 Service line size & type (3/4” K copper,
3/4” sch. 40 galv., 1” sch. 40 PVC, etc...).
 Service line length (from water source
point of connection - POC).
 Static water psi (with no water running).
 Working water psi (with water running).
 Average high/low psi from purveyor.
12
to
CALCULATING WATER
SOURCE CAPACITY & PSI
 Select a maximum system working capacity
that is the most restrictive of these 3 values:
 The pressure loss through the water meter
should not exceed 10% of the minimum static
pressure available in the city water main.
 The maximum flow through the meter for
irrigation should not exceed 75% of the
maximum safe flow of the meter (AWWA standard).
 The velocity of flow through the service line should not
exceed 5 fps (for PVC/poly pipe) or 7 1/2 fps (for
copper/galv/cast iron/ductile iron pipe).
13
CALCULATING WATER SOURCE
CAPACITY EXERCISE
Calculate the maximum system working capacity
based on the following information:
60 PSI Static
5/8 x 3/4 Water Meter
1” Schedule 40 PVC Pipe
Maximum system GPM
14
13 GPM
__________
15 GPM
__________
12 GPM
__________
12 GPM
__________
CALCULATING WATER
SOURCE CAPACITY & PSI
15
Water
Source
Service
Line
Static
Pressure
Maximum
Flow
5/8 x 3/4
Meter
3/4 type K
copper
80 psi
10 gpm
5/8 x 3/4
Meter
1 sch 40
Galv.
60 psi
12 gpm
3/4 Meter
1 type K
copper
70 psi
18 gpm
3/4 Meter
1 sch 40
PVC
50 psi
13 gpm
SPRINKLER SELECTION
& SPACING
Sprinkler
Type
Typical
Spacing
Emission Operating
Style
Pressure
Flow
Rate
Drip/Micro
or Bubbler
0 to 3
feet
point of
use
10 to 60
psi
.01 to 5
gpm
Spray
Head
4 to 15
feet
fixed fan
or pattern
15 to 50
psi
.3 to 5
gpm
Rotory 16 to 100+ rotating 25 to 100+ .5 to 100+
Sprinkler
feet
stream(s)
psi
gpm
16
SPRINKLER SELECTION
& SPACING
 Sprinkler series will often include a fixed
shrub version & different pop-up height
models for irrigating various plants/grasses.
 Sprinkler radius = distance from the
sprinkler to the edge of throw (in feet).
 Sprinkler gpm = flow rate of the
sprinkler with different size nozzle orifices.
 Sprinkler psi = sprinkler operating pressure.
17
SPRINKLER SELECTION
& SPACING
 Overlapping coverage is required for
uniform coverage on all sprinkler layouts.
 Stretched sprinkler spacing will result in
uneven coverage and wet / dry spots.
 Head-to-head spacing = sprinklers spaced
at their expected radii. This is the most
commonly used sprinkler spacing range in
landscape irrigation system design.
18
SPRINKLER SELECTION
& SPACING
 Square pattern = sprinklers placed in a
square pattern, with the same distance
between all 4 sprinklers in the pattern.
Best pattern for areas with 90o corners.
 Triangular pattern = sprinklers placed in a
triangular grid, with the same distance
between all three sprinklers in the pattern.
Good pattern for irregular shaped areas
where overspray is not a problem.
19
SPRINKLER SELECTION
& SPACING
 Equilateral triangular pattern
row spacing formula:
L = S x .866
• L = Distance in feet between sprinkler rows.
• S = distance in feet between sprinklers on a row.
• .866 = a constant.
20
SPRINKLER SELECTION
& SPACING
 Rectangular pattern = like square pattern
but one side of the pattern is closer
together. Best pattern for fighting wind.
 Staggered pattern = combinations of
various spacing patterns to adapt to site
conditions or move around obstacles.
 Sliding pattern = gradual change from one
pattern to another to work around curves.
21
SPRINKLER SELECTION
& SPACING
 This chart shows the maximum spacing
ranges for different wind velocities.
Wind
Velocity
0 to 3
mph
4 to 7
mph
8 to 12
mph
22
Square
Pattern
55% of
Diameter
50% of
Diameter
45% of
Diameter
Triangular
Pattern
60% of
Diameter
55% of
Diameter
50% of
Diameter
Rectangular
Pattern
60% x 50% of
Diameter
60% x 45% of
Diameter
60% x 40% of
Diameter
SPRINKLER SELECTION
& SPACING
 Precipitation rate = the average amount of
water that would be applied to a given area
by all sprinklers in 1 hour (measured in
inches per hour).
 Matched precipitation rates = sprinklers
which apply water at the same rate per hour
no matter the arc of coverage (matching
gpm flow rates to arc of coverage).
23
SPRINKLER SELECTION
& SPACING
 Precipitation rate formula:
96.3 x GPM
S x L
= IPH
• 96.3 = a constant.
• GPM = gallons per minute applied to the
target area by all sprinklers in pattern.
• S = distance in feet of the sprinklers on a row.
• L = distance in feet between sprinkler rows.
• IPH = average inches per hour.
24
CALCULATING PRECIPITATION RATE EXERCISE
Calculate the precip. rate for the sprinkler layout using the
following information: Operating pressure = 45 PSI.
T4-T30-1.3
T4-T30-2.5
T4-T30-5.0
112’
29’
28’
24
58’
CALCULATING PRECIPITATION RATE EXERCISE
Calculate the precip. rate for the sprinkler layout using the
following information: Operating pressure = 45 PSI.
T4-T30-1.3
T4-T30-2.5
T4-T30-5.0
o
o
o
90 - 1.4 GPM 180 - 2.9 GPM 360 - 5.5 GPM
28’
100%
1.4 GPM
50%
1.45 GPM
50%
1.45 GPM
25%
1.375 GPM
29’
25
96.3 x 5.675 GPM
546.5
---------------------- = -----28’ x 29’
812
= .67 inches per hour (PR)
SPRINKLER SELECTION
& SPACING
 Start your sprinkler layout by selecting one
area and measuring it.
 Select a sprinkler spacing range that would
fit in the area (length & width).
 Select a sprinkler with a radius that
will fit your spacing range.
 Lay out your sprinklers starting in the
corners and working your way out.
27
SPRINKLER SELECTION
& SPACING
 Check your sprinkler layout.
 Are sprinklers stretched too far apart
(farther than head-to-head spacing)?
 Are all sprinklers in the pattern
spaced the same distance apart?
 Are there any sprinklers missing in the
pattern (areas of little or no coverage)?
 Will there be much overspray onto
hardscapes or buildings?
28
SPRINKLER SELECTION
& SPACING EXERCISE
Select a sprinkler spacing range that will best fit
the area while minimizing overspray (0-3 MPH wind).
88’
O
O
O
Rectangular spacing 28’ x 29.33’
28’
O
28
O
O
O
O
CIRCUITING SPRINKLERS
INTO VALVE GROUPS
 Never combine sprinklers into the same
valve group if:
 the sprinkler precipitation
rates are not matched.
 the sprinklers have different operating psi.
 the sprinklers cover plant material with
differing water requirements.
 the areas of sprinkler coverage have different
exposures to sun, wind or rain.
30
CIRCUITING SPRINKLERS
INTO VALVE GROUPS
 Select sprinklers with common precipitation
rates, operating psi, plant material and
exposure to combine into valve groups.
 Add up the gpm of all sprinklers in a
group and divide the total by the
maximum gpm available from the
water source. This tells you the number
of valves you will need to supply water
for this group of sprinklers.
31
MAINLINE & LATERAL PIPING
SYSTEM LAYOUT
32
 Draw lateral pipe lines between all
sprinklers on a common valve.
 Center feed (rather than end feed) the zone
if possible to reduce friction losses.
 Select locations for valves (combine where
possible but keep in area of the sprinklers).
 Draw mainline pipe lines between water
source and all valves. Use common lateral
trenches where possible.
SIZING LATERAL &
MAINLINE PIPE
 Pipe should be sized so that:
 the desired gpm & psi can reach each sprinkler.
 water travels through the piping system at
a safe velocity, limiting the possibility of
water hammer & damaging surge pressures.
 the smallest size pipe possible is used to
accomplish the task (for economic reasons).
 Pipe friction loss/velocity charts are used to
select the appropriate size pipe.
33
SIZING LATERAL &
MAINLINE PIPE
 The maximum safe velocity for irrigation
system piping is:
 5 feet per second in PVC or poly pipe.
 7 1/2 feet per second in copper,
galvanized,
cast iron or ductile iron pipe.
 Pipe sizing is done in reverse, starting with
the pipe segment supplying water to the last
or furthest sprinkler from the valve and
working in.
34
SIZING LATERAL &
MAINLINE PIPE
 Use the manufacturers catalog & find the
gpm flow rate of the various sprinklers.
 Use the pipe velocity chart to select a pipe
size that will supply the gpm flow rate of
the sprinkler at a velocity of 5 fps or lower.
 Use the same procedure to size all the pipe
segments remembering to add the total gpm
flow rate of all sprinklers that pipe supplies.
35
SIZING LATERAL &
MAINLINE PIPE
 This chart shows the maximum gpm
flow rate for various sizes of Class 200
PVC pipe at velocities of no more than
5 feet per second.
Pipe
Size
Max
gpm
36
3/4”
1”
10
16
1-1/4” 1-1/2”
26
35
2”
2-1/2”
3”
55
80
120
CIRCUITING SPRINKLERS
& SIZING PIPE EXERCISE
Circuit sprinklers into valve groups, lay out & size the
lateral pipe lines. Water source capacity = 12 GPM.
1804-12Q
1804-12H
1804-12F
3/4”
3/4”
3/4”
3/4”
#1
10.4
1”
3/4”
3/4”
3/4”
3/4”
3/4”
36
1”
3/4”
3/4”
3/4”
3/4”
#2
10.4
SIZING VALVES &
BACKFLOW PREVENTERS
 Use the following guidelines when sizing
valves and backflow preventers:
 Valve pressure loss should not exceed 10%
of
the static psi in the irrigation mainline.
 The valve should be the same size or no
more than one size smaller than the largest
lateral pipe it serves.
 The valve should not be larger than the largest
lateral pipe it serves.
38
CALCULATING SYSTEM
PRESSURE REQUIREMENTS
 Select the worst case valve circuit:




valve with the largest gpm flow rate.
valve with sprinklers requiring highest psi.
valve furthest distance from the water source.
valve at highest elevation above water source.
 Add up all system pressure/friction losses &
add to the pressure required at the sprinklers
on this valve. This is the total system psi
requirement.
39
CALCULATING SYSTEM
PRESSURE REQUIREMENTS
 Subtract the total system psi
requirement from the static psi
available from the water source.
 If the answer is a positive number,
the system will work as designed.
 If the answer is negative, look back over the
design & see where you can change pipe
sizes or add valves to lower pressure losses.
40
PREPARING THE FINAL
IRRIGATION PLAN
 Design at a maximum readable scale of:
 1” = 20’-0” for spray heads or drip.
 1” = 50’-0” for small radius rotors.
 1” = 100’-0” for large radius rotors.
 Use a different symbol for each type of
sprinkler, valve, backflow preventer, etc...
 Inset sprinkler symbols from boundary lines
for easy reading.
41
PREPARING THE FINAL
IRRIGATION PLAN
 Use a different line style for mainline
piping verses lateral line piping.
 Check local codes for POC &
backflow requirements & 120v
power connections for the controller.
 Write out a schedule for each valve showing
by month, the cycle days, average run
times, maximum cycle time & minimum
soak time between cycles.
42
IRRIGATION SCHEDULING
 Valve operating time formula:
ET x 60
= OT
(PR x EFF) x DA
•
•
•
•
•
•
43
ET = evapotranspiration (inches per week).
60 = a formula constant.
PR = precipitation rate.
DA = days of the week available for irrigation.
EFF = system efficiency % (as a decimal).
OT = station operating time per day.
CALCULATING VALVE
OPERATING TIME EXERCISE
Calculate the valve operating time based on:
ET requirement = 1.25” per week
Precipitation rate = .67” per hour
Days for irrigating = 4 days per week
System efficiency = 65%
1.25” ET x 60
75
--------------------------------------------- = -------(.67” PR x .65 Eff.) x 4 Days per week
1.742
44
= 43 minutes operating time per irrigation day
COMPUTER AIDED
IRRIGATION DESIGN
 RainCAD - CAD design package with
irrigation & landscape design modules.
 IrriCalc - Irrigation scheduling
and water use/cost calculations.
 XeriCalc - Drip/Micro irrigation
scheduling & product applications.
 CIT-Space - Sprinkler test/evaluation data.
 IA-Water Audit - Water auditing package.
45