GCO 2431 Irrigation 1

Transcription

1 GCO 2431 Irrigation 1

2 BASIC HYDRAULICS & SYSTEM DESIGN IRRIGATION INSTRUCTOR Doug Callison Area Specifications Manager 1/4/98

3 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

4 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

5 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

6 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

7 STATIC PSI EXERCISE Calculate the static pressure at the following points: Outlet of control valve 60 PSI 100-PEB valve Inlet 60 PSI Static Pressure gauge A Pressure gauge B Pressure gauge C 1-1/4 Class 200 PVC Pipe 60 PSI PSI PSI A B Class 200 PVC Pipe C /4 Class 200 PVC Pipe

8 DYNAMIC PSI EXERCISE Calculate the dynamic pressure at the following points: Outlet of control valve 55 PSI 100-PEB valve Inlet 60 PSI Static Inlet of sprinkler A Inlet of sprinkler B Inlet of sprinkler C 1-1/4 Class 200 PVC Pipe 51.8 PSI 45.1 PSI 38.6 PSI A Falcon Rotor 10 GPM each 10 B 1 Class 200 PVC Pipe 10 C 3/4 Class 200 PVC Pipe

9 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

10 CALCULATING SYSTEM REQUIREMENTS 10 ET = evapotranspiration (water lost to the plants use by evaporation & transpiration) in inches for a certain time period. PET = potential highest ET inches of ET based records and site conditions. (maximum on historical Irrigation design should be based on the site PET or the worst case scenario.

11 11 CALCULATING SYSTEM REQUIREMENTS 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.

12 12 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. to

13 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

14 CALCULATING WATER SOURCE CAPACITY EXERCISE Calculate the maximum system working capacity based on the following information: 60 PSI Static 13 GPM 5/8 x 3/4 Water Meter 15 GPM 1 Schedule 40 PVC Pipe 12 GPM Maximum system GPM 12 GPM 14

15 CALCULATING WATER SOURCE CAPACITY & PSI Water Source Service Line Static Pressure Maximum Flow 5/8 x 3/4 Meter 5/8 x 3/4 Meter 3/4 type K copper 1 sch 40 Galv. 80 psi 10 gpm 60 psi 12 gpm 3/4 Meter 1 type K copper 3/4 Meter 1 sch 40 PVC 70 psi 18 gpm 50 psi 13 gpm 15

16 SPRINKLER SELECTION & SPACING Sprinkler Type Typical Spacing Emission Style Operating 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 Sprinkler 16 to 100+ feet rotating stream(s) 25 to 100+ psi.5 to 100+ gpm 16

17 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

18 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

19 SPRINKLER SELECTION & SPACING 19 Square pattern = sprinklers placed in a square pattern, with the same distance between all 4 sprinklers in the pattern. Best pattern for areas with 90 o 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.

20 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

21 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

22 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 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 22

23 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

24 SPRINKLER SELECTION & SPACING 24 Precipitation rate formula: 96.3 x GPM S x L 96.3 = a constant. = IPH 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.

25 CALCULATING PRECIP- ITATION RATE EXERCISE Calculate the precip. rate for the sprinkler layout using the following information: Operating pressure = 45 PSI. T4-T T4-T T4-T

26 CALCULATING PRECIP- ITATION RATE EXERCISE Calculate the precip. rate for the sprinkler layout using the following information: Operating pressure = 45 PSI. T4-T T4-T T4-T o GPM 180 o GPM 360 o GPM % 1.4 GPM 50% 1.45 GPM 96.3 x GPM = x % 1.45 GPM 25% GPM =.67 inches per hour (PR) 25

27 27 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.

28 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

29 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 O 28 Rectangular spacing 28 x O O O O 28

30 30 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.

31 31 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.

32 32 MAINLINE & LATERAL PIPING SYSTEM LAYOUT 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.

33 33 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.

34 34 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, cast iron or ductile iron pipe. galvanized, 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.

35 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

36 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 3/ /4 1-1/ /2 3 Max gpm

37 CIRCUITING SPRINKLERS & SIZING PIPE EXERCISE Circuit sprinklers into valve groups, lay out & size the lateral pipe lines. Water source capacity = 12 GPM Q H F 3/4 3/4 3/4 # /4 3/4 # /4 3/4 3/4 1 3/4 3/4 3/4 3/4 3/4 36

38 SIZING VALVES & BACKFLOW PREVENTERS Use the following guidelines when sizing valves and backflow preventers: Valve pressure loss should not exceed 10% 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. of 38

39 39 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.

40 40 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.

41 41 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 = 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.

42 42 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.

43 IRRIGATION SCHEDULING Valve operating time formula: ET x 60 = OT (PR x EFF) x DA 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. 43

44 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 = (.67 PR x.65 Eff.) x 4 Days per week = 43 minutes operating time per irrigation day

45 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